1、Designation: D1253 08D1253 14Standard Test Method forResidual Chlorine in Water1This standard is issued under the fixed designation D1253; 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 paren
2、theses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope Scope*1.1 This test method covers the determination of residual chlorine in water by direct amperometric titration.1.2 Within the constraints specified i
3、n Section 6, this test method is not subject to commonly encountered interferences and isapplicable to most waters. Some waters, however, can exert an iodine demand, usually because of organic material, making lessiodine available for measurement by this test method. Thus, it is possible to obtain f
4、alsely low chlorine readings, even though thetest method is working properly, without the users knowledge.1.3 Precision data for this test method were obtained on estuary, inland main stem river, fresh lake, open ocean, and freshcooling tower blowdown water. Bias data could not be determined because
5、 of the instability of solutions of chlorine in water. Itis the users responsibility to ensure the validity of the test method for untested types of water.1.4 In the testing by which this standard was validated, the direct and back starch-iodide titrations and the amperometric backtitration, formerl
6、y part of this standard, were found to be unworkable and were discontinued in 1986. Historical information ispresented in Appendix X1.NOTE 1Orthotolidine test methods have been omitted because of poor precision and accuracy.1.5 The values stated in SI units are to be regarded as standard. No other u
7、nits of measurement are included in this standard.1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of re
8、gulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD1193 Specification for Reagent WaterD2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Close
9、d ConduitsD5847 Practice for Writing Quality Control Specifications for Standard Test Methods for Water Analysis3. Terminology3.1 Definitions: DefinitionsFor definitions of terms used in this test method, refer to Terminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 combined re
10、sidual chlorine, nresidual consisting of chlorine combined with ammonia nitrogen or nitrogenouscompounds.3.2.2 free available chlorine free-available-chlorine residual, nresidual consisting of hypochlorite ions, hypochlorous acid, ora combination thereof.3.2.3 total residual chlorine (chlorine resid
11、ual), nthe amount of available chlorine-induced oxidants present in water at anyspecified period, subsequent to the addition of chlorine.NOTE 2Chlorine present as chloride is neither included in these terms nor determined by this test method.1 This test method is under the jurisdiction ofASTM Commit
12、tee D19 on Water and is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents in Water.Current edition approved Oct. 1, 2008Jan. 15, 2014. Published October 2008February 2014. Originally approved in 1953. Last previous edition approved in 20032008as D1253 03.D1253 08. DOI: 10.15
13、20/D1253-08.10.1520/D1253-14.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM sta
14、ndard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cas
15、es only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.3.1 Discuss
16、ionChlorine present as chloride is neither included in these terms nor determined by this test method. Bromine, bromine combinedwith ammonia or nitrogenous compounds, and chlorine dioxide are not distinguished by this test method from the correspondingchlorine compounds.NOTE 3Bromine, bromine combin
17、ed with ammonia or nitrogenous compounds, and chlorine dioxide are not distinguished by this test method fromthe corresponding chlorine compounds.4. Summary of Test Method4.1 This is an amperometric titration test method utilizing phenylarsine oxide as the titrant. When the titrator cell is immersed
18、in a sample containing chlorine, current is generated. As phenylarsine oxide is added, the chlorine is reduced and the generationof current ceases. When chlorine is present as a chloramine, potassium iodide is added, releasing iodine, which is titrated in asimilar manner. The iodine content is calcu
19、lated in terms of free chlorine.5. Significance and Use5.1 Chlorine is used to destroy or deactivate a variety of unwanted chemicals and microorganisms in water and wastewater.5.2 An uncontrolled excess of chlorine in water, whether free available or combined, can adversely affect the subsequent use
20、of the water.6. Interferences6.1 This test method is not subject to interferences from temperature, color, or turbidity of sample.6.2 Values of pH above 8.0 interfere by slowing the reaction rate. Buffering the sample to pH 7.0 or less eliminates theinterference.6.3 Erratic behavior of the apparatus
21、 in the presence of cupric ions has been reported.6.4 Cuprous and silver ions tend to poison the electrode of the titrator.6.5 Nitrogen trichloride and some N-chloro compounds are often present as products of the chlorination of wastewaters and willtitrate partially as free available chlorine and pa
22、rtially as combined residual chlorine. This error can be avoided only in thedetermination of total residual chlorine.6.6 Exposure to high concentrations of free available chlorine causes a film-type polarization that reverses very slowly. This canbe avoided by diluting the sample with water to less
23、than 10 mg/L of free available chlorine.6.7 If chlorine dioxide is present, an unknown portion titrates as free available chlorine. Total chlorine dioxide titrates as totalresidual chlorine.6.8 Depending upon final pH, chlorination of waters containing ammonia or nitrogenous organic compounds can pr
24、oduce highconcentrations of dichloramine. This compound produces four to five times as much current as monochloramine. The currentproduced by as little as 5 mg/L of dichloramine can cause the microammeter pointer to read offscale even at the end point in thetitration of free available chlorine. This
25、 may be overcome by use of an opposing voltage in the apparatus circuitry. Theinstruments manufacturer should be consulted in this regard.FIG. 1 Wiring Diagram of Amperometric TitratorPlot of Current in A versus PAO Titrant Volume in mlD1253 1426.9 Other oxidizing agents including: ozone, peroxide,
26、iodine, bromine, ferrate, and Caros acid will result in a positiveinterference with this test.7. Apparatus7.1 Amperometric Titration Apparatus3,Refer toAmperometric titration Fig. 1apparatus are available utilizing analog ordigital displays. An instrument employing a digital display is preferred as
27、it will provide better discrimination of current changevs titrant volume addition and the graphical endpoint determination of the test than will an instrument with an analog display. See10.3.2.NOTE 2When the titrator has been out of service for a day or more, check the electrode for sensitivity by n
28、oting the rapidity of the pointer deflection.deflection or the instruments response. If the pointer or instrument display responds slowly after the addition of KI solution, add a small amount ofbiiodate. If it responds slowly to free available chlorine, sensitize it by adding chlorine. Refer to the
29、manufacturers manual for detailed instructions forcleaning and condition the electrode(s) as well as instrument calibration.7.2 GlasswareUse glass sample containers which have been conditioned to eliminate chlorine demands. Condition with watercontaining at least 10 mg/L of residual chlorine for at
30、least 2 h prior to use and then rinse thoroughly.8. Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that allreagents shall conform to the specifications of the Committee on Analytical Reagents of the American
31、Chemical Society.4 Othergrades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lesseningthe accuracy of the determination.8.2 Purity of WaterUnless otherwise indicated, references to water shall be understood to mean reagent wat
32、er conforming toSpecification D1193, Type III, further treated to be free of chlorine demand. Other reagent water types (Type I) may be usedprovided it is first ascertained that the water is of sufficiently high purity to permit its use without adversely affecting the bias andprecision of the test m
33、ethod. Type III water was specified at the time of round robin testing of this method. A suggested methodfor preparation of chlorine demand-free water is to add approximately 20 mg/L of available chlorine to Type III water, let it standfor about a week in darkness, and then expose it to sunlight unt
34、il no chlorine remains. Filtration through a carbon filter is analternative process which requires less time to remove chlorine.8.3 pH 4.0 Buffer SolutionDissolve 243 g of sodium acetate trihydrate and 480 g of glacial acetic acid in water and dilute to1 L. A purchased pH 4.0 buffer of appropriate k
35、nown purity is also acceptable.8.4 pH 7.0 Buffer SolutionDissolve 25.4 g of monobasic potassium phosphate and 86 g of dibasic sodium phosphate in waterand dilute to 1 L. A purchased pH 7.0 buffer of appropriate known purity is also acceptable.8.5 Biiodate, Solution Standard (0.0282 N)Dissolve 0.9163
36、 g of potassium biiodate in water and dilute to 1 L in a volumetricflask. Store in an amber glass-stoppered bottle.8.6 Phenylarsine Oxide, Solution Standard (0.00564 N)Dissolve 0.8 g of phenylarsine oxide in 150 mL of sodium hydroxidesolution (12 g/L). After settling, decant 110 mL of this solution,
37、 add 800 mL of water, and bring to a pH of 9.0 by addinghydrochloric acid (1 + 1). This should require about 2 mL of HCl (1 + 1). Continue acidification with HCl (1 + 1) until a pH of6 to 7 is reached, as indicated by a glass-electrode system; then dilute to a total volume of 1L. Standardize to 0.00
38、564 N against0.0282 N biiodate solution using the titrator (7.1) as the end-point indicator. Add 1 mL of chloroform for preservation.8.7 Potassium Iodide Solution (50 g/L)Dissolve (50 g/L)Dissolve 50 g of KI in water and dilute to 1 L.Add 1 g of sodiumbicarbonate to stabilize the solution. Store in
39、an amber bottle and avoid direct exposure to sunlight.9. Sampling9.1 Collect the sample in accordance with Practices D3370. Take care that the sample is representative and keep it away fromdirect sunlight prior to analysis. Use of only glass sample containers pretreated to eliminate chlorine demand
40、is recommended. See7.2, Glassware.9.2 All tests should be made as soon as possible after collection of the sample (not more than 5 min) because the residualchlorine may diminish with time, due to the chlorine demand of the sample. Where time of contact is important, the elapsed timebetween the addit
41、ion of chlorine and the determination of chlorine should be taken into account.3 Water and Sewage Works, May 1949, p. 171, and Journal American Water Works Association, Vol 34, 1942, pp. 12271240.4 Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington, DC
42、. For Suggestions on the testing of reagents not listed bythe American Chemical Society, see Annual Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and NationalFormulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.D1253 14310. Proc
43、edure10.1 For residual chlorine concentrations of 2.0 mg/L or less, use a 200-mL sample. For greater concentrations, use a 100-mLsample. It is preferable that the size of the sample be such that not more than 2 mL of titrant will be required to complete thetitration.10.2 Determination of Total Resid
44、ual Chlorine:10.2.1 Add 1 mL of KI solution (8.7) to a 200-mL sample and immediately add 1 mL of pH 4.0 buffer solution.solution (8.3).10.2.2 Immerse the electrodes in the sample and start the stirrer. Adjust the microammeter pointer of the potentiometer to theright or high current side of the scale
45、 so the pointer can deflect counterclockwise during the analysis.10.2.2.1 If using an instrument with analog display, adjust the microammeter pointer of the potentiometer to the right or highcurrent side of the scale so the pointer can deflect counterclockwise during the analysis.10.2.2.2 If using a
46、n instrument with digital display, adjust the display using the bias control or other mechanism as stipulatedby the instrument manufacturer.10.2.3 Titrate using standard phenylarsine oxide solution, solution (8.6), adding the titrant in small increments, and noting thedeflection of the microammeter
47、pointer. pointer or digital display with each incremental addition. Plot the progress of the titrationon linear graph paper with current on the vertical axis and titrant volume on the horizontal axis. Add a small volume of titrant,wait a few seconds, and plot the current-volume point on the graph.NO
48、TE 3Digital instruments are available which will automatically add at increments of titrant and plot the progress. When the titration is completed,these instruments also will calculate and display an inflection based endpoint.10.2.4 Readjust When using an instrument with analog display, readjust the
49、 potentiometer several times during the titration, ifnecessary, to bring the pointer back on scale. It is typically not necessary to readjust an instrument with digital display.10.2.5 Continue the analysis by determining at least three points spread over the downward sloping titration curve and at leastthree points after the equivalence or end point. The latter points will indicate practically no change in current. Points just beforethe end point shall be disregarded in its determination. The millilitres of titrant at the end point defined by the in
