1、Designation: D 1252 06Standard Test Methods forChemical Oxygen Demand (Dichromate Oxygen Demand) ofWater1This standard is issued under the fixed designation D 1252; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last r
2、evision. A number in parentheses indicates the year of last reapproval. Asuperscript 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. Scope1.1 These test methods cover the determination
3、 of thequantity of oxygen that certain impurities in water willconsume, based on the reduction of a dichromate solutionunder specified conditions. The following test methods areincluded:Test Method AMacro COD by Reflux Digestion and TitrationTest Method BMicro COD by Sealed Digestion and Spectrometr
4、y1.2 These test methods are limited by the reagents employedto a maximum chemical oxygen demand (COD) of 800 mg/L.Samples with higher COD concentrations may be processed byappropriate dilution of the sample. Modified procedures ineach test method (Section 15 for Test MethodAand Section 24for Test Me
5、thod B) may be used for waters of low CODcontent ( 50 mg/L).1.3 As a general rule, COD results are not accurate if thesample contains more than 1000 mg/LCl. Consequently, thesetest methods should not be applied to samples such asseawaters and brines unless the samples are pretreated asdescribed in A
6、ppendix X1.1.4 This test method was used successfully on a standardmade up in reagent water. It is the users responsibility toensure the validity of these test methods for waters of untestedmatrices.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its
7、use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. For specific hazardstatements, see Sections 8, 15.6, and 24.5.2. Referenced Documents2.1 ASTM Standards:2D 1129 Ter
8、minology Relating to WaterD 1193 Specification for Reagent WaterD 2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD 3223 Test Method for Total Mercury in WaterD 3370 Practices for Sampling Water from Closed ConduitsD 5905 Practice for the Prep
9、aration of Substitute Wastewa-terE60 Practice for Analysis of Metals, Ores, and RelatedMaterials by Molecular Absorption SpectrometryE 275 Practice for Describing and Measuring Performanceof Ultraviolet, Visible, and Near-Infrared Spectrophotom-eters3. Terminology3.1 DefinitionsFor definitions of ot
10、her terms used in thesetest methods, refer to Terminology D 1129.3.2 The term “oxygen demand” (COD) in these test meth-ods is defined in accordance with Terminology D 1129 asfollows:3.2.1 oxygen demandthe amount of oxygen required un-der specified test conditions for the oxidation of water borneorga
11、nic and inorganic matter.4. Summary of Test Methods4.1 Most organic and oxidizable inorganic substancespresent in water are oxidized by a standard potassium dichro-mate solution in 50 % sulfuric acid (vol/vol). The dichromateconsumed (Test Method A) or tri-valent chromium produced(Test Method B) is
12、determined for calculation of the CODvalue.1These test methods are under the jurisdiction of ASTM Committee D19 onWater and are the direct responsibility of Subcommittee D19.06 on Methods forAnalysis for Organic Substances in Water.Current edition approved Feb. 15, 2006. Published February 2006. Ori
13、ginallyapproved in 1953. Last previous edition approved in 2000 as D 1252 00.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page ont
14、he ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.2 The oxidation of many otherwise refractory organics isfacilitated by the use of silver sulfate that acts as a catalyst inthe reaction.4.3 These test methods provide
15、for combining the reagentsand sample in a manner that minimizes the loss of volatileorganic materials, if present.4.4 The oxidation of up to 1000 mg/L of chloride ion isinhibited by the addition of mercuric chloride to form stableand soluble mercuric sulfate complex. A technique to removeup to 40 00
16、0 mg/L chloride is shown in Appendix X1 for TestMethod B. The maximum chloride concentration that may betolerated with the procedure for low COD, Test Method A(15.11), has not been established.4.5 The chemical reaction involved in oxidation of materialsby dichromate is illustrated by the following r
17、eaction withpotassium acid phthalate (KC8H5O4):41 H2SO41 10 K2Cr2O71 2KC8H5O410 Cr2SO4!31 11 K2SO41 16 CO21 46 H2OSince 10 mol of potassium dichromate has the same oxida-tion power as 15 mol of oxygen, the equivalent reaction is:2KC8H5O41 15 O21 H2SO416 CO21 6H2O 1 K2SO4Thus 2 mol of potassium acid
18、phthalate consumes 15 mol ofoxygen. The theoretical COD of potassium acid phthalate is1.175 g of oxygen per gram of potassium acid phthalate (Table1).5. Significance and Use5.1 These test methods are used to chemically determine themaximum quantity of oxygen that could be consumed bybiological or na
19、tural chemical processes due to impurities inwater. Typically this measurement is used to monitor andcontrol oxygen-consuming pollutants, both inorganic and or-ganic, in domestic and industrial wastewaters.5.2 The relationship of COD to other water quality param-eters such as TOC and TOD is describe
20、d in the literature.36. Interference and Reactivity6.1 Chloride ion is quantitatively oxidized by dichromate inacid solution. (1.0 mg/Lof chloride is equivalent to 0.226 mg/Lof COD.) As the COD test is not intended to measure thisdemand, concern for chloride oxidation is eliminated up to1000 mg/L of
21、 chloride by complexing with mercuric sulfate.6.1.1 Up to 40 000 mg/L chloride ion can be removed witha cation based ion exchange resin in the silver form asdescribed in Appendix X1 when using Test Method B. Sincethis pretreatment was not evaluated during the interlaboratorystudy, the user of the te
22、st method is responsible to establish theprecision and bias of each sample matrix.6.2 Oxidizable inorganic ions, such as ferrous, nitrite,sulfite, and sulfides are oxidized and measured as well asorganic constituents.7. Reagents7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests.
23、All reagents shall conform to the specificationsof the Committee on Analytical Reagents of the AmericanChemical Society, where such specifications are available.47.2 Purity of WaterUnless otherwise indicated, referenceto water shall be understood to mean reagent water that meetsthe purity specificat
24、ions of Type I or Type II water, presentedin D 1193.8. Hazards8.1 Exercise extreme care when handling concentrated sul-furic acid, especially at the start of the refluxing step (15.7).8.2 Silver sulfate is poisonous; avoid contact with thechemical and its solution.8.3 Mercuric sulfate is very toxic;
25、 avoid contact with thechemical and its solution.3Handbook for Monitoring Industrial Wastewater, U.S. Environmental Protec-tion Agency, Aug. 1973, pp. 5-10 to 5-12.4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing o
26、f reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,MD.TABLE 1 Test Method A, Recovery of Theoretical COD f
27、orVarious Organic MaterialComponentReactivity, Percent of Theoretical1A2B3C4D5EAliphatic CompoundsAcetone 98 . 96 94 .Acetic acid 92 92 98 . .Acrolein 62 . . . .Butyric acid 89 93 . . .Dextrose 95 . . . .Diethylene glycol 93 . . 70 .Ethyl acetate 95 . . 85 .Methyl ethyl ketone 98 . . 90 .Aromatic Co
28、mpoundsAcetophenone 89 . . . .Benzaldehyde . . . 80 .Benzene 6098 . 41 . .Benzoic acid 98 . . 100 .Dioctyl phthalate 83 . . . .Diphenyl 81 . . . .o-cresol 95 . . 95 .Toluene 83 . . 45 .Potassium acidphthalate100 . . . .Nitrogen CompoundsAcrylonitrile 48 . . 44 .Adenine . . . . 59Aniline 80 . . 74 .B
29、utyl amine 57 . . . .Pyridine 0 . 1 . 2Quinoline . . . . 87Trimethylamine 1 . . . .Tryptophane . . . . 87Uric acid . . . . 61AHamilton, C. E., unpublished data.BMoore, W. A., and Walker, W. W., Analytical Chemistry, Vol 28, 1956, p 164.CDobbs, R. A., Williams, R. T., ibid., Vol 35, 1963 p. 1064.DBuz
30、zell, J. C., Young, R. H. F., and Ryckman, D. W.,“ Behaviors of OrganicChemicals in the Aquatic Environment; Part II, Dilute Systems,” ManufacturingChemists Association, April 1968, p. 34.EChudoba, J., and Dalesicky, J., Water Research, Vol 7, No. 5, 1973, p. 663.D12520629. Sampling9.1 Collect the s
31、ample in accordance with Practices D 3370.9.2 Preserve samples by cooling to 4C if analyzed within24 h after sampling, or preserve for up to 28 days at 4C andatpH2byaddition of concentrated sulfuric acid. Theaddition of 2 mL of concentrated sulfuric acid per litre at thetime of collection will gener
32、ally achieve this requirement. Theactual holding time possible without significant change in theCOD may be less than 28 days, especially when easilyoxidizable substances are present. It is the responsibility of theusers of the test method to ensure the maximum holding timefor their samples.TEST METH
33、OD AMACRO COD BY REFLUX DIGESTION AND TITRATION10. Scope10.1 The amount of dichromate consumed in Test MethodAis determined by titration rather than the spectrophotometricprocedure used in Test Method B. This test method is appro-priate where larger sample volumes would provide betterprecision and b
34、etter representativeness of where equipment orspace limitations exist.10.2 The precision of this test method in standard solutionscontaining low-volatility organic compounds has been exam-ined in the range of approximately 10 to 300 mg/L.11. Summary of Test Method11.1 The sample and standardized dic
35、hromate solution, in a50 % by volume sulfuric solution, is refluxed for a 2-hdigestion period.11.2 Excess dichromate after the digestion period is titratedwith a standard ferrous ammonium sulfate solution usingortho-phenanthroline ferrous complex as an internal indicator.12. Interferences12.1 The te
36、st method does not uniformly oxidize all organicmaterials. Some compounds, for example, are quite resistant tooxidation, while others, such as carbohydrates, are easilyoxidized. A guide to the behavior of various types of organicmaterials is provided in Table 1.12.2 Volatile organics that are diffic
37、ult to oxidize may bepartially lost before oxidation is achieved. Care in maintaininga low-solution temperature (about 40C) and permitting oxi-dation to proceed at the lower temperature for a period of timebefore reflux is initiated will result in higher recoveries oftheoretical COD of volatile orga
38、nics.13. Apparatus13.1 Reflux ApparatusThe apparatus consists of a500-mL Erlenmeyer or a 300-mL round-bottom flask, made ofheat-resistant glass connected to a 300-mm (12-in.) Allihncondenser by means of a ground-glass joint. Any equivalentreflux apparatus may be substituted, provided that a ground-g
39、lass connection is used between the flask and the condenser,and provided that the flask is made of heat-resistant glass.13.2 Sample Heating ApparatusA heating mantle or hotplate capable of delivering sufficient controlled heat to main-tain a steady reflux rate in the reflux apparatus is satisfactory
40、.13.3 Apparatus for Blending or Homogenizing SamplesAhousehold blender is satisfactory.14. Reagents14.1 Ferrous Ammonium Sulfate Solution (0.25 N)Dissolve 98.0 g of ferrous ammonium sulfate solution(FeSO4(NH4)SO46H2O) in water. Add 20 mL of sulfuric acid(H2SO4, sp gr 1.84), cool and dilute to 1 L. S
41、tandardize thissolution daily before use. To standardize, dilute 25.0 mL of0.25 N potassium dichromate solution (K2Cr2O7) to about 250mL. Add 20 mL of sulfuric acid (sp gr 1.84) and allow thesolution to cool. Titrate with the ferrous ammonium sulfatesolution to be standardized, using the phenanthrol
42、ine ferroussulfate indicator as directed in 15.10. Calculate the normalityas follows:N 5 A 3 B!/Cwhere:N = normality of the ferrous ammonium sulfate solution,A = potassium dichromate solution, mL,B = normality of the potassium dichromate solution, andC = ferrous ammonium sulfate solution, mL.14.2 Fe
43、rrous Ammonium Sulfate Solution (0.025 N)Dilute 100 mL of 0.25 N ferrous ammonium sulfate solution to1 L. Standardize against 0.025 N potassium dichromate solu-tion as in 14.1. This solution is required only if COD isdetermined in the range of 10 to 50 mg/L.14.3 Mercuric SulfatePowdered mercuric sul
44、fate(HgSO4).14.4 Phenanthroline Ferrous Sulfate Indicator SolutionDissolve 1.48 g of 1,10-(ortho)-phenanthroline monohydrate,together with 0.70 g of ferrous sulfate (FeSO47H2O), in 100mL of water. This indicator may be purchased already pre-pared.14.5 Potassium Acid Phthalate Solution, Standard (1mL
45、 = 1 mg COD)Dissolve 0.851 g of potassium acid phtha-late (KC8H5O4), primary standard, in water and dilute to 1 L.14.6 Potassium Dichromate Solution, Standard (0.25 N)Dissolve 12.259 g of potassium dichromate (K2Cr2O7) primarystandard grade, previously dried at 103C for 2 h, in water anddilute to 1
46、L in a volumetric flask.14.7 Potassium Dichromate Solution, Standard (0.025N)Dilute 100.0 mL of 0.25 N potassium dichromate solutionto 1 L. This solution is necessary only for determination ofCOD in the range of 10 to 50 mg/L.14.8 Sulfuric Acid-Silver Sulfate SolutionDissolve 15 g ofpowdered silver
47、sulfate (Ag2SO4) in 300 mL of concentratedsulfuric acid (sp gr 1.84) and dilute to 1 L with concentratedsulfuric acid (sp gr 1.84).D125206315. Procedure15.1 Homogenize the sample by blending if necessary.Place 50.0 mLof the sample in a reflux flask. If less than 50 mLof the sample is used, make up t
48、he difference in water, then addthe sample aliquot and mix. Samples containing more than 800mg/LCOD are diluted and mixed precisely with water and 50.0mL of the diluted sample are placed in a reflux flask.NOTE 1If the sample is diluted, it must consume at least 5 mL ofdichromate. Dilute the sample i
49、f more than 20 mL of the titrant is neededto reach the endpoint.15.2 Place 50 mL of water in a reflux flask for the blankdetermination.15.3 Place the reflux flasks in an ice bath and add1gofpowdered mercuric sulfate, 5.0 mL of concentrated sulfuricacid, and several glass beads or boiling stones. Mix well tocomplete dissolution.15.4 With the flasks still in the ice bath, add slowly and withstirring, 25.0 mL of 0.25 N standard potassium dichromatesolution.15.5 With the flasks still in the ice bath, add 70 mL ofsulfuric acid-silver sulfate solution slowl
