1、Designation: D5257 11Standard 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 last re
2、vision. 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 determina-tion of dissolved hexavalent chromium in wastewater, surfacewater, and
3、drinking water.1.2 The precision and bias of this test method has beentested in reagent water and industrial wastewater and has beenfound suitable over the range of approximately 1 to 1000 g/L.See Table 1 for details. Higher levels can be determined byappropriate dilution.1.3 Samples containing very
4、 high levels of anionic species(that is, chloride, sulfate, etc.) may cause column overload.Samples containing high levels of reducing species (that is,sulfides, sulfites, etc.) may cause reduction of Cr(VI) to Cr(III).This can be minimized by buffering the sample to a pH of 9 to9.5, filtering it, s
5、toring it at 6C. aA holding time of 28 daysmay be used if the user can demonstrate that such holding timedoes not affect sample integrity per US EPA 40 CFR 136 PartII.1.4 The values stated in either SI or inch-pound units are tobe regarded as the standard. The values given in parenthesesare for info
6、rmation only.1.5 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 and health practices and determine the applica-bility of regulatory limitations prior to use.2.
7、 Referenced Documents2.1 ASTM Standards:2D1066 Practice for Sampling Steam2D1129 Terminology Relating to Water2D1193 Specification for Reagent Water2D2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on Water2D3370 Practices for Sampling Water from Clos
8、ed Conduits2D5810 Guide for Spiking into Aqueous Samples2D5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water Analysis2.2 EPA Standard:EPA Method 218.6 Determination of Dissolved HexavalentChromium in Drinking Water, Groundwater and IndustrialWastewater Efflue
9、nts by Ion Chromatography3US EPA 40 CFR 1363. Terminology3.1 DefinitionsFor definitions of terms used in this testmethod, refer to Terminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 eluent the ionic mobile phase used to transport thesample through the ion-exchange column.1Thi
10、s 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 March 15, 2011. Published April 2011. Originallyapproved in 1992. Last previous edition approved in 2009 as D5257 0
11、9. DOI:10.1520/D5257-11.2Annual Book of ASTM Standards, Vol 11.01.3Available from Superintendent of Documents, U.S. Government PrintingOffice, Washington, DC 20402.TABLE 1 Determination of Precision and Bias for HexavalentChromiumWaterMatrixAmountAdded,g/LAmountFound,g/LStSoABias,%Reagent 1.2 1.40 0
12、.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 1.85 5.620.0 19.8 1.01
13、 . 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 . 1.7AEach Youden pair was used to calculate one lab data point, So.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken,
14、PA 19428-2959, United States.3.2.2 resolutionthe ability of a column to separate con-stituents under specified test conditions.4. Summary of Test Method4.1 Afixed volume of buffered and filtered sample, typically100 L, is injected into the eluent flow path and separated byanion exchange using an amm
15、onium sulfate based eluent.4.2 After separation, the sample is reacted with an acidicsolution of diphenylcarbohydrazide. Hexavalent chromiumreacts selectively with this reagent to form the characteristicviolet colored complex.4.3 The eluent stream passes through a photometric detectorfor detection o
16、f the chromium diphenylcarbohydrazide com-plex by visible absorbance at 530 nm. Absorbance is propor-tional to the hexavalent chromium concentration.5. Significance and Use5.1 Hexavalent chromium salts are used extensively in themetal finishing and plating industries, in the leather industry asa tan
17、ning agent, and in the manufacture of paints, dyes,explosives, and ceramics. Trivalent chromium salts are used asmordants in textile dying, in the ceramic and glass industry,and in photography. Chromium, in either oxidation state, maybe present in wastewater from these industries and may also bedisc
18、harged from chromate-treated cooling waters.5.2 Hexavalent chromium is toxic to humans, animals, andaquatic life. It can produce lung tumors when inhaled andreadily induces skin sensitization. It is not known whethercancer will result from ingestion of chromium in any of itsvalence states.5.3 Ion ch
19、romatography provides a means of separating thehexavalent chromium from other species present in the sample,many of which interfere with other detection methods. Thecombination of this separation with a sensitive colorimetricdetection method provides a selective and sensitive analyticalmethod for he
20、xavalent chromium with minimal sample prepa-ration.6. Interferences6.1 By virtue of the chromatographic separation essentiallyall interfering species are removed from the hexavalent chro-mium before detection.6.2 Interferences may result from overloading of the ana-lytical column capacity with high
21、concentrations of anionicspecies in the sample. Concentrations of chloride ion or sulfateion up to the equivalent of 1 % NaCl and 3 % Na2SO4do notaffect the separation or detection when using an anion ex-change column and a 100 L sample loop.6.3 The response of 1 mg/L of hexavalent chromium is notaf
22、fected by 1 g/L of chromic ion.6.4 Reducing species may reduce hexavalent chromium inacidic matrices. Preservation at a pH 9 to 9.5 will minimize theeffect of these species.6.5 Trace amounts of Cr are sometimes found in reagentgrade salts. Since a concentrated buffer solution is used in thistest met
23、hod to adjust the pH of samples, reagent blanks shouldbe analyzed to assess the potential for Cr(VI) contamination.Contamination can also come from improperly cleaned glass-ware or contact with caustic or acidic reagents with chromiumcontaining stainless steel or pigmented materials.7. Apparatus7.1
24、Ion ChromatographAn ion chromatograph having thefollowing components configured as shown in Fig. 1.7.1.1 Pump, capable of delivering a constant flow in therange of 1 to 5 mL/min at a pressure of 200 to 2000 psi.7.1.2 Injection Valve A high pressure, low dead volumevalve that allows introduction of 5
25、0 to 250 L of sample intothe eluent stream at up to 2000 psi.7.1.3 Guard Column A column placed before the separa-tor column to protect the separator column from fouling byparticles or strongly absorbed organic constituents.7.1.4 Analytical ColumnA liquid chromatographic col-umn packed with a polyme
26、ric anion exchange resin capable ofseparating chromate from other anions in a sample containinghigh total dissolved solids (for example 3 % Na2SO4).7.1.5 Reagent Delivery ModuleA device capable of de-livering 0 to 2 mL/min of reagent against a backpressure of upto 60 psi.FIG. 1 Diagram of an Ion Chr
27、omatograph Using Post-ColumnReagent Addition and Photometric DetectionD5257 1127.1.6 Mixing Tee and Reaction CoilA device capable ofmixing two flowing streams providing a sufficient reaction timefor post column reaction with minimal band spreading.7.1.7 DetectorA low-volume, flow-through UV-visiblea
28、bsorbance detector with a non-metallic flow path. The recom-mended detection wavelength for hexavalent chromium is 530nm.7.2 Recorder, Integrator, ComputerA device compatiblewith detector output, capable of recording detector response asa function of time for the purpose of measuring peak height ora
29、rea.7.3 eluent Reservoir A container suitable for storingeluent.7.4 SyringeA syringe equipped with a male luer typefitting and a capacity of at least 1 mL.7.5 Summary of Column Requirements:7.5.1 Guard Column A short liquid chromatographiccolumn capable of removing organics from the injected samples
30、o as to minimize organic fouling of the separator column.7.5.2 Analytical ColumnAn anion exchange column ca-pable of providing suitable retention and chromatographicefficiency for chromate ion even in the presence of highamounts of dissolved solids that can occur in wastewatersamples. Note that high
31、 capacity columns will tolerate higherdissolved solids before becoming overloaded. See Section 13for details of the columns used in the collaborative test of thistest method.8. Reagents8.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended
32、 thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the American Chemical Societywhere such specifications are available.4Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without l
33、essening theaccuracy of the determination.8.2 Purity of Water Unless otherwise indicated, refer-ences to water shall be understood to mean reagent waterconforming to Specification D1193, Type I. Other reagentwater types may be used provided it is first ascertained that thewater is of sufficiently hi
34、gh purity to permit its use withoutadversely affecting the bias and precision of the test method.Type II water was specified at the time of round robin testingof this test method.8.3 Chromium Solution, Stock (1000 mg Cr/L)Dissolve0.2828 g of potassium dichromate (K2Cr2O7that has beendried at 105C fo
35、r 1 h) in water. Add 0.1 mL of eluentconcentrate (8.6) to ensure analyte stability. Dilute to 100 mLin a volumetric flask. Alternatively, certified chromium stocksolutions are commercially available through chemical supplyvendors and may be used.8.4 Chromium Solution, Standard (1000 g Cr/L)Pipet1.00
36、 mL of chromium stock solution (see 8.3)and1mLofeluent concentrate intoa1Lvolumetric flask. Dilute to volumewith water.8.5 Reagent Blank Add 1 mL of eluent concentrate (8.6)toa1Lflask and dilute to volume with the water used toprepare the chromium standards.8.6 eluent Concentrate (2.5 M (NH4)2SO4, 1
37、.0 MNH4OH)Dissolve 330 g of ammonium sulfate (NH4)2SO4inabout 500 mL of water.Add 65 mL of concentrated ammoniumhydroxide (NH4OH to sp gr 0.90). Mix well and dilute to 1 Lin a volumetric flask.8.7 eluentTwo different analytical anion exchange col-umns proved satisfactory in the collaborative test th
38、at issummarized in Section 13. Accordingly, the eluent appropriatefor each column is described in 8.7.1 and 8.7.2. eluents shouldbe filtered through a 0.45-m filter and degassed.8.7.1 eluent for IonPac AS7 Column (0.250 M (NH4)2SO4,0.1 M NH4OH)Add 100 mL of eluent concentrate (8.6)toa1 L volumetric
39、flask and dilute to volume with water.8.7.2 eluent for IC Pac Anion HC Column (0.025 M (NH4)2SO4, 0.01 M NH4OH)Add 10 mL of eluent concentrate(8.6)toa1Lvolumetric flask and dilute to volume with water.8.8 Diphenylcarbohydrazide ReagentDissolve 0.5 g of1,5-diphenylcarbohydrazide in 100 mLof reagent g
40、rade metha-nol. Add to about 500 mL of water containing 28 mL ofconcentrated sulfuric acid. Dilute with water, while stirring, to1 Lin a volumetric flask. Filter and degas if necessary to ensurereliable delivery.9. Sampling9.1 Collect the sample in accordance with the applicableASTM Standards as fol
41、lows: Practice D1066, or PracticesD3370.9.2 Filter samples and adjust pH immediately upon sam-pling to minimize any interconversion between Cr III and CrVI species. Filter the sample through a 0.45 m filter. Collectthe filtrate and adjust its pH to 9 to 9.5 using the eluentconcentrate (see 8.6). Shi
42、p and store samples at 6C. Bring toambient temperature prior to analysis. The sample should beanalyzed within 28 days as long as the pH is above 9.0. Adjustfinal calculations to account for sample dilution. The holdingtime is based on changes to US EPA 40 CFR 136 part II, tableII10. Calibration10.1
43、Prepare at least three levels of standards for eachdecade of the concentration range of interest. For standards of1 to 1000 g/L, prepare by diluting measured volumes of thestandard chromium solution (see 8.4) with water in separatevolumetric flasks.10.2 Determine the chromium response for each of th
44、estandards and blank using the procedure defined in Section 11.10.3 Prepare a calibration curve by using a linear plot of thepeak height or area as a function of standard concentration. Donot force the calibration curve through zero. The response ofthe reagent blank should be less than 0.1 g/L hexav
45、alentchromium.4“Reagent Chemicals American Chemical Society Specifications” Am. Chemi-cal Soc., Washington, DC. For suggestions on the testing of reagents not listed bythe American Chemical Society, see “Analar Standards for Laboratory Chemicals,”BDH Ltd., Poole, Dorset, U.K., and the “United States
46、 Pharmacopeia.”D5257 11310.4 Prepare a new calibration curve when new reagents aremade or the hardware is altered.11. Procedure11.1 Set up the ion chromatograph in accordance with themanufacturers instructions.11.2 Adjust the eluent flow rate to 1.5 mL/min. Increase theflow of the post-column reagen
47、t until the flow rate from thedetector outlet line is 2.0 mL/min. so as to have a reagent flowof 0.5 mL/min under operating conditions. Measure the pH ofthe detector effluent to confirm it is 2 or lower.11.3 After the flow rates are adjusted, allow the system toequilibrate for about 15 min.11.4 If u
48、sing a fixed volume sample loop (typically 100 L),load at least 1 mL of sample through the sample port using anappropriate syringe. Inject the sample into the eluent streamand record the chromatogram (see Fig. 2). If using a variablevolume injector, inject the desired sample volume into theeluent st
49、ream and record the chromatogram.12. Calculation12.1 Refer the hexavalent chromium peak height or peakarea to the calibration curve to determine the hexavalentchromium concentration of the injected sample in g/L.12.2 For samples that have been diluted, calculate theoriginal hexavalent chromium concentration in g/L by:g CrVI!/L 5 C 3 F / V.where:C = g Cr(VI)/L read from the calibration curve,F = volume of diluted sample, in mL, andV = volume of undiluted sample in mL.13. Precision and Bias13.1 The following separator columns were
