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2、n American National StandardStandard 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 paren
3、theses 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. Scope*1.1 This test method covers the determination of residual chlorine in w
4、ater by direct amperometric titration.1.2 Within the constraints specified in Section 6, this test method is not subject to commonly encountered interferences and is applicable to most waters. Some waters, however, can exert an iodine demand, usually because of organic material, making less iodine a
5、vailable for measurement by this test method. Thus, it is possible to obtain falsely low chlorine readings, even though the test 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, a
6、nd fresh cooling tower blowdown water. Bias data could not be determined because of the instability of solutions of chlorine in water. It is 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 dir
7、ect and back starch-iodide titrations and the amperometric back titration, formerly part of this standard, were found to be unworkable and were discontinued in 1986. Historical infor- mation is presented in Appendix X1.NOTE 1Orthotolidine test methods have been omitted because of poor precision and
8、accuracy.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility 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.2.
9、 Referenced Documents2.1 ASTM Standards:D 1129 Terminology Relating to Water2D 1193 Specification for Reagent Water2D 2777 Practice for Determination of Precision and Bias ofApplicable Methods of Committee D19 on Water21 This test method is under the jurisdiction of ASTM Committee D19 on Water and i
10、s the direct responsibility of Subcommittee D19.05 on Inorganic Constituents in Water.Current edition approved June 10, 2003. Published July 2003. OriginallyD 3370 Practices for Sampling Water from Closed Con-duits2D 5847 Practice for Writing Quality Control Specifications for Standard Test Methods
11、for Water Analysis33. Terminology3.1 Definitions: For definitions of terms used in this test method, refer to Terminology D 1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 combined residual chlorine, nresidual consisting of chlorine combined with ammonia nitrogen or nitrogenous compoun
12、ds.3.2.2 free available chlorine residual, nresidual consist- ing of hypochlorite ions, hypochlorous acid, or a combination thereof.3.2.3 total residual chlorine (chlorine residual), nthe amount of available chlorine-induced oxidants present in water at any specified period, subsequent to the additi
13、on of chlorine.NOTE 2Chlorine present as chloride is neither included in these terms nor determined by this test method.NOTE 3Bromine, bromine combined with ammonia or nitrogenous compounds, and chlorine dioxide are not distinguished by this test method from the corresponding chlorine compounds.4. S
14、ummary of Test Method4.1 This is an amperometric titration test method utilizing phenylarsine oxide as the titrant. When the titrator cell is immersed in a sample containing chlorine, current is generated. As phenylarsine oxide is added, the chlorine is reduced and the generation of current ceases.
15、When chlorine is present as a chloramine, potassium iodide is added, releasing iodine, which is titrated in a similar manner. The iodine content is calculatedin terms of free chlorine.5. Significance and Use5.1 Chlorine is used to destroy or deactivate a variety of unwanted chemicals and microorgani
16、sms in water and waste- water.5.2 An uncontrolled excess of chlorine in water, whether free available or combined, can adversely affect the subsequent use of the water.approved in 1953. Last previous edition approved in 1996 as D 1253 86 (1996). 2 Annual Book of ASTM Standards, Vol 11.01.3 Annual Bo
17、ok of ASTM Standards, Vol 11.02.*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.1D 1253 03FIG. 1Wiring Diagram of Amperometric Titrator6. Interferences6.1 This test met
18、hod 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 the interference.6.3 Erratic behavior of the apparatus in the presence of cupric ions has been repo
19、rted.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 will titrate partially as free available chlorine and partially as combined residual chlorine. This
20、error can be avoided only in 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 avoided by diluting the sample with water to less than 10 mg/L of free available chlorine.
21、6.7 If chlorine dioxide is present, an unknown portion titrates as free available chlorine. Total chlorine dioxide titrates as total residual chlorine.6.8 Depending upon final pH, chlorination of waters con- taining ammonia or nitrogenous organic compounds can pro- duce high concentrations of dichlo
22、ramine. This compound produces 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 at the end point in the titration of free available chlorine. This may be overcome by use of a
23、n opposing voltage in theapparatus circuitry. The instruments manufacturer should beconsulted in this regard.7. Apparatus7.1 Amperometric Titration Apparatus4,5Refer to Fig. 1.NOTE 4When the titrator has been out of service for a day or more, check the electrode for sensitivity by noting the rapidit
24、y of the pointer deflection. If the pointer responds slowly after the addition of KI solution, add a small amount of biiodate. If it responds slowly to free available chlorine, sensitize it by adding chlorine.7.2 GlasswareCondition with water containing at least 10 mg/L of residual chlorine for at l
25、east 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 all reagents shall conform to the specifications of the Commit- tee on Analytical Reagents of the America
26、n Chemical Society.6Other grades may be used, provided it is first ascertained that4 Water and Sewage Works, May 1949, p. 171, and Journal American WaterWorks Association, Vol 34, 1942, pp. 12271240.5 Amperometric titrators are available commercially from most laboratory supply houses.6 Reagent Chem
27、icals, American Chemical Society Specifications, AmericanChemical 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 and Nati
28、onal Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.2D 1253 03the reagent is of sufficiently high purity to permit its usewithout lessening the accuracy of the determination.8.2 Purity of WaterUnless otherwise indicated, references to water shall be understood to mean reagent w
29、ater conforming to Specification D 1193, Type III, further treated to be free of chlorine demand. A suggested method for preparation of chlorine demand-free water is to add approximately 20 mg/L of available chlorine to Type III water, let it stand for about a week in darkness, and then expose it to
30、 sunlight until no chlorine remains.8.3 pH 4.0 Buffer SolutionDissolve 243 g of sodium acetate trihydrate and 480 g of glacial acetic acid in water and dilute to 1 L.8.4 pH 7.0 Buffer SolutionDissolve 25.4 g of monobasic potassium phosphate and 86 g of dibasic sodium phosphate in water and dilute to
31、 1 L.8.5 Biiodate, Solution Standard (0.0282N)Dissolve0.9163 g of potassium biiodate in water and dilute to 1 L in a volumetric flask. 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 hydroxide solu
32、tion (12 g/L). After settling, decant 110 mL of this solution, add 800 mL of water, and bring to a pH of 9.0 by adding hydrochloric acid (1 + 1). This should require about 2 mL of HCl (1 + 1). Continue acidification with HCl (1 + 1) until a pH of 6 to 7 is reached, as indicated by a glass-electrode
33、system; 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 for preservation.8.7 Potassium Iodide Solution (50 g/L)Dissolve 50 g of KI in water and dilute to 1 L. Add 1 g of sodium
34、bicarbonate to stabilize the solution. Store in an amber bottle and avoid direct exposure to sunlight.9. Sampling9.1 Collect the sample in accordance with Practices D 3370. Take care that the sample is representative and keep it away from direct sunlight prior to analysis.9.2 All tests should be mad
35、e as soon as possible after collection of the sample (not more than 5 min) because the residual chlorine may diminish with time, due to the chlorine demand of the sample. Where time of contact is important, the elapsed time between the addition of chlorine and the deter- mination of chlorine should
36、be taken into account.10. Procedure10.1 For residual chlorine concentrations of 2.0 mg/L or less, use a 200-mL sample. For greater concentrations, use a100-mL sample. It is preferable that the size of the sample be such that not more than 2 mL of titrant will be required to complete the titration.10
37、.2 Determination of Total Residual Chlorine:10.2.1 Add 1 mL of KI solution to a 200-mL sample and immediately add 1 mL of pH 4.0 buffer solution.10.2.2 Immerse the electrodes in the sample and start the10.2.3 Titrate using standard phenylarsine oxide solution,adding the titrant in small increments,
38、and noting the deflection of the microammeter pointer. Plot the progress of the titration on 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.10.2.4 Readju
39、st the potentiometer several times during the titration, if necessary, to bring the pointer back on scale.10.2.5 Continue the analysis by determining at least three points spread over the downward sloping titration curve and at least three points after the equivalence or end point. The latter points
40、 will indicate practically no change in current. Points just before the end point shall be disregarded in its determination. The millilitres of titrant at the end point defined by the intersection of the two linear sections of the titration curve should be recorded.10.3 Determination of Free Availab
41、le Chlorine Residual:10.3.1 Add 1 mL of pH 7.0 buffer solution to a 200-mLsample.10.3.2 Repeat the phenylarsine oxide titration beginning with 10.2.2.10.3.3 Note a rapid deflection of the pointer for each increment of titrant indicates the presence of free available chlorine. Slight counterclockwise
42、 movements of the pointer after addition of individual drops of titrant is a drift effect and does 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 free available chlorine residual
43、 as in 10.3.10.4.2 To the same sample, add 1 mL of KI solution and 1mL of pH 4.0 buffer solution and repeat the titration as in 10.2.11. Calculation11.1 Calculate the various types of chlorine residual, in milligrams per litre, as follows:Chlorine residual, mg/L 5 200 A/Vwhere:A= phenylarsine oxide
44、solution (0.00564 N) required forthe titration of 10.2, 10.3, or 10.4, depending on the specific type of chlorine residual determined, mL, andV= sample used, mL.12. Precision and Bias 712.1 The overall precision (St) and the single operator precision (So) of this test method for free available chlor
45、ine(FAC) and for total residual chlorine (TRC) were determined by eight or nine qualified cooperators each with analysis equipment and reagents at each of five sites. Each site constituted a different chlorinated cooling water matrix: estu- ary, inland main stem river, fresh lake, open ocean, and fr
46、esh cooling tower blowdown. Each site water was chlorinated up tostirrer. Adjust the microammeter pointer of the potentiometer to the right or high current side of the scale so the pointer candeflect counterclockwise during the analysis.7 Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR: D191124.3D 1253 03nine levels. Samples were collected simultaneously