WATER
CHLORINE
(RESIDUAL) NO. 1
STUDY NUMBER 35
ANALYTICAL
REFERENCE SERVICE
U. S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
Public Health Service
Consumer Protection and Environmental Health Service
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WATER CHLORINE (RESIDUAL) NO. 1
STUDY NUMBER 35
Report of a Study Conducted by
ANALYTICAL REFERENCE SERVICE
R. J. Lishka, E. F. McFarren, and J. H. Parker
Division of Criteria and Standards
Bureau of Water Hygiene
U.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
Public Health Service
Consumer Protection and Environmental Health Service
Environmental Control Administration
Cincinnati, Ohio 45202
1969
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FOREWORD
The Analytical Reference Service (ARS) is conducted by the Bureau
of Water Hygiene of the Environmental Control Administration to evaluate
laboratory methods in the environmental field. Cooperative studies by
member organizations, who analyze identical samples and critically
review methodology, provide the mechanism for:
Evaluation of analytical procedures, including
precision and accuracy, by comparison of the
procedures and results reported by participating
laboratories.
Exchange of information regarding method char-
acteristics.
Improvement or replacement of existing methods
by development of more accurate procedures, and
development of new methodology for determination
of new pollution compounds.
Samples are designed to contain measured amounts of selected con-
stituents. Decisions as to qualitative makeup are made by the member-
ship, consultants, and the ARS staff. Notice of each study is sent to the
entire membership. To those who desire to participate, a portion of the
study sample is sent, along with data forms for reporting numerical
values, a critique of the procedures used, comments on modifications,
sources of error, difficulties encountered, or other pertinent factors.
The results and comments received are compiled, and a report of each
study is prepared.
Now primarily directed toward examination of water, in the past
studies have included methods for analysis of air, milk, and food. Some
studies are periodically repeated for the advantage of new members, the
evaluation of new methods, or the reevaluation of existing methods.
The selection of studies is guided by requests from standard methods
committees and the responses to questionnaires periodically circulated
among the membership, which now includes 294 Federal, state, and
municipal agencies; industries; universities; consulting firms; and foreign
agencies.
iii
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STUDIES COMPLETED AND REPORTED
Wat e r- Mine ral s
Water-Metals
Calcium, magnesium, hardness, sulfate,
chloride, alkalinity, nitrite, nitrate, sodium,
and potassium. Studies completed in 1956,
1958, and 1961.
Lead, copper, cadmium, aluminum, chro-
mium, iron, manganese, and zinc. Studies
completed in 1957 and 1962. These same
metals plus silver. Study completed in 1965.
Except for the substitution of magnesium for
aluminum, these same metals were analyzed
by atomic absorption in 1967. Copper, man-
ganese, and aluminum in the presence and
absence of interferences. Study completed
in 1969.
Water- Fluoride
Fluoride in the presence and absence of inter-
ferences, with and without distillation by a
specified procedure. Studies completed in
1958 and 1961, Fluoride by ion-exchange and
fluoride electrode. Study completed in 1969.
Water- Radioactivity
Gross beta activity. Studies completed in
1959 and 1961. Gross beta and strontium-90
activity. Study completed in 1963.
Water-Surfactant
Water-Oxygen Demand
Surfactant in various waters. Studies com-
pleted in 1959, 1963, and 1968.
Biochemical oxygen demand and chemical
oxygen demand. Study completed in 1960.
Chemical oxygen demand. Study completed
in 1965,
Water-Trace Elements
Freshwater Plankton
Arsenic, boron, selenium, and beryllium.
Study completed in 1962. These same metals
plus vanadium. Study completed in 1966,
Evaluation of the precision and accuracy
obtainable by the use of various methods
of plankton counting and identification. Study
completed in 1 964.
Water-Nutrients
Silicate, phosphate, ammonia nitrogen,
organic nitrogen, and nitrate nitrogen.
Study completed in 1966.
IV
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Water-Phenols
Phenol and 2, 4-dichlorophenol in water by-
two specified methods. Study completed in
1966.
Water-Cyanides
Water-Chlorine
Air-Inorganics
Air-Lead
Potassium cyanide and potassium ferricyanide
in water by two specified methods. Study
completed in 1957.
Free and combined chlorine by nine different
methods. Study completed in 1969.
Chloride, sulfate, fluoride, and nitrate in
aqueous solution and on glass-fiber, high-
volume filter mats. Study completed in 1958,
Filter paper tape impregnated with lead.
Study completed in 1961.
A ir- Particulate s
Microscopic identification of some common
atmospheric particulates. Study completed
in 1964.
Air-Sulfur Dioxide
Water-Pesticides
Food-Pesticides
Sulfur dioxide in air by a specified method.
Study completed in 1963.
Lindane, heptachlor epoxide, DDE, and
dieldrin in water. Study completed in 1965.
Lindane, heptachlor, aldrin, heptachlor
epoxide, p,p'-DDE, dieldrin, endrin, o,p'-
DDT, p, p'-DDT, and methoxychlor in water.
Study completed in 1968.
DDT in milk. Study completed in 1962. Lindane,
heptachlor epoxide, DDE, and dieldrin in milk.
Study completed in 1965.
v
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CONTENTS
Page
PREFACE ix
ACKNOWLEDGMENTS xi
PARTICIPANTS IN THIS STUDY xii
ABSTRACT xv
DESIGN OF THE STUDY 1
TREATMENT OF THE DATA 3
RESULTS 4
Sample 1. Free chlorine and combined chlorine. . . 4
Sample 2. Free chlorine . 18
Sample 3. Combined chlorine 29
DISCUSSION 40
COMMENTS OF THE PARTICIPANTS 41
SUMMARY AND CONCLUSIONS 44
REFERENCES 46
APPENDICES 47
A. Methyl Orange Method for Determination ....
of Residual Chlorine 48
B. 4,4%4"-Methylidynetris (N, N-dimethylaniline) •
Method 51
C. Ferrous Method for Free Available Chlorine,. . .
Monorhloramine, Dichloramine,
and Nitrogen Trichloride 60
D. Stabilized Neutral Orthotolidine (SNORT) . . .
Method for Residual Chlorine and Iodine. ... 65
E. Tabulation of Results 71
F. Glossary of Statistical Terms 110
G. Tests for Normality and Rejection of Outliers . . 113
H. Statistical Comparison of Methods with Respect .
to Precision and Accuracy , 116
I. Analytical Reference Service Membership .... 119
vii
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PREFACE
The chlorination of water supplies accomplishes, in addition to the
destruction of microorganisms, a number of other objectives. These
include the improvement of the water as a result of the reaction of the
chlorine with ammonia, iron, manganese, sulfide, and proteineaceous
substances. On the other hand, the reaction of chlorine with compounds
such as phenol may also result in the production of undesirable taste and
odor compounds. If the chlorination is carefully controlled, however,
even the latter can be improved.
In any case, as a result of chlorination, one of the most commonly
performed chemical determinations is the measurement of free available
or combined available chlorine in water. At present, there are five
methods in the 12th edition of Standard Methods for the Examination of
Water and Wastewater for the determination of free and combined
chlorine. These are the following: iodometric (method A), orthotolidine
(methods B and C), orthotolidine-arsenite (method D), amperometric
titration (methods F and G), and ferrous titrimetric (method H). Method
E (drop dilution method) was not included in this study, since it is designed
only for large (greater than 10 mg/liter) chlorine concentrations.
In addition, four new analytical methods have been proposed for
inclusion in the 13th edition. These are the following: methyl orange,
leuco crystal violet, ferrous-DPD, and stabilized neutral orthotolidine
(SNORT).
Unfortunately, none of these have been studied collaboratively,
primarily because no one has been able to determine how to prepare a
chlorine solution that would remain stable for several months. It has,
however, been possible to concoct some stable dry standards. In the
latter case, there is perhaps another problem in that there may be some
question about whether each measured dry aliquot is exactly equivalent
to every other aliquot since these standards are mixtures of at least two
chemicals. In any case, because of the large number of methods avail-
able and the lack of any data on their usefulness, this study was under-
taken in an effort to evaluate and perhaps eliminate some of them.
ix
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ACKNOWLEDGMENTS
Michael J. Taras, Chairman, Joint Editorial Board of Standard
Methods for the Examination of Water and Wastewater suggested this
study to evaluate and compare four proposed chlorine methods and five
methods currently in Standard Methods. He also provided copies of the
proposed methods. (See Appendices A, B, C, and D. )
Robert T. Williams, Chief, Analytical Applications Laboratory,
Waste Identification and Analysis Activities, Cincinnati Water Research
Laboratory, Ohio River Basin Region, provided referee results for the
samples used in this study.
Lawrence J. Kamphake, of the same laboratory, suggested the use
of halazone as a stable, dry sample containing both free and combined
residual chlorine.
Dr. J. Donald Johnson, Department of Environmental Sciences and
Engineering, University of North Carolina, suggested the use of a mixture
of HTH and sodium chloride to prepare a stable, dry sample containing
free chlorine and the addition of ammonia chloride solution to provide
another sample containing combined chlorine. He also reviewed the final
draft of this report and served as a referee by analyzing both pilot and
master samples by several methods.
Dr. George P. Whittle, Department of Civil Engineering, University
of Alabama, the author of the leuco crystal violet method, reviewed the
final draft of this report.
xi
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PARTICIPANTS IN THIS STUDY
Atomic Energy Authority, Didcot, Berkshire, England
Black and Veatch, Kansas City, Missouri
Calgon Corporation, Pittsburgh, Pennsylvania
California State Department of Health, Berkeley
California Water Service Company, San Jose
Chicago Bureau of Water, Illinois
City of Dallas, East Side Purification Plant, Mesquite, Texas
City of Flint Water Plant, Michigan
Connecticut State Department of Health, Hartford
Dalecarlia Filter Plant, Washington, D. C.
Denver Board of Water Commissioners, Colorado
Department of Health and Hospitals, St. Louis, Missouri
DHEW, PHS, Northeast Marine Health Sciences Laboratory, Narragansett,
Rhode Island
Department of Municipal Laboratories, Hamilton, Ontario, Canada
Department of Public Health, Edmonton, Alberta, Canada
Fresno Department of Public Health, California
Hach Chemical Company, Ames, Iowa
Hammond-Montel, Inc. , Elmhurst, New York
Holzmacher, McLendon and Murrell, Melville, New York
Hydro Research Laboratories, Pontiac, Michigan
Idaho Department of Health, Boise
Illinois State Water Survey, Peoria
Illinois State Water Survey, Urbana
Infilco Products, Fuller Company, Tucson, Arizona
Institute of Environmental Sanitation, Taipei, China
Isotopes - A Teledyne Company, Sandusky, Ohio
Los Angeles County Flood Control District, California
Los Angeles Department of Water and Power, California
Mahoning Valley Sanitary District, Youngstown, Ohio
Maryland State Department of Health, Baltimore
Massachusetts Department of Health, Amherst
Mekoroth Water Company, Bnei-Brak, Israel
Memphis Light, Gas and Water Division, Tennessee
Metropolitan Corporation of Greater Winnipeg, Manitoba, Canada
Metropolitan Sanitary District of Greater Chicago, Cicero, Illinois
Metropolitan Utilities District, Omaha, Nebraska
Ministere de la Sante du Quebec, Montreal, Canada
Minnesota Department of Health, Minneapolis
Minneapolis Water Department, Minnesota
New Jersey State Department of Health, Trenton
New York State Conservation Department, Scottsville
New York State Department of Health, Albany
Newcastle and Gateshead Water Company, Newcastle Upon Tyne, England
North Carolina State Department of Water and Air Resources, Raleigh
xii
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North Jersey District Water Supply Commission, Wanaque, New Jersey
Ohio Department of Health, Columbus
Orange County Air Pollution Control District, Anaheim, California
Oregon State Board of Health, Portland
Osaka City Institute of Hygiene, Japan
Pacific Engineering Laboratory, San Francisco, California
Pan American World Airways, Patrick AFB, Florida
Pennsylvania Department of Health, Harrisburg
Philadelphia Suburban Water Company, Bryn Mawr, Pennsylvania
Philadelphia Water Department, Torresdale Laboratory, Pennsylvania
Regional Environmental Health Laboratory (LSGHM), McClellan AFB,
California
Regional Environmental Health Laboratory (SGHK), Kelly AFB, Texas
Research Institute for Public Health, Delft, Netherlands
St. Louis County Water Company, University City, Missouri
Sandia Corporation, Albuquerque, New Mexico
Santa Clara County Health Department, San Jose, California
Scientific Research Council, Kingston, Jamaica, West Indies
South Carolina State Board of Health, Columbia
Springwells Filtration Plant, Dearborn, Michigan
U.S. Army Environmental Hygiene Agency, Edgewood Arsenal, Maryland
USDI, FWPCA Ohio River Basin Project, Evansville, Indiana
USDI, FWPCA, Raritan Arsenal Depot, Edison, New Jersey
USDI, Geological Survey, Little Rock, Arkansas
University of Alabama, University City
Vermont State Public Health Laboratory, Burlington
Washington State Department of Health, Seattle
Washington State University, Pullman
Yonkers Water Bureau, New York
xiii
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ABSTRACT
In this study each participant was shipped three vials of dry powder
and a sealed glass ampoule of solution which, when dissolved and mixed
according to instructions, provided samples containing both free and
combined chlorine. Each analyst was requested to use three preselected
methods from the nine being studied. A total of 72 participants submitted
results indicating that the best accuracy and precision was obtained by
use of the ferrous-DPD method, followed closely by the methyl orange,
SNORT, and amperometric methods. The leuco crystal violet procedure
also gave good results in the analysis of two of the samples but poor on
a third containing a hydrolyzable chlorine (dichloroamide), which may
simply indicate that the method is more specific for free chlorine than
any of the others are. The poorest results were obtained by the use of
the other three orthotolidine procedures. It is likely that the greatest
potential source of error was in the use of distilled water that was not
completely free of chlorine or free of chlorine demand.
xv
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WATER CHLORINE (RESIDUAL) NO. 1
DESIGN OF THE STUDY
In order to obtain maximum stability, the samples were prepared
as dry powders and shipped in small screwcap vials containing about 1
gram of each of the following mixtures:
Sample 1 consisted of finely ground halazone tablets made by Abbott
Laboratories. The manufacturer states that the tablets contain 2. 97
percent active ingredient which is p-(dichlorosulfamyl) benzoic acid and
97. 03 percent inert ingredient consisting of sodium borate and chloride.
The exact amounts of the latter are not specified.
Sample 2 was prepared by thoroughly mixing 19. 2 grams of Olin
Matheson granular HTH (70% available chlorine) with 120 grams of C. P.
sodium chloride. Before mixing, both the HTH and sodium chloride were
ground with a mortar and pestle, and only those portions that passed
through a 60-mesh sieve were used.
Sample 3 was prepared by thoroughly mixing 14. 4 grams of Olin
Matheson granular HTH with 120 grams of C. P. sodium chloride. As
with sample 2, both were ground with a mortar and pestle and passed
through a 60-mesh sieve before mixing. Also sent with this sample was
a glass ampoule containing approximately 20 ml of an ammonia chloride-
borate buffer solution. This solution was prepared by dissolving 15 grams
of ammonia chloride and 5. 7 grams of sodium tetra-borate in 3 liters
of distilled water.
On receipt of these samples, the participants were instructed to
prepare them for analysis as follows:
Sample 1 - Weigh out approximately 0. 1 g and make up to a volume
exactly equivalent to 10, 000 times the sample weight in g. For example,
if 0. 0948 g was weighed out, dissolve in 948 ml of chlorine-free, chlorine-
demand-free water, measured in a graduated cylinder. The sample is
now ready for analysis. Do not dilute any further.
Sample 2 - Weigh out approximately 0.1 g as was done for sample
1 and dilute to volume in the same manner. Dilute 100 ml of this solu-
tion to 1 liter using chlorine-free, chlorine-demand-free water, before
undertaking analysis.
Sample 3 - Weigh out approximately 0.1 g as was done for sample
1 and 2 and dilute to volume in a like manner. To a 1 liter volumetric
flask, add 2 ml of the provided ammonium chloride-borate buffer solu-
tion, 100 ml of chlorine-free, chlorine-demand-free water, and then
exactly 100 ml of the above-prepared sample 3 solution. (Caution:
1
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always add the chlorine solution to the ammonia solution and not vice
versa.) Finally, dilute to 1 liter with chlorine-free, chlorine-demand-
free water.
Instructions for the preparation of chlorine-demand-free water were
sent with the samples and read as follows: Add sufficient chlorine to
distilled water to destroy the ammonia. The amount of chlorine required
will be about 10 times the amount of ammonia nitrbgen present; in no
case should the initial residue be less than 1.0 mg/liter free chlorine,
but generally this amount will be sufficient. Allow the chlorinated dis-
tilled water to stand overnight or longer, then expose to direct sunlight
until all residual chlorine is discharged (usually about 1 day). Since
water used for preparation and dilution of samples must also be free of
chlorine, this water should be checked for absence of chlorine before
use.
The concentrations of free and combined chlorine in these samples
were such that when the participants prepared the samples as instructed,
they would approximate chlorinated water supplies. Since the materials
commercially available and of necessity used in the preparation of these
samples do not permit the calculation of an accurate theoretical chlorine
content, the mean of the results ob^ined by two referee laboratories on
analysis by amperometric titration have been used (see Table 1). These
values agree very closely with the results submitted tpr another referee
laboratory usine these three other methods: SNORT, ferrous-DPD,
and iodometric.
Table 1. COMPOSITION OF SAMPLES
mg/liter in diluted sample
Sample 1
Sample 2
Sample 3
Free chlorine
0. 83
0. 80
0. 04
Total chlorine
1. 83
0. 84
0. 64
Combined chlorine
1.00
0. 04
0. 60
Theoretically, however, sample 2 contained only free chlorine, and
sample 3 only combined chlorine. Thus, the small values indicated for
combined chlorine in sample 2, and for free chlorine in sample 3 are
artifacts due to the inability of the method to determine lesser amounts.
In the announcement of this study, participants were provided with
2
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copies of four new methods for the analysis of chlorine that have been
proposed for inclusion in the 13th edition of Standard Methods for the
Examination of Water and Wastewater, and were requested to choose at
least three methods from these and the five other methods for chlorine
in the present edition of Standard Methods. They were further told that
in order to accomplish the objective of obtaining an approximately equal
number of data on each method, they would be requested to analyze the
samples by the three methods of their choice only if their choices were
rather equally distributed. As it turned out, their choices were rather
equally distributed, and it was necessary to request only a few labora-
tories to analyze the samples by a method other than the three they had
indicated as their choice. This was necessary in order to obtain some
overlap of laboratories submitting results on the different methods.
The participants were further instructed to analyze the samples only
for free and total chlorine. Hence, where combined chlorine is reported
in this report, it is obtained by difference.
TREATMENT OF THE DATA
After the results of analysis were received, the data were coded and
analyzed by computer for normality of distribution and subsequent rejec-
tion of outliers (see Appendix G) that were nonrepresentative because of
errors in calculation, dilution, or other indeterminate factors.
The results for each method were also plotted on normal probability
paper as a visual check on normality of distribution and the possible pres-
ence of outliers. A rather large number of apparent outliers that were
not rejected by the statistical tests programmed into the computer were
investigated more closely. It was found that certain grossly erroneous
results submitted by specific laboratories exhibited a pronounced bias
that was similar in each method used by the particular laboratory. Since
it was obvious that a common factor such as incorrectly prepared samples,
bad dilution water, or incorrectly standardized chlorine reference solu-
tions was responsible, these values also were rejected. A special case
was the large number of outliers obtained for the free and combined chlo-
rine measurement in sample 1 by amperometric titration, where it was
evident that a high free-chlorine result and a low combined-chlorine result
were due to titration for free chlorine at a low pH, probably caused by
failure to rinse the titration cell properly after titration for total chlorine.
After rejection of outliers, the data were then statistically analyzed by
computer for precision and accuracy (see Appendix F), and finally, their
precisions and accuracies were compared for significance of differences
(see Appendix H).
Bar graphs are included in the text to provide a pictorial display of
the data. Rejected values are indicated by broken bars or labelled out-
liers, and values are given for bars off the scale of the chart.
3
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RESULTS
Sample 1: 0. 83 mg/liter free, 1. 00 mg/liter combined, and 1. 83 mg/liter
total chlorine (Table 1; Figures 1 through 12)
This sample was designed to provide both free and combined chlorine
by the use of halazone as the active ingredient.
In the determination of free chlorine in sample 1, the mean value ob-
tained by the SNORT-* method was not significantly different from the
referee value, and nearly as good accuracy was obtained by the ferrous-
DPD'* and methyl orange methods. The precision of the ferrous-DPD
and SNORT methods was significantly better than that of any of the others,
and the amperometric** method was not far behind.
In the measurement of total chlorine, the mean values obtained by
the ferrous-DPD and methyl orange methods were not significantly differ-
ent from the referee values. The amperometric method produced nearly
as good results. On the other hand, the orthotolidine® and orthotolidine-
arsenite^ methods were by far the worst. The precision of the ferrous-
DPD and the amperometric methods was significantly better than that of
all the others.
In the determination of combined chlorine, the mean values obtained
by the use of the methyl orange and the ferrous-DPD methods were not
significantly different from the referee value, and the precision of the
ferrous-DPD method was significantly better than that of all the others.
In the measurement of free, combined, and total chlorine in sample
1 by the leuco crystal violet method, a very interesting phenomenon
occurred.
It appeared that the leuco crystal violet results fell into two groups
(see Figures 1, 2, and 3). The one group measured very little free chlo-
rine but obtained high combined-chlorine results, which agrees with ARS
findings. The other group reported much higher free-chlorine results
but still were below the referee value, and their combined-chlorine results
were also low. Obviously, the results obtained by this group were due
to some differences in technique or in the interpretation of the application
of the procedure. It is also of interest to note that the first group, which
obtained the lowest free-chlorine values and presumably did the procedure
correctly, also obtained the best total-chlorine results (see Figure 3).
4
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Table 2. SUMMARY OF DATA ON SAMPLE 1
(0. 83 mg/liter free, 1. 00 mg/liter combined, and 1. 83 mg/liter total chlorine)
Number of
Number of
Mean
Standard
Relative
Relative
95% tol.
Method
Determination
results
outliers
Mean
error
deviation
error
std. dev.
limits
Methyl orange
Free
26
2
0. 647
-0. 183
0.341
22. 0
52. 7
0. 890
Combined
23
4
1.007
+0. 007
0. 163
0. 7
16. 2
0. 436
Total
26
1
1. 698
-0. 132
0. 338
7. 2
19. 9
0. 884
Leuco crystal violet
Free
18
0
0. 331
-0. 499
0. 372
60. 1
112. 2
1. 048
Combined
18
0
1. 159
+0. 159
0. 572
15. 9
49. 3
1. 612
Total
18
0
1.491
-0. 339
0.483
18. 6
32.4
1. 362
Ferrous- DPD
Free
17
3
0. 710
-0. 120
0. 145
14. 5
20. 4
0. 414
Combined
17
3
1.063
+0. 063
0. 077
6. 3
7. 3
0. 221
Total
19
1
1. 751
-0. 079
0. 164
4. 3
9. 4
0. 457
SNORT
Free
15
2
0. 899
+0.069
0.207
8. 3
23. 0
0. 613
Combined
14
2
0. 861
-0, 139
0.186
13. 9
21. 6
Total
17
1
1. 603
-0. 227
0.419
12.4
26. 1
1. 198
Iodometric
Total
32
0
1. 524
-0. 306
0. 360
16. 7
23. 6
0. 909
Orthotolidine
Free
17
0
0. 525
-0. 305
0. 341
36. 8
65. 0
0. 975
Combined
15
2
0. 420
-0. 580
0.160
58. 0
38. 2
0. 474
Total
18
0
1.073
-0. 757
0. 343
41.4
31. 9
0. 966
Orthotolidine-arsenite
Free
23
0
0. 500
-0. 330
0. 323
39. 8
64. 6
0. 862
Combined
22
1
0. 376
-0. 625
0. 168
62. 4
44. 8
0. 454
Total
23
0
0. 923
-0. 907
0. 323
49. 6
35. 0
0. 863
Amperometric
Free
19
6
0. 581
-0.249
0.237
30. 0
40. 8
0. 660
Combined
19
6
1. 112
+0. 112
0. 161
11.2
14. 5
0. 449
Total
24
1
1. 669
-0. 161
0. 209
8. 8
12. 5
0. 553
Ferrous-OT
Free
18
2
0. 516
-0.314
0. 282
37. 8
54. 6
0. 794
Combined
18
2
0. 824
-0. 176
0.258
17. 6
31. 3
0. 726
Total
19
1
1. 359
-0. 471
0. 357
25. 7
26. 3
Tolerance limits were not calculated since the data is non-normal.
-------
1.6
1.4
1.2
1.0
® 0.8
ui
O 0.6
0.4
0.2
0.0
-0.2
10 20 30 40 50 60 70 80 90 95
99.9 99.99
99
0.01
0.1
PERCENT EQUAL TO OR LES5 THAN ORDERED VALUES
Figure I. Probability plot for free chlorine in sample I by louco crystal violet method.
-------
2.2
2.0
£ 1-4
1.2
U 1-0
0.8
0.6 -
0.4
5 10 20 30 40 SO 60 70 SO 90 95
PERCENT EQUAL TO OR LESS THAN ORDERED VALUES
99.9 99.99
99
0.1
0.01
Figure 2. Probability plot for combined chlorine in sample 1 by leuco crystal violet method.
-------
1.8
1.6
1.4
1.2
~ 1.0
Z 0.8
0.6
0.4
0.2
0.0
0.01
0.1
20 30 40 50 60 70 80 90 95
1
10
99
99.9 99.9'9
PERCENT EQUAL TO OR LESS THAN ORDERED VALUES
Figure 3. Probability plot for total chlorine in sample 1 by leuco crystal violet method.
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X TOTAL CHLORINE
¦ FREE.CHLORINE
TOTAL CHLORINE PRESENT
x x x x x x FREE CHLORINE PRESENT < *
*
<*>
*
*
4)
H
¦*
•-i
*4
^4
O
tM
fO
r>
CM
0"
9-
*
*
(M
**
o*
«D
^1
&
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*
M
r-
«4>
o*
«D
to
«n
f-
*N|
OC
fM
<\l
LABORATORY NUMBER
CO
Figure 4. Bar graph for residual chlorine in sample 1 by methyl orange method.
-------
0»
E
at
O
2.25
1.80
1.35
TOTAL CHLORINE
FREE CHLORINE
TOTAL CHLORINE PRESENT
O 0.90
mJ
0.45
0. 00
a a Techlor'ne
K X X
XXX
XXX
XXX
XXX
XXX
XXX
XXX
XXX
X X
X
PRES
*
N
«D
o
^4
**
^4
CM
CM
-------
2. 60
2.40
2.20
2.00
1.80
® 1.60
E
uT 1.40
Z
S 1.20
O
£ 1.00
u 0.80
0.60
0.40
0.20
0.00
TOTAL CHLORINE
FREE CHLORINE
o
o
•
-------
2.75
TOTAL CHLORINE
FREE CHLORINE
TOTAL CHLORINE PRESENT
1.65
O 1.10
CHLORINE PRESENT
<<*-
CM
CM
CM
f-i
CM
«-«
<-«
CM
CM
CM
CM
40
m
o»
*¦
vs
<*
CM
m
ft
(M
CM
sr
CO
LABORATORY NUMBER
Figure 7. Bor graph for residual chlorine in sample 1 by SNORT method.
-------
TOTAL CHLORINE PRESENT
X
X
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*
o»
«D
m
<*-
in
(M
«M
fSI
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m
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1-*
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1-
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N
m
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ft
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wt
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9816
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r-4
o
IM
<*
T-
-------
2.00
1.60 -
a
* 1.20
Ul
Z
£
o
0.80 =
0.40 -
0.00
TOTAL CHLORINE PRESENT
TOTAL CHLORINE
FREE CHLORINE
CHLORINE PRESENT
A)
IM
IM
CM
CM
«n
«o
a>
¦>»
a
m
LABORATORY NUMBER
Figure 9. Bar graph for residual chlorine in sample 1 by orthotolidine method.
-------
2.00
TOTAL CHLORINE PRESENT
1.60 -
J 1,20
X 0.80
u
0.40 -
0.00
TOTAL CHLORINE
FREE CHLORINE
FREE CHLORINE PRESENT
•->
m—f
N
*•
(M
w-t
m-4
#n
N
CI
<¦
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o
m
N
(M
fM
^4
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N
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—1
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*-
N
«
**
o
«»
-O
»
a
-------
CD
2.45
2.10 -
TOTAL CHLORINE
FREE CHLORINE
TOTAL CHLORINE PRESENT
1.75
in
E 1.40
2 1.05
£ FRfE CHLORINE PRESENT 2 x
0. 70
0.35
rsi
«D
CD
N
*>
m
00
m
r-
r-
W
N
r-
CD
M
OP
CD
r-
O*
*—4
LABORATORY NUMBER
Figure 11. Bar graph for residual chlorine in sample 1 by amperometric method.
-------
X TOTAL CHLORINE
FREE CHLORINE
2.20
2.00
TOTAL CHLORINE PRESENT
M if g
1.80
1.40
1.20
1.00
FREE CHLORINE PRESENT
« g B g
0.80
0. 60
0.40
0.20
H
^4
o
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«v
-o
*•
in
*4
n
m
w4
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N
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00
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m
in
<*
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c
r>-
N
r-
*>
ao
e
C
m
«n
00
*
r-
m
«n
f-
o
m
o>
P-
a-
h-
CM
r-
LABORATORY NUMBER
Figure 12. Bar graph for residual chlorine in sample 1 by ferrous-OT method.
-------
Sample 2: 0. 80 mg/liter free, and 0. 84 mg/liter total chlorine {Table
3; Figures 13 through 21)
This sample was designed to provide only free chlorine, which was
liberated from the mixture of HTH and sodium chloride when dissolved
in chlorine-demand-free water. Repeated analysis by the referee labor-
atories, however, consistently indicated a combined-chlorine content of
0. 04 mg/liter, which is an artifact due to the inability of the method to
determine lesser amounts. Since the sample theoretically contained no
combined chlorine, statistical analysis of the results for combined chlo-
rine are of relatively little value. High values probably indicate contam-
ination of the sample by absorption of ammonia from the atmosphere or
the use of dilution water not free of chlorine demand. Hence, combined-
chlorine results are not summarized in Table 3, but individual values
appear in the tabulated data and are indicated in the bar graphs by the
differences between the values for free and total chlorine (Figures 13
through 21).
In the analysis of sample 2 for free chlorine, the mean values obtained
by the SNORT^ and leuco crystal violet methods were not significantly
different from the referee value. The methyl orange, * ferrous- DPD,
and amperometric methods appear to be nearly as accurate. There were
no significant differences in the precision of any of the methods. Note,
however, that considerably better precision and accuracy was shown by
all methods in the determination of total chlorine, and this result arouses
the suspicion of contamination of the sample by the participants.
In the determination of total chlorine in sample 2, the mean values
obtained by the leuco crystal violet and methyl orange methods were not
significantly different from the referee value. The amperometric, ferrous
DPD, and the SNORT methods were not far behind. Again, none of the
methods were significantly more precise than any of the others, but all
were more precise {as noted above) in*the determination of total chlorine
than in the determination of free chlorine.
The least accurate results were obtainedby the ferrous-OT, 9 the
orthotolidine, ® and the orthotolidine-arsenite methods in the analysis
for both free and total chlorine.
18
-------
Table 3. SUMMARY OF DATA ON SAMPLE 2 (0.80 mg/liter free and 0.84 mg/liter total chlorine)
Number of
Number of
Mean
Standard
Relative
Relative
95% tol.
Method
Determination
results
outliers
Mean
error
deviation
error
std. dev.
limits
Methyl orange
Free
26
2
0.624
-0.176
0.268
22.0
43.0
0. 701
Total
26
2
0.794
-0.047
0.188
5.5
23.7
0.490
Leuco crystal violet
Free
17
1
0.743
-0.057
0.243
7.1
32.7
0.694
Total
17
1
0.816
-0.024
0.204
2,8
25.0
0. 582
Ferrous-DPD
Free
19
1
0.642
-0.158
0.255
19.8
39.8
0. 711
Total
19
1
0. 725
-0.115
0.222
13.7
30. 6
0. 618
SNORT
Free
15
2
0. 698
-0.102
0.243
12. 8
34. 7
0. 719
Total
15
3
0.721
-0.119
0.197
14,2
27.3
0. 582
lodometric
Total
32
0
0.642
-0.198
0.174
23.6
27.0
0.438
Orthotolidine
Free
15
2
0.460
-0. 340
0.297
42,5
64. 6
0. 878
Total
15
3
0.625
-0.215
0.212
25,6
33.9
0. 625
Orthatolldinfi-arsemte
Free
20
3
0.462
-0.339
0.242
42.3
52.4
0. 666
Total
20
3
0.654
-0.186
0.147
22,1
22.5
0.405
Amperonaetric
Free
23
2
0. 600
-0. 200
0.254
25.0
42.3
0. 679
Total
23
2
0.761
-0. 079
0.174
9.4
22. 9
0.466
Ferrous-OT
Free
19
1
0.468
-0. 332
0. 247
41.4
52.6
0. 686
Total
19
1
0. 602
-0.238
0. 202
28.4
33.6
0. 563
-------
to
o
1.40
1.20 -
1.00
o>
S- 0.80
0£
O
X 0.60
u
0.40 -
0.20 -
0.00
TOTAL CHLORINE
FREE CHLORINE
TOTAL CHLORINE PRESENT
FREE CHLORINE PRESENT
f*1
#>4
•M
-
M
£T
CM
CM
a
«r
¦*
1M
m
r-
in
«P
CM
p-
fM
CM
*#•
C«>
00
r-
m
CM
C*
LABORATORY NUMBER
Figure 13. Bar graph for residual chlorine in sample 2 by methyl orange method.
-------
1.25
1.00 —
£ 0.75
2 0.50
X TOTAL CHLORINE
¦ FREE CHLORINE
TOTAL CHLORINE PRESENT
FREE CHLORINE PRESENT
0.25
0.00
LABORATORY NUMBER
CO
Figure 14. Bar graph for residual chlorine in sample 2 by leuco crystal violet method.
-------
to
N5
1.00
_ 0.90
® 0.80
oo
X TOTAL CHLORINE
¦ FREE CHLORINE
uj 0.70
t* 0.60
0. 50
0.40
TOTAL CHLORINE PRESENT
FREE CHLORINE PRESENT
0. 30
0.10
0. 00
«*
(M
sr
N
im
4)
«M
^4
«M
w
CM
o
CM
»«4
W
r-
r-
m
r-
-------
1.44
X TOTAL CHLORINE
FREE CHLORINE
1.08
0.96
9
E 0.84
TOTAL CHLORINE PRESENT
FREE CHLORINE PRESENT
0. 72
0.60
u 0.48
0.36
0. 24
0. 00
w-t
cc
¦4-
r-«
K\
•-t
CM
CM
CM
«n
LABORATORY NUMBER
to
CO
Figure 16. Bar graph for residual chlorine in sample 2 by SNORT method.
-------
to
1.00
0.90 -
0. 80
0.70 -
0. 60
w
E
5 0.50
pe
O
-»
3 0.40
0.30 -
0,20
0.10
0.00
X
X
X
X
TOTALCHLORINE present
X
x
x
• X
X
X
X
X
K
> X
X
X
X
X
X
X
X
X
X
X
X
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X
X
X
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X
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X
X
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to
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*-
-------
1.80
TOTAL CHLORINE
FREE CHLORINE
1.20
1.00
TOTAL CHLORINE PRESENT
0£
o 0.80
FREE CHLORINE PRESENT
w 0.60
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0.20
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CM
<43
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-------
to
aj
X TOTAL CHLORINE
FREE CHLORINE
1.20
1.08
TOTAL CHLORINE PRESENT
0. 84
FREE CHLORINE PRESENT
hi 0.72
Z
5 0.60
u 0.48
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IT
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X TOTAL CHLORINE
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TOTAL CHLORINE PRESENT
E 0.80
FREE CHLORINE PRESENT
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to
CO
0. 91
TOTAL CHLORINE PRESENT
FREE CHLORINE PRESENT
0.77
TOTAL CHLORINE
FREE CHLORINE
0. 63
® 0.56
0.49
« 0.42
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LABORATORY NUMBER
Figure 21. Bar graph for residual chlorine in samp le 2 by ferrous-OT method.
-------
Sample 3: 0. 60 mg/liter combined, and 0. 64 mg/liter total chlorine
(Table 4; Figures 22 through 30)
This sample was designed to provide only combined chlorine by-
using a mixture of HTH and sodium chloride, similar to sample 2, and
adding a specified amount of ammonia chloride-borate buffer solution
after dissolving the mixture in chlorine demand-free water. Repeated
analysis by referee laboratories indicated an average free-chlorine con-
tent of 0. 04 mg/liter, but as in the measurement of combined chlorine
in sample 2, this is an artifact due to the inability of the method to deter-
mine lesser amounts. Statistical analysis of the free-chlorine results
is, therefore, of little value and is not reported in Table 4, but the indi-
vidual values can be found in the tabulated data and are plotted on the bar
graphs (Figures 22 through 30),
In the analysis of sample 3 for combined chlorine, the mean values
obtained by the SNORT, ^ ferrous-DPD, 3 methyl orange,1 and the leuco
crystal violet^ methods were not significantly different from the referee
value. The ferrous-DPD3 was significantly more precise than the other
methods.
In the analysis of sample 3 for total chlorine, the mean values ob-
tained bv the leuco crystal violet, SNORT, ferrous DPD, and the amper-
ometric methods were not significantly different from the referee value,
and the precision of the ferrous-DPD method was significantly better than
that of all the others.
Note that, while the amperometer gave very accurate results for
total chlorine, high values were obtained for free chlorine, and this re-
sult caused the calculated combined chlorine to be low. It is very likely
that the high free-chlorine values were caused by the incomplete rinsing
of the amperometer electrode after the determination of total chlorine.
29
-------
Table 4. SUMMARY OF DATA ON SAMPLE 3 (0. 60 mg/liter combined and 0. 64 mg/liter total chlorine)
Number of
Number of
Mean
Standard
Relative
Relative
95% tol.
Method
Determination
results
outliers
Mean
error
deviation
error
std. dev.
limits
Methyl orange
Combined
26
2
0.572
-0.028
0.224
4.7
39.2
0. 585
Total
26
2
0. 731
+0.091
0.220
14.2
30.1
0. 575
Leuco crystal violet
Combined
17
1
0. 566
-0.034
0.172
5. 7
30. 5
0.493
Total
17
1
0.646
-0. 006
0. 222.
0.9
34.4
0. 636
Ferrous-DPD
Combined
17
2
0. 587
-0.013
0.120
2.2
20.4
0. 342
Total
19
1
0.588
-0.052
0.113
8.1
19,2
0. 314
SNOUT
Combined
15
2
0. 589
-0.011
0.266
1.9
45.2
0. 786
Total
16
2
0. 628
-0. 013
0.238
2.0
8.0
0. 692
Iodometric
Total
30
2
0. 522
-0.118
0.169
18.5
32.4
0.430
Ort hotolidine
Combined
14
0
0.450
-0.150
0.174
25.0
38. 6
Total
17
0
0.511
-0.129
0.190
20.2
37.3
0. 544
Orfhotolidine -arseoite
Combined
20
1
0.446
-0.155
0.198
25. 8
44.5
0. 546
Total
21
2
0. 549
-0. 091
0.154
14. 2
28.0
0. 419
Amperometric
Combined
24
1
0.494
-0.106
0.214
17. 7
43.3
0. 567
Total
24
1
0. 585
-0. 055
0.145
8. 5
24. 8
0. 385
Ferrous-OT
Combined
16
2
0. 459
-0.141
0.120
23. 5
26. 1
0. 347
Total
IB
2
0.476
-0.164
0.123
25.6
25. 8
0. 347
Tolerance limits were not calculated since the data is non-normal.
-------
1. 68
1.56
1.44
1.32
1.20
1.08
v.
E 0.96
iiT
? 0.84
at
O
-« 0.72
X
u
0. 60
0.48
0.36
0.24
0.12
0.00
o
c:
TOTAL CHLORINE *
TOTAL CHLORINE PRESENT
lEECHfORlflE PRESENT
LABORATORY NUMBER
CO
Figure 22. Bar graph for residual chlorine in sample 3 by methyl orange method.
-------
CAl
M
0>
E
1.05
0.96
0, 84
0# 72
0.60 -
Z
o 0.48
ml
Z
u 0* 36
TOTAL CHLORINE
FREE CHLORINE
TOTAL CHLORINE PRESENT
PRESENT
W
aFREE CHLORINE
a>
-4-
CM
o
•-»
O
M
w*
r-
(M
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o
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m
r4
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w
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00
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r-
m
(M
m
m
in
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m
LABORATORY NUMBER
Figure 23. Bar graph for residual chlorine in sample 3 by leuco crystal violet method.
-------
1.04
0. 96
0.88
0.80
^ 0.72
X TOTAL CHLORINE
¦ FREE CHLORINE
TOTAL CHLORINE PRESENT
I 0.40
0.32
FREE CHLORINE
PRESENT
g Q g
g_ g g
0.00
*¦
(SI
r-t
(M
o
o
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4
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ao
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r-
r-
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. 1
r-
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m
CM
r-
00
r-
LABORATORY NUMBER
CO
ca
Figure 24. Bar graph for residual chlorine in sample 3 by ferrous-DPD method.
-------
CO
1.44
1.28
1.12
~ 0.96
o
Er 0.80
ui
s °-64
u 0.48
0.16
0.00
TOTAL CHLORINE
FREE CHLORINE
o
in
x
X
CO
CM
X
X
TOTAL CHLORINE PRESENT
?REE CHLORINE PRESENT
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
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X
X
X
X
X
X
X
X
X
X
*¦
in
«¦*
N
•O
r-
r-
LABORATORY NUMBER
Figure 25. Bar graph for residual chlorine in sample 3 by SNORT method.
-------
0.90
0. 80
0.70
0.60
N
s 0.50
iiT
z
2
o
^ 0.40
u
0.30
0.20
0.10
0.00
TO! AlCHtORINC PRESENT
LABORATORY NUMBER
CO
a
Figure 26. Bar graph for re*idual chlorine in sample 3 by iodometric method.
-------
00
01
0. 88
0.80
0.72
- 0.64
E 0.56
iii
Z 0.48
O 0.40
X TOTAL CHLORINE
¦ FREE CHLORINE
TOTAL CHLORINE PRESENT
x
X
X
X
X
X
X
X
X
X
X
X
0.32 —
0.24
0.16
0.08
0. 00
£fre! chlorinepresent
w-i
«©
«M
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(M
in
«M
-O
»M
N
(M
N
N
rt
N
N
N
CM
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N
N
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•01
N
tn
tn
r-
CO
N
CM
«o
CM
ar>
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m
m
r-
r-t
«o
r-
CM
»¦<
m
LABORATORY NUMBER
Figure 27. Bar graph (or residual chlorine in sample 3 by orthotolidine method.
-------
1.10
1.00
X TOTAL CHLORINE
FREE CHLORINE
0. 90
0. 70
TOTAL CHLORINE PRESENT
g S g
ui 0« 60
O 0.50
«¦> 0.40
0.30
0.20
0.10
PRESENT
0. 00
«o
«M
•n
Ol
o
(V
CM
CM
^4
IM
M
«M
N
m
(V
r»
«D
O*
m
IT
o»
O
•H
C
*
o»
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r-
LABORATORY NUMBER
60
*3
Figure 28. Bar graph for residual chlorine in sample 3 by orthotolidine-arsenite method.
-------
CO
oo
1.05
0.90
0.75 -
E 0.60 -
2 0.45
o
0.30
0.15
0.00
X TOTAL CHLORINE
FREE CHLORINE
TOTAL CHLORINE PRESENT
CHLORINE PRESENT
* K X
X_ X_ X
(St
IV
IM
IM
<4*
(*>
cm
^4
M
CO
H
fM
a*
r-
m
f-
IM
«-•
9
r-
m
CD
CO
fM
CD
o
CD
r-
LABORATORY NUMBER
Figur* 29. Bar graph for residual chlorine in sample 3 by amperometric method.
-------
1.04
0. 96
0.88
0.80
0.72
a
0.64
E
ui
0.56
Z
ec
0.48
O
_j
0.40
u
0. 32
0. 24
0.16
0.08
x TOTAL CHLORINE
FREE CHLORINE
TOTAL CHLORINE PRESENT
0. 00
•c
¦n
r4
r4
tn
O
(M
m*
^4
¦O
¦*
^4
^4
T-t
N
«-«
vl
(M
-
«»
CO
sf
*4
o*
LABORATORY NUMBER
Figure 30. Bar graph for residual chlorine in sample 3 by ferrous-OT method.
CO
CO
-------
DISCUSSION
The dry powder mixtures used in this study were quite stable, and
hence, little variation of the samples because of decomposition was
expected. It was realized, however, that because the dry powders were
mixtures of several chemicals (to achieve stability) some variation be-
tween aliquots might be expected. It was hoped, moreover, that, by
requiring each laboratory to analyze the samples by three different
methods, any difference between the methods would become evident,
even though their precision would be poor. This objective has apparently
been accomplished, though recent investigations in the ARS laboratory
have shown that a chlorine solution sealed in a glass ampoule and stored
in the dark (at room temperature) will remain stable for at least 3 months
and probably longer. This *would appear to be a better way of preparing
chlorine samples for use in future studies.
In the measurement of free chlorine in sample 1, the leuco crystal
violet method produced the poorest results. On the other hand, in the
analysis of sample 2 for free chlorine this procedure produced the best
accuracy and precision. Likewise, in the analysis of sample 3 for com-
bined chlorine, while the precision of the method was not as good as the
ferrous-DPD method, there was no significant difference in accuracy.
Apparently, the leuco crystal violet procedure is capable of inhibiting
the hydrolysis of the more active chlorine liberated from a complex
dichloramide (like the halazone in sample 1) and reacts only with the
actual free chlorine present at any instance of time. ' The poor
results from the analysis of sample 1 by this method do not, therefore,
seem to be cause for rejection of the method but rather for its acceptance
since it gave such excellent results in the analysis of samples 2 and 3
and appears to be more specific in the measurement of free chlorine
than any of the others.
When the leuco crystal violet procedure for total chlorine was used,
both the free and combined chlorine in sample 1 should have oxidized the
iodide ion to hypoiodous acid, which in turn oxidizes the reagent to its
highly colored form, crystal violet. The total chlorine content of sample
1 should, therefore, have been correctly determined by this method. As
previously discussed, the one group that presumably did the test correctly
did obtain good total-chlorine values (see Figure 3). A possible source
of error in the total- chlorine procedure is the failure to dilute the sample
to bring the total-chlorine concentration to less than 1 mg per liter as
prescribed. If the total-chlorine concentration is greater than 1 mg per
liter, the developed color has too great an absorbance for accurate meas-
urement, This may be the explanation for some of the poor total-chlorine
results.
Since the overall results of this study indicate that the ferrous-DPD
40
-------
method gave the best precision and accuracy, it is interesting to note
that a British study10 of 12 chlorine methods in 1965 concluded that, for
the measurement of free chlorine in the presence of combined chlorine
in water, the ferrous-DPD colorimetric method was the most satisfactory.
Furthermore, since sample 1 contained both free and combined chlorine,
and the combined chlorine is obtained by subtraction of the free chlorine
from the total chlorine, this value probably provides the best evaluation
of the methods; the subtraction tends to cancel certain systematic errors
such as may occur in the weighing of the sample or in the use of an im-
properly prepared dilution water. If this premise is accepted, then again
the ferrous-DPD procedure produced the best results - as is also true
for sample 3, which contained only combined chlorine.
The poor results obtained in this study by the use of the orthotolidine,
and orthotolidine-arsenite methods may be due in part to the use of old
permanent glass color comparators or of old permanent liquid-type stand-
ards prepared from chromate-dichromate solutions. Both tend to deteri-
orate slightly with age or may be off on preparation and should occasionally
be checked by comparison with temporary standards prepared from chlo-
rine. This does not, however, explain the poor results obtained with the
ferrous-OT method, since all results for this method were obtained by
titration.
COMMENTS OF THE PARTICIPANTS
METHYL ORANGE
Several participants mentioned that although the reagents were stable,
the developed color was not and began to fade within 1 minute after sample
addition; namely, the time of reaction was more critical than anticipated.
Much variation in the solubility of the dry reagent methyl orange was also
found. Another commented that it should be emphasized that acid, stand-
ard methyl orange, and sample should all be present at a pH of 2. 0 +
0..1. One participant stated that the manganese correction values were
higher than the apparent concentration of available chlorine and hence
were disregarded.
LEUCO CRYSTAL VIOLET
One participant reported that repeated analyses of free chlorine in
sample 1 showed a consistently low result. It was also reported that the
curve for free chlorine was linear only to 0. 8 mg/liter, and this obser-
vation seemed to agree with that of another participant, who stated that
the range of 0.1 to 1. 0 mg/liter for total chlorine was much too concen-
trated to be read on a Beckman B spectrophotometer. Another partici-
pant found free-chlorine results varied as much as 12 percent when trip-
licate samples were run and total chlorine as much as 25 percent when
six samples were run.
41
-------
FERROUS-DPD TITRATION
One participant commented that the sharp endpoints were a big ad-
vantage over the iodometric titration. Another, however, observed a
fading endpoint. It was also reported that both free- and total-chlorine
results checked within 1 or 2 percent when triplicate samples were run.
One analyst observed backdrift of red color in all samples, including
blanks with and without addition of potassium iodide.
SNORT
Numerous comments were made about the developed color's fading
too rapidly. One analyst found that total-chlorine results were always
less than the sum of free chlorine plus monochloramine, even after vol-
ume correction. It was also stated that this method shows a deviation
from Beer's Law. Another commented that the results were found to be
reproducible.
IODOMETRIC TITRATION
The four participants commenting on this method agreed that the
endpoint was difficult to detect at such small concentrations. Consider-
able driftback of color was also noted.
ORTHOTOLIDINE (OT)
One participant noted no difference in free-chlorine results run at
20°C and 1°C, nor in total chlorine by adding reagent before or sifter
sample. Lower total chlorine results were, however, obtained when
samples were cooled to 1°C. Several participants noted that the color
development upon the addition of orthotolidine was much slower than
stated in the literature and was extremely unstable. One stated that
sample 1 took about 81 minutes to reach maximum color for total chlo-
rine. Another reported that color was still increasing after 30 minutes
with sample 1. A third commented that the total chlorine reported for
sample 1 was read at 4 to 5 minutes. After 35 minutes, however, the
value increased from 1. 34 to 1, 78 mg/liter. On the other hand sample
3 reached maximum absorbance in 4 minutes for total chlorine. The
comment was also made that this test showed greater reproducibility
than the methyl orange test. Another found that the standards were
questionable since, when iodometrically standardized hypochlorite solu-
tions were diluted with chlorine-free, chlorine-demand-free water, they
were found to be subject to rapid change.
ORTHOTOLIDINE-ARSENITE (OTA)
One participant felt that the precision of this test was poor. Several
42
-------
participants found that it takes too long to add sample and arsenite to
the reagent to get the lowest possible free-chlorine result. Another
stated that after the determination, a further color development was
observed and a maximum absorbance was recorded after 40 minutes.
A fourth stated that it was impossible to get a result on sample 3, since
it had already started to turn before it could be got into the comparator,
and sample 2 cooled to 1°C showed much less free chlorine (0. 5 mg/liter)
than before being cooled (0. 8 mg/liter), probably because of time delay.
As a result it was suggested that the need for rapid addition of the sample
and reagents should be stressed. One commented that a graduated cylin-
der is convenient for dispensing the sample and that a dropping pipet cal-
ibrated to deliver the proper volume will allow rapid dispensing of the
reagent.
AMPEROMETRIC TITRATION
Several found that if the instrument is used to determine free chlo-
rine after making a test for total chlorine, some of the residual iodide
will cause chloramines to titrate as free chlorine. This effect may be
overcome by making a free-chlorine titration of distilled water to the
endpoint before employing the instrument for actual sample processing.
FERROUS-ORTHOTOLIDINE TITRATION (FERROUS-OT)
One participant commented that Skoog and West (Fundamentals of
Analytical Chemistry, Holt, Rtnehart and Winston, 1963: p. 496) and
others have reported the unsuitability of Mohr's salt as a primary stand-
ard because of variation from the theoretical composition. The Fe {II)
titer of two ferrous ammonium sulfate solutions, prepared separately,
was found to be approximately 10 percent below theoretical. Accordingly,
the Fe (II) solution should be standardized before analysis is undertaken.
Several participants had trouble with reproducibility on duplicate samples
and encountered dubious endpoints. On the other hand, one analyst com-
mented on the sharp endpoints and reproducible results and suggested
that, in determining chloramines, addition of titrant while the color
mixture is acidic may result in overtltration if the brown color is not
due to dichloramine color but to the charring effect of acid. There was
also some confusion about the calculation of total chlorine, and it was
felt that there was such a small amount of chlorine to titrate and that
there were so many reagents to be used and so many separate steps to
be taken before each endpoint that accuracy was impossible, owing to
the multiple sources of error.
43
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SUMMARY AND CONCLUSIONS
Precision data developed by this study are useful only for compari-
son of methods and are not a true representation of the capability of a
specific method, because of the variability in samples likely to be intro-
duced by the method of preparation.
In general, the best overall accuracy and precision was shown by
the ferrous-DPD^ method, followed closely by the methyl orange,
SNORT,4 and amperometric methods (see Table 5). The lack of accuracy
of the old orthotolidine methods6, ' 9 make them the least acceptable,
although all methods (with the possible exception of the ferrous-DPD)
appear to have comparable precision. The statement in the SNORT pro-
cedure that chlorine-demand-free water is not necessary may have caused
some difficulty with all of the methods since chlorine-demand-free water
is mandatory for preparation of the samples. The generally low results
for free chlorine suggest the likelihood of chlorine demand in the water,
most likely in the form of ammonia.
The methyl orange* procedure produced good results, but several
participants complained that the developed color was unstable. A possible
source of difficulty in the methyl orange procedure might be the typo-
graphical error in section 4.2, line 13, that reads "-sample of the methyl
orange-, " and should read "-sample to the methyl orange-. " It would
be helpful also to add the information that 5 ml of methyl orange reagent
will cover the range of 0 to 0. 75 mg/liter, 10 ml for 0. 5 to 1. 9 mg/liter,
and 15 ml for 1.25 to 2. 75 mg/liter.
The leuco crystal violet2 procedure produced poor results for sample
1 but was quite acceptable for samples 2 and 3 (see Table 5). This method
is evidently more specific for actual free chlorine and inhibits the hydrol-
ysis of chlorine in materials such as halazone.
n
The iodometric procedure produced only mediocre results and is
obviously not suitable for such small concentrations of total chlorine.
Despite the varied potential sources of error in the methods studied,
the greatest source of error in chlorine measurement is probably in the
use of distilled water that is not completely free of chlorine or of chlorine
demand.
44
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ladle 5. SUMMARY OF OVERALL PRECISION AND ACCURACY
Method
Free
Sample 1
Combined
Total
Sample 2
Free
Total
Sample 3
Combined
Total
Average
Average Mean Error
Ferrous-DPD
0.120
0.083
0.079
0.158
0.115
0.013
0.052
0.086
Methyl Orange
0.183
0.007
0.132
0.176
0.047
0.028
0.091
0.095
SNORT
0.069
0.139
0.227
0.102
0.119
0.011
0.013
0.097
Am pe romet ric
0.249
0.112
0.161
0.200
0.079
0.106
0.055
0.137
Leueo Crystal Violet
0.499
0.159
0. 339
0.057
0.024
0.034
0.006
0.160a
Ferrous-OT
0.314
0.176
0.471
0. 332
0.238
0.141
0. 164
0.262
Orthoiolidine
0.305
0. 581
0.757
0. 340
0.215
0.150
0.129
0. 354
Orthotolidine-As
0. 330
0.625
0. 907
0. 339
0.186
0.155
0.091
0.376
Iodometric
0. 306
0.198
0. 118
0.027
Average Standard Deviation
Ferrous-DPD
0.145
0.077
0.164
0.255
0.222
0.120
0.113
0.156
Amperornetric
0.237
0.161
0.209
0.254
0,174
0.214
0.145
0. 199
Orthotolidine-As
0.323
0.168
0. 323
0.242
0.147
0.198
0. 154
0. 222
Ferrous-OT
0.282
0.258
0.357
0.247
0.202
0.120
0.123
0.227
Orthotolldine
0. 341
0.160
0.343
0.297
0.212
0.174
0.190
0. 246
Methyl Orange
0.341
0.163
0. 338
0.268
0.188
0. 224
0. 220
0.249
SPOHT
0.207
0.186
0.419
0.243
0.197
0.266
0.238
0.251
Leuco Crystal Violet
0.3-73
0. 572
0.483
0.243
0.204
0.172
0.222
0. 324b
Iodometric
0.360
0.174
0.169
0.234
1 0.030 with results on sample 1 excluded,
b 0.210 with results on sample 1 excluded.
-------
REFERENCES
1. Methyl Orange Method for Determination of Residual Chlorine,
Appendix A.
2. 4,4', 4"-Methylidynetris (N, N-dimethylaniline) Method for Residual
Chlorine (Leuco Crystal Violet). Appendix B.
3. Ferrous Method for Free Available Chlorine, Monochloramine
Dichloramine, and Nitrogen Trichloride (Ferrous-DPD), Appendix
C.
4. Stabilized Neutral Orthotolidine (SNORT) Method for Residual
Chlorine and Iodine. Appendix D.
5. lodometric Method, Standard Methods for the Examination of Water
and Wastewater, pp. 91-93. 12th edition. APHA, AWWA, WPCF.
New York, 1965.
6. Orthotolidine Method. Ibid. pp. 93-100.
7. Orthotolidine-Arsenite (OTA) Method. Ibid. pp. 101-102.
8. Amperometric Titration Method. Ibid. pp. 103-108.
9. Ferrous Titrimetric Method for Free Available Chlorine, Mono-
chloramine, and Dichloramine, and Estimation of Nitrogen Tri-
chloride (Ferrous-OT). Ibid. pp. 108-111.
10. Nicolson, N. J. An Evaluation of the Methods for Determining
Residual Chlorine in Water. Part 1. Free Chlorine. Analyst
90:187, 1965.
11. Black, A. P., and G. P. Whittle. New Methods for the Colori-
metric Determination of Halogen Residuals. Part I. Iodine, Iodide,
and Iodate. JAWWA 59:471, 1967.
12. Black, A. P., and G. P. Whittle. New Methods for the Colori-
metric Determination of Halogen Residuals. Part II. Free and
Total Chlorine. JAWWA 59:607, 1967-.
46
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APPENDICES
-------
APPENDIX A.
METHYL ORANGE METHOD FOR DETERMINATION
OF RESIDUAL CHLORINE
1. GENERAL DISCUSSION
1.1. Principle: Free chlorine bleaches a methyl orange solution
quantitatively. In the pH range below 3, methyl orange has a red color
with an absorption spectrum that exhibits a maximum at a wavelength
of 510 m/u. By measuring the change in absorption at 510 m/^, the con-
centration of free chlorine in a sample containing a known amount of
methyl orange may be established. At pH 2 or more the rate of reaction
of chloramines with methyl orange is very slow. In the presence of
excess bromide ion, chloramines also bleach methyl orange rapidly.
Sodium bromide may, therefore, be added to the sample after the free-
chlorine concentration has been determined, and the additional decrease
in absorption will be due to chloramines.
It is important that there be an excess of methyl orange reagent at
all times. If methyl orange is added to the sample, or if the sample is
added with insufficient mixing, the chlorine present will not bleach the
methyl orange quantitatively. The sample must therefore be added to
the reagent with rapid mixing. When the addition of the sample to methyl
orange produces a colorless solution, the need for a larger quantity of
methyl orange is indicated. The additional methyl orange should not be
added to the mixture, but instead the test should be repeated with a new
sample and the larger quantity of methyl orange.
1.2. pH Control: The final pH of the sample reagent should be approx-
imately 2. A higher pH results in incomplete color development, and a
lower pH increases interference by chlorine-ammonia compounds. Either
hydrochloric or chloroacetic acid may be used to adjust the pH. For
samples with a limited range of alkalinity, hydrochloric acid is a more
convenient reagent. Three drops of 6N HC1 suffice for a total alkalinity
up to 300 mg/liter as CaCC>3 and four drops for a total alkalinity of 300
to 600 mg/liter. The use of 1 ml of chloroacetic acid solution provides
the optimum pH in samples containing up to 1, 000 mg/liter alkalinity in a
50-ml sample.
1. 3. Interference: Although suspended matter interferes, if the
amount of suspended matter is low, a "blank reading" of sample without
methyl orange maybe used to correct the absorbance. Chloride ion inter-
feres, but the addition of 1 mg/ml chloride ion to the methyl orange re-
agent eliminates the interference of chloride in concentrations to 1, 000
mg/liter. In the presence of bromide, chlorine-ammonia compounds
48
-------
will interfere, the extent of interference depending upon the bromide
concentration. Bromine and bromine-ammonia compounds also inter-
fere, producing a false chlorine reading equivalent to the active concen-
tration of the bromine compound present. Ferric and nitrite ion in con-
centrations up to 10 mg/liter do not interfere. Manganic ion (0 to 3
mg/liter) bleaches methyl orange quantitatively, but the bleaching due
to manganese may be evaluated by treating a sample with sodium arsenite
at pH 7 before testing. Sodium arsenite selectively reduces residual
chlorine so that the decrease in absorbance in the subsequent test may
be assumed to be due to the equivalent manganic ion.
2. APPARATUS
Colorimetric equipment: One of the following is required.
2.1. Spectrophotometer, for use at 510 mn and providing a light
path of 1 cm.
2.2. Filter photometer, providing a light path of 1 cm and equipped
with a green color filter exhibiting a maximum transmittance near 510
mjj.
3. REAGENTS
Prepare all reagents with ammonia-free distilled water.
3.1. Stock methyl orange solution: Dissolve 500. 0 mg C14H14N3-
SC>3Na and dilute to 1, 000 ml.
3.2. Standard methyl orange solution: Dilute 100 ml stock methyl
orange solution to 1, 000 ml after adding 1. 67 g sodium chloride, NaCl.
The reagent is stable indefinitely.
3. 3. Acid solution: Either chloroacetic or hydrochloric acid may
be used.
a. Chloroacetic acid solution: Dissolve 91 g CHgClCOOH and
dilute to 100 ml.
b. Hydrochloric acid, 6N. 1 + 1.
3.4. Arsenite buffer: Grind a mixture of 125 mg sodium arsenite,
NaAsC^; 375 mg citric acid, CgHgOy; 14.5 g sodium citrate dihydrate,
Na3CgH507 • 2H2O, together as a dry powder. This buffer produces
a final pH of 7 when 100 mg is dissolved in the sample.
3, 5. Sodium bromide solution: Dissolve 2. 5 g NaBr in 100 ml.
49
-------
4. PROCEDURE
The following procedure is suitable for chlorine concentrations to
2 mg/liter. Where the total available chlorine concentration exceeds
2 mg/liter, dilute the sample with double-distilled, ammonia-free water,
or extend the standard calibration curve for methyl orange by the use of
larger aliquots of methyl orange.
4.1. Calibration curves: Prepare the standard calibration curves
by diluting an iodometrically standardized stock solution of chlorine or
hypochlorite and following the procedure given in Sec. 4.2. Plot the
absorbance versus free chlorine concentration. For greatest accuracy,
perform the calibration at a temperature near that of the samples to be
tested, because the absorbance of methyl orange solutions is slightly
dependent upon temperature. For routine measurements in the 10 to
30°C range, the error from this source is negligible.
4. 2. Free available chlorine: To determine free chlorine, combine
5. 0 ml standard methyl orange solution and the proper volume of acid
solution for pH adjustment. Use 1 ml chloroacetic acid solution or 3 to
4 drops (0.15 to 0. 20 ml) 6N HC1. The final pH must be 2. 0 + 0. 1. Add
the 50-ml sample with mixing. After 1 to 1.5 min, measure the absorb-
ance at 510 m/Li, using a 1-cm light path. If the absorbance is greater
than 0. 10, determine the apparent concentration of free chlorine from
the standard calibration curve. If the absorbance is less than 0. 10,
repeat the test, using 10 ml standard methyl orange solution, or dilute
the sample with chlorine-demand-free water.
If manganese is present, first dissolve 100 mg arsenite buffer re-
agent in the 50-ml sample to reduce the free chlorine present. Then add
the sample of the methyl orange-chloroacetic or hydrochloric acid mix-
ture and measure the absorbance at 510 m/ii after 2 to 2. 5 min. Subtract
the apparent free chlorine due to manganese from the free chlorine ascer-
tained by the preceding determination.
4. 3. Total available chlorine: To determine total chlorine, add 0. 5
ml sodium bromide solution to the sample-reagent mixture after the
determination of the free chlorine. Allow 10 min for the reaction of the
chlorine-ammonia compounds and again measure the absorbance. If
manganese is present, apply the above-mentioned correction to both the
free- and total-chlorine results.
BIBLIOGRAPHY
Sollo, F. W. , Jr., and Larson, T. E. Determination of Free Chlorine
by Methyl Orange. JAWWA 57:1575, 1965.
50
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APPENDIX B.
4, 4\ 4 "-METHYLIDYNETRIS (N, N-DIMETHYLANILINE)
METHOD FOR RESIDUAL CHLORINE
1. GENERAL DISCUSSION
1.1. Principle: The compound 4, 4', 4"-methylidynetris (N, N-
dimethylaniline), also known by the trivial name of leuco crystal violet,
reacts instantaneously with free chlorine to form a bluish color. Inter-
ference from combined available chlorine can be avoided by completing
the test within a 5-minute interval. The correct color development in
the free chlorine-leuco crystal violet reaction depends upon the following
factors and conditions, (a) The solution must be buffered in the pH range
of 3. 6 to 4. 3. (b) A mercuric chloride solution must be added to the
sample either before the addition of a leuco crystal violet solution or
more conveniently in the form of a mixed indicator, (c) The ratio by
weight of leuco crystal violet to chlorine must be at least 30 to 1. (d)
The free-chlorine concentration should not exceed 2. 0 mg/liter. (e)
The mixed indicator solution should be added to the sample in a standard-
ized procedure as described in Sec. 4. la. (f) The test should be com-
pleted within 5 minutes after the mixed indicator addition, (g) The sam-
ple temperature should not exceed 40°C.
The total-chlorine determination involves the reaction of the free
and combined chlorine with iodide ion to produce hypoiodous acid, which
in turn reacts instantaneously with leuco crystal violet to form the dye
crystal violet. The color is stable for days and adheres to Beer's law
over a wide range of total chlorine. The extreme sensitivity of the deter-
mination may necessitate the dilution of the sample with chlorine-demand-
free water to bring the chlorine concentration to the desired range of 1.0
mg/liter total chlorine. The following factors are important in the total
chlorine determination, (a) The solution must be at pH 3. 6 to 4, 3 during
the reaction period, (b) There must be an initial contact of at least 15
seconds' duration between chlorine and iodide ion. (c) The initial iodide
concentration must not exceed 40 mg/liter. (d) The total chlorine con-
centration should not exceed 1. 0 mg/liter. Semipermanent color standards
for the total-chlorine determination can be prepared from crystal violet for
visual matching of samples and standards in nessler tubes or test tubes.
Leuco crystal violet is available commercially in a very pure form
that readily dissolves in water acidified with perchloric acid. The con-
centration of perchloric acid must produce a pH of 1. 5 or less in the final
indicator reagent. The dissolution of leuco crystal violet with perchloric
acid must be carried out in the darkness of amber glass, and the final
solution stored in amber glass or opaque plastic containers to minimize
reagent deterioration. Both leuco crystal violet and the developed crystal
51
-------
violet dye are relatively inert, nontoxic substances, and no special pre-
cautions are required other than those normally observed in the handling
of any chemical reagent.
The preparation and handling of the saturated mercuric chloride re-
quires special precaution owing to the poisonous and corrosive nature of
this chemical. The mixed indicator system, although containing a con-
siderably diluted mercuric chloride solution, should likewise be handled
with care.
Improved accuracy in the determination of residual chlorine with
leuco crystal violet is possible through photometric measurements.
The importance of using only chlorine-demand-free water and scrupu-
lously cleaned glassware is self-evident because the presence of ammonia
in the dilution water or organic matter on the glassware can consume
chlorine and result in low chlorine values.
1.2. Interference: No significant interference from combined avail-
able chlorine occurs when the free chlorine content is determined within
5 minutes after addition of indicator. Fifteen minutes after addition of
indicator the apparent error in the free-chlorine determination is of the
order of 0. 04 mg/liter at 25°C in a sample containing 5.0 mg/liter com-
bined residual chlorine.
The one interference deserving attention in the determination of free
residual chlorine is manganic ion, which increases the apparent residual
chlorine reading. When manganic ion is known to be present, the arse-
nite modification outlined in the OTA method in the 12th Edition of Stand-
ard Methods, page 101, can be applied, the leuco crystal violet indicator
system being substituted for orthotolidine.
Nitrite, nitrate, and ferric compounds do not interfere, while the
normal effect of organic compounds is to reduce the free available chlor-
ine, If suspended matter or organic color is present, removal of or com-
pensation for these substances may be accomplished as prescribed in the
12th Edition of Standard Methods, pages 99-100.
1.3. Minimum detectable concentration: 0.01 mg/liter free available
chlorine, 0. 005 mg/liter total available chlorine.
2. APPARATUS
2.1. Illumination: The light sources to be used for comparison of
samples with standards are described in the 12th Edition of Standard
Methods, Sec. 2. 1, page 95.
52
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2.2. Colorimetric equipment: One of the following is required.
a. Nessler tubes, matched, 50 ml, tall form.
b. Test tubes, matched, with a capacity of at least 10 ml of
sample when the sample surface is near the top of the test tube.
c. Filter photometer, providing a light path of 1 cm or longer
and equipped with an orange filter having maximum transmittance near
592 m|i.
d. Spectrophotometer, for use at 592 m/u, providing a light
path of 1 cm or longer.
2. 3. Cleaning of glassware: All glassware or plastic containers,
including containers for storage of reagent solutions, must be entirely
freed of organic matter. This objective can be attained by recourse to
either the chlorination or chromic acid method after the glassware has
been thoroughly cleaned with suitable detergent and rinsed with distilled
water. The chromic acid method requires less total time, but care is
necessary to protect the laboratory personnel from contact with the
cleaning mixture.
a. Chlorination: Expose all glassware or plastic containers
to water containing at least 10 mg/liter chlorine for 3 hr or more before
use, and then rinse with chlorine-demand-free water. After rinsing,
oven or air dry the glassware in an atmosphere free from organic fumes.
b. Chromic acid: Prepare the chromic acid solution by adding
1 liter concentrated sulfuric acid to 35 ml saturated sodium dichromate
solution contained in a 2-liter beaker. Stir the mixture carefully until
all of the sodium dichromate has dissolved. When cleaning glassware,
carefully heat a suitable volume of chromic acid solution to approximately
50°C. (CAUTION: Use rubber gloves, safety goggles, and protective
clothing in handling this cleaning agent.) Carefully pour the chromic
acid solution into the glassware to be cleaned so that contact is made with
the entire inside surface of the container. Allow the cleaning solution
to remain in the glassware for 2 to 3 min or longer. Carefully empty
the glassware of chromic acid solution and rinse thoroughly with chlorine-
demand-free water. Oven or air dry the glassware away from organic
or other chlorine-consuming fumes.
3. REAGENTS
3.1, Chlorine-demand-free water: Chlorine-demand-free water
can be made by the chlorination or ion-exchange methods. In either
case, best results are obtained when distilled water is used as the pri-
mary source.
53
-------
a. Chlorination: Add sufficient chlorine to distilled water to
destroy the ammonia. The amount of chlorine required will be about
ten times the amount of ammonia nitrogen present; in no event should
the initial residual be less than 1.0 mg/liter free chlorine. Allow the
chlorinated water to stand overnight or longer; then expose to direct sun-
light until all residual chlorine is discharged.
b. Ion exchange: Prepare a 3-foot column of approximately
2. 5 to 5 cm diameter containing strongly acid cation and strongly base
anion exchange resins. Several commercial mixed-bed resins, analyti-
cal grade (Amberlite MB-1), are available, but the analyst should satisfy
himself that ammonia, chloramines, or other compounds that react with
chlorine are removed. Pass the distilled water at a relatively slow rate
through the resin bed and collect in a scrupulously cleaned receiver that
will protect the treated urater from undue exposure to the atmosphere.
c. Prepare all reagent solutions and dilute all samples with
the chlorine-demand-free water.
3.2. Stock chlorine solution: Prepare the stock chlorine or hypo-
chlorite solution from certain commercial solutions (Zonite, a product
of Zonite Products Corp., contains approximately 1 per cent available
chlorine; or household bleach), or by bubbling chlorine gas from a small
lecture-size cylinder into distilled water. For convenience, adjust the
chlorine concentration to approximately 100 ng per ml of solution. Stand-
ardize the stock solution by titrating a suitable aliquot with standard sodi-
um thiosulfate titrant as described in the 12th Edition of Standard Methods.
Iodometric Method A, Sec. 3. 2 and 3. 3, page 93, or by the amperometric
titration method described on pages 103-108.
3. 3. Chlorine solution for temporary total chlorine standards: If
measurements of combined residual chlorine are desired, mix an ammo-
nium sulfate solution with chlorine solution in an ammonia-to- chlorine
ratio of at least 20 to 1. Dissolve 3.89 grams (NH^SC^ in distilled
water and dilute to 1, 000 ml to form a solution containing 1. 0 mg NH3
per 1. 0 ml. React each 2. 0 ml (NH^SC^ solution with each 1. 0 ml stock
chlorine solution, which contains 100 ug per 1.0 ml. Standardize the
combined chlorine solution and use immediately for calibration purposes.
3.4. Buffer solution for free-chlorine determination, pH 4. 0.
a. Potassium hydroxide, 4M. Dissolve 224. 4 g KOH and dilute
to 1 liter with chlorine-demand-free water.
b. Citric acid, 2M. Dissolve 384. 3 g CgHgO^, or 420, 3 g
C6H807 • H2O, and dilute to 1 liter with chlorine-demand-free water.
54
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c. Potassium citrate solution: To 350 ml 4M potassium hydrox-
ide, add with stirring 700 ml 2M citric acid. If desired, prepare smaller
volumes in the ratio of 1 volume of potassium hydroxide to 2 volumes of
citric acid.
d. Acetate solution: Dissolve 161. 2 g glacial acetic acid and
49. 5 g sodium acetate, CHgCOONa, or 82. 1 g CHgCOONa • 3H2O, and
dilute to 1 liter with chlorine-demand-free water.
e. Final buffer solution: Mix equal volumes of potassium citrate
solution (c) with acetate solution (d) to make the final pH 4. 0 buffer solu-
tion for the free-chlorine determination.
3. 5. Stock leuco crystal violet reagent: Measure 500 ml chlorine-
demand-free water and 14,0 ml 85 percent ortho-phosphoric acid into a
brown glass container of at least 1-liter capacity. Introduce a magnetic
stirring bar into the container and mix the acidified water at moderate
speed. Add 3. 0 g 4, 4', 4"-methylidynetris(N, N-dimethylaniline), East-
man Chemical No. 3651, and continue agitation until dissolution is com-
plete. Finally, add 500 ml chlorine-demand-free water. Store in the
brown bottle at room temperature away from direct sunlight. Discard
after 6 months. If a rubber stopper must be used, wrap with Saran or
other plastic wrapping material to protect from contact with the reagent.
3. 6. Saturated mercuric chloride solution: To 20 g HgClg contained
in a 300-ml flask, add 200 ml chlorine-demand-free water. Gently agi-
tate for a few minutes and let stand for 24 hr. (CAUTION: Label the
container with the warning that mercuric chloride is poisonous and corro-
sive. )
3. 7. Mixed indicator: To 600 ml stock leuco crystal violet reagent
in a brown bottle, add 50 ml saturated mercuric chloride solution and
swirl to ensure complete mixing. If desired, prepare smaller volumes
of mixed indicator in the ratio of 12 volumes stock leuco crystal violet
reagent to 1 volume saturated mercuric chloride solution. Follow the
storage directions prescribed in Sec. 3. 5 for the stock leuco crystal
violet reagent.
3. 8. Buffer solution for total chlorine determination, pH 4. 0. Dis-
solve 480 g glacial acetic acid and 146 g sodium acetate, CHgCOONa, or
243 g Ct^COONa • 3H2O, in 400 ml chlorine-demand-free water and
dilute to 1 liter. Transfer the solution to a brown bottle. Add 3.0 g
potassium iodide, KI, to the bottle and shake the bottle to dissolve the
salt. Store the solution in the brown bottle and avoid undue exposure to
the air.
3, 9. Solutions for preparation of semipermanent total-chlorine
standards:
55
-------
a. Buffer solution, pH 4. 0. Dissolve 480 g glacial acetic acid
and 146 g sodium acetate, C^COONa, or 243 g CH^COONa • 3H2O, in
400 ml chlorine-demand-free water and dilute to 1 liter.
b. Crystal violet solution: Dissolve 40. 0 mg crystal violet,
Eastman Chemical No. C 1350, in 500 ml chlorine-demand-free water
containing 20 ml pH 4. 0 buffer solution (3. 9a). Stir for 30 min or more
to effect complete dissolution, then dilute to 1, 000 ml with chlorine-
demand-free water.
4. PROCEDURE
4.1. Temporary chlorine standards: Temporary standards are
recommended for photometric calibration and research work as well as
for visual comparison. Two separate sets of temporary chlorine stand-
ards are mandatory because of the divergent colors developed by free
and combined residual chlorine. Semipermanent color standards for the
total-chlorine determination can be prepared from crystal violet dye and
have a longevity approaching 3 months. The color system produced with
free residual chlorine, on the other hand, differs from the normal crystal
violet shade and is stable for only a few days. Commercially prepared
standards may be purchased from the La Motte Chemical Products Co.,
Chestertown, Maryland 21630, at this time, but it is hoped that a method
of preparing standards will be available to all in the near future,
a. Preparation of temporary free-chlorine standards: Thor-
oughly clean all glassware as described in Sec. 2. 3 and preferably air
or oven dry before use. Prepare temporary chlorine standards from a
suitable volume of stock chlorine solution added to 2 liters of chlorine-
demand-free water contained in an amber glass bottle. Set up a chlorine
series in the range of 0.1 to 2. 0 mg/liter at increments of 0. 1 or 0. 2
mg/liter for visual comparison studies. Standardize the dilute chlorine
solutions by means of the sodium thiosulfate or amperometric titration
methods.
After standardization, measure exactly 50 ml dilute chlorine solution
into a 100-ml glass-stoppered volumetric flask, taking care to introduce
the chlorine solution with a minimum of agitation into the volumetric
flask. By means of a Mohr pipet, add 1. 0 ml pH 4. 0 buffer solution,
Sec. 3, 4, and gently swirl the flask to mix. With another measuring
pipet, add 1. 0 ml mixed indicator, Sec. 3. 7. Standardize the mixed
indicator addition in the following manner. After filling the measuring
pipet to the mark, position the pipet tip inside the neck of the volumetric
flask so that the tip makes contact with the inside glass surface, and
allow the mixed indicator to flow down the inside glass surface to the
sample with a minimum of initial agitation of the sample. Remove the
pipet from the flask and swirl the contents with a quick firm motion to
56
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effect intimate contact between the mixed indicator and the sample.
These steps produce the highest and most consistent absorbance values.
Transfer the colored temporary standards to 50-ml nessler tubes
for visual comparison, or prepare a photometric calibration curve.
Visual comparison: If the temporary standards are prepared di-
rectly in 50-ml nessler tubes, stopper the tube after addition of the
mixed indicator, and mix quickly by inverting the tube several times.
If a smaller sample volume is taken, as, for example, 10 ml contained
in a test tube, reduce the quantity of pH 4. 0 buffer and mixed indicator
to 0. 2 ml each.
Photometric calibration: Transfer the colored temporary standards
of known free-chlorine concentration to cells of 1 cm light path or longer,
and read the absorbance in a photometer at a wavelength of 592 mju against
a distilled water reference. Plot the absorbance values versus chlorine
concentrations to construct a curve that approximates Beer's law in the
lower free-chlorine range and exhibits a slight curvature with the higher
free-chlorine concentrations.
b. Preparation of temporary total-chlorine standards: Pre-
pare standardized solutions in the total-chlorine range of 0.1 to 1. 0
mg/liter. Pipet a 50-ml sample into a 100-ml volumetric flask or 50-
ml nessler tube. Add 0. 5 ml total-chlorine buffer. Sec. 3. 8, mix, and
allow a contact period of at least 15 sec. Add 0. 5 ml mixed indicator
and mix to develop the color. No special precautions are necessary in
the addition and mixing of these solutions.
Photometric calibration; Construct a calibration curve by measur-
ing the absorbance values of the temporary total-chlorine standards at
592 m/u, preferably in 1-cm cells.
4. 2. Semipermanent total-chlorine standards: The variable compo-
sition of commercially available crystal violet dye necessitates a recon-
cilement of the absorbance of the semipermanent standards with the photo-
metric calibration curve. The final semipermanent standards should be
adjusted into agreement with the calibration absorbance values obtained
on temporary total-chlorine standards.
Add the specified volume of crystal violet solution to a 200-ml volu-
metric flask containing 100 ml distilled water and 4. 0 ml pH 4. 0 buffer
solution. Sec. 3. 9a. Dilute to volume with distilled water and compare
the absorbance at 592 mn with the suggested values given in Table B-l
or with the photometric calibration curve. Protect the standards from
direct sunlight and exposure to air to maintain stability for approximately
3 months. Seal the standards in glass ampoules for maximum protec-
tion.
57
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Table B-l. SEMIPERMANENT TOTAL-CHLORINE STANDARDS
Total-chlorine
standard,
mg/liter
Crystal violet
solution,
ml
Absorbance of final
200-ml standard at
5 92 mju in 1-cm cell
0. 1
2. 84
0. 131
0. 2
5. 80
0. 268
0. 3
8. 60
0. 396
0.4
11. 60
0. 530
0. 5
14. 40
0. 660
0. 6
o
CO
t>
1—1
0. 790
0. 7
20. 00
0. 925
0. 8
23. 20
1. 060
0. 9
26. 60
1. 192
1.0
28. 80
1. 320
4.3. Color development of free-chlorine sample: To ensure the
highest accuracy and reproducibility of results, apply the mixed indica-
tor to the unknown sample in the same uniform manner prescribed for
the temporary standards in Sec. 4. la. Match the test sample visually
with the temporary standards, or read the absorbance photometrically
and refer to the standard calibration curve for the free-chlorine equiv-
alent. Complete the determination within 5 min of the addition of the
mixed indicator to obviate interference from combined residual chlorine
composed of mono-, di-, and tri-chloramine and manifested by a slow
increase in color.
The color development due to combined chlorine residuals is negli-
gible at sample temperatures as high as 40°C and slightly accelerated
at higher temperatures. The color with free chlorine develops instan-
taneously, and in the absence of combined residual chlorine is stable for
several days.
4. 4. Color development of total-chlorine samples:
a. Concentrations less than 1. Q mg/liter. Measure a 50-ml
sample into a suitable flask or tube and add 0. 5 ml total-chlorine buffer,
Sec. 3. 8. Mix and wait at least 60 sec. Add 1. 0 ml mixed indicator,
mix, and visually match with standards or read the absorbance photo-
metrically and compare with the calibration curve.
58
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b. Concentrations more than 1. 0 mg/liter: Place approximately
25 ml chlorine-demand-free water in a flask or tube calibrated to con-
tain at least 50 ml. Add 0. 5 ml total-chlorine buffer, Sec. 3. 8, followed
by a known volume of 25 ml or less of the unknown sample. After mixing,
let stand for at least 60 sec. Add 1. 0 ml mixed indicator, mix, and di-
lute to the mark with chlorine-demand-free water. Match visually with
standards or read the absorbance photometrically and compare with the
calibration curve. Select one of the following sample volumes in order
to remain within the optimum chlorine range:
Total chlorine, mg/liter Sample volume required, ml
1.0 to 2.0 25
2.0 to 2.5 20
2.5 to 3. 0 15
3. 0 to 5. 0 10
5. 0 to 10. 0 5
The total-chlorine color develops instantaneously and remains stable
for days. The final color, if too intense for visual matching, may be
diluted, matched with standards, and the initial total chlorine estimated
by applying the dilution factor.
4. 5. Compensation for turbidity and color: Compensate for the
presence of natural color turbidity as described in Standard Methods,
Sec. 7. 4, pages 99 and 100. ~
5. CALCULATION
A X 50
mg/liter total CI =
ml sample
mg/ liter combined CI = B - C
where A = total chlorine measured in mg/liter, B = total chlorine in
mg/liter, and C = free chlorine in mg/liter.
BIBLIOGRAPHY
Standard Methods for the Examination of Water and Wastewater. 12th
edition. APHA, AWWA, WPCF, New York, 1965.
59
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APPENDIX C.
FERROUS METHOD FOR FREE AVAILABLE CHLORINE, MONO-
CHLORAMINE, DICHLORAMINE, AND NITROGEN TRICHLORIDE
1. GENERAL DISCUSSION
1. 1. Principle: N, N-diethyl-p-phenylenediamine (DPD) has been
introduced by Palin* for use in the ferrous method in place of neutral
orthotolidine. The colors produced are more stable, fewer reagents
are required, and a full response in neutral solution is obtained from
dichloramine. In the titrimetric procedure, decolorization by standard
ferrous ammonium sulfate (FAS) titrant is instantaneous and thereby
permits each step to be performed more rapidly. In the colorimetric
version of the method, the standard colors are prepared by use of a
standard potassium permanganate solution. Where complete differentia-
tion is not required, the procedure may be further simplified to give only
free and combined available chlorine or total residual available chlorine.
In the absence of iodide ion free available chlorine reacts instantly
with the N, N-diethyl-p-phenylenediamine (DPD) indicator to produce a
red color. Subsequent addition of a small amount of iodide ion acts
catalytically to cause monochloramine to produce color. Further addi-
tion of iodide ion to excess evokes a rapid response from dichloramine.
Unlike the reaction with neutral orthotolidine, any nitrogen trichloride
present no longer displays color with free available chlorine but is in-
cluded with dichloramine. By adding iodide ion before DPD, however,
a proportion of the nitrogen trichloride is caused to appear with free
available chlorine. A supplementary procedure based upon altering in
this way the order of adding the reagents thus permits the estimation of
nitrogen trichloride.
Chlorine dioxide appears, to the extent of one-fifth of its total avail-
able chlorine content, with free available chlorine. A full response from
chlorine dioxide, corresponding to its total available chlorine content,
may be obtained if the sample is first acidified in the presence of iodide
ion and subsequently brought back to an approximately neutral pH by addi-
tion of bicarbonate ion. Bromine, bromamine,. and iodine react with
DPD indicator and appear with free available chlorine, DPD procedures
for the determination of these halogens and related compounds have been
developed. 2. 3
In a recent comparison of methods for the determination of both free
chlorine and chloramines in water it was concluded that the best colori-
metric method was the DPD method and the best all-round method the
DPD-FAS titration.4" 5
1. 2. pH Control: For accurate results careful pH control is essen-
60
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tial. At the proper pH of 6. 2 to 6. 5, the red colors produced may be
titrated to sharp colorless endpoints. The titration must be carried out
as soon as the red color is formed in each step. Too low a pH in the
first step will tend to make the monochloramine show in the free-chlorine
step and the dichloramine in the monochloramine step. Too high a pH
may cause dissolved oxygen to give a color.
1. 3. Temperature control: In all methods for differentiating free
chlorine from chloramines the higher the temperature the greater the
tendency for the chloramines to react with the reagents and thus lead to
increased apparent free-chlorine results after a fixed time interval. The
exceptions to this are the titration methods, probably due to the speed
with which the titration is completed compared with the 2 to 3 minutes
required for the colorimetric measurement to be made. The DPD methods
are among those least affected by temperature. ®
1. 4. Interference; The only interfering substance likely to be en-
countered in water is oxidized manganese. To correct for this, place
5 ml of buffer solution, one small crystal of potassium iodide, and 0. 5
ml of sodium arsenite solution (500 mg NaAs02 plus 100 ml distilled
water) in the titration flask. Add 100 ml of sample and mix. Then add
5 ml of DPD indicator solution, mix, and titrate with standard ferrous
ammonium sulfate titrant until any red color is discharged, or measure
colorimetrically. The reading is subtracted from reading A obtained by
the normal procedure as described in Sec. 3. la of this method. If the
combined reagent in powder form (see below) is used, the potassium
iodide and arsenite are first added to the sample and mixed, the com-
bined buffer-indicator reagent being added afterwards.
Interference by copper up to approximately 10 mg/liter copper is
overcome by the EDTA incorporated in the reagents. The presence of
EDTA also enhances the stability of the DPD indicator solution by re-
tarding deterioration due to oxidation and in the test itself provides virtu-
ally complete suppression of dissolved oxygen errors by prevention of
trace metal catalysis.
2. REAGENTS
2.1. Phosphate buffer solution: Dissolve 24 g anhydrous disodium
hydrogen phosphate, Na2HPC>4, and 46 g anhydrous potassium dihydrogen
phosphate, KH^PO^, in distilled water. Combine this solution with 100
ml distilled water in which 800 mg disodium ethylenediamine tetraacetate
dihydrate, also called (ethylenedinitrilo) tetraacetic acid sodium salt,
have been dissolved. Dilute to 1 liter with distilled water and add 20 mg
mercuric chloride to prevent mold growth.
2. 2. N, N-diethyl-p-phenylenediamine (DPD) indicator solution:
Dissolve 1 g DPD Oxalate (Eastman Chemical No. 7102) or 1.5 g
61
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p-amino-N:N-diethylaniline sulphate (British Drug Houses chemical
available from Gallard-Schlesinger Chemical Mfg. Corp., 584 Mineola
Ave., Carle Place, Long Island, N. Y. , 11514) in chlorine-free distilled
water containing 8 ml 1 + 3 sulfuric acid and 200 mg disodium ethylene-
diamine tetraacetate dihydrate. Make up to 1 liter, store in an amber
glass-stoppered bottle, and discard when discolored. (The buffer and
indicator are commercially available as a combined reagent in stable
powder form. )
2. 3. Standard ferrous ammonium sulfate (FAS) titrant: Dissolve
1. 106 g Mohr's salt, Fe(NH4)2(S04.)2 " 6H2O in distilled water contain-
ing 1 ml of 1 + 3 sulfuric acid and make up to 1 liter with freshly boiled
and cooled distilled water. This is a primary standard and may be used
for 1 month. Potassium dichromate may be used to check the titer. The
FAS titrant is equivalent to 100 /ig CI per 1. 00 ml.
2.4. Potassium iodide crystals.
2. 5. Potassium iodide solution: Dissolve 50 g KI and dilute to 1
liter, using freshly boiled and cooled distilled water. Store in a brown,
glass-stoppered bottle, preferably in a refrigerator. Discard the solu-
tion when a yellow color develops.
3. PROCEDURE
The quantities given below are suitable for concentrations of total
available chlorine up to 4 mg/liter. Where the total chlorine exceeds
4 mg/liter, use a smaller sample and dilute to a total volume of 100 ml.
Mix the usual volumes of buffer reagent and DPD indicator solution, or
the usual amount of DPD powder, with distilled water before adding suffi-
cient sample to bring the total volume to 100 ml.
3.1. Free available chlorine or chloramine: Place 5 ml each of
buffer reagent and DPD indicator solution in the titration flask and mix
(or use about 500 mg of DPD powder). Add 100 ml sample and mix.
a. Free available chlorine: Titrate rapidly with standard FAS
titrant until the red color is discharged (reading A).
b. Monochloramine: Add one very small crystal of potassium
iodide and mix; or if the dichloramine concentration is expected to be
high, add 0.1 ml (two drops) potassium iodide solution and mix. Con-
tinue titration until the red color is again discharged (reading B).
c. Dichloramine: Add several crystals of potassium iodide
(about 1 g) and mix to dissolve. Allow to stand for 2 minutes and then
continue titration until the red color is again discharged (reading C).
62
-------
In the case of very high dichloramine concentrations, allow a further
2 minutes standing if color driftback indicates slightly incomplete re-
action. When dichloramine concentrations are not expected to be high,
use half the specified amount of potassium iodide.
d. Simplified procedure for free and combined available chlo-
rine or total available chlorine: Omit stage 4 per liter.
Dilute 10 times for use, whereupon 1 ml made up to 100 ml with distilled
water is equivalent to 1 mg/liter CI. The standard colors produced after
adding the prepared permanganate solutions to the buffer reagent and
indicator, as in Sec. 3. 1, may, after the calibration procedure, be titra-
ted against standard FAS titrant solution as a check on the standard color
and on any absorption of permanganate by the distilled water used.
4. CALCULATION
For a 100-ml sample, 1.00 ml standard FAS titrant equals 1. 00
mg/liter available residual chlorine.
If monochloramine is present with nitrogen trichloride, which is
unlikely, it will be included in reading D, in which case NClg is obtained
from 2(D-B).
63
-------
Chlorine dioxide if present, is included in reading A to the extent
of one-fifth of its total available chlorine content.
Reading
A
NCI 3 absent
free CI
NH2C1
nhci2
NCI3 present
B - A
C - B
free CI
NH2C1
D
NHC12 + 1/2 NCI3
free Ci + 1/2 NCI3
2(D - A)
C - D
NCI3
nhci2
BIBLIOGRAPHY
Palin, A. T. The Determination of Free and Combined Chlorine in
Water by the Use of Diethyl-p-phenylene Diamine. JAWWA 49: 873,
1957.
Palin, A. T. Colorimetric Determination of Chlorine Dioxide in Water.
Water and Sewage Works 107: 457, 1960.
Palin, A. T. The Determination of Free Residual Bromine in Water.
Water and Sewage Works 108: 461, 1961.
Nicolson, N. J. An Evaluation of the Methods for Determining Resi-
dual Chlorine in Water. Part 1. Free Chlorine. Analyst 90: 187,
1965.
Nicolson, N. J. Determination of Chlorine in Water. Parts 1 and 2.
Water Research Assoc. , Medmenham, England. Tech. Papers No. 29
(1963), No. 47 (1965).
64
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APPENDIX D.
STABILIZED NEUTRAL ORTHOTOLIDINE (SNORT) METHOD
FOR RESIDUAL CHLORINE AND IODINE
1. GENERAL, DISCUSSION
The orthotolidine method using hydrochloric acid (method B) meas-
ures both free and combined chlorine. Modifications of this method used
to differentiate between free and combined chlorine, the flash test (method
C), and the OTA test (method D), depend on the slightly slower rate of
reaction of orthotolidine in acid solution with combined chlorine than with
free chlorine. The rapid addition of reagents and temperatures near "i°C
are required even with the flash test and OTA methods (C and D).
1.1. Principle: Orthotolidine is quite stable in the reduced form
when stored in brown bottles in the presence of hydrochloric acid. The
stability of oxidized orthotolidine decreases, however, as the pH in-
creases. For this reason, orthotolidine has classically been used at pH
1. 3 and lower. As the pH is increased, the rate of reaction of orthotol-
idine with nitrite, iron, and combined chlorine becomes slower and essen-
tially disappears at pH 7. Although neutral orthotolidine was proposed1
for an analytical method as early as 1939 and used by many others later,
the pH values used by these early workers were below 7, the pH required
to minimize interference, because a stable product could not be produced
at this pH. To obtain correct color development from free chlorine and
orthotolidine, it is necessary to have the pH of the solution at 7. 0 because
of interferences at lower pH, and to produce stable colors at these high
pH values it is necessary to add a stabilizer. It has been noted by Johnson?. 8
that anionic surface-active agents in general stabilize the orthotolidine
product, and "Aerosol OT, " a trademark of the American Cyanamid Co.,
sodium di(2-ethylhexyl) sulfosuccinate is the best stabilizing reagent found
to date. The concentration of stabilizer required for best stability at high
and low temperature is 40 mg for each 100 ml of sample plus reagents.
The ratio by weight of orthotolidine dihydrochloride to chlorine must
be at least 8 to 1. With the concentration of orthotolidine recommended
in the procedure the chlorine concentration must not exceed 6 mg/liter.
The pH of the final solution must be between 6.5 and 7. 5 to minimize
low pH interference and high pH fading. If the pH of the sample is less
than 5 or greater than 9, and in addition the alkalinity is greater than 150
or the acidity greater than 200 mg/liter, the final pH of the solution should
be checked. If the alkalinity is high and the final pH does not lie within
the range 6. 5 to 7. 5, the sample should be adjusted to this range before
analysis.
65
-------
To ensure correct color development, minimum interference, a
pH of 6. 5 to 7. 5, and a ratio of orthotolidine to free chlorine of at least
8 to 1, the sample must be added to the reagents.
The reaction time and temperature are relatively unimportant com-
pared with the usual methods for chlorine determination. For extremely-
large ratios of combined chlorine to free chlorine, however, high tem-
perature and long waiting times are undesirable. At 35° C a 1-mg/liter
monochloramine solution produces a false free-chlorine residual of 0. 01
mg/liter per minute. At high temperature and for long waiting times,
color fading may become important, especially at less than 0. 1 mg/liter
free chlorine. A 1-mg/liter solution of free chlorine fades at the rate
of 0. 005 mg/liter per minute at 35°C.
Iodide can be added in neutral solution to measure monochloramine
and in acidic solution to measure dichloramine. The reaction of iodide
and chloramine yields a concentration of iodine equivalent to the chlora-
mine. In the colorimetric procedure, orthotolidine is present with the
chloramine when iodide is added, and the iodine produced by the chlora-
mine is immediately reduced back to iodide and acts as a catalyst in gen-
erating an amount of blue orthotolidine equivalent to the original chlora-
mine present. Because of this catalytic effect, lesser amounts of iodide
are required compared with amperometric titration, which improves the
separation of the monochloramine and dichloramine fractions.
Other comments in Standard Methods under the orthotolide method
B, Sec. 1, General Discussion, are applicable regarding stability and
preparation of orthotolidine, the use of chlorine-demand-free water, and
precautions for the exclusion of laboratory fumes, reducing agents, and
oxidizing agents from the reagents.
1.2. Interference: When orthotolidine or any other chromogenic
reagent is used to measure residual chlorine, strong oxidizing agents
of any kind form an interference. Such interferences include manganic
compounds, chlorine dioxide, bromine, iodine, and ozone. The reduced
form of these compounds, manganous ion, bromide, chloride, iodide,
and oxygen do not, however, interfere with the method. Reducing agents
such as ferrous compounds, hydrogen sulfide, and oxidizable organic
matter do not form an interference in the analytical method but may inter-
fere in maintaining chlorine residuals by reducing the chlorine residual
by reaction with the chlorine to produce chloride ion, acting simply as
chlorine demand.
Turbidity and color also interfere with the method as with any other
colorimetric method unless the background turbidity or color are com-
pensated for by using a blank. Concentrations of 55 mg/liter iron, 92
mg/liter nitrite, and 6,000 mg/liter chloride do not interfere. The inter-
66
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ference of combined chlorine is insignificant in the determination of free
chlorine except as noted before at high temperature and long waiting times.
Manganic compounds produce up to stoichiometric interference but can
be compensated for by using a blank. In the presence of greater than 0. 01
mg/liter manganic manganese, a blank is prepared by adding 5 ml of sodi-
um arsenite to a 100-ml sample. This sample is then added to the reagents
as usual, and this blank is used as a reference in measuring the free chlo-
rine present, either by zeroing the photometer with this blank or by using
the blank as a reference when making color comparison.
If nitrogen trichloride is present, half reacts as free available chlo-
rine, but the remainder does not interfere in the monochloramine and
dichloramine measurements. Many different organic chloramines are
possible. The extent to which these organic chloramines interfere in
the monochloramine or dichloramine determination steps depends on the
nature of the organic compound; they may appear in either or both frac-
tions.
1.3. Minimum detectable concentration: The SNORT chlorine re-
action is sensitive to free residual chlorine concentrations as small as
approximately 0, 01 mg/liter.
2. APPARATUS
Colorimetric equipment: One of the following is required.
2.1. Filter photometer, providing a light path of 1 cm or longer
for 1 mg/liter free chlorine residual and less, or a light path from 1 to
10 mm above 1-1/2 mg/liter free chlorine residual; also equipped with
a red filter having maximum transmission in the range of 600 to 650 m^t.
2. 2. Spectrophotometer, for use at 625 m/u, providing a light path
noted in Sec. 2,1.
3. REAGENTS
Chlorine-demand-free distilled water recommended below can be
prepared as discussed in Chlorine-Orthotolidine Method B, Sec. 3.1.
It is not an absolute requirement, because chlorine will generally react
with the orthotolidine in the reagents before it can react with demand
compounds.
3.1. Neutral orthotolidine reagent: Add 5 ml concentrated reagent-
grade hydrochloric acid to 100 ml chlorine-demand-free distilled water.
Add 5 ml of this acid solution and 1. 5 g reagent-grade orthotolidine dihy-
drochloride to chlorine-demand-free distilled water and dilute to 1 liter.
Store in a brown bottle and observe the other storage precautions in the
67
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chlorine acid-orthotolidine method B. (CAUTION: Toxic; take care to
avoid ingestion.)
3.2, Buffer-stabilizer reagent; Dissolve 25. 9 g disodium hydrogen
phosphate, Na2HPC>4, 12. 6 g potassium, dihydrogen phosphate, KH2PO4,
8. 0 g "Aerosol OT, 11 di(2-ethylhexyl) sulfosuccinate, in a solution of 500
ml chlorine-demand-free water and 200 ml diethylene glycol monobutyl
ether. Dilute to 1 liter with chlorine-demand-free water. The phos-
phates are reagent-grade chemicals. "Aerosol OT" can be obtained from
the Fisher Scientific Co., Fairlawn, New Jersey, as their 100% solid
reagent. Diethylene glycol monobutyl ether is also available from Fisher
Scientific Co. as their "purified" reagent, boiling point 112 to 114°C at
13 mm of mercury.
3.3. Potassium iodide solution; Dissolve 0.4 reagent-grade KI in
chlorine-demand-free distilled water and dilute to 100 ml. Store in a
brown, glass-stoppered bottle, preferably in a refrigerator. Discard
when a yellow color develops.
3. 4. Sulfuric acid solution: Cautiously add 4 ml concentrated H2SO4
to chlorine-demand-free distilled water and dilute to 100 ml.
3. 5, Sodium carbonate solution: Dissolve 5 g reagent grade Na2COg
in chlorine-demand-free distilled water and dilute to 100 ml.
3. 6. Sodium arsenite solution; Dissolve 5. 0 g NaAs02 in distilled
water and dilute to 1 liter. (CAUTION: Toxic; take care to avoid in-
gestion. )
4. PROCEDURE
4. 1. Calibration of photometer: Construct a calibration curve by
making dilutions of standardized hypochlorite solution prepared as direc-
ted under chlorine demand method A, Sec. 3. 1. Observe the special pre-
cautions listed under chlorine-acid orthotolidine method B, Sec. 3, 5.
Use the same procedure as given below for the preparation of the cali-
bration curve using standardized hypochlorite solutions as used for the
sample.
4. 2. Color development of free chlorine: Use 0. 5 ml neutral ortho-
tolidine and 0. 5 ml stabilizer-buffer reagent with 10-ml samples and 5
ml neutral orthotolidine and 5 ml stabilizer-buffer reagent with 100 ml,
and the same ratio for other volumes. Place the neutral orthotolidine
and stabilizer-buffer mixture in the photometer tube or a 250-ml beaker
on a magnetic stirrer. Mix the reagent slightly and add the sample to
the reagents with gentle stirring. Measure the percent transmittance
and convert to absorbance at 625 mu. The value obtained (A) from the
68
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calibration curve represents the free-chlorine' residual. To minimize
possible interferences from large concentrations of combined chlorine
and high temperature fading, the normal time used between mixing of the
sample with the reagents and reading on the photometer is approximately
2 minutes.
4. 3. Monochloramine: Return any aliquot used for measuring free
chlorine, Sec. 4. 2. , to the sample. Add with stirring 0. 5 ml potassium
iodide solution to each lOO-ml sample or a similar ratio for other sample
volumes. The value obtained (B) from the calibration curve represents
the free-chlorine plus monochloramine residuals.
4. 4. Dichloramine: Return any aliquot used for measuring the mono-
chloramine, Sec. 4. 3. , to the sample. Add with stirring 1 ml sulfuric
acid solution to each 100-ml sample or a similar ratio for other sample
volumes. Allow 30 seconds for color development. Add 2 ml sodium
carbonate solution slowly with stirring or until a pure blue solution re-
turns. The value obtained (C) represents, with a slight dilution correc-
tion, the total chlorine residual: free chlorine, monochloramine, and
dichloramine.
4. 5. Compensation of interferences: Compensate for the presence
of natural color or turbidity as well as manganic compounds by adding
5 ml arsenite to 100 ml sample. Add this blank sample to the reagents
as above. Use the color of the blank to set 100% transmittance or zero
absorbance on the photometer. Measure all samples relative to this blank.
Read from the calibration curve the concentrations of free chlorine present
in the sample.
5. CALCULATION
mg/liter free chlorine residual » A (including one half of trichlo-
ramine if present)
mg/liter monochloramine = B - A (as mg/liter CI)
mg/liter dichloramine = 1.03 C - B (as mg/liter CI)
mg/liter total chlorine = 1. 03 C (as mg/liter CI)
BIBLIOGRAPHY
Scales, F. M. , and Kemp, M. The Fundamental Principles of Chlorine
Sterilization and a New Positive Germicide. Assoc. Bull. (Internat.
Assoc. of Milk Dealers) 31: 187, 1939.
Laux, P. C., and Nickel, J. B. A Modification of the Flash Color Test
69
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Control Break-Point Chlorination. JAWWA 34: 1785, 1942.
Harris, J. C. Colorimetric Determination of Alkyl Benzene Sulfonates.
Anal. Chem. 15: 254, 1943.
Palin, A. T. The Estimation of Free Chlorine and Chloramine in Water.
J. Inst. Water Engrs. 3: 100, 1949.
Aitken, R. W. , and Mercer, D. Photometric Measurement of Residual
Chlorine and Chloramine in Water Using Neutral Orthotolidine. J. Inst.
Water Engrs. 5: 321, 1951.
Palin, A. T. Determining Residual Chlorine in Water by Neutral Ortho-
tolidine Methods - A Progress Report. Water and Sewage Works 101: 74,
1954.
Johnson, J. D. , Okun, D. A. , and Overby, R. A Colorimetric Method
for Chlorine in Dilute Aqueous Solution, 149th Meeting of the American
Chemical Society, Detroit, Mich., April 7, 1965.
Johnson, J. D., Overby, R,, and Okun, D. A. Analysis of Chlorine,
Monochloramine and Dichloramine with Stabilized Neutral Orthotolidine,
85th Annual Conference Am. Water Works Assoc., Portland, Oregon,
June 28, 1965.
70
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wo
1
1
1
z
2
2
3
3
3
3
5
6
7
7
8
8
9
10
10
11
7
3
8
6
7
9
2
1
3
6
8
7
1
1
3
4
4
1
2
8
1
9
8
3
APPENDIX E.
TABULATION OF RESULTS
Table E-l. Sample 1, Free Chlorine (0.83 mg/1)
results
method
LAB, NO.
results
0,07
2
1136
0,90
0.86
3
1136
0.78
0.85
4
1314
0.85
0.78
4
1314
0.82
0* 16
2
1611
0.70
0,76
8
1611
0.65
0.72
1
2112
0.21
0.79
7
2112
1,05
0,82
3
2222
0.15
o
CD
•
O
8
2222
0.10
1.90
8
2222
0.12
0,54
8
2223
0.30
0.70
8
2223
0.28
0,00
2
2311
0.93
0.38
2
2311
0,90
0,64
8
2311
0.92
0,80
6
2411
0.78
0.02
2
2411
0.78
0,02
3
2411
0.06
0,53
1
2411
0,76
0,16
2
2926
1,04
0*64
3
2926
1,15
0,38
8
3122
0,37
0,80
6
3122
0,70
-------
B. NO
3122
3221
3221
3221
3222
3222
3222
3226
3314
3314
3314
3416
3416
3416
3426
3426
3611
3611
3611
3731
3731
3731
3811
3811
2
7
6
3
1
9
3
9
6
4
2
7
1
4
9
6
9
2
4
i
1
9
7
6
(Table E-l continued)
RESULTS METHOD
0.60
7
0.40
9
O
•
o
6
0.40
3
1.15
4
1.35
8
1,30
2
0.07
1
0.17
7
0,15
2
0.16
4
0.41
9
1.78
1
1.24
4
0,07
2
0,21
6
0,11
2
0.60
4
0.62
6
o
•
o
7
0.12
1
0.70
3
0.15
1
0.10
9
LAB. NO.
RESULT*
3811
0.50
4212
0.75
4212
O
•
CD
4212
0.72
4421
0.54
4421
0,32
4511
0.90
4511
0,45
4516
0.76
4516
1,10
4516
0,17
4611
0.86
4611
0.81
4623
0.70
4623
0.80
4623
o
•
o
4711
0.50
4711
0.60
4911
0.92
4911
1.10
5111
O
•
VSI
5221
0.42
5426
0.50
5426
0.50
-------
B. NO
5711
58U
5811
6221
6311
6311
6311
6715
6719
6718
6914
7112
7112
7111
7216
7224
7224
7422
7422
7422
7522
7522
7522
7526
1
8
3
2
7
6
8
2
4
1
8
9
1
9
9
8
3
3
9
7
1
8
4
1
(Table E-l continued)
RESULTS
METHOD
LAB. no.
RE5ULTS
0*08
7
7526
0.71
0.20
9
7622
0.80
0,18
2
7622
0.70
0,05
6
7622
1.00
0.30
7
7722
0.30
1*05
1
7722
0.45
1.50
4
7722
0.33
0.02
9
7813
0.82
0*76
1
7813
0.60
0*83
6
7813
1.84
0*63
1
7824
1.70
0*48
3
7824
1.67
0.47
9
7914
0.63
0.07
8
7914
0.41
0*68
4
7922
0.10
0.22
1
7922
0.48
0*29
7
7922
0.60
1*10
4
7926
0.65
1*20
1
7926
0.83
1.10
7
8111
0.20
0*43
8
8111
0.35
0*51
3
8222
0.77
0.35
7
8222
1.10
0.02
6
8222
0.98
-------
(Table E-l continued)
LAB. NO.
RESULTS
METHOD
LAB. NO.
RESULTS
method
8222
0,87
3
9111
0.82
7
8326
0*64
9
9111
0.75
8
8326
0.82
7
9111
0*82
9
8326
0.96
4
9613
0.13
7
8512
0.80
6
9613
o
•
o
V*
8
8512
0.70
3
9613
0.15
1
8512
0.55
8
9713
0.70
9
8622
0.90
7
9713
0.68
1
8622
1.00
6
9714
0.43
1
8622
1.22
8
9714
0.50
7
8822
0. 80
8
9816
0.03
7
8822
0.74
3
9816
0.03
6
-------
Table E-2. Sample 1, Combined Chlorine (1.00 mg/1)
LAB, NO.
results
method
lab. no.
RESULTS
METHOD
1
1*64
2
1136
0*40
7
1
0.90
3
1136
0,50
6
I
0.96
4
1314
1.13
8
2
0.92
4
1314
0,32
6
2
1.64
2
1611
0,70
7
2
1.06
8
1611
1.05
9
3
1.07
3
2112
1.59
3
0.29
7
2112
1.27
1
3
1.04
8
2222
1.45
3
3
0,86
1
2222
1.48
5
0.10
8
2222
0.60
6
6
0.91
8
2223
0.53
7
7
1.75
2
2223
0.79
1
7
1.09
8
2311
0.92
4
8
1.04
2
2311
1.11
1
8
1.18
8
2311
1,10
9
0.40
6
2411
0,90
1
10
1.48
2
2411
0.97
4
10
1.51
3
2411
1.71
11
0.99
1
2411
1.03
1114
1.09
8
2926
N
CO
•
o
9
1114
1*59
2
2926
0,95
1
1114
0.98
3
3122
1.12
8
1136
1.00
3
3122
0.20
7
75
-------
B. NO
3122
3221
3221
3221
3222
3222
3222
3226
3314
3314
3314
3416
3*U
3416
3426
3426
3611
3611
3611
3731
3731
3731
3811
3811
2
7
3
6
9
1
9
3
6
2
4
7
1
9
4
6
9
2
1
4
1
9
7
6
(Table E-2 continued)
results
method
lAS. NO.
RESULTS
1.00
3
3811
1.10
1.10
3
4212
0.40
1,00
9
4212
1.12
0.30
6
4212
0.30
0.00
8
4421
0.45
0.02
2
4421
1.27
0.07
4
4511
0,65
1.85
1
4511
1.10
0.61
4
4516
0.58
0.40
2
4516
1.71
0.37
7
4516
0.90
0,95
9
4611
0.25
2. 03
1
4611
1.19
0.71
4
4623
0.70
0,20
6
4623
1.00
o
•
u*
IS)
2
4623
0.60
1.09
2
4711
0.50
1.08
8
4711
0.20
0.70
4
4911
0.84
0,88
1
4911
1,02
1.20
3
5111
1.01
0.30
7
5221
1.05
1.16
1
5426
0,50
0.75
9
5426
0.50
-------
B. NO
5711
5811
5811
6221
6311
6311
6311
6715
6715
6715
6914
7112
7112
7112
7216
7224
7224
7422
7422
7522
7522
7522
7526
7526
2
8
3
7
6
8
2
4
1
9
8
1
9
8
3
9
3
9
1
7
1
4
3
8
(Table E-2 continued)
RESULTS
METHOD
|_AB. no.
RESULTS
0.56
7
7622
0.89
1,32
2
7622
1.06
0.63
9
7622
1.05
1.13
6
7722
0.20
0,15
7
7722
0,20
3.50
4
7722
1.07
0.91
1
7813
1.38
0.66
6
7813
0,42
0.99
1
7813
0.11
1.39
9
7824
0,03
1.01
1
7824
0,04
1.04
7914
0.77
1.52
7914
1,00
0.80
9
7922
2,52
0.86
4
7922
5.40
0.83
I
7922
6.60
0.60
7
7926
1.17
0.96
4
7926
0.99
0.10
7
8111
1.56
1.09
3
8111
0.50
0.20
7
8222
1.02
0.96
8
8222
1.10
1.11
1
8222
1.15
0,54
6
8222
1.06
-------
(Table E-2 continued)
LAB, NO.
RESULTS
METHOD
LAB. no.
RESULTS
METHOD
8326
0*21
7
9111
0.47
7
8326
0.32
9
9111
1.00
8
8912
0,40
6
9613
1.93
8
8512
1.00
3
9613
1.25
1
8512
1.30
8
9613
0.61
7
8622
0.35
7
9713
0.85
9
8622
0.20
6
9713
0.82
I
8622
0.00
8
9714
0.35
7
8822
0.95
8
9714
1.23
1
8822
1.00
3
9816
1.47
7
9111
0.93
9
9816
1.47
6
78
-------
NO
1
1
1
2
2
2
3
3
3
3
5
5
6
6
7
7
8
8
8
9
9
10
10
10
1
5
8
3
2
3
7
6
6
5
8
5
7
9
1
2
5
6
8
3
5
7
1
Table E-3. Sample 1, Total Chlorine (1.83 mg/1)
iesults
method
l*b. no.
RESULTS
1.71
2
11
1.52
1.76
3
11
1.85
CO
•
*4
4
1114
1.47
1,70
4
1114
1.62
1.80
2
1114
1.75
1.82
8
1136
1.78
1.89
3
1136
1.30
1.08
7
1136
1.30
1.58
1
1314
1.14
1.R4
8
1314
2.15
1.50
4
1314
1.98
1.60
8
1611
1.77
1.45
8
1611
1,40
1.83
5
1611
1.70
1.75
2
2112
2.32
1.79
8
2112
1.80
1.73
5
2112
1.52
1.82
8
2222
o
r*-
•
o
1.42
2
2222
1.60
1.20
6
2222
1.60
1.38
5
2223
1.08
1.53
3
2223
0.83
1.53
5
2223
1.07
1.50
2
2311
2.00
-------
(Table E-3 continued)
LAB, NO.
RESULTS
METHOD
LAB, no.
RESULTS
METHOD
2311
2,04
1
3416
1,36
9
2311
1*84
4
3426
0,39
2
2411
1,68
1
3426
0,41
6
2411
1.75
4
3611
1,30
4
2411
1.79
8
3611
1.70
8
2411
1.77
2
36U
1,20
2
2926
1.99
1
3731
0.*0
7
2926
1.97
9
3731
1.00
1
3122
0,80
7
3731
1.90
3
3122
1.49
8
3811
1.31
1
3122
1,70
3
3811
0.85
9
322T
1,40
9
3811
1,60
2
3221
1.50
3
4212
1.15
7
3221
0,60
6
4212
1,84
3
3222
1.35
8
4212
1.15
6
3222
1.32
2
4421
0,77
9
3222
1.22
4
4421
1,81
1
3226
1.92
1
4421
1,68
5
3226
1. 50
6
4511
2,00
3
3314
0,54
7
4511
1,10
9
3314
0,77
4
4511
1.51
5
3314
0.55
2
4516
1.34
6
3416
1,95
4
4516
1.88
2
3416
3,81
1
4516
2.00
4
80
-------
B. NO
4611
4611
4611
4623
4623
4623
4711
4711
4711
4911
4911
4911
5111
5111
5221
5221
5426
5426
5426
5711
5711
5811
5811
5811
4
7
1
1
9
6
5
1
8
9
3
4
5
7
1
7
4
7
8
3
5
5
6
(Table E-3 continued)
RESULTS
METHOD
la*, no.
RESULTS
1.11
7
6221
1.18
1.50
5
6311
5.00
2,00
1
6311
0,45
1.50
9
6311
1.96
1,70
4
6715
1,75
1,20
6
6715
1.41
0,30
2
6715
1.49
0,95
5
6914
0.65
i.00
9
6914
1.64
1.94
4
7112
1.59
1.94
1
7112
1.27
1,50
5
7112
1.52
1.93
1
7216
1.54
1.72
5
7216
1,33
1.^7
9
7224
0,89
1.18
5
7224
1,05
1.60
5
7422
1,20
o
o
•
7
7422
2,06
o
o
•
9-4
6
7522
0,55
0.66
7
7522
1,39
1 *33
5
7522
1,60
1,50
2
7522
2,55
0,88
5
7526
1.58
0,83
9
7526
0,56
-------
(Table E-3 continued)
LAB. NO.
RESULTS
METHOD
LAB. no.
RESULTS
METHOD
7526
1.82
1
8111
1.91
1
7622
1*86
8
8222
2.02
3
7622
1*89
2
8222
2.20
4
7622
1.75
3
8222
1.83
8
7722
0.50
7
8222
2.00
1
7722
0.65
6
8326
0.96
9
7722
1.40
8
8326
1.03
7
7813
1*88
8326
0.95
4
7013
1.02
4
8512
1,70
3
7813
1.93
1
8512
1.20
6
7813
2.20
2
8512
1.85
8
7824
1.70
9
8622
1.20
6
7824
1.74
8622
1.25
7
7914
1.40
1
8622
1.2 2
8
79U
1.36
5
8822
1.74
3
7914
1.41
9
8822
1.75
8
7922
3.00
8822
1.45
5
7922
6.00
3
9111
1.29
7
7922
6,70
9
9111
1.75
8
7926
1.82
9
9111
1.75
9
7926
1.81
5
9613
1.49
5
7926
1.82
3
9613
1.40
1
8111
1.35
5
9613
1.98
8
8111
0.70
7
9613
0.74
7
82
-------
(Table E-3 continued)
LAB. NO. RESULT5 MEtHqD
9713 1.50 1
9713 1.51 5
9713 1,55 9
9714 0.05 7
9714 1.54 5
lab. NO. results METHOD
9714 1.66 1
9816 1.50 6
9816 1.58 5
9816 1.50 7
83
-------
Table E-4. Sample 2, Free Chlorine (0.80 mg/1)
LAB. NO.
RESULTS
method
LAB. NO.
RESULTS
method
1
0.80
2
1136
0.40
6
1
0.82
3
1136
0.63
3
1
0.72
4
1314
0.56
6
2
0.78
2
1314
0.55
8
2
0.80
4
1611
0.80
7
2
0.81
8
1611
0.75
9
3
0.60
1
2112
1.06
I
3
0.71
7
2112
1.03
2
3
0.70
8
2222
0.40
3
3
0.71
3
2222
0.02
6
3
0.60
8
2222
0.15
8
6
0.74
8
2223
0.44
1
7
0.70
2
2223
0.68
7
7
0,72
8
2311
0,34
4
S
0.33
2
2311
0,30
1
6
0.60
8
2311
0,33
3
9
0,40
6
2411
0,73
8
10
1.00
2
2411
0,75
1
10
0.98
3
2411
0.75
4
U
0.80
1
2411
0.72
2
1114
0.50
3
2926
0.65
9
1114
0.72
2
2926
0,75
1
1114
0,38
8
3122
0.38
8
1136
0.50
7
3122
0.50
7
R4
-------
NO
3122
3221
3221
322!
3222
3222
3222
3226
3314
3314
33U
3416
3416
3416
3426
3426
3611
3611
3611
3731
3731
3731
3811
3811
1
6
7
3
1
9
9
3
4
6
2
7
1
9
4
6
2
9
1
4
I
9
6
7
(Table E-4 continued)
RESULTS
METHOD
LA9. NO.
RESULTS
0.50
3
38U
0,49
0.40
9
4212
0,78
0.30
6
4212
0.73
0.40
3
4212
0,78
0.68
8
4421
0.55
0.48
4
4421
0,53
0.67
2
4511
0,45
0.03
1
4511
0,60
0.55
2
4516
1,08
0,54
4
4516
1,08
0.52
7
4516
0,96
1,09
4
4611
0,70
0.48
1
4611
0.75
0.00
9
4623
0.60
0.04
2
4623
0,55
0.09
6
4623
0.50
0.66
4
4711
0.45
1.15
8
4711
0.80
1.24
2
4911
0.86
0.40
7
4911
0.82
0,95
1
5111
0.66
1.20
3
5221
0.00
0,40
9
5426
0.30
0.75
2
5426
0.30
-------
(Table E-4 continued)
LAB, NO,
RESULTS
METHOD
LA1?, no.
results
METHOD
5711
0,05
7
7526
0.03
6
5811
0,37
2
7622
0,59
8
5011
0.30
9
7622
0,59
3
6221
0,40
6
7622
0,62
2
6311
0,04
7
7722
0,59
8
6311
0*12
1
7722
0.45
6
6311
O
•
O
4
7722
0,25
7
6715
0,68
6
7813
0,94
2
6715
0*78
1
7813
0,96
1
6715
0,15
9
7813
0,44
4
69U
0,93
1
7824
0,78
7112
0*36
9
7824
0.72
9
7112
0,37
3
7914
0,57
1
7112
0,33
8
7914
0,32
9
7216
0 *60
4
7922
7,15
7224
0,20
7
7922
6,48
3
7224
0*20
1
7922
1,50
7422
1*20
4
7926
0,62
9
7422
1*30
1
7926
0,68
3
7422
1.20
7
8111
o
•
o
7
7522
0.61
8
8111
0,63
1
7522
0.60
3
8222
0,90
7522
0,45
7
8222
1,02
3
7526
0*56
1
8222
1.10
4
86
-------
(Table E-4 continued)
lab. no.
RESULTS
METHOD
LAB. no.
results
method
6222
0.96
1
9111
0.75
8
8326
0.45
9
9111
0.85
9
8326
0,50
<~
9111
0,86
7
6326
0.48
7
9613
0.08
7
8512
0.85
3
9613
0.05
8512
0.80
8
9613
0.10
1
8512
0.85
6
9713
0.60
1
6622
1.20
6
9713
0.55
9
8622
1.36
8
971*
0.57
7
8622
1,10
7
971*
0.46
1
8822
0.22
8
9816
0.15
6
8822
0.23
3
9816
0,15
7
87
-------
Table E-5. Sample 2, Combined Chlorine (0.04 mg/1)
LAB. NO.
RESULTS
METHOD
LAB. NO.
RESULTS
method
1
0.01
2
1136
0.20
7
1
0.01
3
1136
0.30
6
1
0.03
4
1314
0.24
8
2
0.22
2
1314
0.08
6
2
0.18
4
1611
0.05
9
2
0.30
8
2112
O
•
o
u»
1
3
0.11
3
2222
o
•
<*¦
6
3
0.00
7
2222
0.39
8
3
0.12
8
2222
o
H
•
O
3
3
0.02
1
2223
0.00
1
5
0.20
8
2223
0.00
7
6
0.08
8
2311
0.30
4
7
0.05
2
2311
0.47
1
7
0.05
8
2311
0.44
3
8
0.10
8
2411
0.03
4
8
0.17
2
2411
o
•
o
8
9
0.00
6
2411
0,00
1
10
0.01
3
2411
0,15
2
10
0.04
2
2926
0,00
9
11
0.07
1
2926
o
•
O
1
1114
0.08
2
3122
0.10
7
1114
0*09
8
3122
0.10
3
1114
0.03
3
3122
0,12
8
1136
o
•
o
3
3221
0.00
9
88
-------
(Table E-5 continued)
LAB. NO.
RESULTS
method
LA"*, no.
RESULTS
method
3221
0.00
3
4212
0,10
7
3221
0,00
6
4212
0,00
6
3222
0,10
4
4421
0,09
1
3222
0,04
8
4421
0.04
9
3222
0,01
2
4511
0.15
3
3226
0,85
1
45U
0,40
9
3314
0.08
7
4516
0.00
6
3314
0,03
2
4516
0,00
2
3314
0,09
4
4611
0,15
7
3416
0,79
4
4611
0,10
1
3416
0,77
1
4623
0.00
4
3416
0,18
9
4623
0.00
6
3426
0,12
2
4623
0,00
9
3426
0,05
6
4711
0,25
2
3611
0,00
4
4711
O
o
#
o
9
3611
0,00
8
4911
0.02
1
3611
0,30
2
4911
0.04
4
3731
0,05
7
5111
0,00
1
3731
0,13
1
5221
0,64
9
3731
0*10
3
5426
0.20
7
3611
0,05
2
5426
0.20
6
3811
0,08
1
5711
0,51
7
3811
0,00
9
5811
0.03
2
4212
O
*
o
IS!
3
5811
0,00
9
89
-------
(Table E-5 continued)
LAB, NO.
RESULTS
METHOD
LAB, NO.
RESULTS
METHOD
622}
6*40
6
7722
0,35
6
6311
0,42
1
7722
0,25
7
6311
0*00
4
7813
0.24
2
6311
0*08
7
7824
0.08
8
6715
0,02
6
7824
0,06
9
6713
0,35
7914
0.04
1
6715
0,03
1
7914
0,50
9
6914
0,07
1
7926
0,00
9
*112
0»2l
8
7926
0.00
3
7112
0,07
3
8111
0.07
1
7112
0,00
9
8111
0,20
7
7224
0.60
7
8222
0.00
3
7224
0.78
1
8222
0,00
8
7422
0,00
7
8222
0.00
1
7422
O
•
o
1
8222
0,00
4
7522
0.10
8
8326
0,07
9
7322
0,09
3
8326
0,05
4
7322
o
•
O
7
8326
0,09
7
7526
0.45
6
8512
0.00
6
7326
0,12
1
8512
0,15
8
7622
0.03
3
8512
0,00
3
7622
0*23
2
8622
0.00
8
7622
0.02
8
8622
0,20
6
7722
0,00
8
8622
O
N
•
O
7
90
-------
(Table E-5 continued)
lab. no.
RESULTS
METHOD
L.AR, N0§
RESULTS
6822
0.58
8
9613
o
•
O
8822
0,28
3
9T13
0.00
9111
o
•
o
8
9713
0.00
9111
0,10
7
9714
0.12
9111
0.04
9
9714
0.32
9613
0,33
7
9816
0.63
9613
0.52
1
9816
0.61
method
91
-------
Table E-6. Sample 2, Total Chlorine (0,84 mg/1)
lAB. NO.
results
METHOD
La*. no.
RESULTS
METHOD
1
0*81
2
11
0.81
5
1
0.83
3
11
o
•
00
I
i
0.75
4
1114
0,53
3
2
1.00
2
1114
0.80
2
2
0.98
4
1114
0,47
a
2
1.11
8
1136
0.70
7
3
0.62
1
1136
0.68
3
3
0.71
7
1136
0,70
6
3
0.82
8
1314
0.64
6
3
0.82
3
1314
0,79
8
5
0,68
4
1314
0.85
5
5
0*80
8
1611
0.85
5
6
0.82
8
1611
0,75
7
6
0.75
5
1611
0,80
9
7
0.75
2
2112
1,09
I
7
0.77
8
2112
0,92
5
9
0.70
8
2112
1,02
2
8
0.50
2
2222
0,54
8
8
0.69
5
2222
0,38
6
9
0.40
6
2222
0,50
3
9
0.37
5
2223
0,72
5
10
1.00
5
2223
0,68
7
10
1.04
2
2223
0,44
1
10
0.99
3
2311
0,77
3
92
-------
>B, NO
2311
2311
2411
2411
2411
2411
2926
2926
3122
3122
3122
3221
3221
3221
3222
3222
3222
3226
3226
3314
3314
3314
2
6
2
8
4
7
3
1
1
2
9
6
3
7
9
I
5
3
5
9
4
6
2
(Table E-6 continued)
results
METHOD
LAR. NO,
RESULTS
0.77
1
3416
0.18
0# 64
4
3426
0.16
0,76
8
3426
0.14
0.87
2
3611
0,94
0.75
1
3611
1.15
CO
•
o
4
3611
0.66
0.65
9
3731
0.45
0.78
1
3731
1,30
0.50
8
3731
1,08
0.60
7
3811
0,57
0.60
3
3811
0,80
0.40
9
3811
0,40
0*40
3
4212
0,78
0,30
6
4212
0,80
0.58
4
4212
0,83
0.72
8
4421
0,57
0.68
2
4421
0,64
0.88
1
4421
0,59
0.50
6
4511
0,75
0.58
2
4511
0,53
o
*
o
7
4511
0.85
0,63
4
4516
1.04
1.88
4
4516
1,08
1.25
1
4516
0.96
-------
tB. WO
4611
4611
4611
4623
4623
4623
4711
4711
4711
4911
4911
4911
5111
5111
5221
5221
5426
5426
5426
5711
5711
5811
5811
5811
7
4
1
1
6
9
5
1
3
9
8
5
4
7
1
1
4
7
3
8
5
7
1
{Table E-6 continued)
RESULTS
METHOD
LAB. NO.
results
0.85
7
6221
6,80
0.44
5
6311
0.12
0.85
1
6311
0,30
0,55
4
6311
0,54
0.50
6
6715
0,81
o
•
o
9
6715
0.70
0.80
9
6715
0,70
O
•
-*4
O
2
6914
0,70
0.45
5
6914
1,00
0.74
5
7112
0,44
CO
CD
•
o
1
7112
0,36
0.86
4
7112
0.54
0.66
1
7216
0,52
0.76
5
7216
0,59
0.25
5
7224
0,80
0.64
9
7224
0.98
0.33
5
7422
1.40
0.30
7
7422
1.13
0.30
6
7422
1.20
0.56
7
7522
0.69
0.56
5
7522
0.71
0.35
5
7522
0.69
0.40
2
7522
0.65
0.30
9
7526
0.68
-------
(Table E-6 continued)
LAB. NO.
RE5ULTS
method
LAB. NO.
results
method
7526
0.48
6
Sill
0,50
7
7526
0.72
5
Bill
0.70
1
7622
0.05
2
*222
0,90
8
7622
0,62
3
8222
1.02
3
7622
0.61
8
8222
0.96
1
7722
0.50
7
8222
1,10
4
7722
0.59
8
*326
0.52
9
7722
0.80
6
8326
0.57
7
7813
0.42
4
8326
0.55
4
7813
0.76
1
8512
0.95
8
7813
0.69
5
8512
0,85
3
7813
1.18
2
8512
0,85
6
7824
0.78
9
8622
1,30
7
7824
0.86
8
8622
1,40
6
7914
0.81
5
8622
1,36
8
7914
0.82
9
8822
0,41
5
7914
0.61
1
8822
0,51
3
7922
0.08
3
8822
o
CO
•
o
8
7922
0.05
8
9111
0,96
7
7922
0.00
9
9111
0,85
8
7926
0.62
9
9111
0,89
9
7926
0.69
5
9613
0,62
1
7926
0.68
3
9613
0,67
5
8111
0.60
5
9613
0,75
8
95
-------
(Table E-6 continued)
LAB, NO.
RESULTS
method
LAB. no.
RESULTS
method
9613
0.41
7
9714
0.78
1
9713
0.49
5
9714
0.69
7
9713
0.60
1
9816
0,70
5
9713
0.55
9
9816
0.76
6
9714
0.70
5
9816
0.78
7
-------
>. no
1
1
i
2
2
2
3
3
3
3
5
6
7
7
8
8
10
10
11
1114
1114
1114
1314
1314
9
1
2
a
3
6
1
7
1
3
4
4
2
1
B
9
1
7
S
Table E-7. Sample 3, Free Chlorine (0. 04 mg/1)
RESULTS method
0.00
2
0.01
3
0,00
4
0.10
2
0,12
4
0,36
8
0.00
1
0,00
7
0.00
8
0.00
3
0.00
8
0.05
8
0,00
8
0,00
2
0.00
8
0,00
2
0.00
2
0.00
3
0,10
1
0.05
8
0.03
3
0,04
2
0.00
8
0.01
6
lab. NO. results
1611
0.10
1611
0.10
2112
0,19
2112
0,14
2222
0,00
2222
0.00
2222
0.00
2223
0,15
2223
0,20
2311
0,42
2311
o
•
Ul
o
2311
0.48
2411
0,00
2411
0,01
2411
0,01
2411
0,02
2926
0.00
2926
0.00
3122
0.10
3122
0.00
3122
0,00
3221
0,00
3221
0,00
3221
0,00
-------
lB. NO
3222
3222
3222
3226
3314
3314
3314
3416
3416
3416
3426
3426
3611
3611
3611
3731
3731
3731
3811
3811
3811
4212
I
3
9
4
2
6
1
7
4
6
9
2
9
1
4
1
9
7
2
9
6
4
7
(Table E-7 continued)
RESULTS
METHOD
LAB. NO.
RESULTS
0,00
8
4421
0,00
0*00
2
4421
0.00
0,00
4
4511
0,00
0,05
1
4511
0,00
0,05
2
4516
0,00
0,07
4
4516
0,00
O
•
o
7
4516
0.28
0.68
4
4611
0,50
0,02
9
4611
0,45
0,53
1
4623
0,00
0,25
6
4623
0.00
0,04
4623
0,00
0*00
2
4711
0.00
0,00
4
4711
0,00
0,00
8
4911
0,12
0.10
7
4911
0,00
0,00
5111
0,17
0.00
1
5221
0.00
o
•
o
o
9
5711
0.05
0,67
1
5811
0.10
0,30
2
5811
0.00
o
•
o
6
6221
0,07
0,12
7
6311
0.40
0.00
3
6311
0.05
-------
IB. NO
6311
6715
6715
6715
691*
7112
7112
7112
7216
7224
7224
7422
7422
7422
7522
7522
7522
7526
7526
7622
7622
7622
7722
7722
2
4
1
8
9
9
1
9
8
3
3
9
1
7
4
8
1
3
7
9
4
3
8
(Table E-7 continued)
RESULTS METHOD
LAB, NO.
RESULTS
7722
0,10
7813
0.58
7813
0,04
7813
0,12
7824
0.58
7824
0.54
7914
0,00
7914
0,05
7922
0,20
7922
0,65
7922
0.23
7926
0*02
7926
o
•
o
o
8111
0*10
8111
0.00
8222
0,00
8222
0,00
8222
0.00
8222
0.00
8326
0,07
8326
0,05
8326
0.00
8512
o
•
o
o
8512
0.00
0,02
0.02
0,02
0,00
0.10
0,05
0,03
0,43
0.00
0,10
0*10
0.50
0,10
0.50
0.03
0,42
0*05
0.14
0.70
0,00
0.00
0,00
0,40
0.15
8
6
-------
(Table E-7 continued)
LAB* NO.
RESULTS
METHOD
LAB. NO.
RESULTS
METHOD
8512
0.00
6
9613
0,30
7
8622
0,1*
8
9613
0.08
8
8622
0.05
6
9613
0.15
1
8622
0.05
7
9713
0.00
9
8822
0.00
3
9713
0,00
1
8822
0.05
8
971*
0.40
7
9111
0.00
8
9714
0.06
I
9111
0,00
7
9816
0*02
6
9111
0.00
9
9816
0.02
7
100
-------
Table E-8. Sample 3, Combined Chlorine (0. 60 mg/1)
LAB, NO.
RESULTS
method
lab, no.
RESULTS
method
1
0,65
2
1611
0.60
7
1
0.67
3
1611
0.55
9
1
0.67
4
2112
0.95
1
2
0.64
4
2112
0.81
2
2
0.62
2
2222
0.72
3
2
0.52
8
2222
o
•
o*
o
6
3
0.69
3
2222
o
•
o
8
3
0.61
7
2223
0,00
1
3
0.48
1
2223
0,02
7
3
0,70
8
2311
0,14
4
5
o
•
o
8
2311
0,00
3
6
0.59
8
2311
0,30
1
7
0*68
2
2411
0.48
1
7
o
O
8
2411
0,56
2
8
0.22
2
2411
0,47
4
8
0.63
8
2411
0,46
8
10
0.53
3
2926
0,33
9
10
0.60
2
2926
0.47
1
11
0.67
1
3122
0.40
7
1114
0,47
2
3122
0,44
8
1114
0.35
3
3122
0,55
3
1114
0,29
8
3221
0,30
6
1314
0.49
8
3221
0,40
9
1314
0.39
6
3221
0.40
3
101
-------
(Table E-8 continued)
LAB. NO.
RESULTS
METHOD
LA*. NO.
RESULTS
METHOD
3222
0.60
2
4421
0.93
1
3222
0.70
8
4421
0.62
9
3222
0.55
4
4511
0.55
3
3226
0.60
1
4511
0.50
3314
0.20
4516
0.60
6
33U
0.22
4
4516
0.84
3314
0.24
7
4516
0.83
4
3416
1.45
4
4611
0.22
1
3416
0.40
4611
0.29
7
3416
1.37
1
4623
0.10
3426
0.32
4623
0.20
4
3426
0.28
6
4623
0.40
9
3611
0.62
2
4711
0.00
2
3611
0.50
4
4711
0.00
9
3611
0.60
4911
0,70
4
3731
0.80
1
4911
0.59
I
3731
0.70
5111
CM
•
O
1
3731
0.20
7
5221
0.47
9
3811
0.25
1
5711
0.37
7
3811
0.70
2
5811
0.62
3811
0.37
9
5811
0.35
4212
0*53
7
6221
0.68
6
4212
0,70
3
6311
0,81
1
4212
0.60
6
6311
I.10
4
102
-------
(Table E-8 continued)
LAB, NO.
RESULTS
METHOD
LAB. no.
RESULTS
METHOD
6311
0.74
7
7722
0.40
6
6715
0.35
9
7813
0.42
2
6715
0.57
1
7813
0.80
1
6715
0.55
6
7813
0.44
4
69U
0,63
1
782^
0.06
7112
0.03
7824
0,02
7112
0,54
3
7914
0.44
1
7112
0,42
7914
0.37
9
7216
1.05
4
7922
3.20
7224
0,35
7
7922
4.37
3
7224
0.65
1
7922
1.30
9
7422
0.60
7
7926
0.42
7422
0.93
4
7926
0.50
3
7422
0.80
1
8111
CM
*
•
O
1
7522
o
o
m
O
7
8111
0.40
7
7522
0.70
3
8222
0.77
3
7522
0,17
8222
0.75
7526
0.22
6
8222
0.90
1
7526
0.27
1
8222
0.76
4
7622
o
•
o
3
8326
0.45
9
7622
0,49
2
8326
0.55
7
7622
0,42
8
8326
0.73
4
7722
0,00
8
8512
0.60
8
7722
0,20
7
8512
0.45
6
103
-------
(Table E-8 continued)
lab, no.
RESULTS
METHOD
LAB. no.
RESULTS
method
8512
0.50
3
9613
0.30
1
8622
o
•
o
6
9613
0.10
7
8622
0,53
8
9613
0,42
8
8622
0.60
7
9713
0.60
9
8822
0.61
3
9713
O
*c
•
o
1
8822
0.65
8
9714
0.67
1
9111
0.77
7
9714
0.18
7
9111
0,76
9
9816
0,53
6
9111
0,75
8
9816
0, 58
7
104
-------
Table E-9. Sample 3, Total Chlorine (0. 64 mg/1)
LAB. NO.
RESULTS
METHOD
LAB. NO.
RESULTS
METHOD
1
0.65
2
11
0.77
1
1
0.68
3
1114
0,34
8
1
0,67
4
1114
0.38
3
0,72
2
1114
0,51
2
2
0.76
4
1136
0,60
7
2
0,88
8
1136
0,57
3
3
0,69
3
1136
0,60
6
3
0,61
7
1314
0.49
8
3
0,70
8
1314
0,40
6
3
0,48
1
1314
0,40
5
5
0,40
4
1611
0.65
5
5
0.30
8
1611
0.70
7
0.48
5
1611
0.65
9
6
0,64
6
2112
1.14
1
7
0,70
8
2112
0.95
2
7
0.68
2
2112
0.78
5
8
0,61
5
2222
0.72
3
8
0,63
8
2222
0.60
6
8
0.22
2
2222
0,70
8
9
0.05
5
2223
0,33
5
10
0.51
5
2223
0,22
7
10
0. 53
3
2223
0.15
1
10
0.60
2
2311
0,50
3
11
0.88
5
2311
0,62
4
105
-------
B, NO
2311
2411
2411
2411
2411
2926
2926
3122
3122
3122
3221
3221
3221
3222
3222
3222
3226
3226
3314
3314
3314
3416
3416
3416
(Table E-9 continued)
RESULTS METHOD
lab, no.
RESULTS
meth
3426
0,56
2
3426
0.53
6
3611
0,60
8
3611
0,50
4
3611
0,62
3731
0,70
3731
0.30
3731
0,80
3811
1,00
3811
0,92
3BU
0,37
4212
0,65
4212
0,69
4212
0,70
4421
0,71
4421
0,62
4421
0,93
4511
0,50
4511
0,55
4511
0,35
4516
0,84
4516
0,88
4516
o
•
CD
4611
0,74
0,72
0,57
0,49
0,47
0*48
0*33
0,47
0,55
0,44
0,50
0,30
0,40
0,40
0,55
0,70
0,60
0,69
0,24
0,25
0,30
0,29
2.13
0,42
1,90
-------
(Table E-9 continued)
lab, no.
RESULTS
METHOD
LA8, NO.
RESULTS METHOD
4611
0.58
5
6311
0.83 1
4611
0.72
1
6311
1.50 4
4623
0*20
4
63U
0.79 7
4623
0,40
9
6715
0,59 1
4623
0,10
6
6715
0,57 6
4711
0«00
9
6715
0,35 9
4711
0,00
5
6914
0,49 5
4711
0.00
2
6914
0.73 1
4911
0,71
1
7112
0,47 8
4911
0,69
5
7112
0,46 9
4911
0,70
4
7112
0,57 3
5111
0,43
1
7216
0,66 5
5111
0,30
5
7216
1.05 4
5221
0,47
9
7224
0,45 7
5221
0,24
5
7224
0,75 1
5426
0,60
5
7422
1,03 4
5426
0,50
7
7422
1,30 1
5426
0,50
6
7422
1,10 7
5711
0.49
5
7522
0,73 3
5711
CM
<*
•
O
7
7522
0,70 5
58U
0,95
9
7522
0,59 8
sou
0,72
2
7522
0,65 7
58U
0,44
5
7526
0,97 1
6221
0,75
6
7526
0,36 6
107
-------
(Table E-9
continued)
LAB, NO.
RESULTS
METHOD
lab. no.
RESULTS
method
7526
0.52
5
mi
0,40
7
7622
0.42
8
8222
0,75
8
7622
0.50
3
*222
0,76
4
7622
0.49
2
8222
0,90
1
7722
0.30
7
8222
0,77
3
7722
0.55
6
8326
0.73
4
7722
0.40
8
8326
0,50
9
7813
1,00
2
8326
0,62
7
7813
0.92
1
8512
0.50
3
7813
0,67
5
8512
0,45
6
7813
0,48
4
8512
0,60
8
7824
0.60
8
8622
0.65
7
7824
0.60
9
8622
0.67
8
7914
0,33
5
8622
0,65
6
7914
0.49
1
8822
0,61
3
7914
0.37
9
8822
0,38
5
7922
3.85
8
8822
0,70
8
7922
4.60
3
9111
0,75
8
7922
1.50
9
9111
0,76
9
7926
0.52
3
9111
0,77
7
7926
0,42
9
9613
0.50
8
7926
0.50
5
9613
0.40
7
8111
0.52
1
9613
0,46
5
8111
0.36
5
9613
0,45
1
108
-------
(Table E-9 continued)
lab. no.
PESULT5
method
la*, no#
RESULTS
METHOD
9713
0.57
5
9714
0.73
1
9713
0.60
9
9816
o
o
•
o
7
9713
o
<*)
•
o
1
9816
0.44
5
9714
0.58
7
9816
0.55
6
9714
0.61
5
109
-------
APPENDIX F.
GLOSSARY OF STATISTICAL TERMS
A glossary of statistical terms defined as they are used in this
report is presented to ensure uniformity of understanding.
Arithmetic mean The sum of the sample results divided by the
number of results in the sample^ Let X^
(i = 1,2, . . . , n) denote the i results in a
sample of n results. The arithmetic mean
_ n
denoted X is given by X= 2 X^
i=l ~rT'
Halfway point in the results when they have
been arranged in order of magnitude (the
middle result of an odd number of results,
or the average of the middle two for an even
number).
The correctness of a measurement, or the
degree of correspondence between the results
and the true value (actual amount added).
Measures of accuracy Measures that relate to the difference
between the mean of the results and the true
value when the latter is known or assumed.
The following measures apply:
Mean error — The average difference with
regard to sign between the results and the
true value. Equivalently, the difference
between the mean of the results and the true
value (T. V. ).
Mean error = X - T. V.
Relative error — The absolute value of the
mean error expressed as a percentage of
the true value.
Relative error = 1 ^ ^
Precision The reproducibility of sample results or the
degree of agreement among the results.
Median
Accuracy
110
-------
Measures of precision
!
Measures of the variation among the sample
results themselves, i. e. , the spread or
dispersion of the results without regard to
the true value. The following measures
apply.
Sample variance — Sum of squared deviations
of the sample results from their mean divided
by one less than the number of results in the
sample. The sample variance denoted s^
is given by
n - 2
2 pq - X)
s2 = iil
n - 1
where n is the number of results.
Sample standard deviation — Square root of
the sample variance.
I2 (X, - X)2
.. Yi-j—_
» n - 1
Relative standard deviation (coefficient of
variation) — Sample standard deviation
expressed as a percentage of the mean.
Rel. Std. Dev. = -£=- X 100
X
Range — The difference between the largest
and smallest results in the sample.
Confidence limits — Limits within which the
true mean, n, of the population (the theoret-
ically infinite number of possible replications
of the analysis) will lie with probability equal
to 1 - a, where a is the probability that the
limits do not contain the true mean. The
upper and lower 1 - a confidence limits are
given by
Confidence limits ¦ X ±t ,_s/Vn"
a I £
111
-------
where X and s are the sample mean and
standard deviation, ^aj2 *-s uPPer a!2
point of "Student's" t-distribution, and n
is the number of results in the sample used
to compute X.
Tolerance limits — Limits within which one
can state with probability y that at least a
proportion P of the entire population will
lie. The upper and lower tolerance limits
are given by
Tolerance limits = X ± Ks,
where K is the factor for two-sided tolerance
limits for normal populations, ^ The value of
K depends upon the chosen values of y and P.
REFERENCES
1. Natrella, M. G. Experimental Statistics. National Bureau of
Standards, 1963, pp. T-10.
112
-------
APPENDIX G.
TESTS FOR NORMALITY AND REJECTION OF OUTLIERS
Test for normality
The Kolmogorov-Smirnov goodness-of-fit test was used to deter-
mine whether the observations reported could reasonably be thought to
have come from a normal distribution. *
Briefly, the test involves computing the observed cumulative fre-
quency distribution (the percent of values less than or equal to each
value in the distribution) and comparing it with the theoretical normal
cumulative frequency distribution. The point at which the two distri-
butions, theoretical and observed, show greatest divergence is deter-
mined. Reference of the value of the divergence to a table of critical
values for the Kolmogorov-Smirnov goodness-of-fit test indicates whether
such a large divergence is likely on the basis of chance. If such a large
divergence is not likely, the distribution is designated as nonnormal;
otherwise the distribution is designated as normal.
Tests for rejection of outliers
1. If the distribution is designated as nonnormal, the suspected
outlier (the farthest value from the mean) is rejected only if the distance
between it and the mean is greater than three standard deviations; other-
wise the suspected outlier is accepted.
2. If the distribution is designated as normal and the sample size
is less than or equal to 30, the suspected outlier, the farthest value
from the mean, is tested for rejection by a method developed by Dixon. ^
Briefly, this test involves computing a ratio that compares the distance
of the suspected value being tested from its neighbors with the range of
all, or most all, of the observations (depending on the total number of
suspected values in the sample). Reference of the ratio to a table of
critical values for test ratios for gross errors indicates whether such
a large ratio is likely on the basis of chance. If the ratio is greater
than or equal to the critical value, the probability that the suspected out-
lier is from the sample distribution is small; hence, the outlier is rejected.
If the ratio is less than the critical value, the suspected outlier probably
came from the sample distribution; hence, the suspected outlier is accepted.
3. If the distribution is designated as normal, and the sample size
is greater than 30, the suspected outlier is tested for rejection by a
method developed by Santner. ® This method employs the statistic,
X - Xp t where X is the sample mean, XQ is the suspected outlier (the
s
113
-------
farthest value from the mean) and s is the sample standard deviation.
This statistic is compared with a table of critical values to determine
whether its value is larger than would be expected on the basis of chance.
If the statistic is greater than or equal to the critical value, the suspected
outlier is rejected; otherwise, the suspected outlier is accepted.
Application of tests for normality and for rejection of outliers to ARS
studies
The test for normality and the subsequent test for rejection of out-
liers are applied to the observed data in two ways: first, to each method
for a given substance at a given concentration; then to a given substance
at a given concentration regardless of method. In either case, it is first
necessary to determine whether the original distribution is normal or
nonnormal. If the original distribution is designated as nonnormal,
method 1 is used to test for rejection of the suspected outlier farthest
from the mean. If the suspected outlier is not rejected, no further tests
for normality or rejection of outliers are made, and the distribution is
designated as nonnormal. On the other hand, if the suspected outlier is
rejected, the new distribution, which excludes the rejected observation,
is then tested for normality. If the new distribution is nonnormal, the
next suspected outlier is tested for rejection by method 1. This cycle
of testing for normality and testing for rejection of outliers continues
until a suspected value is not rejected or the test for normality designates
the distribution as normal. If the distribution is designated as normal,
subsequent tests for rejection of outliers made by method 2 or 3 are the
same as if the original distribution had been normal. This case is dis-
cussed next.
If the original distribution is designated as normal or a new distri-
bution that was originally nonnormal is designated as normal after the
rejection of one or more outliers, and if the number of observations is
not greater than 30, then method 2 is used to test for rejection the sus-
pected outlier farthest from the mean. If the suspected outlier is not
rejected, no further tests are made, and the distribution is designated
as normal. If the suspected outlier is rejected, then the suspected out-
lier farthest from the mean of the new distribution is tested for rejection,
and so on until the suspected value of a new distribution is not rejected;
when this occurs, no further tests are made, and the final distribution
is designated as normal. On the other hand, if the number of observa-
tions in the original distribution is greater than 30, method 3 is used to
test the suspected outlier for rejection. If the suspected outlier is not
rejected, no further tests are made, and the distribution is designated
as normal. If the suspected outlier is rejected, than the suspected
outlier farthest from the mean of the new distribution, which excludes
the rejected value, is tested for rejection. Testing for outliers continues
by this method until a suspected outlier is not rejected or the number of
114
-------
observations is no longer greater than 30, in which case, method 2 is
used for testing for rejection of any remaining suspected outliers.
REFERENCES
1. Siegel, S. Nonparametric Statistics for the Behavioral Sciences.
McGraw-Hill Book Co., Inc. New York, N, Y., 1956. pp. 47-51.
2. Dixon, W. J., Ratios Involving Extreme Values. Ann. Math. Stat.
22: 68-78, 1951.
3. Personal communication. J. Santner, Mathematical Sciences,
Office of the Director, Robert A. Taft Sanitary Engineering Center,
1966.
115
-------
APPENDIX H.
STATISTICAL COMPARISON OF METHODS WITH
RESPECT TO PRECISION AND ACCURACY
The methods are compared in two ways with respect to precision
and accuracy. In the first case, two methods are compared at a given
concent ration^ with respect to precision and to accuracy. Th^ unknown
variances, a and a ^ (estimated by the sample variances, and s^),
of the two methods are first compared by the F-test^ to determine whether
there is a significant difference in the precision of the two methods. The
unknown means, /Uj and (estimated by the sample means, Xj and X2).
of the two methods are then compared by the t-test to determine whether
there is a significant difference in the accuracy of the two methods. The
t-test employed is based on the result of the F-test, These two tests of
hypotheses will produce one of the following results.
2 2
Outcome 1: /"1 / A<2
2 2
Outcome 3: cr 1 / a , ^ ^
2 2
Outcome 4: cr J j cr ju +
In outcome 1, we conclude that the sample results do not indicate
that a significant difference in either precision or accuracy exists between
the two methods.
In outcome 2, we conclude that there is no indication of a significant
difference in precision between the two methods, but there is a significant
difference in the accuracy of the two methods; specifically, the method
whose sample mean is closer to the true value is deemed the more accur-
ate. In outcome 3, we conclude that there is no indication of a significant
difference in the accuracy of the two methods, but the method with the
smaller sample variance is the more precise.
In outcome 4, we conclude that there is a significant difference in
the precision and in the accuracy of the two methods. The method with
the smaller sample variance is the more precise, and the method whose
sample mean is closer to the true value is the more accurate.
In the second case, more than two methods are compared at a given
level of concentration with respect to precision and accuracy. Bartlett's
116
-------
o
Test is used first to test the hypothesis of equality of the unknown
2
variances, cr ., of the methods in order to compare the precision of the
methods. If we conclude that the precision is the same, the Analysis of
Variance** is then used to test whether a significant difference exists
among the means, /j., in order to compare the accuracy of the methods.
If there is a significant difference among the means. Duncan's Multiple
Range Test ® is used to determine which method means differ signifi-
cantly. If the precision is not the same, then the Kruskal-Wallis One-
way Analysis of Variance by Ranks is used to determine whether a
significant difference exists among the means in order to compare the
accuracy of the methods.
Once again, there are basically four possible outcomes for the above
tests of hypotheses.
2
Outcome 1: all
-------
2. Ibid., pp. 119-20.
3. Ibid. , pp. 136-38.
4. Hicks, C. Fundamental Concepts in the Design of Experiments.
Holt, Rinehart, Winston. New York, N. Y., 1964, pp. 21-28.
5. Ibid,, pp. 31-33.
6. Kramer, C. Extension of Multiple Range Tests to Group Means with
Unequal Numbers of Replications. Biometrics 1_2: 307-310, 1956.
7. Siegel, S. Nonparametric Statistics. McGraw-Hill. New York,
N. Y., 1956, pp. 184-94.
118
-------
APPENDIX I.
ANALYTICAL REFERENCE SERVICE MEMBERSHIP
STATE AGENCIES
Alabama State Department of Public Health, Montgomery
Alabama Water Improvement Commission, Montgomery
Arizona State Department of Health, Phoenix
Arkansas Pollution Control Commission, Little Rock
Arkansas State Department of Health, Little Rock
California Department of Water Resources, Sacramento
California State Department of Public Health, Los Angeles
California State Department of Public Health, Air and Industrial Hygiene
Laboratory, Berkeley
California State Department of Public Health, Sanitation and Radiation
Laboratory, Berkeley
Colorado Department of Public Health, Denver
Connecticut State Department of Health, Hartford
Delaware Water and Air Resources Commission, Dover
District of Columbia Department of Public Health, Washington, D. C.
Florida Department of Agriculture, Tallahassee
Florida State Board of Health, Jacksonville
Florida State Board of Health, Pensacola
Florida State Board of Health, Winter Haven
Hawaii State Department of Health, Laboratories Branch, Honolulu
Hawaii State Department of Health, Occupational and Radiological Health
Section, Honolulu
Idaho Department of Health, Boise
Illinois Department of Public Health, Springfield
Illinois State Water Survey, Champaign
Illinois State Water Survey, Peoria
Indiana State Board of Health, Indianapolis
Iowa State Hygienic Laboratory, Des Moines
Iowa State Hygienic Laboratory, Iowa City
Kentucky State Department of Health, Division of Laboratory Services,
Frankfort
Kentucky State Department of Health, Radiological Health Program,
Frankfort
Lawrence Experiment Station, Massachusetts
Louisiana State Department of Health, New Orleans
Los Angeles County Flood Control District, California
Maryland State Department of Health, Bureau of Environmental Chemistry,
Baltimore
Maryland State Department of Health, Bureau of Laboratories, Baltimore
Maryland State Department of Water Resources, Annapolis
Massachusetts Department of Public Health, Amherst
Massachusetts Department of Public Health, Boston
119
-------
Michigan Department of Conservation, Lansing
Michigan Department of Public Health, Lansing
Minnesota Department of Agriculture, St. Paul
Minnesota Department of Health, Minneapolis
Missouri Department of Health, Jefferson City
Montana Bureau of Mines and Geology, Butte
Montana Health Department, Helena
Nebraska State Department of Health, Lincoln
Nevada State Department of Health, Reno
Nevada State Department of Health and Welfare, Las Vegas
New Hampshire State Department of Health, Concord
New Hampshire Water Supply and Pollution Control Commission, Concord
New Jersey State Department of Health, Trenton
New Mexico Department of Public Health, Santa Fe
New York State Conservation Department, Avon
New York State Conservation Department, Ronkonkoma
New York State Department of Health, Division of Air Resources, Albany
New York State Department of Health, Division of Laboratories and
Research, Albany
New York State Department of Health, Syracuse
New York State Department of Labor, New York City
North Carolina Department of Water and Air Resources, Raleigh
North Dakota State Department of Health, Bismarck
North Jersey District Water Supply Commission, Wanaque
Ohio Department of Agriculture, Reynoldsburg
Ohio State Department of Health, Columbus
Oklahoma State Health Department, Oklahoma City
Oregon State Board of Health, Portland
Pennsylvania Department of Agriculture, Harrisburg
Pennsylvania Department of Health, Division of Air Pollution Control,
Harrisburg
Pennsylvania Department of Health, Water Quality Section, Harrisburg
Puerto Rico Institute of Health Laboratories, Hato Rey
Puerto Rico Aqueduct and Sewer Authority, San Juan
Rhode Island State Department of Health, Providence
South Carolina Pollution Control Authority, Columbia
South Dakota Department of Health, Pierre
Tennessee Department of Public Health, Nashville
Tennessee Stream Pollution Control Authority, Nashville
Texas State Department of Health, Austin
Utah State Department of Health, Salt Lake City
Vermont State Department of Health, Barre
Vermont State Department of Health, Burlington
Virginia State Department of Health, Bureau of Industrial Hygiene,
Richmond
Virginia State Department of Health, Bureau of Laboratories, Richmond
Virginia State Water Control Board, Richmond
120
-------
Washington State Department of Health, Seattle
Washington State Food and Drug Laboratory, Seattle
West Virginia Department of Natural Resources, Charleston
Wisconsin Department of Agriculture, Madison
MUNICIPAL AGENCIES
Albuquerque Department of Environmental Health, Air Management
Division, New Mexico
Albuquerque Department of Environmental Health, Food and Institutional
Division, New Mexico
Baltimore City Health Department, Maryland
Bay Area Air Pollution Control District, San Francisco, California
Beaumont Health Department, Texas
Central Water Filtration Plant, Chicago, Illinois
City of Amarillo, Water Reclamation Department, Texas
City of Charlotte, Water Department, North Carolina
City of Cincinnati, Division of Water Pollution Control, Ohio
City of Durham, Department of Water Resources, North Carolina
City of Erie, Bureau of Water, Pennsylvania
City of Long Beach, Water Department, California
City of Miami, Alexander Orr, Jr. Water Treatment Plant, Florida
City of Newburgh, Water Department, New York
City of New York, Food and Drug Laboratory, New York
City of Niagara Falls, Division of Water Laboratories, New York
City of Philadelphia, Office of the Medical Examiner, Pennsylvania
City of San Jose, Health Department, California
City of Seattle, Water Department, Washington
City of Toledo, Division of Pollution Control, Ohio
City of Yonkers, Bureau of Water, New York
County of Fresno, Department of Public Health, California
County of Los Angeles, Air Pollution Control District, California
Denver Board of Water Commissioners, Colorado
Department of Air Pollution Control, Chicago, Illinois
Department of Public Health, Environmental Health Laboratory,
Philadelphia, Pennsylvania
Department of Public Health, Public Health Laboratory, Philadelphia,
Pennsylvania
Department of Public Works and Utilities, Flint, Michigan
Department of Service and Buildings, Dayton, Ohio
Department of Water and Power, Los Angeles, California
East Bay Municipal Utility District, Oakland, California
Easterly Pollution Control Center, Cleveland, Ohio
Erie County Health Laboratory, Buffalo, New York
Houston City Health Department, Texas
Los Angeles Department of Public Works, Playa Del Rey, California
Louisville Water Company, Kentucky
121
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Metropolitan St. Louis Sewer District, Missouri
Metropolitan Sanitary District of Greater Chicago, Illinois
Metropolitan Utilities District, Omaha, Nebraska
Metropolitan Water District of Southern California, LaVerne
Minneapolis Water Department, Minnesota
Monroe County Health Department, Rochester, New York
Nassau County Department of Health, Hempstead, New York
Nassau County Department of Health, Mineola, New York
New York City Department of Air Pollution Control, New York
New York City Health Department, New York
Orange County Air Pollution Control District, Anaheim, California
Philadelphia Water Department, Pennsylvania
Philadelphia Water Department, Belmont Laboratory, Pennsylvania
Philadelphia Water Department, Torresdale Laboratory, Pennsylvania
Riverside County Air Pollution Control District, California
St, Louis Public Health Laboratories, Missouri
Salem and Beverly Water Supply Board, Beverly, Massachusetts
San Diego County Department of Public Health, California
FEDERAL AGENCIES
Brookhaven National Laboratory, Upton, Long Island, New York
DHEW, PHS, Bureau of Community Environmental Management,
Cincinnati, Ohio
DHEW, PHS, Bureau of Water Hygiene, Bethesda, Maryland
DHEW, PHS, National Air Pollution Control Administration, Washington,
D.C.
DHEW, PHS, Northeast Marine Health Sciences Laboratory, Narragansett,
Rhode Island
DHEW, PHS, Northeastern Radiological Health Laboratory, Winchester,
Massachusetts
DHEW, PHS, Southwestern Radiological Health Laboratory, Las Vegas,
Nevada
First United States Army Medical Laboratory No. 1, Fort George G.
Meade, Maryland
Fourth U.S. Army Medical Laboratory, Fort Sam Houston, Texas
Regional Environmental Health Laboratory (LSGHM), McClellan AFB,
California
Regional Environmental Health Laboratory (SGHK), Kelly AFB, Texas
Reynolds Electrical and Engineering Company, Inc., Las Vegas, Nevada
San Francisco Bay Naval Shipyard, Vallejo, California
Sixth U. S, Army Medical Laboratory, Sausalito, California
Tennessee Valley Authority, Chattanooga
Tennessee Valley Authority, Muscle Shoals, Alabama
U.S. Army Environmental Hygiene Agency, Edge wood Arsenal, Maryland
US DA, Soils Laboratory, Beltsville, Maryland
USDI, FWPCA, AWTR Research Activities, Pomona, California
USDI, FWPCA, Alaska Water Laboratory, College
122
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USDI, FWPCA, Analytical Quality Control, Cincinnati, Ohio
USDI, FWPCA, Chemistry and Physics, Cincinnati, Ohio
USDI, FWPCA, Chicago Program Office, Illinois
USDI, FWPCA, North Atlantic Water Quality Management Office,
Edison, New Jersey
USDI, FWPCA, Ohio River Basin Project, Evansville, Indiana
USDI, FWPCA, Ohio River Basin Project, Wheeling, West Virginia
USDI, FWPCA, Robert S. Kerr Water Research Center, Ada, Oklahoma
USDI, FWPCA, Technical Advisory and Investigations Branch, Cincinnati,
Ohio
USDI, Fish-Pesticide Research Laboratory, Columbia, Missouri
USDI, Geological Survey, Columbus, Ohio
USDI, Geological Survey, Denver, Colorado
USDI, Geological Survey, Harrisburg, Pennsylvania
USDI, Geological Survey, Little Rock, Arkansas
USDI, Geological Survey, Menlo Park, California
Walter Reed Army Medical Center, Washington, D. C.
FOREIGN AGENCIES
Alberta Department of Public Health, Edmonton, Alberta, Canada
Algoma Steel Corporation, Limited, Sault Ste. Marie, Canada
British Coke Research Association, Chesterfield, Derbyshire, England
Central Public Health Engineering Research Institute, Nagpur, India
City's Institute for Health Protection, Belgrade, Yugoslavia
Ciudad Universitaria, Mexico
Department of Energy, Mines and Resources, Ottawa, Ontario, Canada
Department of Health Services and Hospital Insurance, Vancouver, B.C.,
Canada
Department of Municipal Laboratories, Hamilton, Ontario, Canada
Department of National Health and Welfare, Occupational Health Division,
Ottawa, Ontario, Canada
Department of National Health and Welfare, Public Health Engineering
Division, Ottawa, Ontario, Canada
Department of National Health and Welfare, Public Health Engineering
Division, Vancouver, B. C., Canada
Department of Public Health, Sydney, Australia
Institute of Environmental Sanitation, First Section, Taipei, Taiwan,
China
Institute of Environmental Sanitation, Division of Quality and Pollution
Control, Taipei, Taiwan, China
Instituto Nacional de Obras Sanitarias, Caracas, Venezuela
Mekoroth Water Company, Tel-Aviv, Israel
Metropolitan Corporation of Greater Winnipeg, Manitoba, Canada
Metropolitan Water, Sewerage and Drainage Board, Sydney, Australia
National Agricultural Materials, Seoul, Korea
National Institute for Water Research, Pretoria, South Africa
123
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Ontario Water Resources Commission, Toronto, Canada
Osaka City Institute of Hygiene, Japan
Scientific Research Council, Kingston, Jamaica, West Indies
United Kingdom Atomic Energy Authority, Didcot, Berks, England
University of Belgrade, Yugoslavia
University of Leeds, England
Water Commission, Jamaica, West Indies
Water Research Association, Marlow, Buckinghamshire, England
UNIVERSITIES
Iowa State University, Ames
Louisiana State University, Baton Rouge
Medical College of South Carolina, Charleston
New Mexico Institute of Mining and Technology, Socorro
New York University Medical Center, New York
Pennsylvania State University, University Park
Purdue University, Lafayette, Indiana
Oak Ridge Institute of Nuclear Studies, Tennessee
Rensselaer Polytechnic Institute, Troy, New York
Rutgers University, New Brunswick, New Jersey
St. Mary's College, Winona, Minnesota
University of California, Department of Civil Engineering, Berkeley
University of California, Industrial Hygiene Engineering, Berkeley
University of California, Richmond
University of Dayton, Ohio
University of Florida, Gainesville
University of Kansas, Lawrence
University of Minnesota, Minneapolis
University of North Carolina, Chapel Hill
University of Puerto Rico, Mayaguez
University of Vermont, Burlington
University of Wisconsin, Madison
Washington State University, Air Pollution Research Section, Pullman
Washington State University, College of Eng. Research Division, Pullman
Wayne State University, Detroit, Michigan
INDUSTRIES
Aluminum Company of America, Wenatchee, Washington
American Biochemical Laboratory, Baltimore, Maryland
American Public Health Association, Riverside, California
American Water Works Association, New York, New York
Anaconda Company, Grants, New Mexico
ARMCO Steel Corporation, Middletown, Ohio
Battelle Memorial Institute, Columbus, Ohio
Bethlehem Steel Corporation, Bethlehem, Pennsylvania
124
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Black and Veatch, Kansas City, Missouri
Bio-Technics Laboratories, Incorporated, Los Angeles, California
Borg-Warner Corporation, Des Plaines, Illinois
Bowser-Morner Testing Laboratories, Incorporated, Dayton, Ohio
Brown and Caldwell Laboratories, San Francisco, California
Calgon Corporation, Pittsburgh, Pennsylvania
California Water Service Company, San Jose, California
Carnation Research Laboratories, Van Nuys, California
Chrysler Corporation, Detroit, Michigan
Culligan, Incorporated, Northbrook, Illinois
Cyrus Wm. Rice and Company, Pittsburgh, Pennsylvania
Dow Chemical Company, Midland, Michigan
Emery Industries, Incorporated, Cincinnati, Ohio
Fairbanks, Morse and Company Research Center, Beloit, Wisconsin
Goodyear Atomic Corporation, Piketon, Ohio
H. C. Nutting Company, Cincinnati, Ohio
Hach Chemical Company, Ames, Iowa
Hammond-Montel, Incorporated, Elxnhurst, New York
Havens-Emerson, East Patterson, New Jersey
Hill Top Research, Incorporated, Miamiville, Ohio
Holzmacher, McLendon and Murrell, Melville, New York
Hydro Research Laboratories, Pontiac, Michigan
Industrial Chemicals, Incorporated, South Bend, Indiana
1NFILCO, General American Transportation Corporation, Tucson,
Arizona
Ionac Chemical Company, Birmingham, New Jersey
Ionics, Incorporated, Watertown, Massachusetts
Isotopes - A Teledyne Company, Sandusky, Ohio
Isotopes, Incorporated, Palo Alto, California
Johns-Manville Research and Engineering Center, Manville, New Jersey
Kem-Tech Laboratories, Incorporated, Baton Rouge, Louisiana
Kennecott Copper Corporation, Salt Lake City, Utah
Monsanto Company, St. Louis, Missouri
Moutrey and Associates, Incorporated, Oklahoma City, Oklahoma
Nalco Chemical Company, Chicago, Illinois
Pacific Engineering Laboratory, San Francisco, California
Pacific Gas and Electric Company, Emeryville, California
Pan American World Airways, Patrick AFB, Florida
Philadelphia Suburban Water Company, Bryn Mawr, Pennsylvania
Procter and Gamble Company, Cincinnati, Ohio
Radiation Detection Company, Mountain View, California
Ray W. Hawksley Company, Incorporated, Richmond, California
Reynolds Electrical and Engineering Company, Incorporated, Las Vegas,
Nevada
Roy F, Weston, West Chester, Pennsylvania
St. Louis County Water Company, University City, Missouri
Sandia Corporation, Albuquerque, New Mexico
125
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Shell Chemical Company, Princeton, New Jersey
Tenco Hydroscience, Incorporated, Chicago, Illinois
Texas Gulf Sulphur Company, Aurora, North Carolina
Tracerlab, Richmond, California
U.S. Industrial Chemicals Company, Tuscola, Illinois
United States Pipe and Foundry Company, Birmingham, Alabama
W. E. Grace and Company, Lake Zurich, Illinois
Wastewater Analysis Corporation, Lincoln Park, Michigan
Water Pollution Control Federation, Washington, D. C.
Water Service Laboratories, Incorporated, New York, New York
Xerox Corporation, Webster, New York
York Research Corporation, Stamford, Connecticut
126
A US GOVERNMENT PRINTING OFFICE : 1*«* 0~3«t-eSS
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BIBLIOGRAPHIC: Environmental Control Administra- ACCESSION NO.
tion. WATER CHLORINE (RESIDUAL) NO. 1. STUDY
NUMBER 35. Public Health Service Publication No. KEY WORDS;
1988. 1969. 126 pp.
ABSTRACT: In this study each participant was shipped
three vials of dry powder and a sealed glass ampoule
of solution which, when dissolved and mixed according
to instructions, provided samples containing both
free and combined chlorine. Each analyst was re-
quested to use three preselected methods from the
nine being studied. A total of 72 participants sub-
mitted results indicating that the best accuracy and
precision was obtained by use of the ferrous-DPD
method, followed closely by the methyl orange,
SNORT and amperometric methods. The leuco
crystal violet procedure also gave good results in
the analysis of two of the samples but poor on a third
containing a hydrolyzable chlorine (dichloroamide),
which may simply indicate that the method is more
specific for free chlorine than any of the others are.
BIBLIOGRAPHIC: Environmental Control Administra- ACCESSION NO.
tion. WATER CHLORINE (RESIDUAL) NO. 1. STUDY
NUMBER 35. Public Health Service Publication No. KEY WORDS:
1988. 1969. 126 pp.
ABSTRACT: In this study each participant was shipped
three vials of dry powder and a sealed glass ampoule
of solution which, when dissolved and mixed according
to instructions, provided samples containing both
free and combined chlorine. Each analyst was re-
quested to use three preselected methods from the
nine being studied. A total of 72 participants sub-
mitted results indicating that the best accuracy and
precision was obtained by use of the ferrous-DPD
method, followed closely by the methyl orange,
SNORT and amperometric methods. The leuco
crystal violet procedure also gave good results in
the analysis of two of the samples but poor on a third
j containing a hydrolyzable chlorine (dichloroamide),
j which may simply indicate that the method is more
i specific for free chlorine than any of the others are.
BIBLIOGRAPHIC: Environmental Control Administra- ACCESSION NO.
tion. WATER CHLORINE (RESIDUAL) NO. 1. STUDY
NUMBER 35. Public Health Service Publication No. KEY WORDS:
1988. 1969. 126 pp.
J ABSTRACT: In this study each participant was shipped
I three vials of dry powder and a sealed glass ampoule
j of solution which, when dissolved and mixed according
j to instructions, provided samples containing both
j free and combined chlorine. Each analyst was re-
J quested to use three preselected methods from the
j nine being studied. A total of 72 participants sub-
j mitted results indicating that the best accuracy and
j precision was obtained by use of the ferrous-DPD
j method, followed closely by the methyl orange,
j SNORT and amperometric methods. The leuco
] crystal violet procedure also gave good results in
j the analysis of two of the samples but poor on a third
I containing a hydrolyzable chlorine (dichloroamide),
{ which may simply indicate that the method is more
j specific for free chlorine than anv of the others are.
-------
The poorest results were obtained by the use of the
other three orthotolidine procedures. It is likely
that the greatest potential source of error was in
the use of distilled water that was not completely
free of chlorine or free of chlorine demand.
The poorest results were obtained by the use of the
other three orthotolidine procedures. It is likely
that the greatest potential source of error was in
the use of distilled water that was not completely
free of chlorine or free of chlorine demand.
The poorest results were obtained by the use of the
other three orthotolidine procedures. It is likely
that the greatest potential source of error was in
the use of distilled water that was not completely
free of chlorine or free of chlorine demand.
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