4500-Cl⫺ CHLORIDE*

4500-Cl⫺ A. Introduction

1. Occurrence largely a matter of personal preference. The argentometric

method (4500-Cl⫺.B) is suitable for use in relatively clear waters
Chloride, in the form of chloride (Cl⫺) ion, is one of the major when 0.15 to 10 mg Cl⫺ are present in the portion titrated. The
inorganic anions in water and wastewater. The salty taste pro- endpoint of the mercuric nitrate method (4500-Cl⫺.C) is easier to
duced by chloride concentrations is variable and dependent on detect. The potentiometric method (4500-Cl⫺.D) is suitable for
the chemical composition of water. Some waters containing colored or turbid samples in which color-indicated endpoints might
250 mg Cl⫺/L may have a detectable salty taste if the cation is be difficult to observe. The potentiometric method can be used
sodium. On the other hand, the typical salty taste may be absent without a pretreatment step for samples containing ferric ions (if not
in waters containing as much as 1000 mg/L when the predom- present in an amount greater than the chloride concentration), chro-
inant cations are calcium and magnesium. mic, phosphate, and ferrous and other heavy-metal ions. The ferri-
The chloride concentration is higher in wastewater than in raw cyanide method (4500-Cl⫺.E) is an automated technique. Flow
water because sodium chloride (NaCl) is a common article of injection analysis (4500-Cl⫺.G), an automated colorimetric tech-
diet and passes unchanged through the digestive system. Along nique, is useful for analyzing large numbers of samples. Preferably
the sea coast, chloride may be present in high concentrations determine chloride by ion chromatography (Section 4110). Chloride
because of leakage of salt water into the sewerage system. It also also can be determined by the capillary ion electrophoresis method
may be increased by industrial processes. (Section 4140). Methods 4500-Cl⫺.C and G in which mercury, a
A high chloride content may harm metallic pipes and struc- highly toxic reagent, is used require special disposal practices to
tures, as well as growing plants. avoid improper sewage discharges. Follow appropriate regulatory
procedures (see Section 1090).
2. Selection of Method
Six methods are presented for the determination of chloride.
3. Sampling and Storage
Because the first two are similar in most respects, selection is
Collect representative samples in clean, chemically resistant
glass or plastic bottles. The maximum sample portion required is
* Approved by Standard Methods Committee, 1997. Editorial revisions, 2011.
Joint Task Group: 20th Edition (4500-Cl⫺.G)—Scott Stieg (chair), Bradford R. 100 mL. No special preservative is necessary if the sample is to
Fisher, Owen B. Mathre, Theresa M. Wright. be stored.

4500-Cl⫺ B. Argentometric Method

1. General Discussion 3. Reagents

a. Principle: In a neutral or slightly alkaline solution, potas- a. Potassium chromate indicator solution: Dissolve 50 g
sium chromate can indicate the endpoint of the silver nitrate K2CrO4 in a little distilled water. Add AgNO3 solution until a
titration of chloride. Silver chloride is precipitated quantitatively definite red precipitate is formed. Let stand 12 h, filter, and dilute
before red silver chromate is formed. to 1 L with distilled water.
b. Interference: Substances in amounts normally found in b. Standard silver nitrate titrant, 0.0141M (0.0141N): Dis-
potable waters will not interfere. Bromide, iodide, and cyanide solve 2.395 g AgNO3 in distilled water and dilute to 1000 mL.
register as equivalent chloride concentrations. Sulfide, thiosul- Standardize against NaCl by the procedure described in
fate, and sulfite ions interfere but can be removed by treatment 4500-Cl⫺.B.4b; 1.00 mL ⫽ 500 ␮g Cl⫺. Store in a brown bottle.
with hydrogen peroxide. Orthophosphate in excess of 25 mg/L c. Standard sodium chloride, 0.0141M (0.0141N): Dissolve
interferes by precipitating as silver phosphate. Iron in excess of 824.0 mg NaCl (dried at 140°C) in distilled water and dilute to
10 mg/L interferes by masking the endpoint. 1000 mL; 1.00 mL ⫽ 500 ␮g Cl⫺.
d. Special reagents for removal of interference:
1) Aluminum hydroxide suspension—Dissolve 125 g alumi-
2. Apparatus num potassium sulfate or aluminum ammonium sulfate,
AlK(SO4)2 䡠 12H2O or AlNH4(SO4)2 䡠 12H2O, in 1 L distilled
a. Erlenmeyer flask, 250-mL. water. Warm to 60°C and add 55 mL conc ammonium hydroxide
b. Buret, 50-mL. (NH4OH) slowly with stirring. Let stand about 1 h, transfer to a

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 CHLORIDE (4500-Cl⫺)/Mercuric Nitrate Method

large bottle, and wash precipitate by successive additions, with where:

thorough mixing and decanting with distilled water, until free A ⫽ mL titration for sample,
from chloride. When freshly prepared, the suspension occupies a B ⫽ mL titration for blank, and
volume of approximately 1 L. N ⫽ normality of AgNO3.
2) Phenolphthalein indicator solution.
3) Sodium hydroxide (NaOH), 1N.
4) Sulfuric acid (H2SO4), 1N. mg NaCl/L ⫽ (mg Cl⫺/L) ⫻ 1.65
5) Hydrogen peroxide (H2O2), 30%.

4. Procedure 6. Precision and Bias

a. Sample preparation: Use a 100-mL sample or a suitable

A synthetic sample containing 241 mg Cl⫺/L, 108 mg Ca/L,
portion diluted to 100 mL. If the sample is highly colored, add
82 mg Mg/L; 3.1 mg K/L, 19.9 mg Na/L, 1.1 mg NO3⫺-N/L,
3 mL Al(OH)3 suspension, mix, let settle, and filter.
0.25 mg NO2⫺- N/L, 259 mg SO42⫺/L, and 42.5 mg total
If sulfide, sulfite, or thiosulfate is present, add 1 mL H2O2 and
alkalinity/L (contributed by NaHCO3) in distilled water was
stir for 1 min.
analyzed in 41 laboratories by the argentometric method, with
b. Titration: Directly titrate samples in the pH range 7 to 10.
a relative standard deviation of 4.2% and a relative error of
Adjust sample pH to 7 to 10 with H2SO4 or NaOH if it is not in this
1.7%.
range. For adjustment, preferably use a pH meter with a non-
chloride-type reference electrode. (If only a chloride-type electrode
is available, determine amount of acid or alkali needed for adjust-
7. Bibliography
ment and discard this sample portion. Treat a separate portion with
required acid or alkali and continue analysis.) Add 1.0 mL K2CrO4
indicator solution. Titrate with standard AgNO3 titrant to a pinkish HAZEN, A. 1889. On the determination of chlorine in water. Amer. Chem.
yellow endpoint. Be consistent in endpoint recognition. J. 11:409.
KOLTHOFF, I.M. & V.A. STENGER. 1947. Volumetric Analysis, 2nd ed.
Standardize AgNO3 titrant and establish reagent blank value by
Vol. 2; pp. 242–245, 256 –258. Interscience Publishers, New York,
the titration method outlined above. A blank of 0.2 to 0.3 mL is usual. N.Y.
PAUSTIAN, P. 1987. A novel method to calculate the Mohr chloride
5. Calculation titration. In Advances in Water Analysis and Treatment, Proc. 14th
Annu. AWWA Water Quality Technology Conf., November 16 –
20, 1986, Portland, Ore., p. 673. American Water Works Assoc.,
(A ⫺ B) ⫻ N ⫻ 35 450
mg Cl⫺/L ⫽ Denver, Colo.
mL sample

4500-Cl⫺ C. Mercuric Nitrate Method

1. General Discussion 2. Apparatus

a. Principle: Chloride can be titrated with mercuric nitrate, a. Erlenmeyer flask, 250-mL.
Hg(NO3)2, because of the formation of soluble, slightly dis- b. Microburet, 5-mL with 0.01-mL graduation intervals.
sociated mercuric chloride. In the pH range 2.3 to 2.8, diphe-
nylcarbazone indicates the titration endpoint by formation of
3. Reagents
a purple complex with the excess mercuric ions. Xylene
cyanol FF serves as a pH indicator and endpoint enhancer.
Increasing the strength of the titrant and modifying the indi- a. Standard sodium chloride, 0.0141M (0.0141N): See
cator mixtures extend the range of measurable chloride con- 4500-Cl⫺.B.3c.
centrations. b. Nitric acid (HNO3), 0.1N.
c. Sodium hydroxide (NaOH), 0.1N.
b. Interference: Bromide and iodide are titrated with
d. Reagents for chloride concentrations below 100 mg/L:
Hg(NO3)2 in the same manner as chloride. Chromate, ferric, and
1) Indicator-acidifier reagent—The HNO3 concentration of
sulfite ions interfere when present in excess of 10 mg/L. this reagent is an important factor in the success of the
c. Quality control (QC): The QC practices considered to be determination and can be varied as indicated in ¶ a) or b)
an integral part of each method are summarized in Table below to suit the alkalinity range of the sample. Reagent a)
4020:I. contains sufficient HNO3 to neutralize a total alkalinity of

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 CHLORIDE (4500-Cl⫺)/Potentiometric Method

150 mg as CaCO3/L to the proper pH in a 100-mL sample. cates pH less than 2.0; a pure blue indicates pH more than 3.8.)
Adjust amount of HNO3 to accommodate samples of alkalin- For most potable waters, the pH after this addition will be 2.5 ⫾
ity different from 150 mg/L. 0.1. For highly alkaline or acid waters, adjust pH to about 8
a) Dissolve, in the order named, 250 mg s-diphenylcarbazone, before adding indicator-acidifier reagent.
4.0 mL conc HNO3, and 30 mg xylene cyanol FF in 100 mL 95% Titrate with 0.0141N Hg(NO3)2 titrant to a definite purple
ethyl alcohol or isopropyl alcohol. Store in a dark bottle in a endpoint. The solution turns from green-blue to blue a few drops
refrigerator. This reagent is not stable indefinitely. Deterioration before the endpoint.
causes a slow endpoint and high results. Determine blank by titrating 100 mL distilled water containing
b) Because pH control is critical, adjust pH of highly alkaline 10 mg NaHCO3.
or acid samples to 2.5 ⫾ 0.1 with 0.1N HNO3 or NaOH, not with b. Titration of chloride concentrations greater than 100 mg/L:
sodium carbonate (Na2CO3). Use a pH meter with a nonchloride Use a sample portion (5 to 50 mL) requiring less than 5 mL
type of reference electrode for pH adjustment. If only the usual titrant to reach the endpoint. Measure into a 150-mL beaker. Add
chloride-type reference electrode is available for pH adjustment, approximately 0.5 mL mixed indicator reagent and mix well.
determine amount of acid or alkali required to obtain a pH of The color should be purple. Add 0.1N HNO3 dropwise until the
2.5 ⫾ 0.1 and discard this sample portion. Treat a separate color just turns yellow. Titrate with strong Hg(NO3)2 titrant to
sample portion with the determined amount of acid or alkali and first permanent dark purple. Titrate a distilled water blank using
continue analysis. Under these circumstances, omit HNO3 from the same procedure.
indicator reagent.
2) Standard mercuric nitrate titrant, 0.007 05M (0.0141N)— 5. Calculation
Dissolve 2.3 g Hg(NO3)2 or 2.5 g Hg(NO3)2 䡠 H2O in 100 mL
distilled water containing 0.25 mL conc HNO3. Dilute to just (A ⫺ B) ⫻ N ⫻ 35 450
under 1 L. Make a preliminary standardization by following the mg Cl⫺/L ⫽
mL sample
procedure described in 4500-Cl⫺.C.4a. Use replicates containing
5.00 mL standard NaCl solution and 10 mg sodium bicarbonate where:
(NaHCO3) diluted to 100 mL with distilled water. Adjust titrant
to 0.0141N and make a final standardization; 1.00 mL ⫽ 500 ␮g A ⫽ mL titration for sample,
Cl⫺. Store away from light in a dark bottle. B ⫽ mL titration for blank, and
e. Reagent for chloride concentrations greater than 100 N ⫽ normality of Hg(NO3)2.
mg/L—
1) Mixed indicator reagent—Dissolve 0.50 g diphenylcarba-
mg NaCl/L ⫽ (mg Cl⫺/L) ⫻ 1.65
zone powder and 0.05 g bromphenol blue powder in 75 mL 95%
ethyl or isopropyl alcohol and dilute to 100 mL with the same 6. Precision and Bias
alcohol.
2) Strong standard mercuric nitrate titrant, 0.0705M (0.141N)—
A synthetic sample containing 241 mg Cl⫺/L, 108 mg Ca/L,
Dissolve 25 g Hg(NO3)2 䡠 H2O in 900 mL distilled water
82 mg Mg/L, 3.1 mg K/L, 19.9 mg Na/L, 1.1 mg NO3⫺-N/L,
containing 5.0 mL conc HNO3. Dilute to just under 1 L
0.25 mg NO2⫺-N/L, 259 mg SO42⫺/L, and 42.5 mg total alka-
and standardize by following the procedure described in
linity/L (contributed by NaHCO3) in distilled water was ana-
4500-Cl⫺.C.4b. Use replicates containing 25.00 mL standard
lyzed in 10 laboratories by the mercurimetric method, with a
NaCl solution and 25 mL distilled water. Adjust titrant to 0.141N
relative standard deviation of 3.3% and a relative error of 2.9%.
and make a final standardization; 1.00 mL ⫽ 5.00 mg Cl⫺.
7. Bibliography
4. Procedure
KOLTHOFF, I.M. & V.A. STENGER. 1947. Volumetric Analysis, 2nd ed.
a. Titration of chloride concentrations less than 100 mg/L: Vol. 2, pp. 334 –335. Interscience Publishers, New York, N.Y.
Use a 100-mL sample or smaller portion so that the chloride DOMASK, W.C. & K.A. KOBE. 1952. Mercurimetric determination of
content is less than 10 mg. chlorides and water-soluble chlorohydrins. Anal. Chem. 24:989.
Add 1.0 mL indicator-acidifier reagent. (The color of the GOLDMAN, E. 1959. New indicator for the mercurimetric chloride deter-
solution should be green-blue at this point. A light green indi- mination in potable water. Anal. Chem. 31:1127.

4500-Cl⫺ D. Potentiometric Method

1. General Discussion two electrodes. The endpoint of the titration is that instrument
reading at which the greatest change in voltage has occurred
a. Principle: Chloride is determined by potentiometric titra- for a small and constant increment of silver nitrate added.
tion with silver nitrate solution with a glass and silver-silver b. Interference: Iodide and bromide also are titrated as chloride.
chloride electrode system. During titration an electronic volt- Ferricyanide causes high results and must be removed. Chromate
meter is used to detect the change in potential between the and dichromate interfere and should be reduced to the chromic state

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 CHLORIDE (4500-Cl⫺)/Potentiometric Method

or removed. Ferric iron interferes if present in an amount substan-

tially higher than the amount of chloride. Chromic ion, ferrous ion,
and phosphate do not interfere.
Grossly contaminated samples usually require pretreatment.
Where contamination is minor, some contaminants can be de-
stroyed simply by adding nitric acid.
c. Quality control (QC): The QC practices considered to be an
integral part of each method are summarized in Table 4020:I.

2. Apparatus

a. Glass and silver-silver chloride electrodes: Prepare in the

laboratory or purchase a silver electrode coated with AgCl for
use with specified instruments. Instructions on use and care of
electrodes are supplied by the manufacturer.
b. Electronic voltmeter, to measure potential difference be-
tween electrodes: A pH meter may be converted to this use by
substituting the appropriate electrode.
c. Mechanical stirrer, with plastic-coated or glass impeller.
Figure 4500-Clⴚ:1. Example of differential titration curve (endpoint is
3. Reagents 25.5 mL).

a. Standard sodium chloride solution, 0.0141M (0.0141N):

See 4500-Cl⫺.B.3c.
b. Nitric acid (HNO3), conc. 1) Pipet 100.0 mL sample, or a portion containing not more
c. Standard silver nitrate titrant, 0.0141M (0.0141N): See than 10 mg Cl⫺, into a 250-mL beaker. In the absence of
4500-Cl⫺.B.3b. interfering substances, proceed with ¶ b3) below.
d. Pretreatment reagents: 2) In the presence of organic compounds, sulfite, or other
1) Sulfuric acid (H2SO4), 1 ⫹ 1. interferences (such as large amounts of ferric iron, cyanide, or
2) Hydrogen peroxide (H2O2), 30%. sulfide) acidify sample with H2SO4, using litmus paper. Boil for
3) Sodium hydroxide (NaOH), 1N. 5 min to remove volatile compounds. Add more H2SO4, if
necessary, to keep solution acidic. Add 3 mL H2O2 and boil for
15 min, adding chloride-free distilled water to keep the volume
4. Procedure above 50 mL. Dilute to 100 mL, add NaOH solution dropwise
until alkaline to litmus, then 10 drops in excess. Boil for 5 min,
a. Standardization: The various instruments that can be used filter into a 250-mL beaker, and wash precipitate and paper
in this determination differ in operating details; follow the man- several times with hot distilled water.
ufacturer’s instructions. Make necessary mechanical adjust- 3) Add conc HNO3 dropwise until acidic to litmus paper, then
ments. Then, after allowing sufficient time for warmup (10 min), 2.0 mL in excess. Cool and dilute to 100 mL if necessary.
balance internal electrical components to give an instrument Immerse stirrer and electrodes and start stirrer. Make any nec-
setting of 0 mV or, if a pH meter is used, a pH reading of 7.0. essary adjustments according to the manufacturer’s instructions
1) Place 10.0 mL standard NaCl solution in a 250-mL beaker, and set selector switch to appropriate setting for measuring the
dilute to about 100 mL, and add 2.0 mL conc HNO3. Immerse difference of potential between electrodes.
stirrer and electrodes. 4) Complete determination by titrating according to ¶ a4) above.
2) Set instrument to desired range of millivolts or pH units. If an endpoint reading has been established from previous determi-
Start stirrer. nations for similar samples and conditions, use this predetermined
3) Add standard AgNO3 titrant, recording scale reading after endpoint. For the most accurate work, make a blank titration by
each addition. At the start, large increments of AgNO3 may be carrying chloride-free distilled water through the procedure.
added; then, as the endpoint is approached, add smaller and
equal increments (0.1 or 0.2 mL) at longer intervals, so the exact 5. Calculation
endpoint can be determined. Determine volume of AgNO3 used
at the point at which there is the greatest change in instrument (A ⫺ B) ⫻ N ⫻ 35 450
reading per unit addition of AgNO3. mg Cl⫺/L ⫽
mL sample
4) Plot a differential titration curve if the exact endpoint cannot be
determined by inspecting the data. Plot change in instrument read- where:
ing for equal increments of AgNO3 against volume of AgNO3
added, using average of buret readings before and after each addi- A ⫽ mL AgNO3,
tion. The procedure is illustrated in Figure 4500-Cl⫺:1. B ⫽ mL blank, and
b. Sample analysis: N ⫽ normality of titrant.

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 CHLORIDE (4500-Cl⫺)/Automated Ferricyanide Method

6. Precision and Bias CALDWELL, J.R. & H.V. MEYER. 1935. Chloride determination. Ind. Eng.
Chem., Anal. Ed. 7:38.
In the absence of interfering substances, the precision and bias REFFENBURG, H.B. 1935. Colorimetric determination of small quantities
are estimated to be about 0.12 mg for 5 mg Cl⫺, or 2.5% of the of chlorides in water. Ind. Eng. Chem., Anal. Ed. 7:14.
amount present. When pretreatment is required to remove inter- SERFASS, E.J. & R.F. MURACA. 1954. Procedures for Analyzing Metal-
fering substances, the precision and bias are reduced to about Finishing Wastes, p. 80. Ohio River Valley Water Sanitation Com-
0.25 mg for 5 mg Cl⫺, or 5% of amount present. mission, Cincinnati, Ohio.
FURMAN, N.H., ed. 1962. Standard Methods of Chemical Analysis, 6th
7. Bibliography ed., Vol. I. D. Van Nostrand Co., Princeton, N.J.
WALTON, H.F. 1964. Principles and Methods of Chemical Analysis.
Prentice-Hall, Inc., Englewood Cliffs, N.J.
KOLTHOFF, I.M. & N.H. FURMAN. 1931. Potentiometric Titrations, 2nd WILLARD, H.H., L.L. MERRITT & J.A. DEAN. 1965. Instrumental Methods
ed. John Wiley & Sons, New York, N.Y. of Analysis, 4th ed. D. Van Nostrand Co., Princeton, N.J.

4500-Cl⫺ E. Automated Ferricyanide Method

1. General Discussion

a. Principle: Thiocyanate ion is liberated from mercuric thio-

cyanate by the formation of soluble mercuric chloride. In the
presence of ferric ion, free thiocyanate ion forms a highly col-
ored ferric thiocyanate, of which the intensity is proportional to
the chloride concentration.
b. Interferences: Remove particulate matter by filtration or
centrifugation before analysis. Guard against contamination
from reagents, water, glassware, and sample preservation pro-
cess. No chemical interferences are significant.
c. Application: The method is applicable to potable, surface, and
saline waters, and domestic and industrial wastewaters. The concentra-
tion range is 1 to 200 mg Cl⫺/L; it can be extended by dilution.
d. Quality control (QC): The QC practices considered to be an
integral part of each method are summarized in Table 4020:I.

2. Apparatus

a. Automated analytical equipment: An example of the contin- Figure 4500-Clⴚ:2. Flow scheme for automated chloride analysis.
uous-flow analytical instrument consists of the interchangeable
components shown in Figure 4500-Cl⫺:2.
b. Filters, 480-nm.
e. Standard chloride solutions: Prepare chloride standards in
3. Reagents
the desired concentration range, such as 1 to 200 mg/L, using
stock chloride solution.
a. Stock mercuric thiocyanate solution: Dissolve 4.17 g
Hg(SCN)2 in about 500 mL methanol, dilute to 1000 mL with
4. Procedure
methanol, mix, and filter through filter paper.
b. Stock ferric nitrate solution: Dissolve 202 g Set up manifold as shown in Figure 4500-Cl⫺:2 and follow
Fe(NO3)3 䡠 9H2O in about 500 mL distilled water, then care- general procedure described by the manufacturer.
fully add 21 mL conc HNO3. Dilute to 1000 mL with distilled
water and mix. Filter through paper and store in an amber 5. Calculation
bottle.
c. Color reagent: Add 150 mL stock Hg(SCN)2 solution to Prepare standard curves by plotting response of standards
150 mL stock Fe(NO3)3 solution. Mix and dilute to 1000 mL with processed through the manifold against chloride concentra-
distilled water. Add 0.5 mL polyoxyethylene 23 lauryl ether.* tions in standards. Compute sample chloride concentration by
d. Stock chloride solution: Dissolve 1.6482 g NaCl, dried at comparing sample response with standard curve.
140°C, in distilled water and dilute to 1000 mL; 1.00 mL ⫽ 1.00 mg
Cl⫺. 6. Precision and Bias

With an automated system in a single laboratory six sam-

* Brij 35, available from ICI Americas, Wilmington, DE, or equivalent. ples were analyzed in septuplicate. At a concentration ranging

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 CHLORIDE (4500-Cl⫺)/Mercuric Thiocyanate Flow Injection Analysis

from about 1 to 50 mg Cl⫺/L the average standard deviation 7. Bibliography

was 0.39 mg/L. The coefficient of variation was 2.2%. In ZALL, D.M., D. FISHER & M.D. GARNER. 1956. Photometric determina-
two samples with added chloride, recoveries were 104% and tion of chlorides in water. Anal. Chem. 28:1665.
97%. O’BRIEN, J.E. 1962. Automatic analysis of chlorides in sewage. Wastes Eng.
33:670.

4500-Cl⫺ F. (Reserved)

4500-Cl⫺ G. Mercuric Thiocyanate Flow Injection Analysis

1. General Discussion

a. Principle: A water sample containing chloride is injected into

a carrier stream to which mercuric thiocyanate and ferric nitrate are
added. The chloride complexes with the Hg(II), displacing the
thiocyanate anion, which forms the highly colored ferric thiocya-
nate complex anion. The resulting peak’s absorbance is measured at
480 nm. The peak area is proportional to the concentration of
chloride in the original sample.
Also see 4500-Cl⫺.A and Section 4130, Flow Injection Anal- Figure 4500-Clⴚ:3. FIA chloride manifold.
ysis (FIA).
b. Interferences: Remove large or fibrous particulates by filter-
ing sample through glass wool. Guard against contamination from a. Stock mercuric thiocyanate solution: In a 1-L volumetric
reagents, water, glassware, and the sample preservation process. flask, dissolve 4.17 g mercuric thiocyanate, Hg(SCN)2, in about
Substances such as sulfite and thiosulfate, which reduce 500 mL methanol. Dilute to mark with methanol and mix.
iron(III) to iron(II) and mercury(II) to mercury(I), can interfere. CAUTION: Mercuric thiocyanate is toxic. Wear gloves!
Halides, which also form strong complexes with mercuric ion b. Stock ferric nitrate reagent, 0.5M: In a 1-L volumetric
(e.g., Br⫺, I⫺), give a positive interference. flask, dissolve 202 g ferric nitrate, Fe(NO3)3 䡠 9H2O, in approx-
c. Quality control (QC): The QC practices considered to be an imately 800 mL water. Add 25 mL conc HNO3 and dilute to
integral part of each method are summarized in Table 4020:I. mark. Invert to mix.
c. Color reagent: In a 500-mL volumetric flask, mix 75 mL
2. Apparatus stock mercuric thiocyanate solution with 75 mL stock ferric
nitrate reagent and dilute to mark with water. Invert to mix.
Flow injection analysis equipment consisting of: Vacuum filter through a 0.45-␮m membrane filter. The color
a. FIA injection valve with sample loop. reagent also is available as a commercially prepared solution that
b. Multichannel proportioning pump. is stable for several months.
c. FIA manifold with flow cell (Figure 4500-Cl⫺:3). Relative d. Stock chloride standard, 1000 mg Cl⫺/L: In a 105°C oven,
flow rates only are shown. Tubing volumes are given as an dry 3 g primary standard grade sodium chloride, NaCl, over-
example only; they may be scaled down proportionally. Use night. In a 1-L volumetric flask, dissolve 1.648 g primary stan-
manifold tubing of an inert material such as TFE.* dard grade sodium chloride in about 500 mL water. Dilute to
d. Absorbance detector, 480 nm, 10-nm bandpass. mark and invert to mix.
e. Valve control and data acquisition system. e. Standard chloride solutions: Prepare chloride standards for
the calibration curve in the desired concentration range, using the
3. Reagents stock standard (¶ d above), and diluting with water.

Use reagent water (⬎10 megohm) to prepare carrier and all 4. Procedure
solutions.
Set up a manifold equivalent to that in Figure 4500-Cl⫺:3 and
follow method supplied by manufacturer, or laboratory standard
* Teflon, or equivalent. operating procedure for this method.

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 CHLORIDE (4500-Cl⫺)/Mercuric Thiocyanate Flow Injection Analysis

5. Calculations TABLE 4500-Cl⫺:I. RESULTS OF SINGLE-LABORATORY STUDIES WITH

SELECTED MATRICES
Prepare standard curves by plotting absorbance of standards Relative
processed through the manifold versus chloride concentration. Known Standard
The calibration curve gives a good fit to a second-order polyno- Sample/Blank Addition Recovery Deviation
mial. Matrix Designation mg Cl⫺/L % %

Wastewater Reference — 101 —

treatment sample*
6. Precision and Bias plant Blank† 10 104 —
influent 20 102 —
a. Recovery and relative standard deviation: The results of Site A‡ 0 — 0.4
single-laboratory studies with various matrices are given in 10 92 —
Table 4500-Cl⫺:I. 20 101 —
Site B‡ 0 — 0.2
b. MDL: A 100-␮L sample loop was used in the method
10 97 —
described above. Using a published MDL method1 analysts 20 106 —
ran 21 replicates of a 1.0-mg Cl⫺/L standard. These gave a Site C‡ 0 — 0.4
mean of 1.19 mg Cl⫺/L, a standard deviation of 0.027 mg 10 102 —
Cl⫺/L, and an MDL of 0.07 mg Cl⫺/L. This is only an 20 102 —
estimate because the ratio of standard to the MDL is above Wastewater Reference — 101 —
guidelines (see Section 1030C). A lower MDL may be ob- treatment sample*
tained by increasing the sample loop volume and increasing plant Blank† 10 104 —
the ratio of carrier flow rate to reagents flow rate. A higher effluent 20 102 —
MDL may be obtained by decreasing the sample loop volume Site A‡ 0 — 0.3
10 98 —
and decreasing this ratio. 20 101 —
Site B‡ 0 — 0.2
7. Reference 10 99 —
20 103 —
1. U.S. ENVIRONMENTAL PROTECTION AGENCY. 1989. Definition and Site C‡ 0 — 0.4
Procedure for the Determination of Method Detection Limits. 10 91 —
Appendix B to 40 CFR 136 rev. 1.11 amended June 30, 1986. 49 20 97 —
CFR 43430. Landfill Reference — 100 —
leachate sample*
Blank† 10 101 —
20 100 —
Site A§ 0 — 0.3
10 97 —
20 103 —
Site B§ 0 — 0.2
10 89 —
20 103 —
Site C§ 0 — 0.5
10 89 —
20 103 —

* U.S. EPA nutrient QC sample, 51.7 mg Cl⫺/L.

† Determined in duplicate.
‡ Samples diluted fivefold. Samples without known additions determined four
times; samples with known additions determined in duplicate. Typical relative
difference between duplicates 0.2%.
§ Sample from Site A diluted 50-fold, those from B and C 100-fold. Samples
without known additions determined four times; samples with known additions
determined in duplicate; typical relative difference between duplicates 0.5%.

https://doi.org/10.2105/SMWW.2882.079 7