1、Designation: D 1253 08Standard Test Method forResidual Chlorine in Water1This standard is issued under the fixed designation D 1253; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses
2、 indicates the year of last reapproval. Asuperscript epsilon () 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 This test method covers the determination of residualchlorine in water by d
3、irect amperometric titration.1.2 Within the constraints specified in Section 6, this testmethod is not subject to commonly encountered interferencesand is applicable to most waters. Some waters, however, canexert an iodine demand, usually because of organic material,making less iodine available for
4、measurement by this testmethod. Thus, it is possible to obtain falsely low chlorinereadings, even though the test method is working properly,without the users knowledge.1.3 Precision data for this test method were obtained onestuary, inland main stem river, fresh lake, open ocean, andfresh cooling t
5、ower blowdown water. Bias data could not bedetermined because of the instability of solutions of chlorine inwater. It is the users responsibility to ensure the validity of thetest method for untested types of water.1.4 In the testing by which this standard was validated, thedirect and back starch-io
6、dide titrations and the amperometricback titration, formerly part of this standard, were found to beunworkable and were discontinued in 1986. Historical infor-mation is presented in Appendix X1.NOTE 1Orthotolidine test methods have been omitted because of poorprecision and accuracy.1.5 The values st
7、ated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety a
8、nd health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 1129 Terminology Relating to WaterD 1193 Specification for Reagent WaterD 2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Commit
9、tee D19 on WaterD 3370 Practices for Sampling Water from Closed ConduitsD 5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water Analysis3. Terminology3.1 Definitions: For definitions of terms used in this testmethod, refer to Terminology D 1129.3.2 Definitions o
10、f Terms Specific to This Standard:3.2.1 combined residual chlorine, nresidual consisting ofchlorine combined with ammonia nitrogen or nitrogenouscompounds.3.2.2 free available chlorine residual, nresidual consist-ing of hypochlorite ions, hypochlorous acid, or a combinationthereof.3.2.3 total residu
11、al chlorine (chlorine residual), ntheamount of available chlorine-induced oxidants present in waterat any specified period, subsequent to the addition of chlorine.NOTE 2Chlorine present as chloride is neither included in these termsnor determined by this test method.NOTE 3Bromine, bromine combined w
12、ith ammonia or nitrogenouscompounds, and chlorine dioxide are not distinguished by this test methodfrom the corresponding chlorine compounds.4. Summary of Test Method4.1 This is an amperometric titration test method utilizingphenylarsine oxide as the titrant. When the titrator cell isimmersed in a s
13、ample containing chlorine, current is generated.As phenylarsine oxide is added, the chlorine is reduced and thegeneration of current ceases. When chlorine is present as achloramine, potassium iodide is added, releasing iodine, whichis titrated in a similar manner. The iodine content is calculatedin
14、terms of free chlorine.1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.05 on Inorganic Constituentsin Water.Current edition approved Oct. 1, 2008. Published October 2008. Originallyapproved in 1953. Last previous edition
15、approved in 2003 as D 1253 03.2For 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 onthe ASTM website.1Copyright ASTM International,
16、100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5. Significance and Use5.1 Chlorine is used to destroy or deactivate a variety ofunwanted chemicals and microorganisms in water and waste-water.5.2 An uncontrolled excess of chlorine in water, whetherfree available o
17、r combined, can adversely affect the subsequentuse of the water.6. Interferences6.1 This test method is not subject to interferences fromtemperature, color, or turbidity of sample.6.2 Values of pH above 8.0 interfere by slowing the reactionrate. Buffering the sample to pH 7.0 or less eliminates thei
18、nterference.6.3 Erratic behavior of the apparatus in the presence ofcupric ions has been reported.6.4 Cuprous and silver ions tend to poison the electrode ofthe titrator.6.5 Nitrogen trichloride and some N-chloro compounds areoften present as products of the chlorination of wastewatersand will titra
19、te partially as free available chlorine and partiallyas combined residual chlorine. This error can be avoided onlyin the determination of total residual chlorine.6.6 Exposure to high concentrations of free available chlo-rine causes a film-type polarization that reverses very slowly.This can be avoi
20、ded by diluting the sample with water to lessthan 10 mg/L of free available chlorine.6.7 If chlorine dioxide is present, an unknown portiontitrates as free available chlorine. Total chlorine dioxide titratesas total residual chlorine.6.8 Depending upon final pH, chlorination of waters con-taining am
21、monia or nitrogenous organic compounds can pro-duce high concentrations of dichloramine. This compoundproduces four to five times as much current as monochloram-ine. The current produced by as little as 5 mg/L of dichloram-ine can cause the microammeter pointer to read offscale even atthe end point
22、in the titration of free available chlorine. Thismay be overcome by use of an opposing voltage in theapparatus circuitry. The instruments manufacturer should beconsulted in this regard.7. Apparatus7.1 Amperometric Titration Apparatus3,4Refer to Fig. 1.NOTE 4When the titrator has been out of service
23、for a day or more,check the electrode for sensitivity by noting the rapidity of the pointerdeflection. If the pointer responds slowly after the addition of KI solution,add a small amount of biiodate. If it responds slowly to free availablechlorine, sensitize it by adding chlorine.7.2 GlasswareCondit
24、ion with water containing at least 10mg/L of residual chlorine for at least 2 h prior to use and thenrinse thoroughly.8. Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended that3Water and Sewage Works, May 1949, p.
25、 171, and Journal American WaterWorks Association, Vol 34, 1942, pp. 12271240.4Amperometric titrators are available commercially from most laboratory supplyhouses.FIG. 1 Wiring Diagram of Amperometric TitratorD1253082all reagents shall conform to the specifications of the Commit-tee onAnalytical Rea
26、gents of theAmerican Chemical Society.5Other grades may be used, provided it is first ascertained thatthe reagent is of sufficiently high purity to permit its usewithout lessening the accuracy of the determination.8.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood
27、to mean reagent water conformingto Specification D 1193, Type III, further treated to be free ofchlorine demand. Other reagent water types (Type I) may beused provided it is first ascertained that the water is ofsufficiently high purity to permit its use without adverselyaffecting the bias and preci
28、sion of the test method. Type IIIwater was specified at the time of round robin testing of thismethod. A suggested method for preparation of chlorinedemand-free water is to add approximately 20 mg/L ofavailable chlorine to Type III water, let it stand for about aweek in darkness, and then expose it
29、to sunlight until nochlorine remains. Filtration through a carbon filter is analternative process which requires less time to remove chlo-rine.8.3 pH 4.0 Buffer SolutionDissolve 243 g of sodiumacetate trihydrate and 480 g of glacial acetic acid in water anddilute to 1 L.8.4 pH 7.0 Buffer SolutionDis
30、solve 25.4 g of monobasicpotassium phosphate and 86 g of dibasic sodium phosphate inwater and dilute to 1 L.8.5 Biiodate, Solution Standard (0.0282N)Dissolve0.9163 g of potassium biiodate in water and dilute to 1 L in avolumetric flask. Store in an amber glass-stoppered bottle.8.6 Phenylarsine Oxide
31、, Solution Standard(0.00564 N)Dissolve 0.8 g of phenylarsine oxide in 150 mL of sodiumhydroxide solution (12 g/L). After settling, decant 110 mL ofthis solution, add 800 mL of water, and bring to a pH of 9.0 byadding hydrochloric acid (1 + 1). This should require about 2mL of HCl (1 + 1). Continue a
32、cidification with HCl (1 + 1)until a pH of 6 to 7 is reached, as indicated by a glass-electrodesystem; then dilute to a total volume of 1L. Standardize to0.00564 N against 0.0282 N biiodate solution using the titrator(7.1) as the end-point indicator. Add 1 mL of chloroform forpreservation.8.7 Potass
33、ium Iodide Solution (50 g/L)Dissolve 50 g ofKI in water and dilute to 1 L. Add1gofsodium bicarbonateto stabilize the solution. Store in an amber bottle and avoiddirect exposure to sunlight.9. Sampling9.1 Collect the sample in accordance with Practices D 3370.Take care that the sample is representati
34、ve and keep it awayfrom direct sunlight prior to analysis.9.2 All tests should be made as soon as possible aftercollection of the sample (not more than 5 min) because theresidual chlorine may diminish with time, due to the chlorinedemand of the sample. Where time of contact is important, theelapsed
35、time between the addition of chlorine and the deter-mination of chlorine should be taken into account.10. Procedure10.1 For residual chlorine concentrations of 2.0 mg/L orless, use a 200-mL sample. For greater concentrations, use a100-mL sample. It is preferable that the size of the sample besuch th
36、at not more than 2 mL of titrant will be required tocomplete the titration.10.2 Determination of Total Residual Chlorine:10.2.1 Add 1 mL of KI solution to a 200-mL sample andimmediately add 1 mL of pH 4.0 buffer solution.10.2.2 Immerse the electrodes in the sample and start thestirrer. Adjust the mi
37、croammeter pointer of the potentiometerto the right or high current side of the scale so the pointer candeflect counterclockwise during the analysis.10.2.3 Titrate using standard phenylarsine oxide solution,adding the titrant in small increments, and noting the deflectionof the microammeter pointer.
38、 Plot the progress of the titrationon linear graph paper with current on the vertical axis andtitrant volume on the horizontal axis. Add a small volume oftitrant, wait a few seconds, and plot the current-volume pointon the graph.10.2.4 Readjust the potentiometer several times during thetitration, if
39、 necessary, to bring the pointer back on scale.10.2.5 Continue the analysis by determining at least threepoints spread over the downward sloping titration curve and atleast three points after the equivalence or end point. The latterpoints will indicate practically no change in current. Points justbe
40、fore the end point shall be disregarded in its determination.The millilitres of titrant at the end point defined by theintersection of the two linear sections of the titration curveshould be recorded.10.3 Determination of Free Available Chlorine Residual:10.3.1 Add 1 mL of pH 7.0 buffer solution to
41、a 200-mLsample.10.3.2 Repeat the phenylarsine oxide titration beginningwith 10.2.2.10.3.3 Note a rapid deflection of the pointer for eachincrement of titrant indicates the presence of free availablechlorine. Slight counterclockwise movements of the pointerafter addition of individual drops of titran
42、t is a drift effect anddoes not indicate the presence of free available chlorine.10.4 Determination of Combined Available Chlorine Re-sidual:10.4.1 Complete the titration for the determination of freeavailable chlorine residual as in 10.3.10.4.2 To the same sample, add 1 mL of KI solution and 1mL of
43、 pH 4.0 buffer solution and repeat the titration as in 10.2.11. Calculation11.1 Calculate the various types of chlorine residual, inmilligrams per litre, as follows:Chlorine residual, mg/L 5 200 A/Vwhere:5Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washingt
44、on, DC. For Suggestions on the testing of reagents notlisted by the American Chemical Society, see Annual Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.D1253083A = p
45、henylarsine oxide solution (0.00564 N) required forthe titration of 10.2, 10.3,or10.4, depending on thespecific type of chlorine residual determined, mL, andV = sample used, mL.12. Precision and Bias612.1 The overall precision (St) and the single operatorprecision (So) of this test method for free a
46、vailable chlorine(FAC) and for total residual chlorine (TRC) were determinedby eight or nine qualified cooperators each with analysisequipment and reagents at each of five sites. Each siteconstituted a different chlorinated cooling water matrix: estu-ary, inland main stem river, fresh lake, open oce
47、an, and freshcooling tower blowdown. Each site water was chlorinated up tonine levels. Samples were collected simultaneously and ana-lyzed within 5 min of collection by all eight or nine coopera-tors. Duplicate sampling and analysis runs were made at eachlevel.12.2 The Stand Sofor FAC was found to v
48、ary linearly withthe mean concentration of FAC, X, in mg/L, over the range forX from 0.0 to 1.0.12.2.1 For the pooled results from all of the matrices tested:St5 0.025 1 0.199 X n 5 37, r 5 0.848!So5 0.008 1 0.081 X n 5 35, r 5 0.638!where:n = number of runs, andr = correlation coefficients.12.3 The
49、 Stand Sofor TRC was found to vary linearly withthe mean concentration of TRC, Y, in mg/L, over the range forY from 0.0 to 3.5.12.3.1 For the pooled results from all of the matrices tested:St5 0.022 1 0.098 Y n 5 39, r 5 0.865!So5 0.012 1 0.024 Y n 5 38, r 5 0.695!12.4 The bias of the test method could not be determinedsince the instability of solutions of chlorine in water does notpermit the determination of an acceptable true value for TRCand FAC in the samples.12.5 Precision for this test method conforms to PracticeD 2777 77, which was in place at the
