This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles

for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

Designation: D1252 − 06 (Reapproved 2020)

Standard Test Methods for

Chemical Oxygen Demand (Dichromate Oxygen Demand) of
Water1
This standard is issued under the fixed designation D1252; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.

1. Scope 1.7 This international standard was developed in accor-

1.1 These test methods cover the determination of the dance with internationally recognized principles on standard-
quantity of oxygen that certain impurities in water will ization established in the Decision on Principles for the
consume, based on the reduction of a dichromate solution Development of International Standards, Guides and Recom-
under specified conditions. The following test methods are mendations issued by the World Trade Organization Technical
included: Barriers to Trade (TBT) Committee.
Test Method A — Macro COD by Reflux Digestion and Titration
Test Method B — Micro COD by Sealed Digestion and Spectrometry 2. Referenced Documents
1.2 These test methods are limited by the reagents employed 2.1 ASTM Standards:2
to a maximum chemical oxygen demand (COD) of 800 mg/L. D1129 Terminology Relating to Water

iTeh Standards
Samples with higher COD concentrations may be processed by D1193 Specification for Reagent Water
appropriate dilution of the sample. Modified procedures in D2777 Practice for Determination of Precision and Bias of
each test method (Section 15 for Test Method A, and Section Applicable Test Methods of Committee D19 on Water

content (<50 mg/L).

(https://standards.iteh.ai)
24 for Test Method B) may be used for waters of low COD D3223 Test Method for Total Mercury in Water
D3370 Practices for Sampling Water from Flowing Process

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1.3 As a general rule, COD results are not accurate if the
sample contains more than 1000 mg/L Cl−. Consequently, these
Streams
D5847 Practice for Writing Quality Control Specifications
test methods should not be applied to samples such as for Standard Test Methods for Water Analysis
seawaters and brines unless the samples are pretreated as D5905 Practice for the Preparation of Substitute Wastewater
ASTM D1252-06(2020)E60 Practice for Analysis of Metals, Ores, and Related
described in Appendix X1.
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Materials by Spectrophotometry
1.4 This test method was used successfully on a standard E275 Practice for Describing and Measuring Performance of
made up in reagent water. It is the user’s responsibility to Ultraviolet and Visible Spectrophotometers
ensure the validity of these test methods for waters of untested
matrices. 3. Terminology
1.5 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this 3.1 Definitions:
standard. 3.1.1 For definitions of terms used in this standard, refer to
Terminology D1129.
1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 3.2 Definitions of Terms Specific to This Standard—The
responsibility of the user of this standard to establish appro- term “oxygen demand” (COD) in these test methods is defined
priate safety, health, and environmental practices and deter- in accordance with Terminology D1129 as follows:
mine the applicability of regulatory limitations prior to use. 3.2.1 oxygen demand, n—the amount of oxygen required
For specific hazard statements, see Section 8, 15.6, and 24.5. under specified test conditions for the oxidation of water borne
organic and inorganic matter.
1
These test methods are under the jurisdiction of ASTM Committee D19 on
Water and are the direct responsibility of Subcommittee D19.06 on Methods for
2
Analysis for Organic Substances in Water. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Jan. 1, 2020. Published January 2020. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1953. Last previous edition approved in 2012 as D1252 – 06 (2012)ɛ1. Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D1252-06R20. the ASTM website.

Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States

1
 D1252 − 06 (2020)
4. Summary of Test Methods TABLE 1 Test Method A, Recovery of Theoretical COD for
Various Organic Material
4.1 Most organic and oxidizable inorganic substances pres-
Reactivity, Percent of Theoretical
ent in water are oxidized by a standard potassium dichromate Component
1A 2B 3C 4D 5E
solution in 50 % sulfuric acid (vol/vol). The dichromate
Aliphatic Compounds
consumed (Test Method A) or tri-valent chromium produced Acetone 98 ... 96 94 ...
(Test Method B) is determined for calculation of the COD Acetic acid 92 92 98 ... ...
value. Acrolein 62 ... ... ... ...
Butyric acid 89 93 ... ... ...
4.2 The oxidation of many otherwise refractory organics is Dextrose 95 ... ... ... ...
Diethylene glycol 93 ... ... 70 ...
facilitated by the use of silver sulfate that acts as a catalyst in Ethyl acetate 95 ... ... 85 ...
the reaction. Methyl ethyl ketone 98 ... ... 90 ...

4.3 These test methods provide for combining the reagents Aromatic Compounds
and sample in a manner that minimizes the loss of volatile Acetophenone 89 ... ... ... ...
organic materials, if present. Benzaldehyde ... ... ... 80 ...
Benzene 60–98 ... 41 ... ...
4.4 The oxidation of up to 1000 mg/L of chloride ion is Benzoic acid 98 ... ... 100 ...
Dioctyl phthalate 83 ... ... ... ...
inhibited by the addition of mercuric sulfate to form stable and Diphenyl 81 ... ... ... ...
soluble mercuric sulfate complex. A technique to remove up to o-cresol 95 ... ... 95 ...
40 000 mg/L chloride is shown in Appendix X1 for Test Toluene 83 ... ... 45 ...
Potassium acid 100 ... ... ... ...
Method B. The maximum chloride concentration that may be phthalate
tolerated with the procedure for low COD, Test Method A
(15.10), has not been established. Nitrogen Compounds
Acrylonitrile 48 ... ... 44 ...
4.5 The chemical reaction involved in oxidation of materials Adenine ... ... ... ... 59
by dichromate is illustrated by the following reaction with Aniline 80 ... ... 74 ...
Butyl amine 57 ... ... ... ...
potassium acid phthalate (KC8H5O4): Pyridine 0 ... 1 ... 2

iTeh Standards
41 H 2 SO4 110 K 2 Cr 2 O 7 12 KC8 H 5 O 4
→10 Cr2 ~ SO4 ! 3 111 K 2 SO4 116 CO2 146 H 2 O
Quinoline
Trimethylamine
Tryptophane
...
1
...
...
...
...
...
...
...
...
...
...
87
...
87

(https://standards.iteh.ai)
Uric acid ... ... ... ... 61
Since 10 mol of potassium dichromate has the same oxida- A
Hamilton, C. E., unpublished data.
tion power as 15 mol of oxygen, the equivalent reaction is: B
Moore, W. A., and Walker, W. W., Analytical Chemistry, Vol 28, 1956, p. 164.

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C
2 KC8 H 5 O 4 115 O 2 1H 2 SO4 →16 CO2 16 H 2 O1K 2 SO4 Dobbs, R. A., and Williams, R. T., ibid., Vol 35, 1963 p. 1064.
D
Buzzell, J. C., Young, R. H. F., and Ryckman, D. W., “Behaviors of Organic
Thus, 2 mol of potassium acid phthalate consumes 15 mol of Chemicals in the Aquatic Environment; Part II, Dilute Systems,” Manufacturing
Chemists Association, April 1968, p. 34.
oxygen. The theoretical COD of potassium acid phthalate is E
Chudoba, J., and Dalesicky, J., Water Research, Vol 7, No. 5, 1973, p. 663.
ASTM D1252-06(2020)
1.175 g of oxygen per gram of potassium acid phthalate (Table
1).
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5. Significance and Use described in Appendix X1 when using Test Method B. Since
5.1 These test methods are used to chemically determine the this pretreatment was not evaluated during the interlaboratory
maximum quantity of oxygen that could be consumed by study, the user of the test method is responsible to establish the
biological or natural chemical processes due to impurities in precision and bias of each sample matrix.
water. Typically this measurement is used to monitor and 6.2 Oxidizable inorganic ions, such as ferrous, nitrite,
control oxygen-consuming pollutants, both inorganic and sulfite, and sulfides are oxidized and measured as well as
organic, in domestic and industrial wastewaters. organic constituents.
5.2 The relationship of COD to other water quality param-
eters such as TOC and TOD is described in the literature.3 7. Reagents
7.1 Purity of Reagents—Reagent grade chemicals shall be
6. Interference and Reactivity used in all tests. All reagents shall conform to the specifications
6.1 Chloride ion is quantitatively oxidized by dichromate in of the Committee on Analytical Reagents of the American
acid solution. (1.0 mg/L of chloride is equivalent to 0.226 mg/L Chemical Society, where such specifications are available. 4
of COD.) As the COD test is not intended to measure this 7.2 Purity of Water—Unless otherwise indicated, reference
demand, concern for chloride oxidation is eliminated up to to water shall be understood to mean reagent water that meets
1000 mg/L of chloride by complexing with mercuric sulfate.
6.1.1 Up to 40 000 mg/L chloride ion can be removed with
4
a cation based ion exchange resin in the silver form as ACS Reagent Chemicals, Specifications and Procedures for Reagents and
Standard-Grade Reference Materials, American Chemical Society, Washington,
DC. For suggestions on the testing of reagents not listed by the American Chemical
Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset,
3
Handbook for Monitoring Industrial Wastewater, U.S. Environmental Protec- U.K., and the United States Pharmacopeia and National Formulary, U.S. Pharma-
tion Agency, Aug. 1973, pp. 5-10 to 5-12. copeial Convention, Inc. (USPC), Rockville, MD.

2
 D1252 − 06 (2020)
the purity specifications of Type I or Type II water, presented a low-solution temperature (about 40°C) and permitting oxi-
in Specification D1193. dation to proceed at the lower temperature for a period of time
before reflux is initiated will result in higher recoveries of
8. Hazards theoretical COD of volatile organics.
8.1 Exercise extreme care when handling concentrated sul-
furic acid, especially at the start of the refluxing step (15.7). 13. Apparatus
8.2 Silver sulfate is poisonous; avoid contact with the 13.1 Reflux Apparatus—The apparatus consists of a 500-mL
chemical and its solution. Erlenmeyer or a 300-mL round-bottom flask, made of heat-
resistant glass connected to a 300-mm (12-in.) Allihn con-
8.3 Mercuric sulfate is very toxic; avoid contact with the
denser by means of a ground-glass joint. Any equivalent reflux
chemical and its solution.
apparatus may be substituted, provided that a ground-glass
9. Sampling connection is used between the flask and the condenser, and
provided that the flask is made of heat-resistant glass.
9.1 Collect the sample in accordance with Practices D3370.
13.2 Sample Heating Apparatus—A heating mantle or hot
9.2 Preserve samples by cooling to 4°C if analyzed within plate capable of delivering sufficient controlled heat to main-
24 h after sampling, or preserve for up to 28 days at 4°C and tain a steady reflux rate in the reflux apparatus is satisfactory.
at pH < 2 by addition of concentrated sulfuric acid. The
addition of 2 mL of concentrated sulfuric acid per litre at the 13.3 Apparatus for Blending or Homogenizing Samples—A
time of collection will generally achieve this requirement. The household blender is satisfactory.
actual holding time possible without significant change in the
COD may be less than 28 days, especially when easily 14. Reagents
oxidizable substances are present. It is the responsibility of the 14.1 Ferrous Ammonium Sulfate Solution (0.25 N)—
users of the test method to ensure the maximum holding time Dissolve 98.0 g of ferrous ammonium sulfate solution
for their samples. (FeSO4·(NH4)SO4·6H2O) in water. Add 20 mL of sulfuric acid

TEST METHOD A
iTeh Standards (H2SO4, sp gr 1.84), cool and dilute to 1 L. Standardize this
solution daily before use. To standardize, dilute 25.0 mL of

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MACRO COD BY REFLUX DIGESTION AND 0.25 N potassium dichromate solution (K2Cr2O7) to about 250
TITRATION mL. Add 20 mL of sulfuric acid (sp gr 1.84) and allow the
solution to cool. Titrate with the ferrous ammonium sulfate
10. Scope
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10.1 The amount of dichromate consumed in Test Method A
solution to be standardized, using the phenanthroline ferrous
sulfate indicator as directed in 15.10. Calculate the normality
as follows:
is determined by titration rather than the spectrophotometric
ASTM
procedure used in Test Method B. This test method is D1252-06(2020)
appro- N 5 ~ A 3 B ! /C
priate where larger sample volumes would provide better
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where:
precision and better representativeness of where equipment or
N = normality of the ferrous ammonium sulfate solution,
space limitations exist. A = potassium dichromate solution, mL,
10.2 The precision of this test method in standard solutions B = normality of the potassium dichromate solution, and
containing low-volatility organic compounds has been exam- C = ferrous ammonium sulfate solution, mL.
ined in the range of approximately 10 to 300 mg/L. 14.2 Ferrous Ammonium Sulfate Solution (0.025 N)—
Dilute 100 mL of 0.25 N ferrous ammonium sulfate solution to
11. Summary of Test Method
1 L. Standardize against 0.025 N potassium dichromate solu-
11.1 The sample and standardized dichromate solution, in a tion as in 14.1. This solution is required only if COD is
50 % by volume sulfuric solution, is refluxed for a 2-h determined in the range of 10 to 50 mg/L.
digestion period.
14.3 Mercuric Sulfate—Powdered mercuric sulfate
11.2 Excess dichromate after the digestion period is titrated (HgSO4).
with a standard ferrous ammonium sulfate solution using
ortho-phenanthroline ferrous complex as an internal indicator. 14.4 Phenanthroline Ferrous Sulfate Indicator Solution—
Dissolve 1.48 g of 1,10-(ortho)-phenanthroline monohydrate,
12. Interferences together with 0.70 g of ferrous sulfate (FeSO4·7H2O), in 100
mL of water. This indicator may be purchased already pre-
12.1 The test method does not uniformly oxidize all organic
pared.
materials. Some compounds, for example, are quite resistant to
oxidation, while others, such as carbohydrates, are easily 14.5 Potassium Acid Phthalate Solution, Standard (1
oxidized. A guide to the behavior of various types of organic mL = 1 mg COD)—Dissolve 0.851 g of potassium acid phtha-
materials is provided in Table 1. late (KC8H5O4), primary standard, in water and dilute to 1 L.
12.2 Volatile organics that are difficult to oxidize may be 14.6 Potassium Dichromate Solution, Standard (0.25 N)—
partially lost before oxidation is achieved. Care in maintaining Dissolve 12.259 g of potassium dichromate (K2Cr2O7) primary

3
 D1252 − 06 (2020)
standard grade, previously dried at 103°C for 2 h, in water and
dilute to 1 L in a volumetric flask.
14.7 Potassium Dichromate Solution, Standard (0.025 N)—
Dilute 100.0 mL of 0.25 N potassium dichromate solution to 1
L. This solution is necessary only for determination of COD in
the range of 10 to 50 mg/L.
14.8 Sulfuric Acid-Silver Sulfate Solution—Dissolve 15 g of
powdered silver sulfate (Ag2SO4) in 300 mL of concentrated
sulfuric acid (sp gr 1.84) and dilute to 1 L with concentrated
sulfuric acid (sp gr 1.84).
15. Procedure
15.1 Homogenize the sample by blending if necessary.
Place 50.0 mL of the sample in a reflux flask. If less than 50 mL
of the sample is used, make up the difference in water, then add
the sample aliquot and mix. Samples containing more than 800
mg/L COD are diluted and mixed precisely with water and 50.0
mL of the diluted sample are placed in a reflux flask.
NOTE 1—If the sample is diluted, it must consume at least 5 mL of
dichromate. Dilute the sample if more than 20 mL of the titrant is needed
to reach the endpoint. FIG. 1 Test Method A, Chemical Oxygen Demand (COD) Preci-
sion of Determination as Overall Standard Deviation
15.2 Place 50 mL of water in a reflux flask for the blank
determination.
four times with water. Dilute the acid solution to about 300 mL
iTeh Standards
15.3 Place the reflux flasks in an ice bath and add 1 g of
with water and allow the solution to cool to about room
powdered mercuric sulfate, 5.0 mL of concentrated sulfuric
temperature.
acid, and several glass beads or boiling stones. Mix well to
complete dissolution.
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15.4 With the flasks still in the ice bath, add slowly and with
15.9 Add 8 to 10 drops of phenanthroline ferrous sulfate
solution and titrate the excess dichromate with 0.25 N ferrous

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ammonium solution. The color change at the end point will be
stirring, 25.0 mL of 0.25 N standard potassium dichromate
sharp, changing from a blue-green to a reddish hue. If the
solution.
solution immediately turns a reddish-brown upon the addition
15.5 With the flasks still in the ice bath, add 70 mL of of the indicator, repeat the analysis on a smaller sample aliquot.
sulfuric acid-silver sulfate solution slowly suchASTM
that theD1252-06(2020)
solu-
NOTE 3—To avoid unnecessary pollution of the environment, dispose of
tion temperature is maintained as low as possible, preferably
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below 40°C.
mercury-containing waste solution properly. Refer to Test Method D3223,
Appendix XI, for instructions.
NOTE 2—If a particular waste is known to contain no volatile organic 15.10 For waters of low COD (10 to 50 mg/L), use 0.025 N
substances, the acid mixture may be added gradually, with less precaution, potassium dichromate and ferrous ammonium sulfate solutions
while the flask is immersed in the iced bath.
(14.2 and 14.7). If the COD is determined to be higher than 50
15.6 Attach the flasks to the condensers and start the flow of mg/L after using these reagents, reanalyze the sample, using
cold water. (Warning—Take care to ensure that the contents of the more concentrated reagents.
the flask are well mixed; if not, superheating may result and the
mixture may be expulsed from the open end of the condenser.) 16. Calculation
15.7 Apply heat to the flasks and reflux for 2 h. Place a 16.1 Calculate the COD in the sample in milligrams per litre
small beaker or other cover over the open end of each as follows:
condenser to prevent intrusion of foreign material. COD, mg/L 5 ~~ A 2 B ! N 3 8000! /S
15.8 Allow the flasks to cool and wash down the condensers where:
with about 25 mL of water before removing flasks. If a
A = ferrous ammonium sulfate solutions required for titra-
round-bottom flask has been used, transfer the digestate to a
tion of the blank, mL,
500-mL Erlenmeyer flask, washing out the reflux flask three or

4
 D1252 − 06 (2020)
TABLE 2 Test Method A, Recovery and Precision Data
Recovered
Prepared Bias, Statistically
COD, % Bias
COD, mg/L mg/L Significant
mg/L
12.30 12.34 +0.04 +0.33 no
40.2 37.9 −2.3 −5.7 yes
92.0 88.6 −3.4 −3.7 yes
270 257 −13 −4.8 yes

17.6 Prepared Standards—Recoveries of known amounts of

COD in the series of prepared standards (previously described)
were as shown in Table 2.
TEST METHOD B
MICRO COD BY SEALED DIGESTION AND
SPECTROMETRY

18. Scope
FIG. 2 Test Method A, Chemical Oxygen Demand (COD) Bias of
18.1 This test method is essentially equivalent to Test
Determinations Method A, but it utilizes micro volumes of the same reagents
contained in a sealable ampule or a screw-top culture tube and
a spectrophotometer or filter photometer to measure absor-
B = ferrous ammonium sulfate solution required for titration bance or transmittance at selected wavelengths. This test
of the sample, mL, method is applicable where only small sample volumes are
N = normality of the ferrous ammonium sulfate solution, and available and where large numbers of samples need to be
S = sample used for the test, mL.iTeh Standards analyzed. This test method requires less space per analysis and
uses less of the reagents, minimizing costs and volume of
17. Precision and Bias (https://standards.iteh.ai)
5

17.1 The overall precision of Test Method A within the

wastes discharged.
18.2 This test method was tested on Type II reagent water.

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range from 10 to 300 mg/L varies with the quantity being
tested according to Fig. 1.
It is the user’s responsibility to ensure the validity of this test
method for waters of untested matrices.

17.2 The data used in the calculation of precision are from 19. Summary of Test Method
EPA “Method Research Study 3” (1971) thatASTM D1252-06(2020)
involved two 19.1 The dichromate reagent and silver catalyst used in this
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levels of COD, 12.3 mg/L (86 laboratories) and 270 mg/L (82 test method are similar to those used in Test Method A, but the
laboratories), and EPA “Water Pollution Laboratory Perfor- volumes employed are 1⁄20 th of those in Test Method A.
mance Evaluation, No. 8” (1982) that involved two levels of
COD, 40.2 mg/L (65 laboratories) and 92 mg/L (67 laborato- 19.2 A sample aliquot is introduced carefully into an ampule
ries). or screw-top tube so that the sample is layered on top of
previously introduced reagents and remains there until the
17.3 The test data were obtained on reagent grade water and ampule or tube is sealed. This technique limits evolution of
these precision and bias values may not be applicable to more heat of solution until the container is sealed, minimizing the
complex water matrices. It is the user’s responsibility to ensure loss of volatile organics.
the validity of this test method to waters of untested matrices.
19.3 After sealing, the ampule or tube is heated in an oven,
17.4 The precision obtained by the interlaboratory study is sand bath, or heated block at 150 6 2°C for 2 h. The COD
overall, St. Since very carefully standardized samples in very concentration is determined spectrophotometrically after di-
pure water were used rather than natural samples collected by gestion. In the low COD range (5 to approximately 50 mg/L),
usual sampling procedures, the estimates do not include the the loss of hexavalent chromium is measured at 420 nm, while
increase in precision statistics and the potential change in bias for the high range (50 to approximately 800 mg/L), the
that may be attributed to the sample collection activities. increase in trivalent chromium is measured at 600 nm. The
17.5 The trend of the approximately 5 % negative bias is ampule or tube serves as the absorption cell.
shown in Fig. 2.
20. Interferences
5
20.1 Interferences identified in Section 6 are also applicable
Supporting data were taken from “Method Research Study 3” (1971) and
“Water Pollution Laboratory Performance No. 8” (1982), Environmental Protection to the micro procedure.
Agency, National Environmental Research Center, Analytical Quality Control
20.2 Volatile materials will be lost if the sample is mixed
Laboratory, Cincinnati, OH. Supporting data have been filed at ASTM International
Headquarters and may be obtained by requesting Research Report RR:D19-1044. with the reagents before the ampule or tube is sealed. Volatile
Contact ASTM Customer Service at service@astm.org. materials will also be lost during sample homogenization.

5
 D1252 − 06 (2020)
20.3 Potentially, the loss of volatile organics in the micro
procedure will be less than that which may occur in Test
Method A. Thus, results between the two methods may differ if
volatile materials are involved.
20.4 Spectrophotometric interferences may exist due to
turbidity of precipitated salts that are too colloidal to settle in
a reasonable period of time. Centrifugation may be used to
speed separation of the salts. This test method does not address
a titration procedure for the micro-volume, but if the digested
samples do not clear or spectrophotometric interference is
suspected, the COD result can be determined by titration.6 FIG. 3 Typical COD Calibration Curve for Spectrophotometric
20.5 The ampule or tube must have window areas that are COD Method, Ampule Technique (Test Method B)
free of scratches or smudges. If a suitable window area is not
available, do not consider transfer of the sample. The sample 22.2 Potassium Acid Phthalate Solution, Standard (1
and the blank may be titrated and the results used to calculate mL = 1 mg/L)—See 14.5.
a COD value (see 24.10).
22.3 Potassium Dichromate Digestion Solution:
21. Apparatus 22.3.1 High Range—Add 10.216 g of potassium dichromate
(K2Cr2O7) dried at 103°C for 2 h, 167 mL of concentrated
21.1 Spectrophotometer or Filter Photometer, suitable for
sulfuric acid (H2SO4) (sp gr 1.84) and 33.3 g of mercuric
measurements at 600 nm and 420 nm using the ampules or
sulfate (HgSO4) to about 750 mL of water, mix, and let cool.
tubes in 21.3 or 21.3.1 as absorption cells. Filter photometers
Dilute the solution to 1 L with water and mix thoroughly.
and photometric practices shall conform to Practice E60.
22.3.2 Low Range—Add 1.022 g of potassium dichromate,
Spectrophotometers shall conform to Practice E275. For some
(K2Cr2O7) (dried at 103°C for 2 h), 167 mL of concentrated
spectrophotometers, poor sensitivity at 420 nm has been
sulfuric acid (H2SO4) (sp gr 1.84) and 33.3 g of mercuric
iTeh Standards
observed. A suggested minimum sensitivity for the spectropho-
tometer readout is 0.002 absorbance units per milligram per
sulfate (HgSO4) to about 750 mL of water, mix, and cool.
Dilute the solution to 1 L with water and mix thoroughly.
litre of COD for the low range procedure.
21.2 Heating Oven, sand (https://standards.iteh.ai)
22.4 Ferrous Ammonium Sulfate Solution (0.10 N)—Dilute
bath, or block heater capable of
400 mL of 0.25 N ferrous ammonium sulfate solution (see 14.1
maintaining a temperature of 150 6 2°C throughout. If an oven
Document
is used and screw-top tubes are employed, ascertain that the Preview
caps can withstand the oven temperature and solution pressure.
to 1 L. Standardize against 0.25 N potassium dichromate
(K Cr O ) as in 14.1. 2 2 7

The heating device must be equipped with a high temperature 22.5 Ferrous Ammonium Sulfate Solution (0.01 N)—Dilute
shut-off set at 175 to 185°C. 40
ASTM D1252-06(2020)mL of 0.25 N ferrous ammonium sulfate solution (see 14.1)
to 1 L. Standardize against 0.025 N potassium dichromate
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21.3 Culture Tubes, borosilicate glass, 16 by 100 mm, with
(K2Cr2O7) as in 14.1.
TFE-fluorocarbon-lined screw caps. Protect the caps and cul-
ture tubes from dust contamination. 22.6 Phenanthroline Ferrous Sulfate Indicator Solution—
21.3.1 Ampules, borosilicate glass, 10 mL, may be substi- See 14.4. If desired, the indicator may be diluted 1:5 for use in
tuted for the culture tubes in 21.3. These ampules are rotated this test method.
and uniformly sealed with a glass blowing torch after addition
of sample and reagent solutions. The nominal path length of 23. Calibration
these ampules shall be 15 to 20 mm. 23.1 High Range—Dilute the following volumes of COD
21.4 Apparatus for Blending or Homogenizing Samples—A standard solution (see 22.2) to 50 mL with water. The high
tissue homogenizer is recommended. However, a household range procedure may be used for COD determination as low as
blender may be used, but a suitable reduction in particle size 25 mg/L at the discretion of the analyst.
may not be obtained. Potassium Acid Phthalate
Standard Solution, mL COD, mg/L
NOTE 4—A partial round robin, using cellulose filter paper as the
organic material, demonstrated serious difficulties in achieving a repre- 2.5 50
sentative subsample. The use of a blender followed by a tissue homog- 5 100
enizer was required. 10 200
20 400
22. Reagents 30 600
40 800
22.1 Silver Sulfate Catalyst Solution—Dissolve 22 g of
silver sulfate (Ag2SO4) in a 4.09 kg (9 lb) bottle of concen- NOTE 5—A typical COD calibration curve for spectrophotometric COD
method, ampule technique (Test Method B) is shown in Fig. 3.
trated sulfuric acid (H2SO4).
23.2 Low Range—Dilute the following volumes of potas-
6
sium acid phthalate standard solution to 200 mL with water. At
Messenger, A. L., “Comparison of Sealed Digestion Chamber and Standard
Method COD Tests,” Journal Water Pollution Control Federation, Vol 53, No. 2, the discretion of the analyst, the upper limit may be extended
February 1981, pp. 232–236. to approximately 150 mg/L.