An American National Standard

Designation: D 1252 06

Standard Test Methods for

Chemical Oxygen Demand (Dichromate Oxygen Demand) of
Water1
This standard is issued under the fixed designation D 1252; 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 (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.

1. Scope 2. Referenced Documents

1.1 These test methods cover the determination of the 2.1 ASTM Standards: 2
quantity of oxygen that certain impurities in water will D 1129 Terminology Relating to Water
consume, based on the reduction of a dichromate solution D 1193 Specification for Reagent Water
under specified conditions. The following test methods are D 2777 Practice for Determination of Precision and Bias of
included: Applicable Test Methods of Committee D19 on Water
Test Method AMacro COD by Reflux Digestion and Titration D 3223 Test Method for Total Mercury in Water
D 3370 Practices for Sampling Water from Closed Conduits
Test Method BMicro COD by Sealed Digestion and Spectrometry D 5905 Practice for the Preparation of Substitute Wastewa-
ter
1.2 These test methods are limited by the reagents employed E 60 Practice for Analysis of Metals, Ores, and Related
to a maximum chemical oxygen demand (COD) of 800 mg/L. Materials by Molecular Absorption Spectrometry
Samples with higher COD concentrations may be processed by E 275 Practice for Describing and Measuring Performance
appropriate dilution of the sample. Modified procedures in of Ultraviolet, Visible, and Near-Infrared Spectrophotom-
each test method (Section 15 for Test Method A and Section 24 eters
for Test Method B) may be used for waters of low COD
content (< 50 mg/L). 3. Terminology
1.3 As a general rule, COD results are not accurate if the 3.1 DefinitionsFor definitions of other terms used in these
sample contains more than 1000 mg/L Cl. Consequently, these test methods, refer to Terminology D 1129.
test methods should not be applied to samples such as 3.2 The term oxygen demand (COD) in these test meth-
seawaters and brines unless the samples are pretreated as ods is defined in accordance with Terminology D 1129 as
described in Appendix X1. follows:
1.4 This test method was used successfully on a standard 3.2.1 oxygen demandthe amount of oxygen required un-
made up in reagent water. It is the users responsibility to der specified test conditions for the oxidation of water borne
ensure the validity of these test methods for waters of untested organic and inorganic matter.
matrices.
1.5 This standard does not purport to address all of the 4. Summary of Test Methods
safety concerns, if any, associated with its use. It is the 4.1 Most organic and oxidizable inorganic substances
responsibility of the user of this standard to establish appro- present in water are oxidized by a standard potassium dichro-
priate safety and health practices and determine the applica- mate solution in 50 % sulfuric acid (vol/vol). The dichromate
bility of regulatory limitations prior to use. For specific hazard consumed (Test Method A) or tri-valent chromium produced
statements, see Sections 8, 15.6, and 24.5. (Test Method B) is determined for calculation of the COD
value.
1
These test methods are under the jurisdiction of ASTM Committee D19 on
2
Water and are the direct responsibility of Subcommittee D19.06 on Methods for For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Analysis for Organic Substances in Water. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved Feb. 15, 2006. Published February 2006. Originally Standards volume information, refer to the standards Document Summary page on
approved in 1953. Last previous edition approved in 2000 as D 1252 00. the ASTM website.
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 D 1252 06
4.2 The oxidation of many otherwise refractory organics is TABLE 1 Test Method A, Recovery of Theoretical COD for
facilitated by the use of silver sulfate that acts as a catalyst in Various Organic Material
the reaction. Reactivity, Percent of Theoretical
Component
4.3 These test methods provide for combining the reagents 1A 2B 3C 4D 5E
and sample in a manner that minimizes the loss of volatile Aliphatic Compounds
organic materials, if present. Acetone 98 ... 96 94 ...
Acetic acid 92 92 98 ... ...
4.4 The oxidation of up to 1000 mg/L of chloride ion is Acrolein 62 ... ... ... ...
inhibited by the addition of mercuric chloride to form stable Butyric acid 89 93 ... ... ...
Dextrose 95 ... ... ... ...
and soluble mercuric sulfate complex. A technique to remove Diethylene glycol 93 ... ... 70 ...
up to 40 000 mg/L chloride is shown in Appendix X1 for Test Ethyl acetate 95 ... ... 85 ...
Method B. The maximum chloride concentration that may be Methyl ethyl ketone 98 ... ... 90 ...
Aromatic Compounds
tolerated with the procedure for low COD, Test Method A Acetophenone 89 ... ... ... ...
(15.11), has not been established. Benzaldehyde ... ... ... 80 ...
4.5 The chemical reaction involved in oxidation of materials Benzene 6098 ... 41 ... ...
Benzoic acid 98 ... ... 100 ...
by dichromate is illustrated by the following reaction with Dioctyl phthalate 83 ... ... ... ...
potassium acid phthalate (KC8H5O4): Diphenyl 81 ... ... ... ...
o-cresol 95 ... ... 95 ...
41 H2SO4 1 10 K2Cr 2O7 1 2 KC8H5O4 Toluene 83 ... ... 45 ...
10 Cr2~SO4!3 1 11 K2SO4 1 16 CO2 1 46 H2O Potassium acid 100 ... ... ... ...
phthalate
Nitrogen Compounds
Since 10 mol of potassium dichromate has the same oxida- Acrylonitrile 48 ... ... 44 ...
tion power as 15 mol of oxygen, the equivalent reaction is: Adenine ... ... ... ... 59
Aniline 80 ... ... 74 ...
2 KC8H5O4 1 15 O2 1 H2SO4 16 CO2 1 6 H2O 1 K2SO4 Butyl amine 57 ... ... ... ...
Pyridine 0 ... 1 ... 2
Thus 2 mol of potassium acid phthalate consumes 15 mol of Quinoline ... ... ... ... 87
oxygen. The theoretical COD of potassium acid phthalate is
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Trimethylamine 1 ... ... ... ...

Tryptophane ... ... ... ... 87
1.175 g of oxygen per gram of potassium acid phthalate (Table
Uric acid ... ... ... ... 61
1). A
Hamilton, C. E., unpublished data.
B
Moore, W. A., and Walker, W. W., Analytical Chemistry, Vol 28, 1956, p 164.
5. Significance and Use C
Dobbs, R. A., Williams, R. T., ibid., Vol 35, 1963 p. 1064.
D
Buzzell, J. C., Young, R. H. F., and Ryckman, D. W., Behaviors of Organic
5.1 These test methods are used to chemically determine the Chemicals in the Aquatic Environment; Part II, Dilute Systems, Manufacturing
maximum quantity of oxygen that could be consumed by Chemists Association, April 1968, p. 34.
E
Chudoba, J., and Dalesicky, J., Water Research, Vol 7, No. 5, 1973, p. 663.
biological or natural chemical processes due to impurities in
water. Typically this measurement is used to monitor and
control oxygen-consuming pollutants, both inorganic and or- 7. Reagents
ganic, in domestic and industrial wastewaters.
5.2 The relationship of COD to other water quality param- 7.1 Purity of ReagentsReagent grade chemicals shall be
eters such as TOC and TOD is described in the literature. 3 used in all tests. All reagents shall conform to the specifications
of the Committee on Analytical Reagents of the American
Chemical Society, where such specifications are available. 4
6. Interference and Reactivity
7.2 Purity of WaterUnless otherwise indicated, reference
6.1 Chloride ion is quantitatively oxidized by dichromate in to water shall be understood to mean reagent water that meets
acid solution. (1.0 mg/L of chloride is equivalent to 0.226 mg/L the purity specifications of Type I or Type II water, presented
of COD.) As the COD test is not intended to measure this in D 1193.
demand, concern for chloride oxidation is eliminated up to
1000 mg/L of chloride by complexing with mercuric sulfate. 8. Hazards
6.1.1 Up to 40 000 mg/L chloride ion can be removed with 8.1 Exercise extreme care when handling concentrated sul-
a cation based ion exchange resin in the silver form as furic acid, especially at the start of the refluxing step (15.7).
described in Appendix X1 when using Test Method B. Since 8.2 Silver sulfate is poisonous; avoid contact with the
this pretreatment was not evaluated during the interlaboratory chemical and its solution.
study, the user of the test method is responsible to establish the 8.3 Mercuric sulfate is very toxic; avoid contact with the
precision and bias of each sample matrix. chemical and its solution.
6.2 Oxidizable inorganic ions, such as ferrous, nitrite,
sulfite, and sulfides are oxidized and measured as well as
organic constituents. 4
Reagent Chemicals, American Chemical Society Specifications, 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, U.K., and the United States Pharmacopeia
3
Handbook for Monitoring Industrial Wastewater, U.S. Environmental Protec- and National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,
tion Agency, Aug. 1973, pp. 5-10 to 5-12. MD.

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 D 1252 06
9. Sampling time of collection will generally achieve this requirement. The
9.1 Collect the sample in accordance with Practices D 3370. actual holding time possible without significant change in the
9.2 Preserve samples by cooling to 4C if analyzed within COD may be less than 28 days, especially when easily
24 h after sampling, or preserve for up to 28 days at 4C and oxidizable substances are present. It is the responsibility of the
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at pH < 2 by addition of concentrated sulfuric acid. The users of the test method to ensure the maximum holding time
addition of 2 mL of concentrated sulfuric acid per litre at the for their samples.

TEST METHOD AMACRO COD BY REFLUX DIGESTION AND TITRATION

10. Scope 14. Reagents

10.1 The amount of dichromate consumed in Test Method A 14.1 Ferrous Ammonium Sulfate Solution (0.25 N)
is determined by titration rather than the spectrophotometric Dissolve 98.0 g of ferrous ammonium sulfate solution
procedure used in Test Method B. This test method is appro- (FeSO4(NH4)SO46H2O) in water. Add 20 mL of sulfuric acid
priate where larger sample volumes would provide better (H2SO4, sp gr 1.84), cool and dilute to 1 L. Standardize this
precision and better representativeness of where equipment or solution daily before use. To standardize, dilute 25.0 mL of
space limitations exist. 0.25 N potassium dichromate solution (K2Cr2O7) to about 250
10.2 The precision of this test method in standard solutions mL. Add 20 mL of sulfuric acid (sp gr 1.84) and allow the
containing low-volatility organic compounds has been exam- solution to cool. Titrate with the ferrous ammonium sulfate
ined in the range of approximately 10 to 300 mg/L. solution to be standardized, using the phenanthroline ferrous
sulfate indicator as directed in 15.10. Calculate the normality
11. Summary of Test Method as follows:
N 5 ~A 3 B!/C
11.1 The sample and standardized dichromate solution, in a
50 % by volume sulfuric solution, is refluxed for a 2-h
digestion period. where:
11.2 Excess dichromate after the digestion period is titrated N = normality of the ferrous ammonium sulfate solution,
with a standard ferrous ammonium sulfate solution using A = potassium dichromate solution, mL,
ortho-phenanthroline ferrous complex as an internal indicator. B = normality of the potassium dichromate solution, and
C = ferrous ammonium sulfate solution, mL.
12. Interferences 14.2 Ferrous Ammonium Sulfate Solution (0.025 N)
Dilute 100 mL of 0.25 N ferrous ammonium sulfate solution to
12.1 The test method does not uniformly oxidize all organic 1 L. Standardize against 0.025 N potassium dichromate solu-
materials. Some compounds, for example, are quite resistant to tion as in 14.1. This solution is required only if COD is
oxidation, while others, such as carbohydrates, are easily determined in the range of 10 to 50 mg/L.
oxidized. A guide to the behavior of various types of organic 14.3 Mercuric SulfatePowdered mercuric sulfate
materials is provided in Table 1. (HgSO4).
12.2 Volatile organics that are difficult to oxidize may be 14.4 Phenanthroline Ferrous Sulfate Indicator Solution
partially lost before oxidation is achieved. Care in maintaining Dissolve 1.48 g of 1,10-(ortho)-phenanthroline monohydrate,
a low-solution temperature (about 40C) and permitting oxi- together with 0.70 g of ferrous sulfate (FeSO47H2O), in 100
dation to proceed at the lower temperature for a period of time mL of water. This indicator may be purchased already pre-
before reflux is initiated will result in higher recoveries of pared.
theoretical COD of volatile organics.
14.5 Potassium Acid Phthalate Solution, Standard (1
mL = 1 mg COD)Dissolve 0.851 g of potassium acid phtha-
13. Apparatus late (KC8H5O4), primary standard, in water and dilute to 1 L.
13.1 Reflux ApparatusThe apparatus consists of a 14.6 Potassium Dichromate Solution, Standard (0.25 N)
500-mL Erlenmeyer or a 300-mL round-bottom flask, made of Dissolve 12.259 g of potassium dichromate (K2Cr2O7) primary
heat-resistant glass connected to a 300-mm (12-in.) Allihn standard grade, previously dried at 103C for 2 h, in water and
condenser by means of a ground-glass joint. Any equivalent dilute to 1 L in a volumetric flask.
reflux apparatus may be substituted, provided that a ground- 14.7 Potassium Dichromate Solution, Standard (0.025
glass connection is used between the flask and the condenser, N)Dilute 100.0 mL of 0.25 N potassium dichromate solution
and provided that the flask is made of heat-resistant glass. to 1 L. This solution is necessary only for determination of
13.2 Sample Heating ApparatusA heating mantle or hot COD in the range of 10 to 50 mg/L.
plate capable of delivering sufficient controlled heat to main- 14.8 Sulfuric Acid-Silver Sulfate SolutionDissolve 15 g of
tain a steady reflux rate in the reflux apparatus is satisfactory. powdered silver sulfate (Ag2SO4) in 300 mL of concentrated
13.3 Apparatus for Blending or Homogenizing SamplesA sulfuric acid (sp gr 1.84) and dilute to 1 L with concentrated
household blender is satisfactory. sulfuric acid (sp gr 1.84).

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 D 1252 06
15. Procedure 15.8 Allow the flasks to cool and wash down the condensers
15.1 Homogenize the sample by blending if necessary. with about 25 mL of water before removing flasks. If a
Place 50.0 mL of the sample in a reflux flask. If less than 50 mL round-bottom flask has been used, transfer the digestate to a
of the sample is used, make up the difference in water, then add 500-mL Erlenmeyer flask, washing out the reflux flask three or
the sample aliquot and mix. Samples containing more than 800 four times with water. Dilute the acid solution to about 300 mL
mg/L COD are diluted and mixed precisely with water and 50.0 with water and allow the solution to cool to about room
mL of the diluted sample are placed in a reflux flask. temperature.
15.9 Add 8 to 10 drops of phenanthroline ferrous sulfate
NOTE 1If the sample is diluted, it must consume at least 5 mL of solution and titrate the excess dichromate with 0.25 N ferrous
dichromate. Dilute the sample if more than 20 mL of the titrant is needed
ammonium solution. The color change at the end point will be
to reach the endpoint.
sharp, changing from a blue-green to a reddish hue. If the
15.2 Place 50 mL of water in a reflux flask for the blank solution immediately turns a reddish-brown upon the addition
determination. of the indicator, repeat the analysis on a smaller sample aliquot.
15.3 Place the reflux flasks in an ice bath and add 1 g of
powdered mercuric sulfate, 5.0 mL of concentrated sulfuric NOTE 3To avoid unnecessary pollution of the environment, dispose
of mercury-containing waste solution properly. Refer to Test Method
acid, and several glass beads or boiling stones. Mix well to D 3223, Appendix XI for instructions.
complete dissolution.
15.4 With the flasks still in the ice bath, add slowly and with 15.10 For waters of low COD (10 to 50 mg/L), use 0.025 N
stirring, 25.0 mL of 0.25 N standard potassium dichromate potassium dichromate and ferrous ammonium sulfate solutions
solution. (14.2 and 14.7). If the COD is determined to be higher than 50
15.5 With the flasks still in the ice bath, add 70 mL of mg/L after using these reagents, reanalyze the sample, using
sulfuric acid-silver sulfate solution slowly such that the solu- the more concentrated reagents.
tion temperature is maintained as low as possible, preferably
below 40C. 16. Calculation
16.1 Calculate the COD in the sample in milligrams per litre
NOTE 2If a particular waste is known to contain no volatile organic
substances, the acid mixture may be added gradually, with less precaution,
as follows:
while the flask is immersed in the iced bath. COD, mg/L 5 ~~A 2 B!N 3 8000!/S
15.6 Attach the flasks to the condensers and start the flow of
cold water.(WarningTake care to ensure that the contents of where:
the flask are well mixed; if not, superheating may result and the A = ferrous ammonium sulfate solutions required for titra-
mixture may be expulsed from the open end of the condenser.) tion of the blank, mL,
15.7 Apply heat to the flasks and reflux for 2 h. Place a B = ferrous ammonium sulfate solution required for titra-
small beaker or other cover over the open end of each tion of the sample, mL,
condenser to prevent intrusion of foreign material. N = normality of the ferrous ammonium sulfate solution,
and
S = sample used for the test, mL.

17. Precision and Bias 5

17.1 The overall precision of Test Method A within the
range from 10 to 300 mg/L varies with the quantity being
tested according to Fig. 1.
17.2 The data used in the calculation of precision are from
EPA Method Research Study 3 (1971) that involved two
levels of COD, 12.3 mg/L (86 laboratories) and 270 mg/L (82
laboratories), and EPA Water Pollution Laboratory Perfor-
mance Evaluation, No. 8 (1982) that involved two levels of
COD, 40.2 mg/L (65 laboratories) and 92 mg/L (67 laborato-
ries).
17.3 The test data were obtained on reagent grade water and
these precision and bias values may not be applicable to more
complex water matrices. It is the users responsibility to ensure
the validity of this test method to waters of untested matrices.

5
Supporting data were taken from Method Research Study 3 (1971) and
Water Pollution Laboratory Performance No. 8 (1982), Environmental Protection
Agency, National Environmental Research Center, Analytical Quality Control
FIG. 1 Test Method A, Chemical Oxygen Demand (COD) Precision Laboratory, Cincinnati, OH. These documents are available from ASTM Headquar-
of Determination as Overall Standard Deviation ters as RR:D 19-1044.
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17.4 The precision obtained by the interlaboratory study is
overall, St. Since very carefully standardized samples in very
pure water were used rather than natural samples collected by
usual sampling procedures, the estimates do not include the
increase in precision statistics and the potential change in bias
that may be attributed to the sample collection activities.
17.5 The trend of the approximately 5 % negative bias is
shown in Fig. 2.
17.6 Prepared StandardsRecoveries of known amounts
of COD in the series of prepared standards (previously
described) were as shown in Table 2.

FIG. 2 Test Method A, Chemical Oxygen Demand (COD) Bias of

Determinations

TABLE 2 Test Method A, Recovery and Precision Data

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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

TEST METHOD BMICRO COD BY SEALED DIGESTION AND SPECTROMETRY

18. Scope 19.3 After sealing, the ampule or tube is heated in an oven,
18.1 This test method is essentially equivalent to Test sand bath, or heated block at 150 6 2C for 2 h. The COD
Method A, but it utilizes micro volumes of the same reagents concentration is determined spectrophotometrically after di-
contained in a sealable ampule or a screw-top culture tube and gestion. In the low COD range (5 to approximately 50 mg/L),
a spectrophotometer or filter photometer to measure absor- the loss of hexavalent chromium is measured at 420 nm, while
bance or transmittance at selected wavelengths. This test for the high range (50 to approximately 800 mg/L), the
method is applicable where only small sample volumes are increase in trivalent chromium is measured at 600 nm. The
available and where large numbers of samples need to be ampule or tube serves as the absorption cell.
analyzed. This test method requires less space per analysis and
uses less of the reagents, minimizing costs and volume of 20. Interferences
wastes discharged. 20.1 Interferences identified in Section 6 are also applicable
18.2 This test method was tested on Type II reagent water. to the micro procedure.
It is the users responsibility to ensure the validity of this test
method for waters of untested matrices. 20.2 Volatile materials will be lost if the sample is mixed
with the reagents before the ampule or tube is sealed. Volatile
19. Summary of Test Method materials will also be lost during sample homogenization.
19.1 The dichromate reagent and silver catalyst used in this 20.3 Potentially, the loss of volatile organics in the micro
test method are similar to those used in Test Method A, but the procedure will be less than that which may occur in Test
volumes employed are 120 th of those in Test Method A. Method A. Thus, results between the two methods may differ if
19.2 A sample aliquot is introduced carefully into an ampule volatile materials are involved.
or screw-top tube so that the sample is layered on top of 20.4 Spectrophotometric interferences may exist due to
previously introduced reagents and remains there until the turbidity of precipitated salts that are too colloidal to settle in
ampule or tube is sealed. This technique limits evolution of a reasonable period of time. Centrifugation may be used to
heat of solution until the container is sealed, minimizing the speed separation of the salts. This test method does not address
loss of volatile organics. a titration procedure for the micro-volume, but if the digested

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D 1252 06
samples do not clear or spectrophotometric interference is sulfuric acid (H2SO4) (sp gr 1.84) and 33.3 g of mercuric
suspected, the COD result can be determined by titration.6 sulfate (HgSO4) to about 750 mL of water, mix, and cool.
20.5 The ampule or tube must have window areas that are Dilute the solution to 1 L with water and mix thoroughly.
free of scratches or smudges. If a suitable window area is not 22.4 Ferrous Ammonium Sulfate Solution (0.10 N)Dilute
available, do not consider transfer of the sample. The sample 400 mL of 0.25 N ferrous ammonium sulfate solution (see 14.1
and the blank may be titrated and the results used to calculate to 1 L. Standardize against 0.25 N potassium dichromate
a COD value (see 24.10). (K2Cr2O7) as in 14.1.
22.5 Ferrous Ammonium Sulfate Solution (0.01 N)Dilute
21. Apparatus 40 mL of 0.25 N ferrous ammonium sulfate solution (see
21.1 Spectrophotometer or Filter Photometer, suitable for section 14.1) to 1 L. Standardize against 0.025 N potassium
measurements at 600 nm and 420 nm using the ampules or dichromate (K2Cr2O7) as in 14.1.
tubes in 21.3 or 21.3.1 as absorption cells. Filter photometers 22.6 Phenanthroline Ferrous Sulfate Indicator Solution
and photometric practices shall conform to Practice E 60. See 14.4. If desired, the indicator may be diluted 1:5 for use in
Spectrophotometers shall conform to Practice E 275. For some this test method.
spectrophotometers, poor sensitivity at 420 nm has been
observed. A suggested minimum sensitivity for the spectropho- 23. Calibration
tometer readout is 0.002 absorbance units per milligram per 23.1 High RangeDilute the following volumes of COD
litre of COD for the low range procedure. standard solution (see 22.2) to 50 mL with water. The high
21.2 Heating Oven, sand bath, or block heater capable of range procedure may be used for COD determination as low as
maintaining a temperature of 150 6 2C throughout. If an oven 25 mg/L at the discretion of the analyst.
is used and screw-top tubes are employed, ascertain that the
caps can withstand the oven temperature and solution pressure. Potassium Acid Phthalate
The heating device must be equipped with a high temperature Standard Solution, mL COD, mg/L
shut-off set at 175 to 185C. 2.5 50
5 100
21.3 Culture Tubes, borosilicate glass, 16 by 100 mm, with 10 200
TFE-fluorocarbon-lined screw caps. Protect the caps and cul- 20 400
ture tubes from dust contamination. 30 600
40 800
21.3.1 Ampules, borosilicate glass, 10 mL, may be substi-
tuted for the culture tubes in 21.3. These ampules are rotated NOTE 5A typical COD calibration curve for spectrophotometric COD
and uniformly sealed with a glass blowing torch after addition method, ampule technique (Test Method B) is shown in Fig. 3.
of sample and reagent solutions. The nominal path length of 23.2 Low RangeDilute the following volumes of potas-
these ampules shall be 15 to 20 mm. sium acid phthalate standard solution to 200 mL with water. At
21.4 Apparatus for Blending or Homogenizing SamplesA the discretion of the analyst, the upper limit may be extended
tissue homogenizer is recommended. However, a household to approximately 150 mg/L.
blender may be used, but a suitable reduction in particle size Potassium Acid Phthalate
may not be obtained. Standard Solution, mL COD, mg/L
1 5
NOTE 4A partial round robin, using cellulose filter paper as the 2 10
organic material, demonstrated serious difficulties in achieving a repre- 4 20
6 30
sentative subsample. The use of a blender followed by a tissue homog-
8 40
enizer was required. 10 50

22. Reagents 23.3 Use the procedure in Section 24 to analyze the pre-
22.1 Silver Sulfate Catalyst SolutionDissolve 22 g of pared standard solutions and a procedural blank of water. For
silver sulfate (Ag2SO4) in a 4.09 kg (9 lb) bottle of concen- the high COD range, determine the spectrophotometric absor-
trated sulfuric acid (H2SO4). bance of each standard and blank at a wavelength of 600 nm.
22.2 Potassium Acid Phthalate Solution, Standard (1
mL = 1 mg/L)See 14.5.
22.3 Potassium Dichromate Digestion Solution:
22.3.1 High RangeAdd 10.216 g of potassium dichromate
(K2Cr2O7) dried at 103C for 2 h, 167 mL of concentrated
sulfuric acid (H2SO4) (sp gr 1.84) and 33.3 g of mercuric
sulfate (HgSO4) to about 750 mL of water, mix, and let cool.
Dilute the solution to 1 L with water and mix thoroughly.
22.3.2 Low RangeAdd 1.022 g of potassium dichromate,
(K2Cr2O7) (dried at 103C for 2 h), 167 mL of concentrated

6
Messenger, A. L., Comparison of Sealed Digestion Chamber and Standard
Method COD Tests, Journal Water Pollution Control Federation, Vol 53, Number FIG. 3 Typical COD Calibration Curve for Spectrophotometric
2, February 1981, pp. 232236. COD Method, Ampule Technique (Test Method B)

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 D 1252 06
For the low COD range, determine the spectrophotometric to settle (normally about 30 min). Rapid cooling will generate
absorbance of each standard and blank at a wavelength of 420 colloidal precipitates that are difficult to settle.
nm. Since the change in absorbance for the low range is 24.8 Make spectrophotometric readings using the ampules
negative with increasing COD, it may be convenient to read the or culture tubes as the absorption cells. Transfer of cooled
blank and standards against water and plot the absorbance solution should not be considered because the solution is
difference versus COD concentration. supersaturated and solids will precipitate that are difficult to
23.4 Prepare calibration curves for each range by plotting settle.
the absorbance of each standard on the abscissa and milligrams 24.9 Measure the absorbance of the low range solutions at
per litre of COD on the ordinate. For the low range procedure, 420 nm and the high range solutions at 600 nm. (See Note 3.)
the correlation will have a negative slope; for the high range 24.10 Precision and bias in this test method has not ad-
procedure, the slope is positive. dressed a titration procedure for the micro-volume, but if a
spectrophotometric interference is suspected because of turbid-
24. Procedure ity or possibly high results, the result may be checked by
24.1 Place 1.5 mL of digestion solution (22.3.1 for the high titrating the suspected sample and the blank. Add one drop of
range procedure or 22.3.2 for the low range procedure) in a phenanthroline ferrous sulfate solution (22.6), and titrate to the
culture tube (21.3) or glass ampule (21.3.1). color change with 0.1 N ferrous ammonium sulfate solution
(22.4) for high range samples or with 0.01 N ferrous ammo-
NOTE 6Accurate addition of the digestion volume in the low range nium sulfate solution (22.5) for low range samples. Follow the
procedure is important because the loss of hexavalent chromium is
measured.
same procedure with the procedural blank. The titrant volume
for the blank will be about 3 mL. If this volume is not available
24.2 Add 3.5 mL of silver sulfate catalyst solution (22.1),
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in the ampule or tube, the digested sample must be transferred

mix, and allow to cool. If the mixed reagents are to be stored, to a container of suitable volume for titration. Calculate the
store the sealed or capped solution in the dark. COD using the equation in Test Method A (16.1).
NOTE 7Several manufacturers offer similar catalyst and digestion
solutions already combined in ampules or culture tubes. If the commercial
25. Calculation
preparations are used, the manufacturers directions as to sample size 25.1 Determine the COD value directly from the respec-tive
should be followed. The analyst should visually inspect any purchased calibration curves constructed for the purpose. See Section 23.
system to determine that reagent volumes are uniform and should develop 25.1.1 If the sample was prediluted, apply the appropriate
calibration curves to confirm or replace precalibrated readouts. dilution factor to the result.
24.3 Homogenize the sample if necessary. 25.2 Report all results in milligrams per litre.
24.4 Carefully add 2.5 mL of the sample, standard, or blank
down the side of the tube or ampule so that a layer is formed 26. Precision and Bias 7
on top of the reagents. Cap the tubes or seal the ampules. 26.1 Precision and bias information was developed in a
24.5 Mix the sealed ampules or tubes thoroughly. It is collaborative test by seven laboratories with Type II water. For
feasible to mix tubes by holding the tube by the cap and other matrices, these data may not apply. Each prepared sample
shaking vigorously. Complete integrity of the TFE- was analyzed on three different days by the same operator in
fluorocarbon liner in the screw cap is imperative. The ampule each laboratory.
or tube will become hot because of heat of solution. 26.2 Test samples were prepared by dissolving weighed
(WarningIf handling the ampule or tube directly, use amounts of potassium acid phthalate in Type II water. Four sets
insulated gloves, or place the ampules or tubes in a rack for of samples, two sets for the low COD range and two sets for
mixing. Use normal laboratory precautions for possible contact the high COD range, were submitted to the laboratories.
with the hot, corrosive reagents from broken ampules or tubes.) 26.3 The laboratories followed instructions to dilute one
24.6 After mixing, place the ampules or tubes in an oven or sample set in each range with Type II water. The resulting
heating device at 150 6 2C for 2 h. dilutions provided concentrations of 5, 12, 27, and 45 mg/L
24.7 Allow the ampules or tubes to cool at room tempera- COD in the low range and 27, 90, 350, and 750 mg/L in the
ture. After about 5 min, mix the contents of the ampule or tube high range.
thoroughly (to mix condensed water into the solution). There- 26.4 The other set of samples in each range was diluted with
after, permit the solution to cool and permit precipitated solids Type II water plus 1000 mg/L of chloride ion to provide the
same COD concentrations in the low and high ranges as
identified in 26.3.
TABLE 3 Test Method B, Recovery, Precision and Bias for Low 26.5 Recovery, overall precision, and bias results for the
Range, Type II Water low range samples, Type II water, are presented in Table 3 and
Amount Amount Standard
Statistical are shown in Fig. 4.
Bias, Significance
Added, Recovered, Deviation,
6% (95% confi-
26.6 Recovery, overall precision, and bias results for the
mg/L mg/L mg/L
dence level) low range samples, Type II water plus 1000 mg/L of chloride
5 6.76 4.02 +35 no ion, are presented in Table 4 and are illustrated in Fig. 5.
12 13.10 3.37 +9 no
27 26.10 2.86 5 no
7
45 43.91 3.69 2 no Supporting data are available from ASTM Headquarters. Request RR: D19-
1044.

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D 1252 06

FIG. 4 Test Method B, Correlation of Collaborative Test Data COD

Determination by Micro Procedure Type II Water FIG. 5 Test Method B, Correlation of Collaborative Data COD
Determination by Micro Procedure Type II Water Plus 1000 mg/L
Chloride Ion
TABLE 4 Test Method B, Recovery, Precision and Bias for Low
Range, Type II Water plus 1000 mg/L Chloride Ion
TABLE 5 Test Method B, Recovery, Precision and Bias for High
Statistical
Amount Amount Standard Range, Type II Water
Bias, Significance
Added, Recovered, Deviation,
6% (95 % confi- Statistical
mg/L mg/L mg/L Amount Amount Standard
dence level Bias, Significance
Added, Recovered, Deviation,
6% (95 % confi-
5 9.33 8.15 +87 yes mg/L mg/L mg/L
dence level)
12 17.39 7.89 +45 yes
27 28.65 5.23 +6 no 27 26.61 4.55 1 no
45 44.56 8.02 1 no 90 92.00 23.13 +2 no
350 329.00 44.15 6 no
750 736.07 20.11 2 yes

26.7 Recovery, overall precision, and bias results for the

high range samples, Type II water, are presented in Table 5 and
are illustrated in Fig. 6. 27. Quality Control (QC)
26.8 Recovery, overall precision, and bias results for the In order to be certain that analytical values obtained using
high range samples, Type II water plus 1000 mg/L of chloride this test method are valid and accurate within the confidence
ion, are presented in Table 6 and are illustrated in Fig. 7. limits of the test, the following QC procedures must be
26.9 The higher positive bias and lower precision at lower followed when running the test.
concentrations of COD in the presence of chloride ion is not The samples are always performed in a batch that consists of
fully understood. All of the bias may not be the result of a set of samples accompanied by control samples. Batches
oxidation of chloride ion to chlorine. Laboratories identified must be sized such that the control samples in the batch can be
problems with turbidity, but turbidity causes a negative bias in assured to be indicative of the variables affecting the remaining
the low range procedure. A secondary source of positive bias samples in the batch. All variables affecting the batch must
may have been organic material adsorbed from laboratory affect all samples in the batch in a statistically equivalent
atmosphere on the sodium chloride added to the dilution water. manner. The maximum size of a batch is determined by
26.10 The negative bias in results at the 750 mg/L concen- identifying the key variables affecting the batch and assuring
tration may have been partially a result of incomplete transfer that these variables do not vary significantly during a batch. If
of the sample from the shipment bottle to the prepared dilution. batch sizes are too large, the user runs the risk of inappropri-
When refrigerated, the potassium acid phthalate, at the shipped ately rejecting portions of a batch. If batch sizes are too small,
concentration, was observed to crystallize from solution on the the cost of control sample analysis becomes higher.
surface of the sample bottle. Laboratories were notified of the In addition to other factors limiting batch size indicated in
problem. this section, the following variables must remain constant

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 D 1252 06

FIG. 6 Test Method B, Correlation of Collaborative Test Data COD

Determination by Micro Procedure Type II Water

TABLE 6 Test Method B, Recovery, Precision and Bias for High

Range, Type II Water plus 1000 mg/L Chloride Ion
Statistical
Amount Amount Standard
Bias, Significance
Added, Recovered, Deviation,
6% (95 % confi-
mg/L mg/L mg/L
dence level)
27 42.06 7.76 +56 yes
90 92.83 14.18 +3 no
350 331.44 52.56 5 no
750 686.89 104.00 8 yes
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during a batch: analyst, instrument, and day. Recommended tion of stock solutions used to prepare calibration standards.
maximum batch sizes are specified in the table below These results will verify the accuracy of the calibration
Batch type Maximum batch size standards.
Method A 20 27.2 Initial demonstration of laboratory capability
Method B 50
An initial demonstration of capability must be performed if a
27.1 Calibration and calibration verification laboratory has not performed the test before or reperformed if
27.1.1 Instrumentfor Method B. either the instrument or analyst changes to assure that results
27.1.1.1 A calibration curve must be prepared with each equivalent to those obtained in the method collaborative study
batch of samples as specified in section 23. The calibration can be achieved.
standards must be digested with the samples in the batch. 27.2.1 For method A and method B, high range, prepare a
27.1.1.2 Calibration must be verified at the end of the batch 100 mg/L standard of primary grade potassium acid phthalate
by checking a mid-range standard. The measured COD must be (as in section 23.3). For method B, low range, prepare a 30
within 10 % of the rated value of the standard. mg/L standard (as in section 23.2). Analyze seven replicates of
27.1.1.3 If the calibration check fails, check for and resolve the appropriate standard.
any spectrophotometer problems. Recalibrate the spectropho-
27.2.2 Calculate the mean and standard deviation of the
tometer and re-measure the absorbance of the ampules or
seven values and compare to the acceptable ranges of precision
tubes.
and bias in the following table. The demonstration must be
27.1.2 Standardizationfor Method A
repeated until the single operator precision and the mean
27.1.2.1 Ferrous Ammonium sulfate Solution titrant (sec-
recovery are with the limits given.
tion 14.1) must be re-standardized with each batch of samples
Acceptable range Acceptable range
analyzed. The batch must be completed with one preparation of Method/Level
of recovery of precision
titrant. Method A (100 mg/L) 86106 mg/L <6.9 mg/L
27.1.3 Independent reference material (IRM) Method B, High Range (100 mg/L) 69135 mg/L <20 mg/L
Method B, Low Range (30 mg/L) 2337 mg/L <5 mg/L
Analyze a certified reference material following the prepara-

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 D 1252 06

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FIG. 7 Test Method B, Correlation of Collaborative Test Data COD
Determination by Micro Procedure Type II Water Plus 1000 mg/L
Chloride Ion

If a concentration other than that specified above is used for distilled water, especially when a new lot of reagents is used.
laboratory capability testing, refer to D 5847 for information Any significant increase in blank absorbance should be inves-
on applying the F test and t test in evaluating the acceptability tigated.
of the mean and standard deviation. 27.5 Sample spiking and replicates
27.3 Laboratory control sample (LCS) 27.5.1 Spiking
To insure that the performance of the test method is in control,
Chemical Oxygen Demand is a composite, procedurally
one LCS must be analyzed with each batch of samples to
defined analyte. Recovery of constituents is a composite
assure continued performance within the limits established by
function of the recoveries of each compound present. For this
the method collaborative testing.
reason, spiking a sample with a pure material with an experi-
The LCS will be the same material and concentration used mental COD does not reveal anything about the absolute level
for the initial demonstration of capability and must be taken
of recovery of the constituents in the original sample. Com-
through all of the steps of the analytical method, including
parison of matrix specific results across various oxygen de-
preservation and pretreatment. The result obtained for the LCS
mand methods and calculations of theoretical COD from
must fall within the limits in the table below.
constituent analysis may reveal the presence of refractory
Batch type LCS acceptance range compounds.
Method A 100 mg/L 6 12 mg/L
Method B, high range 100 mg/L 6 30 mg/L 27.5.2 Replicates
Method B, low range 30 mg/L 6 8 mg/L
It is the responsibility of the method user to assure that
If the result does not fall within these limits, analysis of reported results are of known and acceptable precision. Repli-
samples is halted until the problem is corrected, and either all cates by matrix and level should be run to establish real world
samples in the batch must be re-analyzed, or the results must be sample precision. This should be done by running duplicates in
qualified with an indication that the method was not perform- numerous batches and combining the data to obtain a precision
ing within acceptance criteria. estimate. The collaborative study precision data can be used as
27.4 Method blank (Blank) a benchmark for these results. If the relative standard deviation
Method A, the amount of titrant needed for the blank is of the real world sample results is significantly larger than that
subtracted (blank correction). Analysts should monitor the from the collaborative study, the results should be annotated
amount of titrant used for blanks. Any significant change for end users.
should be investigated. 27.6 Batch control sample (BCS)
For Method B, the method blank is used as the zero 27.6.1 It is strongly recommended that a challenging control
concentration point on the calibration curve. Since the calibra- standard be run in duplicate beginning and end in each
tion standards are taken through the entire analytical process, batch. This material is intended to be responsive to critical
any absorbance due to blank levels is automatically subtracted. performance factors of the method, specifically, chloride inter-
Analysts should monitor the absorbance of the blank against ference and catalyst effectiveness.

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27.6.2 This BCS should be made to have approximately the of-control conditions on a BCS should be investigated and the
same COD levels as used in the initial demonstration of batch re-analyzed. Up-dating of these control chart limits
capability. 100 % of the COD should come from high purity should never cause the control limits to broaden without
acetic acid. In addition, the BCS should have 1000 mg/L sufficient cause.
background chloride level. 27.6.4 Once these control charts have been established, they
Alternatively, diluted substitute wastewater (D 5905), spiked can replace the regular use of the Laboratory Control Sample.
with acetic acid may be used as the BCS. In either case, it is The LCS should still be run periodically to assure compliance
vital that the BCS can be made up routinely and reproducibly. with the control limits established in the method.
27.6.3 After performance of the method has been validated
through the initial demonstration of capability, collect 20 to 30 28. Keywords
pairs of BCS data. Construct Shewhart control charts for 28.1 chemical oxygen demand; COD; demand; oxygen
precision (range chart) and recovery (X-bar chart). Any out- demand

APPENDIX

(Nonmandatory Information)

X1. PRETREATMENT OF WASTEWATER SAMPLES

X1.1 Chloride can cause a positive interference when The COD digestion vial can be placed in a small Erlenmeyer
determining the chemical oxygen demand of wastewater flask on an analytical balance. This sample will be used for
samples. Samples with chloride levels up to 4 % can be treated blank correction.
with a styrene based cation exchange resin in the silver form X1.2.4 A small amount of each sample (5 mL) should be
with a capacity of 4.5 meq for the removal of chloride, used to purge the pre-rinsed filters. Each neutralized sample
bromide, and iodide. The pretreatment described in this appen- should be treated as in section X1.2.3.

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dix was not evaluated during the interlaboratory study; there- X1.2.5 Prepare the calibration standards in 1 wt. percent
fore, the user of this procedure is responsible for determining sodium chloride (10 g NaCl per liter of reagent water) at the
the actual precision and bias for each particular sample type. COD concentration levels in this standard.
The treated samples are analyzed by Test Method D 1252 as X1.2.6 Digest the samples and standards as directed in Test
described in Test Method B, Micro COD Procedure. The Method B of this standard.
reported result should be designated as dissolved COD since
the sample must be filtered during the pretreatment. X1.3 Discussion
X1.3.1 The supporting data were obtained from a single
X1.2 Procedure
laboratory and were not evaluated according to Practice
X1.2.1 Due to the silver contained in the cation exchange D 2777. The data contained in Table X1.1,Table X1.2, and Fig.
resin filters, samples need to be neutralized prior to filtration to X1.1 show the analytical results for COD using the procedure
prevent leaching, which may interfere with the analysis. Since in this appendix. The data present the percent recovery of KHP
sulfuric acid is the common preservative a NaOH solution can at 20 mg/L and 100 mg/L at various levels of chloride.
be used for neutralization. If the preserved samples are highly
acidic, a more concentrated NaOH solution can be used thus TABLE X1.1 Single Laboratory Evaluation, Chloride
preventing dilution of the sample. Concentration vs. Spike Recoveries
X1.2.2 Rinse the cation exchange resin filter by drawing 10 Chloride Concentration 20 mg/L KHP, 100 mg/L KHP,
mL of reagent water into a disposable syringe and placing the (mg/L) COD Recovery (%) COD Recovery (%)
filter on the end of the syringe. Displace the deionized water 3035 96 106
through the filter into a waste container. Each filter will have to 12 140 84 99
be rinsed with reagent water prior to filtering a sample. 18 210 111 104
24 280 114 100
X1.2.3 Weigh 2 g of reagent water through a prerinsed 36 420 106 104
cation exchange resin filter directly into a COD digestion vial.

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 D 1252 06
TABLE X1.2 Single Laboratory Duplicates
KHP Spiked Salt Solutions COD Result (mg/L) RPDA
100 mg/L KHP in 5000 ppm NaCl 106.7 3.0
110
20 mg/L KHP in 30 000 ppm NaCl 24.5 1.2
24.8
100 mg/L KHP in 30 000 ppm NaCl 106.3 0.4
106.7
20 mg/L KHP in 40 000 ppm NaCl 24.5 5.9
26
100 mg/L KHP in 40 000 ppm NaCl 102 0.0 FIG. X1.1 Chloride Concentration vs. Spike Recoveries
102
A
RPD=Relative percent difference.

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