1、Designation: D5257 11D5257 17Standard Test Method forDissolved Hexavalent Chromium in Water by IonChromatography1This standard is issued under the fixed designation D5257; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of
2、 last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers procedures for the determination of dissolved hexavalent chromium in wastewater, surface wat
3、er,and drinking water.1.2 The precision and bias of this test method has been tested in reagent water and industrial wastewater and has been foundsuitable over the range of approximately 1 to 1000 g/L. See Table 1 for details. Higher levels can be determined by appropriatedilution.1.3 Samples contai
4、ning very high levels of anionic species (that is, chloride, sulfate, etc.) may cause column overload. Samplescontaining high levels of reducing species (that is, sulfides, sulfites, etc.) may cause reduction of Cr(VI) to Cr(III). This can beminimized by buffering the sample to a pH of 9 to 9.5, fil
5、tering it, storing it at 6C. aAA holding time of 28 days may be usedif the user can demonstrate that such holding time does not affect sample integrity per US in accordance with U.S. EPA 40 CFR136, Part II.1.4 The values stated in either SI or inch-pound units are to be regarded as the standard. The
6、 values given in parentheses arefor information only.mathematical conversions to inch-pound units that are provided for information only and are not consideredstandard.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityo
7、f the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine theapplicability of regulatory limitations prior to use.1.6 This international standard was developed in accordance with internationally recognized principles on standardizatio
8、nestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D1066 Practice for Sampling SteamD1129 Terminology Relati
9、ng 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 Closed ConduitsD5810 Guide for Spiking into Aqueous SamplesD5847 Practice for Writing Quality Control Spe
10、cifications for Standard Test Methods for Water Analysis2.2 U.S. EPA StandardStandards:3U.S. EPA 40 CFR 136 Guidelines Establishing Test Procedures for the Analysis of PollutantsU.S. EPA Method 218.6 Determination of Dissolved Hexavalent Chromium in Drinking Water, Groundwater and IndustrialWastewat
11、er Effluents by Ion ChromatographyUS EPA 40 CFR 1361 This test method is under the jurisdiction ofASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents in Water.Current edition approved March 15, 2011Dec. 1, 2017. Published April 2011December 2
12、017. Originally approved in 1992. Last previous edition approved in 20092011as D5257 09.D5257 11. DOI: 10.1520/D5257-11.10.1520/D5257-17.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume in
13、formation, refer to the standards Document Summary page on the ASTM website.3 Available from Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402.Superintendent of Documents, 732 N. Capitol St., NW,Washington, DC 20401-0001, http:/www.access.gpo.gov.This document is not
14、 an ASTM standard 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
15、. In all cases 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.
16、Terminology3.1 DefinitionsDefinitions: For definitions of terms used in this test method, refer to Terminology D1129.3.1.1 For definitions of terms used in this standard, refer to Terminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 continuing calibration blank, na solution con
17、taining no analytes (of interest) which is used to verify blank response andfreedom from carryover.3.2.2 continuing calibration verification, na solution (or set of solutions) of known concentration used to verify freedom fromexcessive instrumental drift; the concentration is to cover the range of c
18、alibration curve.3.2.3 eluenteluent, nthe ionic mobile phase used to transport the sample through the ion-exchange column.3.2.4 resolutionresolution, nthe ability of a column to separate constituents under specified test conditions.3.2.5 total recoverable chromium, na descriptive term relating to th
19、e forms of chromium recovered in the acid-digestionprocedure specified in this test standard.4. Summary of Test Method4.1 Afixed volume of buffered and filtered sample, typically 100 L, is injected into the eluent flow path and separated by anionexchange using an ammonium sulfate based eluent.4.2 Af
20、ter separation, the sample is reacted with an acidic solution of diphenylcarbohydrazide. Hexavalent chromium reactsselectively with this reagent to form the characteristic violet colored complex.4.3 The eluent stream passes through a photometric detector for detection of the chromium diphenylcarbohy
21、drazide complexby visible absorbance at 530 nm. Absorbance is proportional to the hexavalent chromium concentration.5. Significance and Use5.1 Hexavalent chromium salts are used extensively in the metal finishing and plating industries, in the leather industry as atanning agent, and in the manufactu
22、re of paints, dyes, explosives, and ceramics. Trivalent chromium salts are used as mordantsin textile dying, in the ceramic and glass industry, and in photography. Chromium, in either oxidation state, may be present inwastewater from these industries and may also be discharged from chromate-treated
23、cooling waters.5.2 Hexavalent chromium is toxic to humans, animals, and aquatic life. It can produce lung tumors when inhaled and readilyinduces skin sensitization. It is not known whether cancer will result from ingestion of chromium in any of its valence states.5.3 Ion chromatography provides a me
24、ans of separating the hexavalent chromium from other species present in the sample,many of which interfere with other detection methods. The combination of this separation with a sensitive colorimetric detectionmethod provides a selective and sensitive analytical method for hexavalent chromium with
25、minimal sample preparation.6. Interferences6.1 By virtue of the chromatographic separation essentially all interfering species are removed from the hexavalent chromiumbefore detection.TABLE 1 Determination of Precision and Bias for HexavalentChromiumWaterMatrixAmountAdded,g/LAmountFound,g/LSt SoA Bi
26、as,%Reagent 1.2 1.40 0.16 0.15 + 16.61.6 1.87 0.65 . + 16.96.0 6.68 1.03 0.53 + 11.38.0 8.64 1.10 . + 8.016.0 17.4 2.25 0.77 + 8.820.0 21.4 2.31 . + 7.0100 101 1.91 3.76 + 1.0140 143 5.52 . + 2.1800 819 24.3 12.7 + 2.4960 966 18.5 . + 7.3Waste 6.0 5.63 1.17 0.55 6.28.0 7.31 1.91 . 8.616.0 15.1 2.70
27、1.85 5.620.0 19.8 1.01 . 1.0100 98.9 4.36 3.31 1.1140 138 8.39 . 1.4800 796 60.6 27.1 0.5960 944 72.1 . 1.7A Each Youden pair was used to calculate one lab data point, So.D5257 1726.2 Interferences may result from overloading of the analytical column capacity with high concentrations of anionic spec
28、ies inthe sample. Concentrations of chloride ion or sulfate ion up to the equivalent of 1 % NaCl and 3 % Na2SO4 do not affect theseparation or detection when using an anion exchange column and a 100 L sample loop.6.3 The response of 1 mg/L of hexavalent chromium is not affected by 1 g/L of chromic i
29、on.6.4 Reducing species may reduce hexavalent chromium in acidic matrices. Preservation at a pH 9 to 9.5 will minimize the effectof these species.6.5 Trace amounts of Cr are sometimes found in reagent grade salts. Since a concentrated buffer solution is used in this testmethod to adjust the pH of sa
30、mples, reagent blanks should be analyzed to assess the potential for Cr(VI) contamination.Contamination can also come from improperly cleaned glassware or contact with caustic or acidic reagents with chromiumcontaining stainless steel or pigmented materials.7. Apparatus7.1 Ion ChromatographAn ion ch
31、romatograph having the following components configured as shown in Fig. 1.7.1.1 Pump, capable of delivering a constant flow in the range of 1 to 5 mL/min at a pressure of 200 to 2000 psi.1379 to 13790 kPa (200 to 2000 psi).7.1.2 Injection ValveAhigh pressure, low dead volume valve that allows introd
32、uction of 50 to 250 Lof sample into the eluentstream at up to 2000 psi.13 790 kPa (2000 psi).7.1.3 Guard ColumnA column placed before the separator column to protect the separator column from fouling by particlesor strongly absorbed organic constituents.FIG. 1 Diagram of an Ion Chromatograph Using P
33、ost-Column Reagent Addition and Photometric DetectionD5257 1737.1.4 Analytical ColumnA liquid chromatographic column packed with a polymeric anion exchange resin capable ofseparating chromate from other anions in a sample containing high total dissolved solids (for example 3 % Na2SO4).7.1.5 Reagent
34、Delivery ModuleA device capable of delivering 0 to 2 mL/min of reagent against a backpressure of up to 60psi.7.1.6 Mixing Tee and Reaction CoilA device capable of mixing two flowing streams providing a sufficient reaction time forpost column reaction with minimal band spreading.7.1.7 DetectorAlow-vo
35、lume, flow-through UV-visible absorbance detector with a non-metallic flow path. The recommendeddetection wavelength for hexavalent chromium is 530 nm.7.2 Recorder, Integrator, ComputerA device compatible with detector output, capable of recording detector response as afunction of time for the purpo
36、se of measuring peak height or area.7.3 Eluent ReservoirA container suitable for storing eluent.7.4 SyringeA syringe equipped with a male luer type fitting and a capacity of at least 1 mL.7.5 Summary of Column Requirements:7.5.1 Guard ColumnA short liquid chromatographic column capable of removing o
37、rganics from the injected sample so as tominimize organic fouling of the separator column.7.5.2 Analytical ColumnAn anion exchange column capable of providing suitable retention and chromatographic efficiencyfor chromate ion even in the presence of high amounts of dissolved solids that can occur in
38、wastewater samples. Note that highcapacity columns will tolerate higher dissolved solids before becoming overloaded. See Section 13 for details of the columns usedin the collaborative test of this test method.8. Reagents8.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. Unless
39、 otherwise indicated, it is intended that allreagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society wheresuch specifications are available.4 Other grades may be used, provided it is first ascertained that the reagent is of sufficiently h
40、ighpurity to permit its use without lessening the accuracy of the determination.8.2 Purity of WaterUnless otherwise indicated, references to water shall be understood to mean reagent water conforming toSpecification D1193, Type I. Other reagent water types may be used provided it is first ascertaine
41、d that the water is of sufficientlyhigh purity to permit its use without adversely affecting the bias and precision of thethis test method. Type II water was specifiedat the time of round robin testing of this test method.8.3 Chromium Solution, Stock (1000 mg Cr/L)Dissolve 0.2828 g of potassium dich
42、romate (K2Cr2O7 that has been dried at105C for 1 h) in water.Add 0.1 mL of eluent concentrate (8.6) to ensure analyte stability. Dilute to 100 mL in a volumetric flask.Alternatively, certified chromium stock solutions are commercially available through chemical supply vendors and may be used.8.4 Chr
43、omium Solution, Standard (1000 g Cr/L)Pipet 1.00 mL of chromium stock solution (see 8.3) and 1 mL of eluentconcentrate into a 1 L 1-L volumetric flask. Dilute to volume with water.8.5 Reagent BlankAdd 1 mLof eluent concentrate (8.6) to a 1 L1-Lflask and dilute to volume with the water used to prepar
44、ethe chromium standards.8.6 eluent Concentrate (2.5 M (NH4)2SO4, 1.0 M NH4OH)Dissolve 330 g of ammonium sulfate (NH4)2SO4 in about 500 mLof water. Add 65 mL of concentrated ammonium hydroxide (NH4OH to sp gr 0.90). Mix well and dilute to 1 L in a volumetricflask.8.7 eluentEluentTwo different analyti
45、cal anion exchange columns proved satisfactory in the collaborative test that issummarized in Section 13. Accordingly, the eluent appropriate for each column is described in 8.7.1 and 8.7.2. eluentsEluentsshould be filtered through a 0.45-m filter and degassed.8.7.1 eluent for IonPac AS7 Column (0.2
46、50 M (NH4)2SO4, 0.1 M NH4OH)Add 100 mL of eluent concentrate (8.6) to a 1 Lvolumetric flask and dilute to volume with water.8.7.2 eluentEluent for IC Pac Anion HC Column (0.025 M (NH4)2SO4, 0.01 M NH4OH)Add 10 mL of eluent concentrate(8.6) to a 1 L volumetric flask and dilute to volume with water.8.
47、8 Diphenylcarbohydrazide ReagentDissolve 0.5 g of 1,5-diphenylcarbohydrazide in 100 mL of reagent grade methanol.Add to about 500 mL of water containing 28 mL of concentrated sulfuric acid. Dilute with water, while stirring, to 1 L in avolumetric flask. Filter and degas if necessary to ensure reliab
48、le delivery.4 “Reagent ChemicalsReagent Chemicals, American Chemical Society Specifications”Specifications, Am.American Chemical Soc.,Society, Washington, DC. Forsuggestions on the testing of reagents not listed by the American Chemical Society, see “AnalarAnalar Standards for Laboratory Chemicals,”
49、Chemicals, BDH Ltd., Poole,Dorset, U.K., and the “United States Pharmacopeia.”United States Pharmacopeia and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.D5257 1748.9 Filter PaperPurchase suitable filter paper.Typically the filter papers have a pore size of 0.45-m membrane. Material suchas fine-textured, acid-washed, ashless paper, or glass fiber paper are acceptable. The user must first ascertain that the filter paperis of sufficient purity to use without adversely affecting the bias and pr
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