April 1978
600478019
Environmental Monitoring Series
COMPA
FOft
TOTAL AVAILABLE
IN VARIOUS
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL MONITORING series.
This series describes research conducted to develop new or improved methods
and instrumentation for the identification and quantification of environmental
pollutants at the lowest conceivably significant concentrations. It also includes
studies to determine the ambient concentrations of pollutants in the environment
and/or the variance of pollutants as a function of time or meteorological factors.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/4-78-019
April 1978
COMPARISON OF METHODS FOR THE DETERMINATION
OF TOTAL AVAILABLE RESIDUAL CHLORINE
IN VARIOUS SAMPLE MATRICES
by
Daniel F. Bender
Physical and Chemical Methods Branch
Environmental Monitoring and Support Laboratory
Cincinnati, Ohio 45268
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U. S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Environmental Monitoring and
Support Laboratory, U. S. Environmental Protection Agency, and approved for
publication. Mention of trade names or commercial products does not con-
stitute endorsement or recommendation for use.
11
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FOREWORD
Environmental measurements are required to determine the quality of am-
bient waters and the character of waste effluents. The Environmental Moni-
toring and Support Laboratory - Cincinnati conducts research to:
o Develop and evaluate techniques to measure the presence and concen-
tration of physical, chemical, and radiological pollutants in water,
wastewater, bottom sediments, and solid waste.
o Investigate methods for the concentration, recovery, and identifi-
cation of viruses, bacteria, and other microbiological organisms in
water; and to determine the responses of aquatic organisms to water
quality.
o Develop and operate an Agency-wide quality assurance program to
assure standardization and quality control of systems for monitoring
water and wastewater.
The amendments to the guidelines establishing test procedure for the
analysis of pollutants published in the Federal Register, December 1, 1976,
specify the methods that are approved for the analysis of total available re-
sidual chlorine. Among these methods are the iodometric titration, the am-
perometric titration, and the iodometric and amperometric back titrations.
The N,N-diethyl-p-phenylenediamine (DPD) colorimetric and titrimetric methods
have been given interim approval pending laboratory investigation. This re-
port is a laboratory investigation of these methods as well as several recent-
ly developed methods and some test kits which employ the DPD colorimetric pro-
cedure. The methods are applied, without modification, to various sample ma-
trices. Accuracy relative to the colorimetric titration method and precision
are determined.
Dwight G. Ballinger, Director
Enviornmental Monitoring § Support Laboratory
Cincinnati
111
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ABSTRACT
Ten different methods for determining total available residual chlorine,
all based on the iodine-iodide reaction, were tested without modification on
four sample matrices. Their precision was determined by seven replicate de-
terminations. Accuracy, as compared to the iodometric starch titration me-
thod, was determined in terms of percent yield. Observations regarding ad-
vantages, disadvantages, deviations from the expected and problems involved
in the determination are recorded. The data are presented in tables arranged
for instructive purposes and in a figure intended to present the data in re-
duced form for easier appraisal.
The information obtained can be used by the analyst in determining which
method is most suitable for a particular matrix. The data show the importance
of the nature of the sample matrix. The necessity of comparing several me-
thods in order to be certain of the accuracy is also obvious given the data.
This report covers a period from March 1976 to November 1976 and was com-
pleted as of November 12, 1976.
IV
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CONTENTS
Foreword iii
Abstract iv
Tables vi
I. Introduction 1
II. Summary and Conclusion 3
III. Experimental 4
Reagents and Equipment 4
Analytical Methods 4
Samples and Sample Preparation 5
IV. Results and Discussion g
Methods 8
Comparison 17
References
28
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TABLES
Number Page
1 Precision for the Determination of Total Available
Residual Chlorine in Various Sample Matrices by
the Iodo-I Method 8
2 Precision and Accuracy for the Determination of Total
Available Residual Chlorine in Various Sample
Matrices by the Iodo-II Method 9
3 Precision and Accuracy of the Determination of Total
Available Residual Chlorine in Various Sample
Matrices by the Amp-1 Method 10
4 Precision and Accuracy of the Determination of Total
Available Residual Chlorine in Various Sample
Matrices by the Amp-11 Method 12
5 Precision and Accuracy of the Determination of Total
Available Residual Chlorine in Various Sample
Matrices by the DPD-FAS Method 13
6 Precision and Accuracy of the Determination of Total
Available Residual Chlorine in Various Sample
Matrices by the DPD Colorimetric Method 14
7 Precision and Accuracy of the Determination of Total
Available Residual Chlorine in Various Sample
Matrices by the Flux Monitor 15
8 Precision and Accuracy of the Determination of Total
Available Residual Chlorine in Various Sample
Matrices by the Electrode 17
9 Precision and Accuracy of the Determination of Total
Available Residual Chlorine in Various Sample
Matrices by the CN-66 Kit 18
10 Precision and Accuracy of the Determination of Total
Available Residual Chlorine in Various Sample
Matrices by the Mini-20 Method 19
VI
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Number
11 Precision of Total Available Residual Chlorine
Determination of Calcium Hypochlorite in Distilled Water 21
12 Determination of Total Available Residual
Chlorine in Drinking Water 22
13 Determination of Total Available Residual
Chlorine in River Water 23
14 Determination of Total Available Residual Chlorine in
Sewage After Secondary Treatment 24
15 Determination of Total Available Residual Chlorine in
Raw Sewage Chlorinated in Laboratory .... 25
VII
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SECTION I
INTRODUCTION
Total available residual chlorine analysis is important in monitoring
the safety of drinking water to insure that the proper level needed to de-
stroy harmful organisms is maintained. It is also important in determining
the amount of residual chlorine needed to properly treat sewage and indus-
trial wastewater. The amount of residual chlorine present must be adequate
for disinfection, yet not be so much in excess as to cause detriment to the
body of water into which it is discharged.
There can be a large variation in the composition of sewage and indus-
trial wastewater insofar as interferences are concerned. The amount of tur-
bidity, organic matter, ionic material, solids, color, buffering capacity and
overall clarity can vary greatly. The choice of analytical method depends
upon the nature of the sample as well as on the analytical parameters of the
available methods themselves. The fact that the analysis must be performed
immediately on site due to the ephemeral nature of residual chlorine must
also be considered.
The procedures for the determination of total available residual chlorine
are actually measures of the total oxidizing power of the solution. There are
a number of components of the solution that are responsible for this oxidi-
zing property. When determining one particular oxidizing agent, the others
are regarded as interferences that must be eliminated or otherwise accounted
for. In a chlorination operation the predominant oxidizing power comes from
the chlorination process; other minor constituents contribute negligibly and
can be ignored. There are some modifications to the procedure to eliminate
interfering oxidizing agents where they are known to be present in concen-
trations that interfere significantly.
When chlorine or calcium hypochlorite is added to water it becomes hypo-
chlorite ion, referred to as free available chlorine. If ammonia is present,
as is usually the case, chloramines form. These chloramines are referred to
as combined available chlorine. The total available residual chlorine pro-
cedures studied here simultaneously determine free and combined available
chlorine.
All of the studied methods involve the same basic reaction: the oxida-
tion of iodide reagent to iodine in a solution buffered af pH 4. The main
difference between the methods is in how the iodine is determined. There are
also minor differences in the nature of the buffer and reagent concentrations.
The result is calculated as mg/1 chlorine using the molecular weights of the
species involved.
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The recommended method for the determination of total available residual
chlorine in sewage and industrial wastewater effluents is the iodometric back
titration using an amperometric endpoint. Variations such as the forward
titration or the use of a starch endpoint are allowed as the nature of the
sample permits. The N,N-diethyl-p-phenylenediamine (DPD) colorimetric or
titrimetric methods are permitted as interim methods pending laboratory
evaluation (1,2).
There are a large number of other available methods which have been com-
pared in the literature (3-6). Some of the comparisons involve the deter-
mination of free rather than total available residual chlorine; however, much
of the information concerns questions related to both determinations because
of the similarities between them. There are some variations in the applica-
tion of the amperemeter and the DPD method due to commercially designed in-
struments and kits. In addition there are new or newly improved electrochem-
ical methods not compared previously.
This study was initiated to provide information on which a decision can
be based as to which method is most appropriate for particular sample
matrices. Data were investigated concerning the precision, accuracy, range
and other factors as well as the general advantages, disadvantages and prob-
lems likely to be encountered in applying the methods to actual samples.
The study covers the approved methods, some commercial variations of the
approved methods and some new electrochemical methods and instrumentation.
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SECTION II
SUMMARY AND CONCLUSION
The following figure is a schematic representation showing the relative
accuracy of the methods. The figure is a convenient and instructive means of
comparing the various methods and an aid in selecting the proper method. For
drinking water only the CN-66 is far out of line. For river water the results
are spread over a wide range of relative accuracies with the titrimetric
methods grouped together. For the secondary treated sewage the methods can be
placed into a number of overlapping groups, making the drawing of conclusions
difficult.
Each of the methods has been shown to work well in certain matrices but
not in others. This emphasizes the importance of the nature of the sample
matrix. Turbidity, color, buffering capacity and ionic content are obvious
factors to consider in selecting a method. Comparison of each method with at
least one of the methods recommended in the Federal Register should be made
to insure that the results are compatible. This is expecially true for indus-
trial wastewaters.
The data in this report will provide information in determining which
methods are most likely to be successful for a particular sample matrix.
When other than an approved (2) method is desired, the desired mechanism of
obtaining alternate test procedure approval for compliance with legislation
must be used.
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SECTION III
EXPERIMENTAL
REAGENTS AND EQUIPMENT
The reagents and their preparation are described in the references per-
taining to the individual methods as mentioned further into this report.
Commercially prepackaged reagents were used where available.
Commercially available microburets in the zero to ten and zero to two
millimeter range were also used. The spectrophotometer was a single beam,
digital readout Perkin-Elmer Coleman 54B. The sample holder, cell and am-
perometer of a Wallace and Tiernan Amperometric Titrator were used. Due to
the age of the various rubber valves of the delivery system, the volume of
reagent delivered in each case was in error. It was decided that a micro-
buret would be more precise and was therefore used. The delivery system was
replaced by running a piece of tubing from the tip of the microburet to the
cell. The tubing was washed with distilled water after each day of use in
order to minimize damage due to contact time with the reagents. An Orion
Residual Chlorine Selective Ion Electrode and Model 801 Digital Readout Ex-
panded Scale pH Meter were used. A prototype model of the NBS Residual
Chlorine Flux Monitor was also evaluated. Because there are so many kit
forms of the DPD colormetric method available, only two were chosen as repre-
sentative of DPD kits: The Hach CN-66 kit and the Bausch and Lomb Mini-20
Portable Spectrophotometer with a kit of reagents.
ANALYTICAL METHODS
The following methods were compared using procedures as described in the
references. The nomenclature given below is used in the tables for concise-
ness.
Iodo-I: This appears in reference (7), page 316, as "Method 409A lodometric
Method I." It is the forward titration with 0.00564 N uhenylarsine oxide
(PAD). The PAO reagent was purchased from Wallace and Tiernan and checked by
titrating with primary standard potassium biiodate solution prepared in the
laboratory. The blank correction was found to be negligible with the dis-
tilled water and the reagents used.
Iodo-II: This appears in reference (7), page 318, as "Method 409B lodometric
Method II." It is the back titration with 0.0282 N_ iodine. The iodine
released by the reaction of the reagents with the sample is immediately con-
sumed by 0.00564 N^phenylarsine oxide. The excess PAO is then titrated with
0.0282 N^ iodine. (The normality of the iodine was actually slightly less, but
a correction factor was used in the calculations so that the number of milli-
-------
liters of iodine was corrected for the nomality.)
Amp-I: This appears in reference (7), page 322, as "Method 409C Amperometric
Titration Method" and in the manual (8), supplied with the Wallace and
Tiernan Instrument. The prepackaged reagent solutions that come with the
Wallace and Tiernan instrument were used, but the delivery system was not
(see above). The method is essentially the same as Iodo-I except that the
endpoint involves the deflection of the amperometer needle instead of the ob-
servation of the starch color change.
Amp-II: This appears in reference (7), page 318, as part of "Method 409B
lodometric Method II" and in the Wallace and Tiernan manual. It is essen-
tially the Iodo-II method with an amperometric endpoint instead of a starch
endpoint.
DPP-FAS: This appears in reference (7), page 329, as "Method 409E DPD
Ferrous Titrimetric Method." Only the total available residual chlorine de-
termination was performed, thus iodine was being titrated by standard ferrous
ammonium sulfate solution in all cases.
DPD Colorimetric: This appears in reference (7), page 322, as "Method 409F
DPD Colorimetric Method." The 12 X 75 cm mini curvettes were used in the
Perkin Elmer Coleman 54B Spectrophotometer. The procedure for total available
residual chlorine (by going straight to step 4e) was used. After the absor-
bancesof the standard solutions were determined, they were titrated with FAS.
This experimentally obtained number was then used to calculate the calibra-
tion curve.
Flux Monitor: The National Bureau of Standards has developed an instrument
that electrochemically measures iodine flowing through a cell (9,10). A
number of prototype models are being tested in various laboratories. One of
these prototypes was made available to EMSL - Cincinnati for testing. The in-
vestigation in this laboratory was concerned with performance and applicabi-
lity to various matrices. The electronic circuitry and mechanical flow opera-
tion was not studied; however, some information concerning these characteris-
tics was obtained as problems arose and is included in the discussion.
Electrode: Selective-ion electrodes are available for the measurement of
total available residual chlorine. The principle involves the oxidation of
iodide in the presence of pH 4 buffer. Instead of a titration or a Colori-
metric reading, the iodine is measured by an electrode. The Orion electrode
and system were arbitrarily selected for this study. The procedure used was
that provided in the Orion manual (11).
CN-66: A large number of kits are available that utilize the DPD Colorimetric
method. The Hach CN-66 kit was chosen as being representative. The direc-
tions and prepackaged reagents that accompany the kit were used (12).
Mini-20: The Bausch and Lomb total available residual chlorine kit, utilizing
a portable Spectrophotometer called the Mini-20, was arbitrarily selected as
another kit form of the DPD Colorimetric method. The direction and prepack-
aged reagents supplied with the kit were used (13).
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SAMPLES AND SAMPLE PREPARATION
Samples chosen for study included distilled water, tap water, river water,
a sewage plant effluent and raw sewage. All but the tap water required the
addition of chlorine in the form of calcium hypochlorite.
This was prepared as a saturated calcium hypochlorite solution and
stored in a dark bottle. This was added to each sample matrix when needed in
order to produce the desired concentration of hypochlorous ions. The exact
concentration was then determined by the Iodo-I method. This method served as
the standard of comparision throughout; all comparisions were made relative
to the Iodo-I result as the arbitrarily chosen true value.
The sample matrix water was placed in a 3-liter volumetric flask equipped
with a ground glass stopper. If necessary some saturated calcium hypochlorite
was added to adjust the level of chlorine. As a rule of thumb four drops
would produce 0.5-1.0 mg/1 concentration, however if a demand was present, ad-
justment became more difficult. Samples of river water and sewage were under
constant aeration to retard the production of anaerobic bacteria.
The chlorine was adjusted by determining the concentration by the Iodo-I
method. Seven replicates were immediately run by the method being compared.
Then another run was made by the Iodo-I method. The values of the two Iodo-I
determinations were often exactly the same or were extremely close so that
their average could be called the "true value."
Distilled Water: The distilled water was passed through a Millipore Super-Q
system and was found to be chlorine and chlorine-demand free.
Drinking Water: This was taken from the coldwater tap in the laboratory. No
spike was necessary.
River Water: Five gallons of sample was collected from the Ohio River,
brought to the laboratory and put under aeration. The seven replicates for
the ten procedures were run as rapidly as possible, requiring approximately a
week.
Chlorine had to be added to satisfy the demand and produce a useful con-
centration. There was no naturally occuring chlorine level.
Secondary Treated Sewage: A 5-gallon sample of secondary treated sewage was
taken at the Clermont County Sewage Treatment Works. The source of the
sewage was primarily of commmunity origin. There was a "natural" chlorine
level (i.e., added during treatment) that gradually dissipated over several
days, so that eventually some saturated calcium hypochlorite solution had to
be added to the volumetric flask. The sample was clear to very slightly
yellow.
Raw Sewage: Five gallons of sample were collected at the Cincinnati Sewage
Treatment Plant. The source was of mixed domestic and industrial origin and
had received no treatment. The sample was deep straw colored with high sol-iris
content. These varied from fine, non-settlement to large, settleable
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particles. The 5-gallon carboy was swirled before transfer to the 3-liter
flask to maintain the most difficult possible sample as a stringent test of
those methods that could be applied to this sample.
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SECTION IV
RESULTS AND DISCUSSION
Three replicates of calcium hypochlorite in distilled water were run in
order to eliminate from consideration any method that may be totally imprecise
as well as to obtain a feeling for what to expect in analyzing more complex
samples. The results are shown in Tables 1 through 10. Various levels were
determined except for the Flux monitor and the Mini-20 whose ranges are more
limited. As all methods were found to be precise, accuracy data in the dis-
tilled water matrix were not determined having little practical value. How-
ever, accuracy data were obtained for the two DPD kits using a distilled water
matrix because kits are often inaccurate, having sacrificed accuracy for sim-
plicity. The individual methods are discussed below.
METHODS
Iodo-I The Iodo-I method was found to be applicable to^all of the sample ma-
trices studied, although the end point was difficult to observe for the raw
sewage. The fact that most methods were within 10% of the value obtained by
the Iodo-I method made its choice as the arbitrary true value credible. Had
there been large differences in results, the Amp-II method would have been
used for this purpose. Results indicating the precision of the method are
shown in Table 1. As expected, the precision is better for simple matrices
and at higher concentrations. The difficulty in perceiving the end point is
largely responsible for any poorer precision obtained, especially in the case
of raw sewage samples. Another factor of interest, not pursued here, is the
delay in the formation of the blue color in the raw sewage samples. This
phenomenon! might be peculiar to this sample and was not investigated because
raw sewage samples are seldom analyzed for this constituent. They were used
here merely to test the method under extreme conditions.
Iodo-II The titration of excess PAO with iodine using a starch end point pro-
duced results (Table 2) that lead to the conclusion that the method is equiva-
lent to the Iodo-I procedure for these particular samples. The maximum
possible volume of titrant is 1 ml, otherwise the concentration of total
available residual chlorine is calculated to be a negative number. This leads
to less precision because of more potential experimental error.
Amp-I The titration of iodine with PAO using an amperometric end point is
reasonably precise and accurate for certain samples. The results (Table 3)
are low for sewage samples as described, especially for raw sewage where the
recovery is actually 44%. The suggestion (8) that Amp-II be used instead is
verified, although the fact that the Iodo-I method works and has the same
initial chemistry leads to the conclusion that perhaps some research with
varying reagent concentrations might produce a more useful method.
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TABLE 1. PRECISION FOR THE DETERMINATION OF TOTAL AVAILABLE RESIDUAL
CHLORINE IN VARIOUS SAMPLE MATRICES BY THE IODO-I METHOD
SAMPLE a
MATRIX
Distilled Water
Drinking Water
River Water
Domestic Sewage
Raw Sewage
AVERAGE
mg/1
0.25
4.02
0.68
0.30
1.11
0.48
STANDARD DEVIATION
+_ mg/1
0.001
0.03
0.04
0.03
0.06
0.09
RELATIVE
STANDARD
DEVIATION, %
0.23
0.76
5.2
9.7
5.9
18.0
a
Three replicates for distilled water. Seven replicates for other samples,
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TABLE 2. PRECISION AND ACCURACY FOR THE DETERMINATION OF TOTAL AVAILABLE
RESIDUAL CHLORINE IN VARIOUS SAMPLE MATRICES BY THE IODO-H METHOD
SAMPLE S
MATRIX
Distilled Water
Drinking Water
River Water
Domestic Sewage
Raw Sewage
AVERAGE
mg/1
0.41
3.51
0.84
0.84
0.87
0.55
STANDARD
DEVIATION
+_ mg/1
0.05
0.12
0.04
0.02
0.07
0.09
RELATIVE
STANDARD
DEVI ATI ON, %
12.2
3.3
4.3
2.7
7.6
16.0
b
TRUE
VALUE %RECOVERY
0.85 98.8
0.78 107.7
1.00 87.0
0.5° 100°
Three replicates for distilled water. Seven replicates for other samples.
Arbitrarily assigned to the Iodo-I value.
This sample at the time run was fading rapidly. This is reflected in the
high standard deviation as well as in the attempt to accurately determine
the true value at any given time.
10
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TABLE 3. PRECISION AND ACCURACY OF THE DETERMINATION OF TOTAL AVAILABLE
RESIDUAL CHLORINE IN VARIOUS SAMPLE MATRICES BY THE AMP-I METHOD
SAMPLE3
MATRIX
AVERAGE
mg/1
STANDARD
DEVIATION
1 mg/1
RELATIVE
STANDARD
DEVIATION, %
TRUEb
VALUE
%RECOVERY
Distilled Water
Drinking Water
River Water
Domestic Sewage
0.38
3.50
0.97
0.57
0.41
0.02
0.006
0.03
0.02
0.03
6.1
0.16
2.6
3.0
6.9
0.94
0.56
0.50
103.2
101.8
82.0
Raw Sewage
a Three replicates for distilled water. Seven replicates for other samples,
b Arbitrarily assigned to the Iodo-I value.
c Very poor recovery, see text.
11
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Amp-II The titration of excess PAO with iodine using an amperometric end-
point produces the results shown in Table 4. The method worked well in
drinking water and distilled water, however the accuracy was low for secon-
dary-treated sewage. The results for raw sewage could not be determined.
For raw sewage sample wherein 0.21 mg/1 was obtained by the Amp-II method,
the DPD-FAS Method gave 0.11 mg/1 and the Iodo-II Method, 1.01 mg/1. The
sample was too complex to allow comparison.
DPD-FAS Results of the titration of iodine produced from potassium iodide
with ferrous ammonium sulfate using DPD as the indicator agree with results of
the Iodo-I Method to a remarkable degree even in spiked raw sewage (Table 5).
The actual reading was consistently somewhat higher by 6 to 8%, within one
standard deviation. For the raw sewage the endpoint is difficult to observe
but not as difficult as that for starch. Of course, neither result is neces-
sarily correct for raw sewage, based on the results obtained in the Amp-II
experiments above. On another raw sewage sample the DPD-FAS gave a value of
0.80 mg/1 whereas the Amp-I gave a result approximately 50% lower (0.35 mg/1).
The color intensifies with the first addition of FAS, and increases with
each additional increment, followed by some fading. The mechanism of this
phenomenon is not understood, but could be useful in increasing the sensiti-
vity of the DPD-Colorimetric Method. The value obtained by this method was
consistently 6 to 8% higher than that obtained by the Iodo-I method. Al-
though the values are within one standard deviation of one another, and thus
considered the same member, the bias was always positive.
DPD Colorimetric The DPD colorimetric method also consistently produces a
slightly higher result than the Iodo-I Method (Table 6). In addition, the
presence of color and solids in the sample presents a problem; thus, the raw
sewage could not be run by this method.
The calibration curve does not follow Beer's Law; it is slightly curved.
Also, there is some fading that increases as the concentrations increase.
This may be the reason for the calibration curve being non-linear.
Flux Monitoring The Flux Monitor gave fairly precise and accurate results for
river water (Tabel 7). Solid material must be absent because of the narrow
passages of the cell and the flowmeter. Passage of the sample through a fil-
ter has been suggested as a correction for this; however, the filter also
gradually clogs and affects the flow. The flow is extremely sensitive to the
head pressure from both the sample intake and drain tubes. The height of
each in relation to the console of the instrument is critical in determining
whether the rheostatically controlled pump can achieve the flow rate necessary
for the digital readout to be directly in mg/1. As both the intake and drain
must be b'e'tow the instrument, it was placed 18 in. above the bench surface on
which the sample container and drain were placed.
The flowmeter reading often drifted, thus requiring close attention. Con-
trol of the line voltage (which causes variations in the pump speed) of a dif-
ferent flowmeter might improve the flow characteristics of the system. Flow-
meters that contain metal valves have proven susceptible to corrosion by
iodine (14).
12
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TABLE 4. PRECISION AND ACCURACY OF THE DETERMINATION OF TOTAL AVAILABLE
RESIDUAL CHLORINE IN VARIOUS SAMPLE MATRICES BY THE AMP II METHOD
SAMPLEa
MATRIX
AVERAGE
mg/1
STANDARD
DEVIATION
+_ mg/1
RELATIVE b
STANDARD TRUE
DEVAITION, % VALUE
%RECOVERY
Distilled Water
Drinking Water
River Water
Domestic Sewage
Raw Sewage
0.58
3.53
0.82
0.68
1.10
0.21
0.05
0.07
0.05
0.06
0.09
0.09
8.8
2.0
5.9 0.83
9.4 0.66
8.3 1.45
41.0
— — _ _
98.8
103.0
75.7
a Three replicates for distilled water. Seven replicates for other samples.
b Arbitrarily assigned to the Iodo-I value.
c This sample gave 0.11 by the DPD-FAS METHOD and 1.01 by the Iodo-II Method.
13
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TABLE 5. PRECISION AND ACCURACY OF THE DETERMINATION OF TOTAL AVAILABLE
RESIDUAL CHLORINE IN VARIOUS SAMPLE MATRICES BY THE DPD-FAS METHOD
SAMPLEa AVERAGE
MATRIX mg/1
STANDARD
DEVIATION
+_ mg/1
RELATIVE
STANDARD
DEVIATION^
TRUEb
VALUE
%RECOVERY
Distilled Water 0.34
0.65
3.45
Drinking Water 0.98
River Water 0.79
Domestic Sewage 1.08
Raw Sewage 0.79
0.02
0.003
0.02
0.01
0.01
0.02
0.03
5.6
0.5
0.5
1.2
1.4
1.8
3.3
0.91
0.73
1.20
0.75
107.7
108.2
90.0
105.3
a Three replicates for distilled water. Seven replicates for other samples.
b Arbitrarily assigned to the Iodo-I value.
14
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TABLE 6. PRECISION AND ACCURACY OF THE DETERMINATION OF TOTAL AVAILABLE
RESIDUAL CHLORINE IN VARIOUS SAMPLE MATRICES BY THE DPD COLORIMETRIC METHOD
SAMPLE
MATRIX
AVERAGE
mg/1
STANDARD
DEVIATION
+ mg/1
RELATIVE b
STANDARD TRUE
DEVIATION, % VALUE
%RECOVERY
Distilled Water
Drinking Water
River Water
Domestic Sewage
Raw Sewage c
0.39
3.61
0.94
0.86
1.07
0.012
0.11
0.008
0.02
0.03
3.1
3.2
0.8 0.86
1.9 0.70
2.4 1.01
109.3
122.9
106.0
— — — —
a Three replicates for distilled water. Seven replicates for other samples.
b Arbitrarily assigned to the Iodo-I value.
c Too much color and solids to be run.
15
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TABLE 7. PRECISION AND ACCURACY OF THE DETERMINATION OF TOTAL AVAILABLE
RESIDUAL CHLORINE IN VARIOUS SAMPLE MATRICES BY THE FLUX MONITOR
STANDARD RELATIVE
SAMPLEa AVERAGE DEVIATION STANDARD TRUE
MATRIX mg/1 + mg/1 DEVIATION^ VALUE %RECOVERY
Distilled Water 0.54 0.04 7.5
Drinking Water 0.84 0.02 1.9
River Water 0.39 0.07 17.1
Domestic Sewage 0.74 0.02 2.6
Raw Sewage
0.91 92.3
0.50 78.0
0.75 98.7
a Three replicates for distilled water. Seven replicates for other samples.
b Arbitrarily assigned to the Iodo-I value.
c Too high in solids to risk running. Previous researchers experienced
clogging in the cell.
16
-------
There is a great deal of noise within the digital readout, especially
when setting the high standard value at 0.433 mg/1. It has been suggested
(14) that this may be due to improper mixing as the stream flows from the
standard generating cell to the detector cell and that some adjustment could
be made to correct for this in future design generations of the instrument.
In the batch operation using distilled water, the response time—from
zero to the sample reading—was approximately 3 minutes, during which approxi-
mately 400 ml of sample were consumed. However, once continuous monitoring
has begun and the instrument is no longer starting at zero millivolts, the
response time may be faster.
During analysis of tapwater, bubbles formed and could be observed on the
flowmeter walls. They form on the flowmeter ball and effect the flow reading
as well as forming in the detector cell where they effect the millivolt
output reading. They must be mechanically removed by tapping. The bubble
formation has been attributed to supersaturation when the water was put under
pressure for delivery (14) .
Electrode The electrode was found to be accurate for drinking water and one
particular sample of secondary-treated sewage. However, river water and a
different sample of the same source of secondary sewage had low results. Raw
sewage tests produced a continuous upward drift (Table 8). The pH of the
secondary treated sewage was initially 8.7; after the reagents were added it
was 4.1, and therefore the capacity was not exceeded. The iodate standard
was titrated and was found to be correct.
CN-66 This kit produced unacceptably high results for drinking water, extrem-
ely low results for river water but only slightly high results in distilled
water and secondary treated domestic sewage. The precision was remarkable
considering the subjective nature of the colorimetric measurement (Table 9).
When the concentration of total available residual chlorine is above the
maximum concentration shown on the color wheel (e.g. approximately 5 mg/1) the
color is a slightly different shade. This could be useful as a warning
signal. If this slightly-off shade is matched it will give a false reading.
For example the slightly-off shade read 2.68 mg/1 on the color wheel when it
read 5.32 mg/1 by the DPD Colorimetric Method.
It has been reported (15) that the color wheel fades in the presence of
sunlight. This was not investigated in this work, but it is a possible diffi-
culty that must be considered if outdoor readings are involved and should be
checked occasionally even if it is only used in indoor lighting situations.
Mini-20 The comparison of results (Table 10) shows that the method produces
precise but inaccurate results. Results were very much higher for distilled
water and drinking water, somewhat lower for secondary treated domestic sewage
and very much lower for river water.
COMPARISON
In order to more conveniently compare the methods for a particular sample
17
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TABLE 8. PRECISION AND ACCURACY OF THE DETERMINATION OF TOTAL AVAILABLE
RESIDUAL CHLORINE IN VARIOUS SAMPLE MATRICES BY THE ELECTRODE
SAMPLEa
MATRIX
AVERAGE
mg/1
STANDARD
DEVIATION
+_ mg/1
RELATIVE
STANDARD
DEVIATION ,%
TRUE b
VALUE
%RECOVERY
Distilled Water
Drinking Water
River Water
Domestic Sewage
Raw Sewage
0.34
3.85
0.88
0.72
0.71
0.83
0.003
0.07
0.03
0.02
0.03
0.04
0.9
1.7
3.1
3.3
3.8
4.7
0.84
0.96
0.95
0.80
104.8
75.0
75.0
103.8
a Three replicates for distilled water. Seven replicates for other samples.
b Arbitrarily assigned to the Iodo-I value.
c Millivolt reading continuously increased. Sample gave 2.5 +_ 0.2 mg/1 by
electrode, 3.6 mg/1 by Amp II and 8.5 mg/1 by DPD-FAS at this time.
18
-------
TABLE 9. PRECISION AND ACCURACY OF THE DETERMINATION OF TOTAL AVAILABLE
RESIDUAL CHLORINE IN VARIOUS SAMPLE MATRICES BY THE CN-66 KIT
SAMPLEa
MATRIX
AVERAGE
mg/1
STANDARD
DEVIATION
+ mg/1
RELATIVE
STANDARD
DEVIATION, %
b
TRUE
VALUE
%RECOVERY
Distilled Water0
Drinking Water
River Water
Domestic Sewage
Raw Sewage
0.44
1.43
1.22
0.39
1.92
— _ - -
0.012
0.006
0.04
0.02
0.10
_
2.6
0.4
3.4
4.2
5.1
— — _
0.91
0.75
1.75
_ — — —
134.1
52.0
109.7
_
a Three replicates for distilled water. Seven replicates for other samples.
b Arbitrarily assigned to the Iodo-I value.
c When the same solutions were transferred to a spectrophotometer cell and
read, then compared to a standard curve prepared as in the DPD Colorimetric
Method the results were 0.42 +_ 0.02 mg/1 and 1.35 +_ 0.03 mg/1. If these
values are called the "true value" the recoveries from the kit method are
105% and 106% respectively.
d Turbidity and deep straw color prevented raw sewage from being analyzed.
19
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TABLE 10. PRECISION AND ACCURACY OF THE DETERMINATION OF TOTAL AVAILABLE
RESIDUAL CHLORINE IN VARIOUS SAMPLE MATRICES BY THE MINI-20 METHOD
STANDARD RELATIVE .
SAMPLEa AVERAGE DEVIATION STANDARD TRUE
MATRIX mg/1 +_ mg/1 DEVIATION, % VALUE %RECOVERY
Distilled Water 0.44 0.01 2.3
Drinking Water 0.45 0.02 3.9
River Water 0.16 0.01 6.0
Domestic Sewage 0.58 0.03 5.0
Raw Sewage
0.30 146.7
0.40 112.5
0.65 24.6
0.75 77.0
a Three replicates for distilled water Seven replicates for other samples.
b Arbitarily assigned to the Iodo-I value.
20
-------
matrix the data from the first ten tables have been rearranged into Tables
11 through 14. From these data the following conclusions have been estab-
lished.
Distilled Water All of the methods are accurate to less than 12.2%, the
deviation being greater at lower concentrations. This is single laboratory,
single operator precision based on only three determinations. The purpose
was to clearly identify inferior methods, of which there are none (Table 11).
Drinking Water Seven replicates were run. The precision was calculated and
the average compared with the results obtained by the Iodo-I Method as an
arbitrary measure of the accuracy. All of the results (Table 12) were within
10% except for the Mini-20 (12.5% high) and then the CN-66 (34.1% high).
River Water The titration methods, forward and back, were slightly high com-
pared with the Iodo-I Method, but were within 10%. The DPD Colorimetric
Method was very high (22.9%). The electrical methods were low and the kits
were very low (Table 13). For the kits, a study involving pH and the amounts
and concentrations of the reagents is indicated because the laboratory DPD
Colorimetric Method produced results with the error in the opposite directioa
Secondary Treated Sewage With this sample the methods produced several
groups of values (Table 14). The DPD-FAS, DPD Colorimetric Flux Monitor and
CN-66 were within 10% of the Iodo-I Method. The Iodo-II, Amp I, Amp II,
Electrode and Mini-20 were lower, but were grouped within slightly greater
than 10% error of one another. In view of the arbitrary nature of the choice
of Iodo-I as the standard of comparison, it is difficult to state that one
set is low or the other set high.
Raw Sewage Raw mixed domestic and industrial sewage was used as a matrix in
order to provide an extremely complex sample. It contained a high chlorine
demand that had to be satisfied before the level in the range of the methods
could be attained. Extremely erratic results were obtained when it was run
by different methods (Table 15). Fresh sample remained constant enough for
the analysis of seven replicates, but as the sample aged the chlorine value
began fading rapidly over the seven replicate determinations (Table 15, run
number 4).
The starch endpoint could be observed but with difficulty. The DPD-FAS
endpoint was slightly easier to observe. For the electrode the millivolt
reading continually drifted upward. Because of the color and/or solids, a
number of methods could not be run with this sample.
The amperometric endpoint produced no problem in observation. However,
the accuracy of the results for the Amp II, while difficult to assess,
appears to be poor.
21
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TABLE 11. PRECISION OF TOTAL AVAILABLE RESIDUAL CHLORINE
DETERMINATION OF CALCIUM HYPOCHLORITE IN DISTILLED WATER
METHOD
AVERAGE3
mg/1
STANDARD
DEVIATION
+ mg/1
RELATIVE
STANDARD
DEVIATION, '•
Iodo-I
Iodo-II
Amp- 1
Amp- I I
DPD-FAS
DPD Color
Flux Monitor
Electrode
CN-66
Mini-20
0.25
4.02
0.41
3.51
0.38
3.50
0.58
3.53
0.34
0.65
3.45
0.39
3.61
0.54
0.34
3.85
0.44
1.43
0.44
0.001
0.03
0.05
0.12
0.02
0.006
0.05
0.07
0.02
0.003
0.02
0.012
0.11
0.04
0.003
0.07
0.012
0.006
0.01
0.23
0.76
12.2
3.3
6.1
0.16
8.8
2.0
o.'s
3.1
3.2
7.5
0.9
1.7
2.6
0.4
2.3
a Three determinations.
22
-------
TABLE 12. DETERMINATION OF TOTAL AVAILABLE RESIDUAL
CHLORINE IN DRINKING WATER
METHOD
AVERAGE
mg/1
STANDARD
DEVIATION
+_ mg/1
RELATIVE
STANDARD
DEVIATION ,%
TRUE*1'
VALUE
%RECOVERY
Iodo-I
Iodo-II
Amp- 1
Amp- I I
DP D- FAS
DPD Color
Flux Monitor
Electrode
CN-66
Mini-20
0.68
0.84
0.97
0.82
0.98
0.94
0.84
0.88
1.22
0.45
0.04
0.04
0.03
0.05
0.01
0.008
0.02
0.03
0.04
0.02
5.2
4.3
2.6
5.9
1.2
0.8
1.9
3.1
3.4
3.9
0.85
0.94
0.83
0.91
0. 86
0.91
0.84
0.91
0.40
98.8
103.2
98.8
107.7
109.3
92.8
104.8
134.1
112.5
a Seven replicates
b Arbitrarily assigned to Iodo-I value
23
-------
TABLE 13. DETERMINATION OF TOTAL AVAILABLE RESIDUAL
CHLORINE IN RIVER WATER
METHOD
AVERAGE
mg/1
STANDARD
DEVIATION
+_ mg/1
RELATIVE
STANDARD
DEVIATION, %
TRUEb
VALUE
%RECOVERY
Iodo-I
Iodo-II
Amp- 1
Amp- I I
DPD-FAS
DPD Color
Flux Monitor
Electrode
CN-66
Mini-20
0.30
0.84
0.57
0.68
0.79
0.86
0.39
0.72
0.39
0.16
0.03
0.02
0.02
0.06
0.01
0.02
0.07
0.02
0.02
0.01
9,7
2.7
3.0
9.4
1.4
1.9
17.1
3.3
4.2
6.0
0.78
0.56
0.66
0.73
0.70
0.50
0.96
0.75
0.65
107.7
101.8
103.0
108.2
122.9
78.0
75.0
52.0
24.6
a Seven replicates
b Arbitrarily assigned to Iodo-I value.
24
-------
TABLE 14. DETERMINATION OF TOTAL AVAILABLE RESIDUAL
CHLORINE IN SEWAGE AFTER SECONDARY TREATMENT
METHOD
AVERAGEa
mg/1
STANDARD
DEVIATION
+_ mg/1
RELATIVE
STANDARD
DEVIATION, %
TRUEb
VALUE
%RECOVERY
Iodo-I
Iodo-II
Amp- 1
Amp- I I
DPD-FAS
DPD Color
Flux Monitor
Electrode
CN-66
Mini-20
1.11
0.87
0.41
1.10
1.08
1.07
0.74
0.71
0.83
1.92
0.58
0.06
0.07
0.03
0.09
0.02
0.03
0.02
0.03
0.04
0.10
0.03
5.9
7.6
6.9
8.3
1.8
2.4
2.6
3.8
4.7
5.1
5.0
1.00
0.50
1.45
1.20
1.01
0.75
0.95
0.80
1.75
0.75
87.0
82.0
75.9
90.0
106.0
98.7
75
103.8
109.7
77.0
a Seven replicates
b arbitrarily assigned to Iodo-I value.
25
-------
TABLE 15. DETERMINATION OF TOTAL AVAILABLE RESIDUAL
CHLORINE IN RAW SEWAGE CHLORINATED IN LABORATORY
RUN NUMBER
METHOD
mg/1
1.
2.
3.
4.
Amp- I I
DPD-FAS
Iodo-II
Iodo-I
DPD-FAS
Amp- 1
DPD-FAS
Iodo-II
DPD-FAS
0.21
0.11
1.01
0.75
0.79
0.35
0.80
0.55
0.76
0.40
+ 0.03
^0.09
initial-
final
5.
After 5 minutes
After 15 minutes
Amp-II
DPD-FAS
Electrode
A
2.25
2.73
B
2.17
2.73
3.55
8.45
continuous
drift, two
determinations
(A and B)
NOTE:
in run number 1- Iodo-II »DPD-FAS, in run number 4 lodo^! DPD-FAS and
in run number 1, DPD-FAS Amp-II.
26
-------
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REFERENCES
1. "Guidelines Establishing Test Procedure for Analyses of Pollutants,"
Federal Register, 38, No. 199, pp.28758-28760, October 16, 1973.
2. "Amendments. Guidelines Establishing Test Procedure for the Analysis
of Pollutants," Federal Register, 41, No. 232, pp. 52780-52786, December
1, 1976.
3. Nicolson, N. J., "An Evaluation of the Methods for Determining Residual
Chlorine in Water. Part I. Free Chlorine," Analyst, 90, No. 1069, pp.
187-198, April 1965.
4. Lishka, R. J., McFarren, E. F. and Parker, J. H., "Water Chlorine
(Residual) No. 1, Study Number 35," Analytical Reference Service, U.S.
Dept. HEW, 1969.
5. Lishka, R. J. and McFarren, E. F., "Water Chlorine (Residual) No. 2,
Report Number 40," Analytical Reference Service, U.S. Environmental
Protection Agency, 1971.
6. Guter K. J., Cooper, W. J., and Sorber, C. A., "Evaluation of Existing
Field Test Kits for Determining Free Chlorine Residuals in Aqueous
Solutions," J.A.W.W.A.. 66, pp. 38-43, January 1974.
7. "Standard Methods for the Examination for Water and Wastewater," 14th
ed., American Public Health Association, Washington D.C., 1975.
8. "Instruction Book, Amperemeter Titrator, No. WAA 50.261," Pennwalt Corp-
oration, Wallace and Tiernan Division, Belleville, New Jersey 07109.
9. "Instruction Manual for Chlorine Flux-Monitor," National Bureau of
Standards, Gaithersburg, Maryland 20706.
10. Marinenko, G., Huggett, R. J., and Friend, D. G., "An Instrument with
Internal Calibration for Monitoring Chlorine Residuals in Natural Waters,"
Journal of the Fisheries Research Board of Canada, 33, pp. 822-826, 1976.
11. "Proposed Test for Total Chlorine Residual in Water and Wastewater,"
Orion Research Inc., Cambridge, Massachusetts, 02139.
12. "Instuctions Hach Kit Model CN-66," Hach Chemical Company, Ames, Iowa
50010.
13. "Instructions Chlorine (Free and Total)," Bausch and Lomb, Analytical
Systems Division, Rochester, New York.
28
-------
14. Ruegg, F., Private Communication, U.S. Department of Commerce, National
Bureau of Standards, Gaithersburg, Maryland.
15. Hicks, G., Private Communications, Cincinnati Water Works, Cincinnati,
Ohio.
29
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/4-78-019
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Comparison of Methods for the Determination of Total
Available Residual Chlorine in Various Sample Matrice.
5. REPORT DATE
April 1978 issuing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Daniel F. Bender
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Environmental Monitoring and Support Laboratory
Office of Research and Development
U. S. Environmental Protection Agency
Cincinnati, OH 45268
10. PROGRAM ELEMENT NO.
1 BD 612
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Monitoring and Support Lab.-Cin., OH
Office of Research and Development
U. S. Environmental Protection Agency
Cincinnati, OH 45268
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA/600/06
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Ten different methods for determining total available residual chlorine, all
based on the iodine-iodide reaction, were tested without modification on four
sample matrices. Their precision was determined by seven replicate determinations.
Accuracy as compared to the iodometric starch titration method, was determined in
terms of percent yield. Observations regarding advantages, disadvantages, deviations
from the expected and problems involved in the determination are recorded. The data
are presented in tables arranged for instructive purposes and in a figure intended
to present the data in reduced form for easier appraisal.
The information obtained can be used by the analyst in determining which method
is most suitable for a particular matrix. The data show the importance of the na-
ture of the sample matrix. The necessity of comparing several methods in order to be
certain of the accuracy is also obvious given the data.
This report covers a period from March 1976 to November 1976 and was completed
as of November 12, 1976.,
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COS AT I Field/Group
Chlorine
Chemical Analysis
Water Analysis
Comparison
Evaluation
Residual Chlorine
Total Available Residual
Chlorine
99A
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (ThisReport)
unclassified
21. NO. OF PAGES
38
20. SECURITY CLASS (Thispage)
unrl aggi fi Art
22. PRICE
EPA Form 2220-1 (9-73)
30
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