1、Designation: D 5257 03Standard Test Method forDissolved Hexavalent Chromium in Water by IonChromatography1This standard is issued under the fixed designation D 5257; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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, a
3、nd 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 v
4、ery 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
5、, storing it at 4C and analyzing it within 24 h.1.4 The values stated in SI units are to be regarded as thestandard.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
6、 safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:D 1066 Practice for Sampling Steam2D 1129 Terminology Relating to Water2D 1192 Specification for Equipment for Sampling Waterand Steam in Closed Conduits2D 1
7、193 Specification for Reagent Water2D 2777 Practice for Determination of Precision and Bias ofApplicable Methods of Committee D-19 on Water2D 3370 Practices for Sampling Water from Closed Con-duits2D 5810 Guide for Spiking into Aqueous Samples2D 5847 Practice for the Writing Quality Control Specific
8、a-tions for Standard Test Methods for Water Analysis22.2 EPA Standard:EPA Method 218.6 Determination of Dissolved HexavalentChromium in Drinking Water, Groundwater and IndustrialWastewater Effluents by Ion Chromatography33. Terminology3.1 DefinitionsFor definitions of terms used in this testmethod,
9、refer to Terminology D 1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 eluant the ionic mobile phase used to transport thesample through the ion exchange column.3.2.2 resolutionthe ability of a column to separate con-stituents under specified test conditions.4. Summary of Test Method4.
10、1 Afixed volume of buffered and filtered sample, typically100 L, is injected into the eluant flow path and separated byanion exchange using an ammonium sulfate based eluant.1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.
11、05 on Inorganic Constituentsin Water.Current edition approved Jan. 10, 2003. Published January 2003. Originallyapproved in 1992. Last previous edition approved in 1997 as D 5257 97.2Annual Book of ASTM Standards, Vol 11.01.3Available from Superintendent of Documents, U.S. Government PrintingOffice,
12、Washington, DC 20402.TABLE 1 Determination of Precision and Bias for HexavalentChromiumWaterMatrixAmountAdded,g/LAmountFound,g/LStSoABias,%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
13、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 . 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
14、, 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, PA 19428-2959, United States.4.2 After separation, the sample is reacted with an acidicsolution of diphenylcarbohydrazide. Hexavalent chromiumr
15、eacts selectively with this reagent to form the characteristicviolet colored complex.4.3 The eluant stream passes through a photometric detectorfor detection of the chromium diphenylcarbohydrazide com-plex by visible absorbance at 530 nm. Absorbance is propor-tional to the hexavalent chromium concen
16、tration.5. Significance and Use5.1 Hexavalent chromium salts are used extensively in themetal finishing and plating industries, in the leather industry asa tanning agent, and in the manufacture of paints, dyes,explosives, and ceramics. Trivalent chromium salts are used asmordants in textile dying, i
17、n the ceramic and glass industry,and in photography. Chromium, in either oxidation state, maybe present in wastewater from these industries and may also bedischarged from chromate-treated cooling waters.5.2 Hexavalent chromium is toxic to humans, animals, andaquatic life. It can produce lung tumors
18、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 chromatography provides a means of separating thehexavalent chromium from other species present in the sample,many of which interfere with othe
19、r detection methods. Thecombination of this separation with a sensitive colorimetricdetection method provides a selective and sensitive analyticalmethod for hexavalent chromium with minimal sample prepa-ration.6. Interferences6.1 By virtue of the chromatographic separation essentiallyall interfering
20、 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 concentrations of anionicspecies in the sample. Concentrations of chloride ion or sulfateion up to the equivalent of 1 % NaCl and 3 % Na2SO4d
21、o 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 notaffected 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 mini
22、mize 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 method to adjust the pH of samples, reagent blanks shouldbe analyzed to assess the potential for Cr(VI) contamination.Contamination can also com
23、e from improperly cleaned glass-ware or contact with caustic or acidic reagents with chromiumcontaining stainless steel or pigmented materials.7. Apparatus7.1 Ion ChromatographAn ion chromatograph having thefollowing components configured as shown in Fig. 1.7.1.1 Pump, capable of delivering a consta
24、nt 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 50 to 250 L of sample intothe eluant stream at up to 2000 psi.7.1.3 Guard Column A column placed before the separa-tor column to protect the s
25、eparator column from fouling byparticles or strongly absorbed organic constituents.7.1.4 Analytical ColumnA liquid chromatographic col-umn packed with a polymeric anion exchange resin capable ofseparating chromate from other anions in a sample containinghigh total dissolved solids (for example 3 % N
26、a2SO4).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.7.1.6 Mixing Tee and Reaction CoilA device capable ofmixing two flowing streams providing a sufficient reaction timefor post column reaction with minimal band spreading.
27、7.1.7 DetectorA low-volume, flow-through UV-visibleabsorbance detector with a non-metallic flow path. The recom-mended detection wavelength for hexavalent chromium is 530nm.FIG. 1 Diagram of an Ion Chromatograph Using Post-ColumnReagent Addition and Photometric DetectionD52570327.2 Recorder, Integra
28、tor, ComputerA device compatiblewith detector output, capable of recording detector response asa function of time for the purpose of measuring peak height orarea.7.3 Eluant Reservoir A container suitable for storingeluant.7.4 SyringeA syringe equipped with a male luer typefitting and a capacity of a
29、t 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 sampleso as to minimize organic fouling of the separator column.7.5.2 Analytical ColumnAn anion exchange column ca-pable of providing suitable retent
30、ion and chromatographicefficiency for chromate ion even in the presence of highamounts of dissolved solids that can occur in wastewatersamples. Note that high capacity columns will tolerate higherdissolved solids before becoming overloaded. See Section 13for details of the columns used in the collab
31、orative test of thistest method.8. Reagents8.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the American Chemical Societywhere such spec
32、ifications are available.4Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.8.2 Purity of Water Unless otherwise indicated, refer-ences to water shall be understood to mean rea
33、gent waterconforming to Specification D 1193, Type I. Other reagentwater types may be used provided it is first ascertained that thewater is of sufficiently high purity to permit its use withoutadversely affecting the bias and precision of the test method.Type II water was specified at the time of r
34、ound 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 for 1 h) in water. Add 0.1 mL of eluantconcentrate (8.6) to ensure analyte stability. Dilute to 100 mLin a volumetric flask.8.4 Chromium Soluti
35、on, Standard (1000 g Cr/L)Pipet1.00 mL of chromium stock solution (see 8.3)and1mLofeluant concentrate intoa1Lvolumetric flask. Dilute to volumewith water.8.5 Reagent Blank Add 1 mL of eluant concentrate (8.6)toa1Lflask and dilute to volume with the water used toprepare the chromium standards.8.6 Elu
36、ant Concentrate (2.5 M (NH4)2SO4, 1.0 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 EluantTwo different analytical anion exchange col-umns proved satisf
37、actory in the collaborative test that issummarized in Section 13. Accordingly, the eluant appropriatefor each column is described in 8.7.1 and 8.7.2. Eluants shouldbe filtered through a 0.45-m filter and degassed.8.7.1 Eluant for IonPac AS7 Column (0.250 M (NH4)2SO4,0.1 M NH4OH)Add 100 mL of eluant
38、concentrate (8.6)toa1 L volumetric flask and dilute to volume with water.8.7.2 Eluant for IC Pac Anion HC Column (0.025 M (NH4)2SO4, 0.01 M NH4OH)Add 10 mL of eluant concentrate(8.6)toa1Lvolumetric flask and dilute to volume with water.8.8 Diphenylcarbohydrazide ReagentDissolve 0.5 g of1,5-diphenylc
39、arbohydrazide in 100 mLof reagent grade 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
40、the applicableASTM Standards as follows: Practice D 1066, SpecificationD 1192, or Practices D 3370.9.2 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 it
41、s pH to 9 to 9.5 using the eluantconcentrate (see 8.6). Ship and store samples at 4C. Bring toambient temperature prior to analysis. Analyze this stabilizedfiltrate within 24 h. Adjust final calculations to account forsample dilution.10. Calibration10.1 Prepare at least three levels of standards for
42、 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 thestandards and blank using the procedure defin
43、ed 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 hexavalentchromium.10.4 Prepare a new calibration c
44、urve 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 eluant flow rate to 1.5 mL/min. Increase theflow of the post-column reagent until the flow rate from thedetector outlet line is 2.
45、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.4“Reagent Chemicals American Chemical Society Specifications” Am. Chemi-cal Soc., Washington, DC. For suggestions on the testing of reagents not listed b
46、ythe American Chemical Society, see “Analar Standards for Laboratory Chemicals,”BDH Ltd., Poole, Dorset, U.K., and the “United States Pharmacopeia.”D525703311.3 After the flow rates are adjusted, allow the system toequilibrate for about 15 min.11.4 If using a fixed volume sample loop (typically 100
47、L),load at least 1 mL of sample through the sample port using anappropriate syringe. Inject the sample into the eluant streamand record the chromatogram (see Fig. 2). If using a variablevolume injector, inject the desired sample volume into theeluant stream and record the chromatogram.12. Calculatio
48、n12.1 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:
49、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 used in thecollaborative test high capacity separator column5and lowcapacity separator column.613.2 The collaborative test of this test method was per-formed in reagent water and wastewater by fifteen laboratoriesusing one operator each. For reagent water the test used tenlevels of concentration comprised of five Youden pairs rangingfrom 1.2 to 960
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