ASTM D5257-17 Standard Test Method for Dissolved Hexavalent Chromium in Water by Ion Chromatography.pdf

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1、Designation: D5257 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 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.Higher levels can be determined by appropriate dilution.1.3 Samples containing very high levels of anionic

4、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, storing it at 6C. A holdi

5、ng time of 28 daysmay be used if the user can demonstrate that such holding timedoes not affect sample integrity in accordance with U.S. EPA40 CFR 136, Part II.1.4 The values stated in SI units are to be regarded asstandard. The values given in parentheses are mathematicalconversions to inch-pound u

6、nits that are provided for informa-tion only and are not considered standard.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, health, and environmental prac

7、tices and deter-mine the applicability of regulatory limitations prior to use.1.6 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides an

8、d Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D1066 Practice for Sampling SteamD1129 Terminology Relating to WaterD1193 Specification for Reagent WaterD2777 Practice for Determination of Precision and B

9、ias ofApplicable 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 Specificationsfor Standard Test Methods for Water Analysis2.2 U.S. EPA Standards:3U.S. EPA 40 CFR 136 G

10、uidelines Establishing Test Proce-dures for the Analysis of PollutantsU.S. EPA Method 218.6 Determination of DissolvedHexavalent Chromium in Drinking Water, Groundwaterand Industrial Wastewater Effluents by Ion Chromatogra-phy3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this

11、standard, refer toTerminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 continuing calibration blank, na solution containingno analytes (of interest) which is used to verify blank responseand freedom from carryover.3.2.2 continuing calibration verification, na solution (orset of

12、 solutions) of known concentration used to verify freedomfrom excessive instrumental drift; the concentration is to coverthe range of calibration curve.3.2.3 eluent, nthe ionic mobile phase used to transport thesample through the ion-exchange column.1This test method is under the jurisdiction of AST

13、M Committee D19 on Waterand is the direct responsibility of Subcommittee D19.05 on Inorganic Constituentsin Water.Current edition approved Dec. 1, 2017. Published December 2017. Originallyapproved in 1992. Last previous edition approved in 2011 as D5257 11. DOI:10.1520/D5257-17.2For referenced ASTM

14、standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from U.S. Government Printing Office, Superintendent ofDocuments, 732 N

15、. Capitol St., NW, Washington, DC 20401-0001, http:/www.access.gpo.gov.*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 StatesThis international standard was developed in accord

16、ance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.121 3.2.4 resolution, nthe ability

17、 of a column to separateconstituents under specified test conditions.3.2.5 total recoverable chromium, na descriptive termrelating to the forms of chromium recovered in the acid-digestion procedure specified in this test standard.4. Summary of Test Method4.1 Afixed volume of buffered and filtered sa

18、mple, typically100 L, is injected into the eluent flow path and separated byanion exchange using an ammonium 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 characte

19、risticviolet colored complex.4.3 The eluent 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 concentration.5. Significance and Use5.1 Hexavalent chromium s

20、alts 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, in the ceramic and glass industry,and in photography. Chr

21、omium, 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 when inhaled andreadily induces skin sensitization. It i

22、s 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 other detection methods. Thecombination of this separation w

23、ith 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 species are removed from the hexavalent chro-mium befor

24、e 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 % Na2SO4do notaffect the separation or detection when using an an

25、ion 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 minimize theeffect of these species.6.5 Trace amounts of Cr

26、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 come from improperly cleaned glass-ware or contact with cau

27、stic 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 constant flow in therange of 1 to 5 mL/min at a pressure of 13

28、79 to 13 790 kPa(200 to 2000 psi).7.1.2 Injection ValveA high pressure, low dead volumevalve that allows introduction of 50 to 250 L of sample intothe eluent stream at up to 13 790 kPa (2000 psi).7.1.3 Guard ColumnAcolumn placed before the separatorcolumn to protect the separator column from fouling

29、 byparticles or strongly absorbed organic constituents.FIG. 1 Diagram of an Ion Chromatograph Using Post-ColumnReagent Addition and Photometric DetectionD5257 17221 7.1.4 Analytical ColumnA liquid chromatographic col-umn packed with a polymeric anion exchange resin capable ofseparating chromate from

30、 other anions in a sample containinghigh total dissolved solids (for example 3 % Na2SO4).7.1.5 Reagent Delivery ModuleA device capable of deliv-ering 0 to 2 mL/min of reagent against a backpressure of up to60 psi.7.1.6 Mixing Tee and Reaction CoilA device capable ofmixing two flowing streams providi

31、ng a sufficient reaction timefor post column reaction with minimal band spreading.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.7.2 Recorder, Integrator, ComputerA device co

32、mpatiblewith detector output, capable of recording detector response asa function of time for the purpose of measuring peak height orarea.7.3 Eluent ReservoirA container suitable for storing elu-ent.7.4 SyringeA syringe equipped with a male luer typefitting and a capacity of at least 1 mL.7.5 Summar

33、y of Column Requirements:7.5.1 Guard ColumnA short liquid chromatographic col-umn capable of removing organics from the injected sample soas to minimize organic fouling of the separator column.7.5.2 Analytical ColumnAn anion exchange column ca-pable of providing suitable retention and chromatographi

34、cefficiency 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 collaborative test of thiste

35、st 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 specifications are availab

36、le.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 WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water conformingto S

37、pecification D1193, Type I. Other reagent water types maybe used provided it is first ascertained that the water is ofsufficiently high purity to permit its use without adverselyaffecting the bias and precision of this test method. Type IIwater was specified at the time of round robin testing of thi

38、stest 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 eluentconcentrate (8.6) to ensure analyte stability. Dilute to 100 mLin a volumetric flask. Alternatively, certified chromium stocksolu

39、tions are commercially available through chemical supplyvendors and may be used.8.4 Chromium Solution, Standard (1000 g Cr/L)Pipet1.00 mL of chromium stock solution (see 8.3)and1mLofeluent concentrate into a 1-Lvolumetric flask. Dilute to volumewith water.8.5 Reagent BlankAdd 1 mLof eluent concentra

40、te (8.6)toa 1-L flask and dilute to volume with the water used to preparethe chromium standards.8.6 eluent 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 dilu

41、te to 1 Lin a volumetric flask.8.7 EluentTwo different analytical anion exchange col-umns proved satisfactory in the collaborative test that 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 filt

42、er 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 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 concen-trate (8.6) to a 1 L volu

43、metric flask and dilute to volume withwater.8.8 Diphenylcarbohydrazide ReagentDissolve 0.5 g of1,5-diphenylcarbohydrazide 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. Fi

44、lter and degas if necessary to ensurereliable delivery.8.9 Filter PaperPurchase suitable filter paper. Typicallythe filter papers have a pore size of 0.45-m membrane.Material such as fine-textured, acid-washed, ashless paper, orglass fiber paper are acceptable. The user must first ascertainthat the

45、filter paper is of sufficient purity to use withoutadversely affecting the bias and precision of this test method.9. Sampling9.1 Collect the sample in accordance with the applicableASTM standards as follows: Practice D1066, or PracticesD3370.9.2 Filter samples and adjust pH immediately upon sam-plin

46、g to minimize any interconversion between Cr(III) andCr(VI) species. Filter the sample through a 0.45-m filter (8.9).Collect the filtrate and adjust its pH to 9 to 9.5 using the eluentconcentrate (see 8.6). Ship and store samples at 6C. Bring to4Reagent Chemicals, American Chemical Society Specifica

47、tions, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention

48、, Inc. (USPC), Rockville,MD.D5257 17321 ambient 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 U.S. EPA 40 CFR 136, Part II,Table II.10. Calibra

49、tion10.1 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 thestandards and blank using the procedure defined in Section 11.10.3 Read directly in concentration if this capability isprovided with the instrument or plot a calibration curve byusing a linear plot of the peak height or