ENVIRONMENTAL PROTECTION AGENCY

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WATER CHLORINE (RESIDUAL) NO. 2

        REPORT NUMBER 40
        Report of a Study Conducted by

     ANALYTICAL REFERENCE SERVICE
       R. J. Lishka and E. F. McFarren
           Water Hygiene Division
   ENVIRONMENTAL PROTECTION AGENCY
          Office of Water Programs
           Cincinnati, Ohio 45213
                  1971

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                            FOREWORD

       The Analytical Reference Service (ARS) is conducted by the
Water Hygiene Division of the Environmental Protection Agency 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
constituents.  Decisions as to qualitative makeup are made by the mem-
bership, 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 numer-
ical values, a critique of the procedures used, comments on modifica-
tions, 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 299 Federal,
state, and municipal agencies; industries; universities; consulting
firms; and foreign agencies.
                                 iii

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Water-Minerals
Water-Metals
Water-Fluoride
Water- Radioactivity
Water-Surfactant
Water-Oxygen Demand
Water-Trace Elements
COMPLETED STUDIES

   Calcium,  magnesium, hardness, sulfate,
   chloride,  alkalinity, nitrite, nitrate, sodium,
   and potassium; study No.  1 completed in
   1956, No. 2 in 1958 and No. 3 in 1961.

   Lead,  copper,  cadmium,  aluminum, chro-
   mium,  iron, manganese,  and zinc; study No.
   1 completed in 1957 and No. 2 in 1962. These
   same metals plus silver;  study No.  3 com-
   pleted in 1965.  Except for the substitution of
   magnesium for aluminum, these same metals
   were analyzed by atomic absorption in 1967;
   study No. 4.  Copper, manganese, and alum-
   inum in the presence and  absence of interfer-
   ences;  study No. 5 completed in 1969.  Alum-
   inum,  beryllium and barium by atomic absorp-
   tion; study No. 6 completed in 1970.

   Fluoride in the presence and absence of inter-
   ferences, with and without distillation by a
   specified procedure; study No. 1 completed
   in  1958 and No.  2 in 1961.  Fluoride by ion-
   exchange and fluoride electrode;  study No.  3
   completed in 1969.

   Gross beta activity; study No. 1 completed
   in  1959 and No.  2 in 1961.  Gross beta and
   strontium-90 activity; study No.  3 completed
   in  1963.

   Surfactant in various waters; study No. 1
   completed in 1959, No. 2 in 1963 and No. 3
   in  1968.

   Biochemical oxygen demand and chemical
   oxygen demand; study No.  1 completed in
   1960.  Chemical oxygen demand; study No.
   2 completed in 1965.

   Arsenic, boron,  selenium,  and beryllium;
   study No. 1 completed in  1962.  These same
   metals  plus vanadium; study No.  2 completed
   in 1966.
                                iv

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Freshwater Plankton
Water-Nutrients
Water-Phenols
Water-Cyanides
Water-Chlorine
Air-Inorganics
Air-Lead
Air-Particulates
Air-Sulfur Dioxide
Water-Pesticides
Evaluation of the precision and accuracy
obtainable by the use of various methods of
plankton counting and identification; study
No. 1 completed in 1964.

Silicate, phosphate,  ammonia nitrogen,
organic nitrogen, and nitrate nitrogen;
study No. 1 completed in  1966.  Ammonia
nitrogen, nitrate nitrogen and ortho, poly,
and organic phosphate; study No. 2 completed
in 1969.

Phenol and 2,  4-dichlorophenol in water by
two specified methods; study No. 1 completed
in 1966.

Potassium cyanide and potassium ferricyanide
in water by two  specified  methods;  study No.
1 completed in 1967.

Free and combined chlorine by nine different
methods; study No. 1 completed in 1969;
study No. 2 completed in  1970.

Chloride, sulfate, fluoride, and nitrate  in
aqueous solution and on glass-fiber,  high-
volume filter mats; study No. 1 completed
in 1958.

Filter paper tape impregnated with lead;
study No. 1 completed in  1961.

Microscopic identification of some  common
atmospheric particulates; study No.  1 com-
pleted in 1964.

Sulfur dioxide in air by a  specified method;
study No. 1 completed in  1963.

Lindane, heptachlor epoxide, DDE,  and
dieldrin in water; study No. 1 completed in
1965.   Lindane, heptachlor,  aldrin,  hepta-
chlor epoxide, p, p'-DDE, dieldrin,  endrin,
o, p'-DDT,  p, p'-DDT, and methoxychlor in
water; study No. 2 completed in 1968.  Lin-
dane,  heptachlor epoxide, dieldrin,  hepta-
chlor,  p, p'-DDT and endrin; study No. 3
completed in 1970.

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Food-Pesticides          DDT in milk; study No. 1 completed in 1962.
                          Lindane, heptachlor epoxide,  DDE,  and diel-
                          drin in milk; study No.  2  completed in 1965.

Water-Physics            Total alkalinity, pH,  specific conductance
                          and total residue in water; study No. 1 com-
                          pleted in 1970.
       Copies of these reports are available from ARS on request as
long as the present supply lasts.  In most cases reports published
prior to 1965 are no longer available.  Order by title; namely, Water
Metals No. 4, or Water Surfactant No. 3, etc.

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                       CONTENTS
PREFACE	ix
ACKNOWLEDGMENTS	  x
PARTICIPANTS IN THIS STUDY	xi
ABSTRACT	xiii
DESIGN OF THE STUDY	  1
TREATMENT OF THE DATA	3
RESULTS 	  3
     Sample 1. Free chlorine	3
     Sample 2. Free chlorine	18
     Sample 3. Combined chlorine	33
COMMENTS OF THE PARTICIPANTS	48
SUMMARY AND CONCLUSIONS	51
BIBLIOGRAPHY	56
APPENDICES	57
     A. DPD Colorimetric Method for Free Chlorine,
        Monochloramine, Dichloramine,
        and Nitrogen Trichloride	58
     B. Tabulation of Results	62
     C.Glossary of Statistical Terms	81
     D. Tests for Normality and Rejection of Outliers  . ...  84
     E. Comparison of Methods for Statistically Significant
        Differences in  Precision and Accuracy	87
     F. Analytical Reference Service Membership	90
                            vii

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                             PREFACE

       In a previous study nine different methods for the determination
of chlorine were studied.  As a result of that study it was concluded,
among other things, that the precision of all the methods was poorer
than anticipated, probably because of the variability introduced by the
preparation of samples from dry mixtures.

       It has since been observed that a fairly strong chlorine solution
sealed in a glass ampoule and stored in the dark will remain stable  for
at least three months.  It seemed advisable, therefore,  to repeat the
study using the liquid samples to assure more homogeneity of sample
aliquots.  In addition,  the DPD colorimetric procedure was  substituted
for one of the orthotolidine methods, since the former has been shown
by a British study to be  one of the best methods and the  latter was found
to be one of the poorest  in the previous ABS study.
                                 IX

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                      ACKNOWLEDGMENTS

       Robert T. Williams,  Chief, Analytical Applications Laboratory,
Waste Identification and Analyses Activities,  Cincinnati Water Research
Laboratory, Ohio River Basin Region,  provided referee results for the
samples used in this study.

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                 PARTICIPANTS IN THIS STUDY


Alberta Department of Public Health, Edmonton,  Alberta, Canada
Allentown City Laboratory,  Pennsylvania
Arizona State  Health Laboratory, Phoenix
Borg-Warner  Corporation, Des Plaines, Illinois
Brown and Caldwell Laboratories, San Francisco, California
Calgon Corporation,  Pittsburgh,  Pennsylvania
California State Department of Public Health, Los Angeles
California Water  Service Company, San Jose, California
Central Water Filtration Plant,  Chicago, Illinois
City of Charlotte  Water Department, North Carolina
City of Erie, Bureau of Water, Pennsylvania
City of Long Beach, Water Department,  California
City of New York, Department of Health, New York
City of Yonkers,  Bureau of Water,  New York
County of Fresno, Department of Public  Health, California
Denver Board of Water Commissioners,  Colorado
Department of the Army, APO,  New York
Department of Municipal Laboratories,  Hamilton, Ontario, Canada
Department of National Health and Welfare,  Public Health Engineering
   Division, Vancouver, B.C.,  Canada
Department of Water and Power, Los Angeles,  California
DHEW, PHS,  Northeast Water Hygiene Laboratory,  Narragansett,
   Rhode Island
Emery Industries, Incorporated, Cincinnati, Ohio
First United States Army Medical Laboratory,  Fort  Sam Houston,
   Texas
Goodyear Atomic Corporation, Piketon,  Ohio
Hackensack Water Company, New Milford, New Jersey
Harris Laboratories,  Incorporated,  Lincoln, Nebraska
Illinois State Water Survey,  Peoria
Illinois State Water Survey,  Urbana
Indiana State Board of Health, Indianapolis
Institute of Environmental Sanitation, First  Section,  Taipei, Taiwan,
   China
Isotopes - A Teledyne  Company,  Sandusky,  Ohio
Lawrence Experiment  Station,  Massachusetts,
Los Angeles County Flood Control District,  California
Los Angeles Department of Public Works, Playa  Del Key, California
Louisiana State Department  of Health,  New Orleans
Mekoroth Water Company, Tel-Aviv, Israel
Metropolitan Corporation of Greater Winnipeg,  Manitoba, Canada
Metropolitan Sanitary District of Greater Chicago, Illinois
Metropolitan Sewer District, Cincinnati, Ohio
Metropolitan Water,  Sewerage and Drainage Board,  Sydney, Australia
Minneapolis Water Department, Minnesota

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Monroe County Health Department,  Rochester, New York
National Institute for Water Research, Pretoria,  South Africa
New Jersey State Department of Health, Trenton
New York State Department of Health, Albany
North Carolina Department of Water and Air Resources, Raleigh
North Jersey District Water Supply Commission,  Wanaque
Ohio State Department of Health, Columbus
Oklahoma State Board of Health,  Oklahoma City
Orange County Air Pollution Control District, Anaheim,  California
Oregon State Board of Health, Portland
Pacific Gas and Electric Company,  Emeryville, California
Pan American World Airways,  Patrick AFB,  Florida
Philadelphia Suburban Water Company,  Bryn Mawr, Pennsylvania
Philadelphia Water Department, Belmont Laboratory,  Pennsylvania
Philadelphia Water Department, Torresdale Laboratory,  Pennsylvania
Regional Environmental Health Laboratory (SGHK),  Kelly AFB, Texas
Sandia Corporation, Albuquerque, New Mexico
San Diego County Department of Public Health, California
Sixth U. S. Army Medical Laboratory, Sausalito,  California
Springwells Filtration Plant, Dearborn,  Michigan
St.  Louis County Water Company, University City, Missouri
Suffolk County Department of Health,  Smithtown,  New  York
United States Pipe and Foundry Company, Birmingham, Alabama
U. S. Army Environmental Hygiene Agency,  Edgewood Arsenal,
   Maryland
USDI,  FWQA,  AWTR Research Activities, Pomona, California
USDI,  FWQA,  Chemistry and Physics, Cincinnati,  Ohio
Virginia State  Department of Health, Bureau of Industrial Hygiene,
   Richmond
Washington State  Department of Health, Seattle
Washington State  University, College of Engineering, Research
   Division, Pullman
Water  Commission, Jamaica, West Indies
                                xii

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                            ABSTRACT

       In this study each participant was shipped four sealed glass
ampoules of concentrated solution which when diluted according to
instructions, provided two samples  containing free chlorine and one
containing combined chlorine.  Each analyst was requested to use two
preselected methods from the seven being studied but unfortunately not
all complied and although 71 participants submitted results, only  seven
were submitted for the leuco crystal violet method; whereas sixteen to
thirty results  were obtained for each of the other methods.  Statistical
analysis of these results indicated that the best accuracy and precision
was obtained by leuco crystal violet and the stabilized neutral ortho-
tolidine (SNORT) procedures, followed by DPD-titrlmetric,  ampero-
metric titration, DPD-colorimetric and methyl orange.   By far the
poorest was the orthotolidine-arsenite (OTA) procedure.
                                 Xlll

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              WATER CHLORINE (RESIDUAL) NO. 2

                     DESIGN OF THE STUDY

       In order to obtain maximum stability, the samples were pre-
pared as liquid concentrates and shipped in sealed glass ampoules.
Samples 1,  2, and 3 were hypochlorite solutions (Zonite) of different
concentrations.  Ampoule 4 contained an ammonium chloride-borate
buffer solution which was to be mixed with sample 3 to produce a com-
bined chlorine solution.

       When diluted 10 ml to one liter with chlorine-free,  chlorine-
demand free water according to instructions, the samples approximated
chlorinated water supplies (see Table 1).

               Table 1.  COMPOSITION OF SAMPLES


Free chlorine
Total chlorine

Sample 1
0.44
0.44
mg/ liter in
Sample 2
0. 98
0.98
diluted sample
Sample 3
(0.00) 0. 05a
0. 66
  aSee section on "Treatment of the Data. "

       The stock solution was standardized by iodometric titration,
and intermediate dilutions were also checked by iodometric titration.
The concentrated samples were also diluted according to instructions
and checked amperometrically by the Analytical Reference Service
staff and by another referee laboratory.  The results agreed very
closely with the calculated value based on the iodometric titrations of
the stock solution.

       Instructions for the  preparation of chlorine-free, chlorine-
demand free water by three different methods were sent with the
samples; these were  as follows:

       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 case should the initial residual be less
than 1. 0 mg/1 free chlorine but generally this amount will be sufficient.
Allow the chlorinated distilled water to stand overnight or longer, then
expose to direct sunlight until all residual chlorine is discharged (usu-
ally about one 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.

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       The Blak-Ray B-100A long wave ultraviolet lamp (Arthur H.
Thomas Company, catalogue number 6323k) will also slowly dechlori-
nate heavily chlorinated (100 mg/1) distilled water stored in 9 and 18-
liter glass bottles.  The radiation is directed through the side of the
closed bottle with the blue glass fluorescent filter removed from the
lamp.

       Chlorine-demand free water can also be prepared by the use of
an ion-exchange resin.  This can be done by mixing 1. 6 liters IR-120
and 3. 2 liters of  IR-400 or using the ready mixed analytical grade
Amberlite MB-1  in a  3-foot column of approximately 2. 5 to 5 cm diam-
eter.  Pass distilled water at a relatively slow rate through the  resin
bed and collect in a scrupulously clean receiver that will protect the
treated water from undue  exposure to the atmosphere.

       Participants were  also instructed to observe the following pre-
cautions.

1.  Be sure to use chlorine free,  and chlorine-demand free water in
    the preparation of all solutions.

2.   Use only scrupulously clean glassware; namely, glassware  soaked
    overnight in  acid (potassium dichromate cleaning solution) or in a
     1 to 100 dilution of Clorox and then rinsed with  chlorine free, and
    chlorine-demand free water and dried.

3.   To protect the chlorine free,  chlorine-demand free water, use a
    sulfuric acid or calcium chloride trap on the air inlet to the stop-
    pered storage bottle.   Withdraw the water by a  glass siphon
    arrangement through  the same stopper.  Unless this is done, the
    water may very quickly absorb  ammonia  from the atmosphere.
    Otherwise, prepare the water fresh daily.

       In order to obtain  approximately an equal number of data for
each method, participants were requested in the announcement letter
to indicate on their reply  form the two methods they intended to use.
As a result of unequally distributed returns, some participants were
asked to analyze  the samples by a method other than one of the two
methods they had indicated.  Unfortunately, very few complied.

       In the announcement of this study the participants were provided
with a copy of the DPD  colorimetric procedure, and were told that
copies of the methyl orange,  leuco crystal violet, DPD titrimetric,
and stabilized neutral orthotolidine procedures could be found in the
appendices of the previous "Water Chlorine (Residual) No.  1" report,
which was sent to those participants who requested it.  They were also
reminded that the amperometric and orthotolidine-arsenite (OTA)

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procedures could be found in the  12th edition of Standard Methods for
the Examination of Water and Wastewater.
                   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
rejection of outliers (see Appendix D) that were nonrepresentative be-
cause of errors in calculation, dilution, or other indeterminate factors.
After rejection of outliers, the data were then statistically analyzed by
computer for precision and accuracy (see Appendix C), and finally,
their precisions and accuracies were compared for significance of
differences  (see Appendix E).

       If sample 3  was prepared according to instructions, there would
be no free chlorine present.   However, it is not  possible to divide by
zero and obtain a numerical value in the calculation of the relative error.
The  true value for free chlorine in sample 3, therefore,  was changed
to the overall mean value of 0. 05 to permit complete analysis of the
data by computer.  This value is also more realistic than zero since it
is about the minimum amount that can be measured by any of the methods;
namely, is equivalent to the variation in the determination of a blank.

        For  unknown reasons  (perhaps, because a different batch of
ampoules were used) the chlorine content dropped  after  shipment in
most of the  ampoules containing sample 1.  The  results obtained on the
analysis of this sample, therefore,  can be used only for  comparative
purposes and not as a measure of the overall precision or accuracy of
the methods.

                             RESULTS

SAMPLE 1:  0.44 mg/liter free, 0.44 mg/liter total chlorine (Table 2;
             Figures 1 through 14)

        This sample was designed to provide only free chlorine at a con-
centration likely to be encountered in analysis of treated potable water.
Although the sample was analyzed after being sealed in glass ampoules
and  good agreement with the calculated value was obtained by the two
referee analysts, an unexplained slow demand apparently reduced the
shlorine concentration about 50%.  There is little value,  therefore, in
considering the accuracy of the determinations except for comparison
Detween methods.  The precision data, likewise, is useful only for  corn-
Daring the methods and should not be used for predicting the  degree of
Drecision obtainable by any of the methods.

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                                  Table 2.  SUMMARY OF DATA ON SAMPLE 1
                                (0. 44 mg/liter free,  0. 44 mg/liter total chlorine)
Method Determination
Methyl orange
Leuco crystal violet
Orthotolidine - ar s enite
SNORT
DPD-colorimetric
DPD-titrimetric
Amperometric titration
Orthotolidine
DPD-colorimetric
Free
Total
Free
Total
Free
Total
Free
Total
Free
Total
Free
Total
Free
Total
Free
Total
Free
Trt+'il
No. of
results
22
22
7
7
29
28
18
17
28
27
17
17
23
23
1
2
1
No- of Mean
outliers
0
0
0
0
0
1
0
0
0
1
0
0
0
0
0
0
n
0.221
0.269
0. 190
0.231
0. 158
0. 187
0. 199
0.242
0. 178
0.227
0.181
0.242
0. 199
0.251
0.170
0.200
n finn
Mean
error
-0.219
-0. 171
-0.250
-0.209
-0.282
-0.253
-0.241
-0. 198
-0.263
-0.213
-0.259
-0.198
-0.241
-0. 189



Standard
deviation
0. 143
0. 162
0.085
0.055
0.090
0.098
0.093
0.092
0. 102
0.100
0.110
0. 103
0.106
0.072



Rel.
error
49. 69
38.84
56. 82
47.40
64.03
57.47
54.67
44.92
59.66
48.32
58.82
44.92
54. 74
42. 98


Relative
std. dev.
64. 68
60.26
44.56
23.85
56. 79
52.21
46.64
38. 11
57.51
44.12
60.71
42.45
53.23
28.64


95% tol.
limits
0
0
0
0
0
0
0
0
0
0
0
0
0
0
.386
.437
.339
.221
.231
.252
.262
.264
.263
.260
.314
.294
.283
. 192
Total
error
114. 86
112. 59
95.31
72. 59
104. 95
101. 90
97.04
87.00
106. 18
94.00
108.86
91.77
102. 95
75. 63
(N, N-dimethyl)

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0.48




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                                CM
                                cr
                                IV
«M
fM
to
                                                                 m  in  in
                                     NUMBER
Figure 1. Bar  graph  for free residual  chlorine in sample 1 by
          methyl  orange method.

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0. 56
0.48
0.40
0.32
0.24
0. 16
0.09
0.00


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x x x x
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                                            LABORATORY  NUMBER
                Figure 2. Bar graph  for  total  residual  chlorine in sample 1 by
                          methyl orange  method.

-------
  OB

  E
      0.44
  |   0.22
  _i

  "   0. 00
AMOUN
x x
X X
X X
x x
X X
T ADDED
X X
X X
x x
X

X X
X X
X X
MEAN

X
X

                fM
                 m
                                 fM
                                 rv
                         LABORATORY NUMBER

  Figure 3.  Bar graph for free residual  chlorine in sample 1 by
            leuco crystal violet method.
  «  o.
  E

   »
  UJ

  ±   0.22
  oc
  o
  —1


  "   0. 00
AMOUNT ADDED
X
X
X
X X X X X X
X X X X X X
x MEAN
                fM

                CM

                fM
fM

CM
                                            m
                                                  fM
                         LABORATORY, NUMBER
Figure 4. Bar graph  for total  residual chlorine  in sample \  by
         leuco crystal violet method.

-------
   0. 4B
                                              AMOUNT ADDED
   0. 40
   0.3;
00

E
   0. 24
   0. 16
   0.08
                                  x
                                  x
                                            X   X
                                            X   X
                                                                  XXX


                                                                  XXX
                                                                             MEAN
   0.00
                                                    LABORATORY NUMBER

               Figure 5.  Bar graph  for  free residual  chlorine in sample  1  by orthotolidine-
                          arsenite method.

-------


fa*
E
LU
Z
CE
CD
—t
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0. 48
0.40
0. 32
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0.00


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AMOUNT ADDED x

xxxxxxxxxxxxxxxxx
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                                    LABORATORY NUMBER

Figure 6, Bar graph for  total  residual  chlorine in sample  1  by  orthotolidine-
          arsenite method.

-------
0.48
0.32
0. 16
0.00

X
X
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ADDED
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                   eg   .-«   i— i    .-4
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-------
0.48
0.32'
0.16
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X
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                                   CVJ
                                                   «M   -*
                                                             (M
                                                             1^   1^1
                                                                       CM
                                                                       (M
IM
CM
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OD
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                                                                                       CM
     IM
     (M
                                            LABORATORY NUMBER
                        Figure a. Bar graph  far total  residual chlorine in  sample \ by
                                 stabilized neutral orthotolidine method.

-------
                                             AMOUNT ADDED
0. 40
0. 24
0. 16
0. 08
0. 00-
                                                                       K  X
XXXXXXXXXXX

xxxxxxxxxxxxxxx

xxxxxxxxxxxxxxx
xxxxxxxxxxxxxxx
                                                                           MEAN
                     X
                     X
                                                LABORATORY NUMBER

              Figure  9.  Bar graph for  free  residual chlorine in sample 1  by  DPO-colorimetric
                         method.

-------
  o.sol
                                                                    AMOUNT ADDED
                                                                                                   K   X
                                                                                                   «   *
                                                                                                   X
                                                                                                   X   X
0.401
^ 0.301
   0. ZOl
                    X
                    X
                    X
                       X
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                                            X

                                            X
                            X

                            X
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                                  X

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X
                                                                                       X
                                                                                       X
                     X
                     X
                     X

                                            X
                                            X

   0. 101
   o.ool

                                                  LABORATORY NUMBER

                 Figure 10.  Bar graph for total residual chlorine  in sample  1  by  DPD-colorimetric
                            method.

-------



1

1

0.32

i

i

'
0. 16

i

<

'

0.00

X
X
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ADDED
X
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M    «    «••   m
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                       CM
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                                  CM   •-•
                                             IM
                     LABORATORY NUMBER
Figure 11.  Bar graph for free residual  chlorine in sample 1  by
           DPD-titrimetric method.

-------
    0.48
    0.36
!±f  0.24
    0.12
    0.00

X
X
X
X
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X
X
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MOUNT
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X
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                             01    <-4   ft
                                             •€>
                                                                                      fM    *•«
                                                LABORATORY NUMBER

                            Figure 12.  Bar graph for  total residual  chlorine in sample 1 by
                                       DPD-titrimetric method.

-------
0.48





0. 36








0.24







0. 12







0.00

X
X
X
X
X
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AMOUNT
X
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ADD
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           (M  CM  
-------
   0.48
   0.36
uT 0.24
   0.12
   0.00

X
X
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X
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X
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-far






                                                                  
N
CM
00
                 CO
                 CM
                                                    LABORATORY NUMBER
                           Figure 14. Bar  graph for total  residual  chlorine in sample  1  by
                                      amperometric titration method.

-------
         All mean values differed significantly from the initially deter-
mined true value.  The methyl orange results produced the least mean
error for both free and total chlorine measurement indicating somewhat
better accuracy than the other methods.  On the other hand, the methyl
orange results were significantly less precise than both OTA and SNORT
results  in the measurement of total chlorine.  There were no other signif-
icant differences in precision for either free or total chlorine results.
However, the leuco crystal violet results had the least standard deviation
for both free and total chlorine,  but because of the small number of
participants using this method, this observation may not be meaningful.

         According to the total error, the leuco crystal violet results
were the best and the methyl orange  results the poorest for both free
and total chlorine.  None of the methods,  however, can be considered
acceptable on the basis of the results obtained on this sample because
as previously stated, the sample decomposed during  shipment; even if
the overall mean were to be considered the true value, the results would
still be  unacceptable.


SAMPLE 2:  0. 98 mg/liter free, 0. 98 mg/liter total  chlorine (Table 3;
             Figures 15 through 28)

         This sample was designed to provide only free chlorine at about
the maximum concentration likely to be encountered in analysis of treated
potable  water.

         For the free chlorine measurement,  all method means differed
significantly from the true value except for methyl orange.

         For total chlorine, all but methyl orange, OTA, and DPD titri-
metric differed significantly from the true value.

         The precision data is more  involved.  For free chlorine,  leuco
crystal  violet is significantly more precise than all the rest except for
SNORT,  which was significantly more precise than methyl orange,  OTA,
DPD titrimetric and amperometric titration.  The DPD colorimetric
method  was significantly more precise than methyl orange, OTA,  and
DPD titrimetric.  Amperometric titration was significantly more precise
than both methyl orange and OTA.

         For total chlorine, leuco crystal violet was  significantly more
precise than all except methyl orange.   Amperometric titration was
significantly more precise than methyl orange, OTA  and DPD titrimetric.
Both SNORT and DPD colorimetric were significantly more precise than
methyl orange and OTA.  DPD titrimetric  was significantly more precise
than OTA.  On examination of the statistical data in Table 3,  the large
difference in standard deviations for methyl orange and leuco crystal
18

-------
                                 Table 3.  SUMMARY OF DATA ON SAMPLE 2
                                (0. 98 mg/liter free,  0. 98 mg/liter total chlorine)
Method Determination
Methyl orange
Leuco crystal violet
Orthotolidine-arsenite
SNORT
DPD- color imetric
DPD-titrimetric
Amperometric titration
Orthotolidine
DPD- color imetric
Free
Total
Free
Total
Free
Total
Free
Total
Free
Total
Free
Total
Free
Total
Free
Total
Free
Total
No. of
results
23
23
4
4
30
30
16
15
26
27
17
16
23
22
1
2
1
No. of ,.
... Mean
outliers
0
0
2
2
0
0
1
1
3
2
0
1
0
1
0
0
0. 936
0. 974
0.895
0. 912
0. 782
0. 878
0.868
0.873
0.827
0.883
0.788
0. 921
0.750
0. 861
0. 100
0.700
1 nnn
Mean
error
-0.
-0.
-0.
-0.
-0.
-0.
-0.
-0.
-0.
-0.
-0.
-0.
-0.
-0.
-0.

044
006
085
070
198
102
113
107
153
097
192
059
230
119
280

Standard
deviation
0. 315
0.301
0.042
0.015
0.335
0.325
0. 120
0.142
0.171
0. 152
0.298
0.205
0.206
0. 137
	

Rel.
error
4.53
0. 62
8. 67
7. 14
20.20
10.37
11.48
10. 95
15. 62
9. 94
19.57
6.06
23. 51
12.11


Relative
std. dev.
33.
30.
4.
1.
42.
37.
13.
16.
20.
17.
37.
22.
27.
15.


70
95
70
64
84
04
80
31
72
18
87
29
45
96
95% tol.
lim its
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
843
806
268
096
854
829
348
420
448
393
853
596
550
371
Total
error
68.83
62.12
17.24
10.20
88.57
76.81
35.95
39. 97
50.57
40.83
80.51
47. 89
65.46
40.14
(N,  N-dimethyl)

-------
2.08
1. 80
 1.52-
 1. 26
0. 98













X
X
X
X
X
X
X
X
X
X
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X
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X












AMOUNT ADDED
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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0.70
0.42
0. 14'
            •o   t->
            fW   —«
»
   O<
                                                  LABORATORY NUMBER
                         Figure 15. Bar  graph for  free residual  chlorine  in  sample 2 by
                                    methyl  orange  method.

-------










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1.82



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1. 26


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•a-  f
tM  •-•
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         o>  •->   >-i
         
                           IM   co   o        f

                             LABORATORY  NUMBER
                           IM   ^
                           -<   Ol
«»
,4
in
   Figure 16.  Bar graph  for total  residual  chlorine  in sample 2 by
                methyl orange method.

-------
-   1.54

:   i.i2
Ul
I   0.70

5   0. 28
                       AMOUNT  ADDED
                        SWH
                         X    X

                         x
                         X
MEAN
                                         r\j         •$•
                                         f>J         CD
                              LABORATORY NUMBER

       Figure 17.  Bar graph for free  residual chlorine  in  sample 2 by
                  leuco crystal violet method.
at
E
CHLORINE
1.
1.
0.
0.
12
70
AMOUNT ADDED
^f * * ^ » W x f ^^
y<. MEAN
^<
                        cv    -<    rg    —•         4-
                        IM    r^    >i    «»         to


                              LABORATORY NUMBER

      Figure  18. Bar graph  for  total residual  chlorine in sample  2  by
                leuco crystal  violet method.
22

-------
               1.47
               1. IP
                                                    AMOUNT ADDED
                   •-*- «~8—8 -$- -6—$ -3- -g- ft -8—S - S- •
                                                                 X
                                                                -Ji.
                                                                                MEAN
               0. 07
                                                            LABORATORY NUMBER

                            Figure  19.  Bar  graph  for  free  residual  chlorine in sample 2 by orthotolidine-
                                        arsenite method.
CO
CO

-------
1.47
                                      AMOUNT ADDED
o. ni
0. 63
                                   X  X   X  X   X
          X   X  X   X
                                                                   MEAN
                        X   X  X   X  X
          X   X  X   X
          X   X  X   X

          X   X  X   X
0.35
0. 071
                                                  LABORATORT NUMER
                 Figure  20.  Bar graph  for  total  residual chlorine  in sample 2 by  orthotolidine-
                             arsenite method.

-------





	
\
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.

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                                        fM    OJ   ~*    r-«    CM   CM    -4
                                        ^W    ^^   V"4    ^^    ^^   ^^    ^p

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                                                                               ro
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CM    ^
cr    «
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rg
cr
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CO
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                                                             LABORATORY  NUMBER

                                        Figure  21.  Bar  graph for free residual chlorine  in  sample  2  by
                                                   stabilized neutral orthotolidine method.

-------
1.
.

0.



0.



0.
0.
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12
no


84



70



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                                      ^4    >-4   (M
                                                 «M
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CM    CM    CM
fM    ~*        o>
                      LABORATORY  NUMBER
Figure 22. Bar graph for total residual chlorine  in sample 2  by
           stabilized neutral orthotolidine method.

-------
2. 10
1. 82
1. 54
1.26
0. !>8
                                                     AMOUNT ADDED
                                                                           MEAN
0.70
 0.42
0.14
                                                  LABORATORY NUMBER
                Figure  23.  Bar graph  for  free residual chlorine in sample  2  by  DPD-colorimetric
                            method.

-------
2. 10f
 1.821
 1.54
o. nal
                     MOUNT ADDED
                     X
                     X
                    •*-—
                     X
X

X
X
                                                                      MEAN
0. 70<
0.421
0.
                                                  LABORATORY NUMBER
               Figure 24.  Bar graph  for  total  residual  chlorine  in  sample 2 by  DPD-colorimetric
                           method.

-------
1.
1.




0.




0.





0.



0.

12




84




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28








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to
CD
                                         •-•   «M
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                                                                                                                  «VJ
                                                            LABORATORY NUMBER

                                       Figure 25. Bar graph for  free  residual  chlorine in sample 2 by
                                                  DPD-titrimetric  method.

-------
1.40
1.12
0. 84
0. 56
0.28
0.00






AMOUNT ADDED
w ^W-^WWftfVt*
X X X X X X
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                                            LABORATORY  NUMBER

                        Figure 26. Bar graph  for total residual  chlorine in sample 2  by
                                  DPD-titrimetric method.

-------
   0. 98
   0.84
   0.70
=i 0.56
   0.42
    0.28
    0.14

X
X
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            fM
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-------
0. 98
0.70
0.42
0. 14

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        N   CM   en
        CM   «M   -O
        o»   m   o>
        r-   r«-   •*•
m   m   CM
CM   -+   01
f-   •«   OB
oo   o>   «o
                                                  LABORATORY NUMBER
                        Figure 2B.  Bar  graph  for  total residual  chlorine  in sample  2  by
                                    amperometric  titration method.

-------
violet would appear significant.  However, the F-test employed to deter-
mine significance of differences in precision takes into account the num-
ber of values  for each method.  The very small number of results (4)
for the leuco crystal violet method compared to 23 values for methyl
orange prevents the difference in precision from being statistically sig-
nificant.  In addition,  two outliers were rejected from the total of 6
results  submitted for leuco crystal violet, while the methyl orange
results  were statistically normal and no values were rejected.

         According to the total error,  leuco crystal violet would be con-
sidered excellent for both free and total chlorine measurement, SNORT
would be acceptable for both free and total, and DPD titrimetric, DPD
colorimetric, and amperometric titration would be acceptable only for
total chlorine measurement.   Again, the OTA method was the poorest.

         It is  interesting to note the large discrepancy between free and
total chlorine results for the two titration procedures. Apparently,  the
DPD titrimetric and amperometric titration methods have greater diffi-
culty with free chlorine measurement than the  other methods.


SAMPLE 3:  0. 05 mg/liter free, 0. 66 mg/liter total chlorine (Table 4;
             Figures 29 through 42)

         This sample was designed to provide only combined chlorine
to simulate an insufficiently chlorinated water  having no free chlorine
residual.  However, as explained  under "Treatment of the Data, " the
value of 0. 05  mg/liter free chlorine has been selected as the "true"
value to facilitate computation,  and as a more  realistic estimate of the
measurable amount present.

         It is  evident that the OTA method is outstandingly inaccurate,
and significantly less precise than all the other methods for free chlorine
measurement.  Leuco crystal violet was significantly more precise than
all the other methods; SNORT was significantly more  precise than all
the methods except leuco crystal violet; and DPD titrimetric was signif-
icantly more precise than all except leuco crystal violet and SNORT.

         In the measurement of  total chlorine (combined chlorine),  the
mean values for OTA,  DPD colorimetric,  and  amperometric titration
differ significantly from the true value.  OTA and DPD colorimetric
were also significantly less precise than methyl orange, leuco  crystal
violet, SNORT, and DPD titrimetric.  SNORT,  in addition,  was also
more precise than amperometric titration.

         According to the total error,  methyl orange, leuco crystal vio-
let,  SNORT, and DPD titrimetric  would be considered acceptable for
total chlorine measurement.
                                                                  33

-------
                                  Table 4.   SUMMARY OF DATA ON SAMPLE 3
                                (0. 05 mg/liter free,  0. 66 mg/liter total chlorine)
Method Determination
Methyl orange
Leuco crystal violet
Orthotoltdine-arsenite
SNORT
DPD-colorimetric
DPD-titrimetric
Amperometric titration
Orthotolidine
DPD-colorimetric
Free
Total
Free
Total
Free
Total
Free
Total
Free
Total
Free
Total
Free
Total
Free
Total
Free
X^ital
No. of
results
18
22
4
6
27
29
15
15
26
25
13
15
19
23
1
2
1
No. of „„
Mean
outliers
4
0
2
1
1
0
2
2
2
3
4
2
3
0
0
0
0.049
0.689
0.000
0.653
0. 164
0.568
0.002
0. 628
0.036
0.763
0.012
0. 629
0.038
0. 552
0.100
0.700
9 nnn
Mean
error
-0.
0.
-0.
-0.
0.
-0.
-0.
-0.
-0.
0.
-0.
-0.
-0.
-0.
0.

006
029
050
007
114
092
048
032
014
103
038
031
012
108
040

Standard
deviation
0.055
0. 143
0.000
0.089
0.195
0.218
0.004
0. 110
0.057
0. 210
0.019
0. 121
0.040
0.171



Rel.
error
12.01
4.34
100.00
1.01
228.20
14.00
96.00
4. 85
27. 60
15.58
77.00
4.75
23.20
16.34



Relative
std. dev.
111.31
20.79
0.00
13.64
118.78
38.37
207.02
17. 51
158. 23
27.58
165.37
19.24
103. 84
30. 99



95% tol.
limits
0.155
0.386
0.000
0.394
0.506
0.559
0.012
0.325
0.149
0.553
0.059
0.357
0.111
0.457



Total
error
232.00
47.75
100.00
28.06
1007.80
79. 93
112.40
38. 15
256.40
79.33
153.40
41.33
182.80
68.21


(N, N-dimethyl)

-------
0.25
0.20
0.15
0.10
0.05
0.00






















































AMOUNT ADDED
X
X
X
X
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-------
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                                              LABORATORY NUMBER
                     Figure 30. Bar  graph for total  residual chlorine in sample  3  by
                                methyl  orange method.

-------

- 0.20
E
•
3?
1 0.10
o
	 1
I
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AMOUNT ADDED
XXX
     ^          f"-    fM    <»">    ro

                        LABORATORY NUMBER
Figure 32.  Bar graph for total  residual chlorine in sample 3 by
           leuco crystal violet method.
                                                             37

-------
  0.75
  0. 60
"* 0.45
  0. 30
   x  x
   X  X
X  X  X   X  X  X

X  X  X   X  X  X
                                    MEAN
                                                                             f—S--B—g—5—g—g-
                                                                   XXX
  0. 00
        xxxxxxxx

        XXX
                                              LABORATORY NUMBER

               Figure 33. Bar graph for free residual  chlorine  in  sample  3 by ortnotolidine-
                          arseni te method.

-------
!. 14
                                                                                                     x
                                                                                                     x
                                                                                                     X
                                                                                                     X
                                                                                                 X
                                                                                                 X
0. 7K
                                  AMOUNT ADDED
0. 60
     - * -3- -£- §- -9- -9-8—iS- -& -3- -x- fr-9- -6 -
                                                                      MEAN
0.42
0. 24
0.06
                                               LABORATORY NUMBER

                Figure  34.  Bar  graph  for  total  residual chlorine  in sample 3 by orthotolidine-
                           arsenite method.

-------
cc.
C3
U. ZD
0. 20
0. 15
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. 00






X
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                                                LABORATORY NUMBER

                           Figure 35.  Bar graph  for  free  residual chlorine in sample 3 by
                                      stabilized neutral  orthotolidine method.

-------
0. 96
0. 84
0.72
0. 60
0.48
0. 36












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-------
   0. 20
₯  0. 15
   0. 10
   n. 05
                                           AMOUNT ADDED
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                                                                                                      X   X   X  X  X

                                                                                                  X   X   X   X  X  X

                                                                                          xxxxxxxx
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                                                        LABORATORY NUMBER
                  Figure  37.  Bar graph  for free residual  chlorine  in sample  3  by  DPD-colorimetric
                               method.

-------
1. 32






1.08




0. 84

0. 60

0. 36
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-------
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-------
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-------
0. 25
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-------
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-------
              COMMENTS OF THE PARTICIPANTS

Methyl Orange Method

1.  We were unable to obtain reproducible standard curves for either
    the SNORT or Methyl Orange methods by following the instructions
    accompanying the samples.  Our basic approach was:

    a.   "Clorox" was standardized iodometrically.

    b.   Suitable dilutions of "Clorox" were prepared as standards.

    c.   The freshly prepared standard samples were run following the
         recommended procedure.

         The results obtained were consistently unreproducible.  Fading
         of the methyl orange color required about 10 minutes for a stable
         absorbance,  yet the method indicates 2-2.5 minutes for free
         C12.  "Clorox" should not contain any combined Cl2-  (ed.  note:
         The method indicates 1   1.5 min. for free Cl^, and 10 min.
         for combined C12).

         The results obtained were completely erratic and random.
         Values much too high as well as too low were obtained.  This
         is presumably caused by absorption and/or volatilization and/or
         reaction of the C^ with water impurities.  Pretreatment of
         glass surfaces with diluted "Clorox" (16 ppm C12), as recom-
         mended, did not improve the situation.  Volatilization was  min-
         imized by keeping the solution stoppered and by minimizing
         elapsed time.  The pH was checked and found to be within the
         indicated range for both methods.  Satisfactory reproducible
         standard curves were then obtained for both methods by "in
         situ" dilution and reaction of the C12 standards using a  diluted
         "Clorox" solution containing 164 ppm Cl2, rather than the indi-
         cated 0   2 ppm C12.  (ed. note: The method indicates  a suit-
         able range of 0 - 2 ppm C12, but does not  specify the  strength
         of stock chlorine standard solution to be used).

2.  The SNORT method would appear to be superior  to the Methyl
    Orange method because:

         a.   The standard curve data are more consistent.

         b.   The color is stable.

         c.   Color comparisons are compared directly with a blank
         rather than involving sample and blank comparisons against
         a third  sample,  water in this case.
 48

-------
3.  We analyzed the samples using hydrochloric acid and chloroacetic
    acid to adjust the test pH.  Results were identical.

4.  Absorbance decreased drastically after 1.0 minute with sample 3
    (combined chlorine).  Two standard curves are required.  One for
    0   1 ppm (low range), and one for 0-2 ppm (high range).

5.  Some difficulty in reproducing standard curve.

Leuco-Crystal Violet Method

1.  Our leuco crystal violet curve for free chlorine is linear only to
    0. 7 mg/1. In the range of 0.5   0. 7 mg/1 for total chlorine,  the
    developed color  was not stable and began to fade within 1 minute
    after indicator addition.  Therefore, it was necessary to prepare
    a  1 + 1 dilution of test sample 3  prior to the  total chlorine deter-
    mination.

    In both "Water Chlorine (Residual) Studies 1 and 2" and in our own
    independent evaluation of the leuco crystal violet method for chlorine
    we have consistently had difficulty with reproducibility of colors
    with free chlorine concentrations greater than 0. 7 mg/1.  In this
    study, we finally worked out our own technique in order to obtain
    better reproducibility.  We used 250 ml beakers instead of 100 ml
    volumetric flasks.  The tip of the  pipet was placed just under the
    spout of the beaker  and the indicator was allowed to flow down the
    inside glass  surface to the sample with a minimum of initial agita-
    tion of the sample.  We also learned that for samples containing a
    free chlorine concentration greater than 0. 7 mg/1, the rate of addi-
    tion of 1 ml of indicator solution is quite critical to color develop-
    ment.   We used  a standard 15 second addition time.

2.  Color development for free chlorine was slow.  About 5 minuted
    were required for development.

3.  No correlation was  apparent with DPD.  Too tedious  for routine,
    rapid analyses by central labs.

4.  Obtained no color development with leuco crystal violet in sample
    or standards.


Orthotolidine-Arsenite Method

1.  Used Taylor slide comparator as standard.   Results  at best are
    good to ± 0. 1 mg/1.   We found that it takes too long to add sample
    and arsenite to the sample to get lowest possible free Cl2 result
    unless temperature  is near 0°C.
                                                                  49

-------
2.  Test was carried out using an ice bath at 1. 6° C.  The temperature
    of the sample caused the cuvettes to fog up in seconds making accu-
    rate and timed readings nearly impossible.  As this test doesn't
    guarantee accurate results over  1°C during the addition of the re-
    agents, I don't find this test  very practical or convenient.


Stabilized Neutral Orthotolidine Method

1.  Approximate range of free and total chlorine  in the samples would
    be very valuable in knowing what range of standards to use in con-
    structing the curves.  Rapidity in analysis is essential.

2.  The total chlorine results  were found to be less than the sum of
    free chlorine + monochloramine, even after repeated tests with
    new sets of reagents.   In the  determination of free  chlorine in
    sample 3 there was a gradual increase in color development after
    one minute.

3.  Calibration curve must be run several times  to get reproducible
    points.  Mixing step is critical.

4.  Absorbance began to increase after 2 minutes development with
    sample 3.

5.  This is our preferred colorimetric method.


DPP-Color ime trie

1.  We found that the wavelength of maximum absorbance for DPD
    oxalate is 552 m/u.  An equally well-defined peak does occur at
    515 m/u but this peak is 0. 023 ± . 001 absorbance units lower.  We
    found no apparent differences in  the chlorine  residuals determined
    at each wavelength if a calibration curve is prepared for each wave-
    length.

2.  A  second reading of standards read about five minutes after initial
    readings indicated fading of color.

3.  Readings fade too fast for  DU Spectrophotometer.

4.  Sample 3 was very unstable   increased absorbance with time.

5.  Very unstable color changed markedly between 15 and 30 minutes
    after development,  which is  almost instantaneous.

6.  Timing is a very critical factor  in this test.  Slight deviation from
    precise timing will inevitably give erroneous results.
50

-------
    Reaction times specified for mono, di, and trichloramines are
    difficult to follow with large  samples.

    Red color fades on addition of KI crystals when testing for dichlor-
    amine.
)PD-Titrimetric Method

    It appears that this method is not applicable to chlorine analysis in
    this range because of the low volume of titrant required.

    This method is preferred above the methyl orange method.

    Timing of readings appears to be critical.  Permanganate standards
    are better than chlorine standards.  More reliable and easier to
    work with.

:.   The directions for the calculations could be more explicit.


imperometric Method

    In sample 3 the free chlorine endpoint was  difficult to detect.  With
    the first addition of phenyl arsenoxide, there is a definite movement
    of the microammeter pointer to the left (down).  We did not exper-
    ience this with the free chlorine titration of distilled water to the
    endpoint prior to each sample processing.


                 SUMMARY AND CONCLUSIONS

        Sample 1 showed an unexplained loss of approximately 50% of
ts total chlorine, making the absolute accuracy and precision data
neaningless.   Nevertheless,  the data is useful  for comparison of the
nethods.  Samples 2 and 3 were  stable and maintained their initial
ralues throughout the study.  As  explained previously,  the free chlorine
:ontent of sample 3 is an artifact, and actually  is zero. This data, also,
s useful only for comparison.

        As shown in Table 5, the best overall accuracy was obtained
vith the methyl orange procedure, as indicated by the low average mean
:rror. This apparently good performance unfortunately is nullified by
he poor precision (Table  6) as indicated by the consistently high standard
leviation. Methyl orange performed acceptably only for total chlorine
n sample 3.  Examination of the bar graphs,  figures 15, 16, 30, how-
;ver,  indicates in the case of the free  and total chlorine measurement
n sample 2 and the total chlorine measurement in sample 3, that the
arge  standard deviation is due mainly to three  divergent results at each
                                                                 51

-------
Table 5.  SUMMARY OF OVERALL ACCURACY
            (Average Mean Error)
Method
Methyl Orange
Sample 1
Free Total
-0.219 -0.
Leuco Crystal Violet -0. 250 -0.
SNORT
DPD- Titrimetric
DPD-Colorimetric
Ampe rometric
OTA
-0.241 -0.
-0.259 -0.
-0.263 -0.
-0.241 -0.
-0.282 -0.
171
209
198
198
213
189
253
Sample
Free
-0.
-0.
-0.
-0.
-0.
-0.
-0.
044
085
113
192
153
230
198
2
Total
-0.
-0.
-0.
-0.
-0.
-0.
-0.
006
070
107
059
097
119
102
Sample 3
Free Total
-0.006
-0.050
-0.048
-rO.038
-0.014
-0.012
+0. 114
+0. 029
-0.007
-0.032
-0.031
+0. 103
-0.108
-0.092
Overall
Average
0.079
0.112
0. 123
0. 130
0.140
0. 150
0.174
Omitting all data
on Sample 1 and
Free on Sample 3
0.026
0.054
0.084
0.094
0.117
0.152
0.130








-------
Table 6.  SUMMARY OF OVERALL PRECISION
        (Average Standard Deviation)
Method
Sample 1
Free Total
Leuco Crystal Violet 0. 085 0. 055
SNORT
Amperometric
DPD-Colorimetric
DPD- Titrimetric
Methyl Orange
OTA
0.093 0.092
0.106 0.072
0.102 0.100
0.110 0.103
0.143 0.162
0.090 0.098
Sample
Free
0.042
0.120
0.206
0. 171
0.298
0.315
0.335
2
Total
0.015
0. 142
0.137
0.152
0.205
0. 301
0.325
Sample 3
Free Total
0.000
0.004
0.040
0.057
0.019
0.055
0. 195
0.089
0. 110
0.171
0.210
0.121
0. 143
0.218
Overall
Average
0.048
0.094
0. 122
0.132
0. 143
0.187
0.210
Omitting all data
on Sample 1 and
Free on Sample 3
0.049
0. 124
0. 171
0.177
0.208
0.253
0.293








-------
end of the array.  The symmetry of their distribution prevents their
rejection by statistical tests, but it is evident that the other 17 results
are very accurate and precise.   The logical conclusion,  therefore,  is
that the method is capable of excellent accuracy and precision in spite
of difficulties encountered by a few analysts.

         The apparently excellent performance of leuco crystal violet
is somewhat inconclusive because  of the very small amount of data for
this method.  Beyond all doubt,  the SNORT procedure performed well
and produced acceptable results  for the three most meaningful determi-
nations; namely,  free  and total chlorine in sample 2, and total chlorine
in sample 3.  This data is summarized in the last column of Table 5.
According to the  overall average of the most meaningful data, the two
DPD procedures,  colorimetric and titrimetric were nearly equal in
overall performance.  Better accuracy was  obtained with the  DPD titra-
tion (Table 5),  while the DPD colorimetric showed better precision
(Table 6).  The DPD colorimetric  data shows better precision than the
DPD titrimetric results for  samples 1 and 2,  possibly indicating diffi-
culty mainly with measurement of  combined chlorine as  in sample  3.
The overall performance of the amperometric titration ranked below
the DPD methods, and an acceptable performance was obtained only for
the total chlorine measurement in  sample 2.

         The poorest results were  obtained with the orthotolidine-
arsenite (OTA) procedure.   The  data shows  the method to be the least
in precision and next to last  in accuracy and is unacceptable for all
determinations.  The average total error (Table 7) for OTA is one third
more than the next poorest method; methyl orange.

         In samples 1  and 2, containing only free chlorine,  the rather
similar differences between  means for free  and for total chlorine  suggests
that,  regardles-s  of method used, a common source of error may be am-
monia in the distilled water, on the glassware, or in the laboratory atmos-
phere.  The generally better precision for total than for free  chlorine
measurement,  likewise seems to indicate contamination of the samples
by the participants.
54

-------
Table 7. SUMMARY OF OVERALL (AVERAGE) TOTAL ERROR
Method
Sample 1
Free Total
Leuco Crystal Violet 95. 31 72. 59
SNORT
DPD-Titrimetric
Amperometric
DPD-Colorimetric
Methyl Orange
OTA
97.04 87.00
108.86 91.77
102. 95 75. 63
106.18 94.00
114.86 112.59
104. 95 101. 90
Sample
Free
17.24
35. 95
80. 51
65.46
50.57
68.83
88.57
2
Total
10.20
39. 97
47.89
40. 14
40.83
62.12
76.81
Sample
Free
100.00
112.40
153.40
182. 80
256.40
232.00
1007.80
3
Total
28.06
38. 15
41.33
68.21
79. 33
47.75
79. 93
Overall
Average
53. 90
68.42
87.29
89.20
104. 55
106. 36
243. 33
Omitting all data
on Sample 1 and
Free on Sample 3
18.52
38.02
56.64
57. 94
56. 90
59.56
81. 77








-------
                         BIBLIOGRAPHY

1.   Methyl Orange Method; Analytical Reference Service report "Water
    Chlorine (Residual) No.  1. " Public Health Service Publication No.
    1988, 1969.

2.   Leuco Crystal Violet Method; ibid.   Correction: Incorrectly refer-
    enced to 12th edition of Standard Methods for the Examination of
    Water and Wastewater.  APHA, AWWA, WPCF.  New York, 1965.
    Should have been referenced as follows:

         a. New Methods  for the Colorimetric Determination of Halogen
           Residuals.  Part I.  Iodine,  Iodide, and lodate.  Black,
           A. P. and G.  P. Whittle.  J. A. W. W. A.  59:471, April,
           1967.

         b. New Methods  for the Colorimetric Determination of Halogen
           Residuals.  Part II.  Free and Total Chlorine.  Black,
           A. P. and G.  P. Whittle.  J.A.W.W.A.  59:607, May, 1967.

3.   Orthotolidine-Arsenite (OTA) Method; Standard Methods for the
    Examination of Water and Wastewater, pp  101-102,  12th edition.
    APHA,  AWWA, WPCF.   New York,  1965.

4.   Stabilized Neutral Orthotolidine (SNORT) Method for Residual Chlo-
    rine and Iodine; Analytical  Reference Service report "Water Chlorine
    (Residual) No. 1. " Public  Health Service Publication No.  1988,
    Cincinnati,  Ohio,  1969.

5.   DPD-Colorimetric Method  for Free Chlorine, Monochloramine,
    Dichloramine, and Nitrogen Trichloride.  Appendix A.

6.   DPD-Titrimetric Method; Ferrous Method for Free Available Chlo-
    rine, Monochloramine, Dichloramine,  and Nitrogen Trichloride.
    Analytical Reference Service report "Water Chlorine (Residual)
    No.  1."  Public Health Service Publication No. 1988, Cincinnati,
    Ohio, 1969.

7.   Amperometric Titration Method; Standard Methods for, the Exami-
    nation of Water and Wastewater, pp. 103-108.  12th edition. APHA,
    AWWA, WPCF.  New York, 1965.

8.   Orthotolidine Method.  Ibid.  pp.  93-100.

9.   Same as method 5 except N, N-dimethyl-p-phenylenediamine was
    substituted for N, N-diethyl-p-phenylenediamine.
56

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APPENDICES
                             57

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                           APPENDIX A

     DPD COLORIMETRIC METHOD FOR FREE CHLORINE,
          MONOCHLORAMINE, DICHLORAMINE, AND
                   NITROGEN TRICHLORIDE

1.  GENERAL DISCUSSION

    1.1.  Principle:  This is a colorimetric version of the Palin DPD
method and is based upon the same principles.  Instead  of titrating with
standard ferrous ammonium sulfate (FAS) solution as in the Ferrous
Method the colors are evaluated by means of a colorimetric procedure.

2.  APPARATUS

    Colorimetric Equipment  One of the following is required

    2. 1.  Spectrophotometer, for use at a wavelength of 515 m/u and
providing a light path of 1 cm  or longer.

    2.2.  Filter Photometer,  equipped with a filter having maximum
transmission in the wavelength range of 490 to 530 m,u and providing a
light path of  1 cm or longer.

3.  REAGENTS

    3. 1.  Phosphate buffer solution: Dissolve 24 g anhydrous disodium
hydrogen phosphate, Na HPO.,  and 46 g anhydrous potassium dihydrogen
phosphate KH PO.,  in distilled  water.   Combine this solution with 100
ml distilled water in which 0. 8 g disodium ethylenediamine tetraacetate
dihydrate,  also called (ethylenedinitrilo) tetraacetic acid sodium salt,
has been dissolved.  Dilute to 1 liter with distilled water and ai3d'-2Drnig
mercuric chloride to prevent mold growth.  (The presence of the mer-
curic chloride  also prevents interference in the free chlorine test that
might  otherwise be caused by trace amounts of iodide in the reagents).

    3. 2.  N, N-Diethyl-p-phenylenediamine  (DPD)  indicator reagent:
Dissolve 1 g DPD Oxalate  (Eastman Chemical No.  7102) or 1. 5 g
p-amino-N:N-diethyl-aniline 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,  also called (ethylenedinitrilo) tetraacetic
acid sodium  salt. Make up to 1 liter, store in a brown  glass stoppered
bottle  and discard when discolored.
 58

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    3. 3.  Potassium iodide crystals.

4.   PROCEDURE

    4. 1.  Calibration of photometer or colorimeter:  Calibrate the
available instrument with chlorine (a) or potassium permanganate (b)
solutions.

    a.  Chlorine solutions:  Prepare chlorine standards in the range of
0. 05 to  4 mg/1 from chlorine water and chlorine demand-free distilled
water.  Develop the color by  first placing 5 ml phosphate buffer solution
and 5 ml DPD indicator reagent in a flask and then adding 100 ml chlorine
standard with thorough mixing as described in Sec. 4. 2 - 4. 3.  Fill the
photometer or colorimeter cell from the flask and read the color at 515
m/j.   Return the contents of the cell to the flask and titrate the solution
with standard ferrous ammonium sulfate (FAS) titrant as a check on the
chlorine concentration.

    b.  Potassium permanganate solutions:  Prepare a stock solution
containing 891 mg KMnO. per I, 000 ml.  Dilute 10. 00 ml stock solution
to 100 ml with distilled water in a volumetric flask.  When 1 ml of this
solution is made up to 100 ml with distilled water a chlorine equivalent
of 1. 00  mg/1 will be produced during the DPD reaction.   Prepare a
series of permanganate standards encompassing the chlorine equivalent
range of 0. 05 to 4 mg/1.  Develop the color by first placing 5 ml phos-
phate buffer and 5 ml DPD indicator reagent in a flask and then adding
100 ml  standard with thorough mixing as described in Sec. 4. 2  - 4. 3.
Fill the photometer or colorimeter cell from the flask and read the color
at 515 my.  Return the contents of the  cell to the flask and titrate the
solution with standard ferrous ammonium sulfate (FAS) titrant as a check
on any absorption of permanganate  by the distilled water.

    4. 2.  Volume of sample:  Use a sample volume appropriate to the
particular photometer or colorimeter available.  Since the following
procedure is based on the use of  10-ml volumes, adjust the quantities
of reagents proportionately for alternate sample volumes.

    Dilute the sample when the total available  chlorine exceeds 4 mg/1.

    4. 3.  Free chlorine:  Place 0. 5 ml each of buffer reagent and DPD
indicator reagent in a test tube or photometer cell.  Add 10-ml of sample
and mix.  Read the color immediately (reading A).

    4. 4.  Monochloramine:   Continue by adding one very small crystal
of potassium iodide and mix.  If the dichloramine concentration is ex-
pected to be high,  instead of  the small crystal,  preferably add  0. 1 ml
(two drops) of freshly prepared potassium iodide solution (0. 1 g/100 ml).
Read the color immediately (reading B).
                                                                  59

-------
NC10 Absent
free Cl
NH2C1
NHC12
--
NC10 Present
free Cl
NH2C1
NHC12 + iNCl
free Cl + yNCl
NC13
NHCln
    4. 5.  Dichloramine;  Continue by adding a few crystals of potassium
iodide (about 0. 1 g) and mix to dissolve.  Allow to stand for about 2 min
before reading the color (reading C).

    4. 6.  Nitrogen trichloride: Absence of color in step 4. 3 (free
chlorine) indicates the absence of nitrogen trichloride.  Otherwise pro-
ceed as follows:

    Place a very small crystal of potassium iodide in a clean test tube
or photometer cell.  Add 10-ml of sample and mix.  Then add 0. 5 ml
each of buffer and indicator reagents and mix.  Read the color immedi-
ately  (reading D).

5.  CALCULATION

        Reading

           A

         B   A

         C   B

           D

       2(D   A)

         C   D
    Should monochloramine be present with nitrogen trichloride, which
is unlikely,  include in reading D,  in which case NC1_ is obtained from
2(D - B).
                            Bibliography

1.   Palin, A. T.  The Determination of Free and Combined Chlorine
    in Water by the  Use of Diethyl-p-phenylene Diamine.   JAWWA.
    49:873.  1957.

2.   Palin, A. T.  Colorimetric Determination of Chlorine Dioxide in
    Water.  Water and Sewage Works  107:457.  1960.

3.   Palin, A. T.  The Determination of Free Residual Bromine in
    Water.  Water and Sewage Works  108:461.  1961.

4.   Nicolson, N. J.   An Evaluation of the Methods for Determining
    Residual Chlorine in Water.   Part 1.  Free Chlorine.  Analyst
    90:187.  1965.
60

-------
5.   Nicolson, N. J.  Determination of Chlorine in Water.  Parts 1 and
    2.  Water Research Assoc., Medmenham, England.  Tech.  Papers
    No. 29.  1963, 47.  1965.

6.   Palin, A. T.  Methods for the Determination,  in Water,  of Free
    and Combined Available  Chlorine, Chlorine Dioxide and Chlorite,
    Bromine, Iodine,  and Ozone using Diethyl-p-phenylenediamine
    (DPD).   J. Inst. Water Engrs.  21:537.   1967.

7.   Palin, A. T.  Determination of Nitrogen Trichloride in Water.
    JAWWA.  60:847.  1968.
                                                                 61

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                     APPENDIX B,




               TABULATION OF RESULTS





       Table B-l.  Sample 1. Free Chlorine
LAB. kIC*
1
1
1
1
1
9
3
4
4
4
1136
1136
1211
1211
1314
1314
1322
1322
1436
1924
1924
1924
2112
2112
RESULTS
0.26
0.25
0.24
0.23
0.24
0.21
0,22
0.21
0.00
0.17
0.10
0.18
0.08
0.12
0.15
0.12
0.20
0,20
0.01
0.20
0.18
0.20
0.19
0-.20
METHOD
i
2
3
4
6
3
7
1
6
8
6
3
6
7
3
4
3
7
5
4
3
7
1
4
LAH. NO.
2222
2222
2222
2411
2411
2411
2411
2513
2513
2611
2611
2626
2626
2926
2926
3111
3111
3122
3122
3126
3126
3221
3222
3222
RESULTS
0.10
0.09
0.07
0.28
0.27
0.27
0.29
0.10
0.22
0,12
0.12
0.10
0.25
0.20
0.33
0.35
0.20
0.13
0.15
0.30
0.30
0.25
0.25
0.07
METHOD
7
3
5
1
5
7
Z
6
5
3
7
3
5
1
4
5
3
7
3
4
1
5
4
2
62

-------
(Table B-l continued)
LAB. NC.
3226
3226
3416
3416
4314
4314
4322
4322
4511
4511
4522
4611
4611
4611
4611
4711
4711
4911
4911
4963
496?
5111
5111
5116
RESULTS
0.23
0.25
0.09
0.13
0.14
0.21
0.00
0.00
0.28
0.17
0.15
0.14
0.17
0.05
0.15
0.16
0.00
0.05
0.04
0.40
0.33
0.16
0.50
0.47
METHOD
2
4
2
4
1
4
6
5
6
5
7
1
3
3
1
2
5
4
1
7
3
3
1
1
LAB. NO.
5116
5136
5136
5524
5524
b823
5931
5963
5963
6112
6112
6311
6311
6314
6314
6314
6552
6552
6812
6812
6816
6816
7112
7112
RESULTS
0,25
0.15
0.17
0.26
0.26
0.45
0,00
0,00
0,00
0,20
0.19
0.02
0.01
0.13
0.14
0.10
0.15
0.08
0,23
0.15
0.02
0.15
0,00
0,00
METHOD
6
5
3
1
6
7
3
3
1
1
5
3
4
5
6
7
3
5
5
3
6
5
7
5
                                        63

-------
                        (Table B-l continued)
LAB. NO.
7123
7123
7222
7222
722*
7522
7522
7526
7526
7622
7622
7824
782*
7846
7846
7911
7911
7914
7914
7922
7922
8111
8111
«222

8222
RESULTS
0.20
0,31
0.17
0.19
0.25
0.05
0.05
0.04
0.27
0.15
0.10
0.15
0.20
0.23
0.24
0,09
0,15
0.18
0.27
0.20
0.20
n.27
0.28
0.28

0.30
METHOD
3
6
7
5
1
3
7
1
6
5
4
7
5
1
2
1
4
5
3
7
5
5
6
7

6
LAB. NO.
8222
8222
8222
8242
8242
8622
8622
8723
8723
8622
8822
8822
8922
8922
9613
9613
9613
9713
9713
9714
9714
9822
9822

9922

RESULTS
0.30
0.27
0.33
0.20
0.10
0.23
0.17
0.35
0,38
0.24
0.24
0.25
0.21
0.19
0.23
0,24
0.22
0,40
0.55
0.09
0.10
0.21
0.19

0.32

METHOD
5
1
4
3
5
7
3
7
5
5
6
7
7
4
7
5
4
3
1
3
1
6
3

4

64

-------
Table B-2.  Sample 2, Free Chlorine (0. 98 mg/1)
LAB. NO.
1
1
1
I
1
3
3
4
4
4
1136
1136
1211
1211
1314
1314
1322
1322
1436
1924
192*
192*
2112
2112
RESULTS
0.92
C.92
0.95
0.95
0.94
0.99
0.94
0.11
0.12
0.10
0.36
0.70
0.58
0.53
0.43
0.68
0.85
0.88
0.57
0.86
0.87
0.87
0.89
0.85
METHOD
i
2
3
4
6
3
7
1
6
8
6
3
6
7
3
4
3
7
5
4
3
7
1
4
LAB. NO.
2222
2222
Z222
2411
2411
2411
2411
2513
Z513
2611
2611
2626
2626
2926
2926
3111
3111
3122
3122
3126
3126
3221
3222
3222
RESULTS
0.70
0.70
0.96
0.92
0.91
0.85
0.88
0.82
0.90
0.60
0,60
0.50
0.78
0,98
0.96
1.70
1.20
0.73
0.66
1.05
1.01
0.80
0,35
0.70
METHOD
3
7
5
5
7
2
1
5
6
3
7
3
5
1
4
5
3
3
7
1
4
5
2
4
                                                       65

-------
                       (Table B-2 continued)
LAB. NC.
3226
3226
4314
4314
4322
4322
4511
4511
4522
46li
4611
4611
4611
4711
4711
4911
4911
496?
4963
5111
5111
5116
5116
5136
RESULTS
0.87
0.87
1.04
0.98
0.60
0.63
0.95
0.90
0.60
0.85
0.50
0.96
0.80
0.50
0.40
0.62
0.62
0.55
1. 00
0.86
1.05
1.50
0.95
0.85
METHOD
2
4
1
4
6
5
6
5
7
1
3
1
3
2
5
1
4
7
3
3
1
1
6
5
LA*. NO.
5136
5524
5524
5823
5931
5963
5963
6112
6112
6311
6311
6314
6314
6314
6552
6552
6715
6715
6715
6812
6812
6816
6616
7112
RESULTS
0.70
1.01
1.26
1.00
0.09
0.82
0.60
0.78
0.81
0.02
0.14
0.87
0.89
0.77
0.31
0.02
0.95
1.35
1.07
0.97
0.93
0.55
0.28
0.62
METHOD
3
6
1
7
3
1
3
5
1
4
3
6
5
7
3
5
1
3
5
5
3
5
6
5
66

-------
(Table B-2 continued)
LAB. NC.
7112
7123
7123
7222
7222
7224
7522
7522
7526
7526
7622
7622
7824
782*
7846
7846
7911
7911
7914
7914
7922
7922
8111
8111
8222
RESULTS
0.60
1.10
1.17
0.76
0.86
0.80
0.30
0.35
0.76
0.40
0.95
0.90
0.83
0.85
0.9^
0.99
0.97
O.H6
J.,11
0.88
0.25
2.«0
1.10
1.00
0.89
METHOD
7
3
6
5
7
1
7
3
6
1
5
4
7
5
2
1
1
4
3
5
7
5
6
5
7
LAB. NO.
8222
8222
8222
8222
8242
8242
8622
8622
8723
8723
8822
8822
8822
8922
8922
9613
9613
9613
9713
9713
9714
9714
9822
9822
9922
RESULTS
0.96
1.01
0.98
0.95
0.65
0.80
0.90
0.90
1.13
0.95
0.90
0.92
0.88
0.84
0.78
0.91
0.87
0.89
1.60
1.70
1.02
0.95
0.95
0.85
0.98
METHOD
5
4
6
1
5
3
3
7
5
7
7
5
6
7
4
7
4
5
3
1
1
3
6
3
4
                                         67

-------
         Table B-3.  Sample 3, Free Chlorine (0.005 mg/1)
LAB. NO.
1
1
1
1
1
3
3
4
4
ft
1136
1136
1211
1211
1314
131
-------
(Table B-3 continued)
LAB. NO.
3416
4314
4314
4322
4322
4511
4511
4522
4611
4611
4611
4611
4711
4711
4911
4911
4963
4963
5111
5111
5116
5116
5136
5136
RESULTS
0.210
0.030
0.010
0.000
0.000
0.000
0.000
0.100
o.ono
0.060
0.050
0.130
0.000
0.250
0.000
0.000
0.100
0,240
0.240
0.510
0.050
0.430
0.000
0.000
METHOD
4
1
4
6
5
6
5
7
1
1
3
3
5
2
1
4
7
3
3
1
6
1
3
5
LAB. NO.
5524
55Z4
5823
5931
S963
S963
6112
6112
6311
6311
6314
6314
6314
6552
6552
6812
6812
6816
6816
7112
7112
7123
7123
7222
RESULTS
0.150
0.000
0.680
0.090
0.100
0.100
0.000
0,000
0.030
0.010
0.000
0.000
0,000
0.000
0.560
0,020
0.080
0,040
0.050
0,000
0.000
0.310
0.360
0.000
METHOD
i
6
7
3
3
1
5
1
3
4
7
6
5
5
3
3
5
6
5
7
5
6
3
5
                                        69

-------
                       (Table B-3 continued)
LAB. NO.
7222
722*
7524
7522
7526
7526
7622
7622
782*
782*
78*6
7911
7911
791*
7911*
7922
7922
8111
8111
8222
8222
8222
8222
8222
RESULTS
0.000
0.250
o.oso
0,000
0.150
0.1*0
0.000
0.000
0.200
0.160
0.060
0.010
0.0*0
0.580
0.190
2.000
0.200
0.000
0.000
0.000
0.000
o.ooo
0.000
0.000
METHOD
7
1
7
3
1
6
5
*
5
7
1
*
1
3
5
5
7
5
6
1
5
6
7
*
LAB. NO.
82*2
82*2
9622
8622
8723
8723
H822
8822
8822
B922
8922
9613
9613
9613
9713
9713
971*
971*
9822
9822
9922



RESULTS
0.200
0.750
0.100
0.050
0.020
0.100
0.020
0,0*0
0.050
0,000
0,050
0.050
0.000
0,010
0.900
0,750
0,100
0.310
0.150
0.200
0.000



METHOD
3
5
7
3
7
5
6
5
7
*
7
7
*
5
1
3
1
3
3
6
*



70

-------
Table B-4.  Sample 1, Total Chlorine (0.44 mg/1)
LAB. NO.
I
1
1
1
1
3
3
4
it
4
1136
1136
1211
1211
1314
1314
1322
1322
1436
1924
1924
1924
2112
2112
RESULTS
0.34
O.Z5
0.32
0.26
0.29
0.30
O.Z4
0.29
0,00
0.20
0.30
0.37
0.18
0.18
0.15
0.07
0.27
0.25
0.01
0.18
0.18
0.20
0.20
0.19
METHOD
1
2
3
4
6
3
7
1
6
8
3
6
6
7
3
4
7
3
5
4
3
7
4
1
LAS. NO.
2222
2222
2222
2411
2411
2411
2411
2513
2513
2611
2611
2626
2626
2926
2926
3111
3111
3122
3122
3126
3126
3221
3222
3222
RESULTS
0.12
0.23
0.23
0.31
0.28
0.28
0.29
0.22
0.14
0.15
O.U
0.15
0.27
0.15
0.33
1.17
1.10
0.22
0.22
0.30
0.30
0.25
0.15
0.30
METHOD
3
5
7
1
5
7
2
5
6
7
3
3
5
1
4
5
3
7
3
4
1
5
2
4
                                                       71

-------
                       (Table B-4 continued)
L«B. NC.
3226
3226
3322
3322
3416
3416
4314
4314
4322
4322
4511
4511
4522
4611
46U
4611
46U
4711
4711
4911
4911
4963
496'J
5111
RESULTS
0.25
0.24
0.20
0.50
0.30
0.28
0.15
0.14
0.16
0.15
0.20
0.32
0.25
0.05
0.20
0. 15
0.20
0.16
o.oo
r>.04
0.04
0.40
0.33
0.^1
METHOD
4
2
3
9
4
2
4
1
5
6
5
6
7
3
1
1
3
2
5
4
1
7
3
1
LAB. NO.
5111
5116
5116
5136
5136
5524
5524
5823
5931
5963
5963
6112
6112
6311
6311
6314
6314
6314
6552
6552
6812
6812
6816
6816
RESULTS
0.17
0.10
0.49
0.15
0.17
0,49
0.26
0.45
0.00
0.00
0.00
0.24
0.26
0.02
0.32
0,18
0.16
0.17
0.17
0.49
0.16
0.25
0,32
0,35
METHOD
3
6
1
5
3
1
6
7
3
3
1
5
1
3
4
6
7
5
3
5
3
5
6
5
72

-------
(Table B-4 continued)
LAB. NO.
7112
7112
7123
7123
7222
7222
7224
7522
7522
7526
7526
7622
7622
7824
7824
7846
7846
7911
7911
7914
7914
792Z
7922
8111
Bill
RESULTS
0.23
0.14
0.32
0.22
0.19
0.19
0.55
0.15
",20
0.35
0.12
0.23
0.27
0.20
0.25
O.Z5
0.25
0.12
0.18
0.28
0.18
0.20
0.20
0.35
0.35
METHOD
7
5
6
3
7
5
1
3
7
6
1
5
4
5
7
1
2
1
4
3
5
7
5
6
5
LAB. NO.
8222
8222
8222
8222
8222
8242
8242
8622
8622
8723
8723
8822
8822
8822
8922
9613
9613
9613
9713
971.3
9714
9714
9822
9822
9922
RESULTS
0.33
0.30
0.30
0.27
0.28
0.20
0.20
0.17
0.23
0.35
0.38
0.24
0.24
0.25
0.26
0.26
0.28
0.30
0,40
0.55
0.17
0.20
0.25
0.25
0.36
METHOD
4
5
6
1
7
3
5
3
7
7
5
6
5
7
7
5
4
7
3
1
3
1
6
3
4
                                         73

-------
          Table B-5.  Sample 2, Total Chlorine  (0.98 mg/1)
LAB. NO.
1
1
1
1
X
3
3
4
it
4
1136
1136
1211
1211
1314
1314
1322
1322
1436
1924
192*
1924
2112
2112
RESULTS
0.98
0.92
1.02
0.92
0."8
1.07
0.98
0.17
0.17
1.00
0.88
0.90
0.69
0.69
0.52
0.59
1. .02
0.95
0.57
0.79
O.S7
0.87
O.S5
0.89
METHOD
1
2
3
4
6
3
7
1
6
6
6
3
6
7
3
4
7
3
5
4
3
7
4
1
LAB. NO.
2222
2222
2222
2411
2411
2411
2411
2513
2513
2611
2611
2626
2626
2926
2926
3111
3111
3122
3122
3126
3126
3221
3222
3222
RESULTS
0.80
l.Ofl
0.93
0.95
0,94
0.90
0.92
0.82
0.90
0.70
0.80
0.70
0.95
0.92
0.96
1.81
1.40
0.84
0.85
1.05
1.05
0.80
0.45
0.75
METHOD
3
5
7
7
5
2
1
5
6
3
7
3
5
1
4
5
3
3
7
1
4
5
2
4
74

-------
(Table B-5 continued)
LAB. NO.
3226
322ft
332Z
3322
4314
43l'«
4322
4322
4511
45U
452H
4611
46U
4611
4611
4711
4711
4911
4911
4963
4963
5111
5111
5116
9ESULTS
0.90
0.87
0.40
1.00
0.85
1..10
0.83
0.80
0.92
0.95
0.77
0.65
1.10
0.85
1.06
o.«o
0.64
n,60
0.63
1.02
0.55
1.13
0."5
1.50
METHOD
2
4
3
9
4
1
5
6
5
6
7
3
3
1
1
5
2
4
1
3
7
1
3
1
LAB. NO.
5116
5136
5136
5524
5524
5823
5931
5963
5963
6112
6112
6311
6311
6314
6314
6314
6552
6552
6715
6715
6715
6812
6812
6816
RESULTS
0.70
0.71
0.85
1.01
1.31
1.00
0,35
0.60
0.86
0.78
0.89
2.16
o.u
0.94
0.84
0.92
0.33
1.10
0.96
1.00
1.35
0.97
0.93
0.55
METHOD
6
3
5
6
1
7
3
3
1
5
1
4
3
5
7
6
3
5
1
5
3
5
3
5
                                         75

-------
                       (Table B-5 continued)
LAB. NO.
6816
7112
7H2
7123
7123
7222
7222
7224
7522
752Z
7526
7526
7622
7622
782*
7824
7846
7846
7911
7911
7914
7914
7922
7922
PESULTS
0.48
0.70
0.65
1.35
1.33
0.86
0.84
0.80
0.55
0.50
0,91
0.57
0.98
0,90
0.87
0.90
0.93
1.02
1.05
n.94
O.R8
1.12
0.25
2.00
METHOD
6
7
5
3
6
7
5
1
7
3
6
1
5
4
7
5
2
1
1
4
5
3
7
5
LAB. NO.
8111
8111
8222
8222
8222
8222
82Z2
8242
8242
8622
8622
8723
8723
R822
8822
8822
8922
9613
9613
9613
9713
9713
9714
9714
RESULTS
1.10
1.28
0.95
0.89
0.98
1.01
0,96
0.65
0.90
1.00
0.90
0.99
1.13
1.00
0.92
0.92
0.94
0.95
0.92
1.00
1.70
1.60
1.01
1.09
METHOD
5
6
1
7
6
4
5
5
3
3
7
7
5
7
5
6
7
4
5
7
1
3
3
1
76

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                    (Table B-5 continued)
LAB. NO.   RESULTS    METHOD
  9822        1.00        6



  9822        0.95        3



  9922        1.06        4
                                                          77

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         Table B-6.  Sample 3,  Total Chlorine (0. 66 mg/1)
LAB. NO.
1
1
1
1
1
3
3
4
4
4
U36
1136
1211
1211
1314
1314
1322
1322
1436
1924
1924
1924
2U2
2112
RESULTS
0.62
0.60
0.65
0.64
0.61
0.67
0.62
0.81
0.48
0.60
0.65
0.76
O.HI
0.61
0.37
0.06
0.63
0.60
0.13
0.43
0.-54
0.53
0.55
f.62
METHOD
1
2
3
4
6
3
7
1
6
3
3
6
6
7
3
4
7
3
5
4
7
3
4
1
LAB. NO.
2222
Z222
2222
2411
2411
2411
2411
2513
2513
2611
2611
2626
2626
2926
2926
3111
3111
3122
3122
3126
3126
3221
3222
3222
RESULTS
0,60
0.60
0.93
0.64
0.62
0.65
0,61
1.54
0,99
0.15
0.35
0.63
0.40
0.61
0,54
1.25
1.20
0.53
0,57
0.80
0.79
0.60
0.25
0,60
METHOD
3
7
5
2
5
1
7
6
5
7
3
5
3
4
1
5
3
3
7
1
4
5
2
4
78

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(Table B-6 continued)
LAB. NO.
3226
3226
3322
3322
3416
3416
4314
4314
4322
4322
4511
4511
4522
46U
4611
4611
4611
4711
4711
4911
4911
4963
4963
5111
RESULTS
0.68
0.71
0.80
2.00
0.85
0.82
0.58
0.56
0.70
0.70
0.67
0.68
0.53
0.69
0.67
0.65
0.33
0.58
1.20
O.bO
".49
0.59
0.12
0.54
METHOD
2
4
8
9
4
2
4
1
5
6
6
5
7
1
1
3
3
2
5
4
1
3
7
3
LAB. NO.
5111
5116
5116
5136
5136
5524
5524
5823
5931
5963
5963
6112
6112
6311
6311
6314
6314
6314
6552
6552
6812
6812
6816
ft816
RESULTS
0.96
0.71
0.40
0.40
0.60
0,40
0.66
0.68
0.34
0.65
0.25
0.60
0.61
1.55
0.10
0.66
0.66
0.59
1.30
0.73
0,67
0.74
0.82
0.62
METHOD
i
i
6
3
5
1
6
7
3
1
3
5
1
4
3
6
5
7
5
3
3
5
5
6
                                        79

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                      (Table B-6 continued)
LAB. NO.
7112
71U
7121
7123
7222
7222
7224
7524
7522
7526
7526
7622
7622
782*
7824
784«
7844
7911
7911
7914
7914
7922
7922
Sill
8111
RESULTS
0.60
0.70
0.50
0.41
0.82
0.61
0.90
0.47
0.60
1.08
0.71
0.66
0.57
0.64
1.80
0.60
0.66
0.73
0.57
0.82
0.69
O.ZO
2.00
0.77
0.77
METHOD
7
5
3
6
7
5
1
7
3
6
1
5
4
7
5
2
1
1
4
3
5
7
5
6
<5
LAB. NO.
8222
8222
8222
8222
8222
8242
8242
8622
8622
8723
8723
8822
8822
8822
8922
9613
9613
9613
9713
9713
9714
9714
9822
9822
9922
RESULTS
0.69
0.64
0.63
0.62
0.64
0.75
0.90
0,52
0.50
0.76
0.69
0.59
0.56
0.65
0.63
0.59
0.62
0.60
1.00
0.85
0.67
0.73
0.67
0.47
0.73
METHOD
4
1
5
6
7
5
3
7
3
5
7
6
5
7
7
7
5
4
1
3
3
1
6
3
4
80

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                           APPENDIX C

              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 Xj
                        (i   1,2,  .... n) denote the i  results in a
                        sample of n results.  The arithmetic mean
                                            	 n
                        denoted X is given by X= S  X^
Median
Accuracy
Measures of accuracy
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 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 =
                       X   T. V.
                         T. V.
                                                           X 100
Precision
The reproducibility of sample results or the
degree of agreement among the results.
                                                                81

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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        _ 9
                                  2   (Xi   xr
                             s2 = 1=1
                                       n - 1

                         where n is the number of results.

                         Sample standard deviation — Square root of
                         the sample variance.
                                         n - 1

                         Relative standard deviation (coefficient of
                         variation) —  Sample standard deviation
                         expressed as a percentage of the mean.

                             Rel.  Std.  Dev.  = -JU-  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"
                                                      ct IA
82

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                       where X and s are the sample mean and
                       standard deviation, t  .„ is the upper a 12
                       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-^ided tolerance
                       limits for  normal populations.  The value of
                       K depends upon the chosen values of y and P.

Total error             A criterion for judging acceptability of analytical
                       methods.  The total error is given by

                       Absolute value of mean error + 2(Std. Dev.) v lnri
                                                       	 A 1UU
                                         True Value

                       On the basis of this total error,  methods can
                       be  divided into three categories:  excellent (total
                       error 25% or less), acceptable (total error 50%
                       or  less),  and unacceptable (total error greater
                       than 50%).

                           REFERENCES

    Anon., Guide for the Measures of Precision and Accuracy.  Anal.
    Chem.  34_ 364R, 1962.

    Natrella, M. G.  Experimental Statistics.  National Bureau of
    Standards.  1963.  p.  T-10.

    McFarren, E, F. , R. J.  Lishka, and J. H.  Parker.  Criterion for
    Judging Acceptability  of Analytical Methods.  Anal. Chem.  42;.358,
    1970.
                                                                 83

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                            APPENDIX D

   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  X0   < where X is the sample mean, XQ is the suspected outlier (the
84

-------
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
                                                                   85

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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.
    2J2: 68-78, 1951.

3.  Personal communication. J. Santner, Mathematical Sciences,
    Office of the Director, Robert A. Taft Sanitary Engineering Center,
    1966.
86

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                           APPENDIX E

COMPARISON OP METHODS FOR STATISTICALLY SIGNIFICANT

          DIFFERENCES IN 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
 concentration with respect to precision and to accuracy.  The unknown
 variances, n-   and tr  (estimated by the sample variances,  s 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 jU2 (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: cr 1   ^ 2'  Ml  =  M2

                               2    2
                 Outcome 2: o-   = 
-------
Test3 is used first to test the hypothesis of equality of the unknown
             o
variances, n- ., of the methods in order to compare the precision of the
methods.  If we conclude that the precision is the same,  the Analysis of
Variance4 is then used to test whether a significant  difference exists
among the means,  p.,  in order to compare the accuracy of the methods.
If there is a  significant difference among the means.  Duncan's Multiple
Range  Test ^> 6 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 cr .  are equal, all/j. are equal
                             2
           Outcome 2:  all er .  are equal, not all ju.  are equal
                                 2
           Outcome 3:  not all cr . are equal,  all /J.  are equal
                                 2
           Outcome 4:  not all cr . are equal,  not all /J. are equal


    In outcome 1,  we  conclude that the sample results do not indicate
a significant difference in either the precision or the accuracy of the
methods.

    In outcome 2,  we  conclude that there is no indication of a significant
difference in the  precision of the methods; however, at least one method
does differ significantly from the rest with  respect to accuracy, and
Duncan's Multiple  Range Test indicates which methods differ.  For ex-
ample,  in comparing four methods, we might conclude n    p  and f*    ^
but u   and u   differ significantly from /J  and n  • or we might conclude
that u    n  = p.    but n  differs significantly from u , /u0, and ^..
     1    A    o       4                            1   £        o

    In outcome 3,  we  conclude that there is no indication of a significant
difference in the  accuracy of the methods,  but at least one method differs
significantly from the  rest with respect  to precision.

    In outcome 4,  we  conclude that the methods differ significantly with
respect to both precision and accuracy.

                           REFERENCES

1.   Ostle, B. Statistics  in Research.  Iowa State University Press.
    Ames, Iowa,  1963, p. 123.

-------
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 jj^: 307-310, 1956.

7.  Siegel, S. Nonparametric  Statistics.  McGraw-Hill.  New York,
   N.Y. ,  1956, pp. 184-94.
                                                                  89

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                           APPENDIX F

       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
90

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Massachusetts Department of Public Health, Amherst
Massachusetts Department of Public Health, Boston
Michigan Department of Conservation, Lansing
Michigan Department of Public Health, Lansing
Minnesota Department of Agriculture,  St. Paul
Minnesota Department of Health,  Minneapolis
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    Concord
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    Albany
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    Research, Albany
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    Harrisburg
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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
                                                                91

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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
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
92

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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
Metropolitan St. Louis Sewer District, Missouri
Metropolitan Sanitary District of Greater Chicago, Illinois
Metropolitan Utilities District, Omaha, Nebraska
Metropolitan Water District of Southern California,  La Verne
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, Washing-
    ton,  D. C.
DHEW, PHS,  Northeast Marine Health Sciences Laboratory, Narra-
    gansett,  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
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Tennessee Valley Authority, Chattanooga
Tennessee Valley Authority, Muscle Shoals, Alabama
U. S. Army Environmental Hygiene Agency, Edgewood Arsenal,  Maryland
USDA, Soils  Laboratory,  Beltsville, Maryland
USDI,  FWQA, AWTR Research Activities, Pomona, California
USDI,  FWQA, Alaska Water Laboratory, College
USDI,  FWQA, Analytical  Quality Control,  Cincinnati,  Ohio
USDI,  FWQA, Chemistry and Physics,  Cincinnati, Ohio
USDI,  FWQA, Chicago Program  Office, Illinois
USDI,  FWQA, North Atlantic Water Quality Management Office,
   Edison, New Jersey
USDI,  FWQA, Ohio River Basin Project, Evansville, Indiana
USDI,  FWQA, Ohio River Basin Project, Wheeling, West Virginia
USDI,  FWQA, Robert S.  Kerr Water Research Center, Ada,  Oklahoma
USDI,  FWQA, 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
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Institute 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
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
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American Public Health Association,  Riverside, California
American Water Works Association, New York, New York
Anaconda Company,  Grants,  New Mexico
ARMCO Steet Corporation, Middletown,  Ohio
Battelle Memorial Institute, Columbus, Ohio
Bethlehem Steel Corporation,  Bethlehem, Pennsylvania
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,  Elmhurst, New York
Havens-Emerson,  East Paterson,  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
INFILCO, General American Transportation Corporation,  Tucson,
     Arizona
lonac 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
Kern-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
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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
Shell Chemical Company, Princeton,  New Jersey
Tenco Hydroscience,  Incorporated, Chicago,  Illinois
Texas Gulf Sulphur Company,  Aurora,  North Carolina
Trapelo/West, Richmond,  California
U. S.  Industrial Chemicals Company,  Tuscola,  Illinois
United States Pipe and Foundry Company,  Birmingham,  Alabama
W.  R.  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
  U.S. GOVERNMENT PRINTING OFFICE; 1971- 759-277/2111                                    97

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