ASTM D6994-2015 3963 Standard Test Method for Determination of Metal Cyanide Complexes in Wastewater Surface Water Groundwater and Drinking Water Using Anion Exchange Chromatograph.pdf

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1、Designation: D6994 15Standard Test Method forDetermination of Metal Cyanide Complexes in Wastewater,Surface Water, Groundwater and Drinking Water UsingAnion Exchange Chromatography with UV Detection1This standard is issued under the fixed designation D6994; the number immediately following the desig

2、nation indicates the year oforiginal adoption or, in the case of revision, the year of 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 the de

3、termination of the metalcyanide complexes of iron, cobalt, silver, gold, copper andnickel in waters including groundwaters, surface waters, drink-ing waters and wastewaters by anion exchange chromatogra-phy and UV detection. The use of alkaline sample preservationconditions (see 10.3) ensures that a

4、ll metal cyanide complexesare solubilized and recovered in the analysis (1-3).21.2 Metal cyanide complex concentrations between 0.20 to200 mg/L may be determined by direct injection of the sample.This range will differ depending on the specific metal cyanidecomplex analyte, with some exhibiting grea

5、ter or lesser detec-tion sensitivity than others. Approximate concentration rangesare provided in 12.2. Concentrations greater than the specificanalyte range may be determined after appropriate dilution.This test method is not applicable for matrices with high ionicstrength (conductivity greater tha

6、n 500 meq/L as Cl) and TDS(greater than 30 000 mg/L), such as ocean water.1.3 Metal cyanide complex concentrations less than 0.200mg/L may be determined by on-line sample preconcentrationcoupled with anion exchange chromatography as described in11.3. This range will differ depending on the specific

7、metalcyanide complex analyte, with some exhibiting greater orlesser detection sensitivity than others. Approximate concen-tration ranges are provided in 12.2. The preconcentrationmethod is not applicable for silver and copper cyanide com-plexes in matrices with high TDS (greater than 1000 mg/L).1.4

8、The test method may also be applied to the determina-tion of additional metal cyanide complexes, such as those ofplatinum and palladium. However, it is the responsibility of theuser of this standard to establish the validity of the test methodfor the determination of cyanide complexes of metals othe

9、rthan those in 1.1.1.5 The presence of metal complexes within a sample maybe converted to Metal CN complexes and as such, are alteredwith the use of this method. This method is not applicable tosamples that contain anionic complexes of metals that areweaker than cyanide complexes of those metals.1.6

10、 The values stated in SI units are to be regarded asstandard. The values given in parentheses are mathematicalconversions to inch-pound units that are provided for informa-tion only and are not considered standard.1.7 This standard does not purport to address all of thesafety concerns, if any, assoc

11、iated 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. For specific hazardstatements, refer to Section 9.2. Referenced Documents2.1 ASTM Standards:3D1129 T

12、erminology Relating to WaterD1193 Specification for Reagent WaterD2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD3856 Guide for Management Systems in LaboratoriesEngaged in Analysis of W

13、aterD5810 Guide for Spiking into Aqueous SamplesD5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water AnalysisD6696 Guide for Understanding Cyanide Species3. Terminology3.1 Definitions:3.1.1 For a definition of terms used in this standard, refer toTerminology D

14、1129.3.2 Definitions of Terms Specific to This Standard:1This 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 Oct. 1, 2015. Published October 2015. Originallyapprove

15、d in 2004. Last previous edition approved in 2010 as D6994 10. DOI:10.1520/D6994-15.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org

16、. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.*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.

17、2.1 anion exchange chromatography, na type of liquidchromatography in which anionic analytes are separated bydifferential retention on an anion exchange resin and detectedby an appropriate detection mechanism.3.2.2 eluent, nthe liquid mobile phase used in anionexchange chromatography to transport th

18、e sample through thechromatography system.3.2.3 analytical column, nthe chromatography columnthat contains the stationary phase for separation by ion ex-change.3.2.3.1 DiscussionThe column is packed with anion ex-change resin that separates the analytes of interest based ontheir retention characteri

19、stics prior to detection.3.2.4 guard column, na short chromatography column thatis placed before the analytical column to protect the latter fromparticulates and impurities that may cause fouling.3.2.5 anion trap column, na high-capacity, low-pressureanion exchange column used to remove reagent impu

20、ritiesfrom the eluent stream.3.2.5.1 DiscussionThe anion trap column is placed be-tween the eluent reservoir and the gradient pump.3.2.6 gradient elution, na type of elution in which theeluent composition is steadily altered throughout the analysisin order to provide for an adequate separation of th

21、e analytes ofinterest prior to detection.3.2.7 gradient pump, na liquid chromatography pump thatis capable of performing gradient elutions.3.2.8 total cyanide, nthe sum total of all of the inorganicchemical forms of cyanide.3.2.8.1 DiscussionTotal cyanide thus includes both freecyanide and anionic m

22、etal cyanide complexes.3.2.9 metal cyanide complex, na negatively charged ioniccomplex consisting of one or more cyanide ions bound to asingle transition metal cation.3.2.9.1 DiscussionAlso referred to as metal-complexedcyanides, these complexes have the general formula:MCN!b#x2(1)where:M = transiti

23、on metal cation,b = number of cyanide groups, andx = ionic charge of the transition metal complex.3.2.9.2 DiscussionMetal cyanide complexes are relativelystable and require moderate to highly acidic conditions in orderto dissociate and form free cyanide. Based on their stability,metal cyanide comple

24、xes are divided into two categories:“weak metal cyanide complexes” and “strong metal cyanidecomplexes.” Examples of strong metal cyanide complexesinclude the iron cyanide complexes prevalent in many cyanidecontaining industrial wastewaters. The iron cyanide complexesare considered to be among the mo

25、st stable and least toxicforms of cyanide. Refer to Guide D6696 for a more detaileddiscussion of aqueous cyanide species.3.2.9.3 DiscussionThe metal cyanide complexes can formsalts with a variety of alkali and transition metal cations. Thesealkali metal cyanide complex salts are soluble under alkali

26、neconditions (1-3).3.2.10 free cyanide, nthe form of cyanide recognized asbeing bioavailable and toxic.3.2.10.1 DiscussionFree cyanide may be present as eithermolecular HCN or the anion CN- depending on the pHconditions. Refer to Guide D6696 for a more detailed discus-sion of aqueous cyanide species

27、.4. Summary of Test Method4.1 Dissolved metal cyanide complexes are determined byanion exchange chromatography. For samples containing from0.2 to 200 mg/L metal cyanides a sample volume of 0.1 mL isinjected directly into the ion chromatograph where the metalcyanide analytes are separated by being di

28、fferentially retainedon the anion exchange column (4). The concentration rangewill differ depending on the specific metal cyanide analyte,with some complexes exhibiting greater or lesser detectionsensitivity than others based on their molar absorptivity. Referto 12.2 for actual concentration ranges

29、for individual metalcyanide complexes. The metal cyanide complexes are elutedfrom the column by the eluent gradient and detected as signalpeaks using UV absorption at 215 nm. Their concentrations inthe sample are determined by comparison of the analyte peakarea with a standard calibration plot. Unde

30、r the alkalineconditions of the analysis, ferricyanide (Fe(CN)63-)isre-duced to ferrocyanide (Fe(CN)64-) (1, 2), yielding a singleanalyte peak. Any unreduced ferricyanide will be exhibited astailing on the ferrocyanide peak.4.2 For samples containing from 0.50 to 200 g/L, dissolvedmetal cyanide comp

31、lexes are determined by using anionexchange chromatography coupled with on-line sample pre-concentration (4, 5).Twenty mLof sample is passed through ananion exchange concentrator column. As the sample passesthrough the column, the metal cyanide complexes are retainedand concentrated on the column wh

32、ile the remainder of thesample matrix is directed to waste. Following concentration,the metal cyanide analytes are eluted from the concentratorcolumn through gradient elution, into the chromatograph andonto an anion exchange column where the remainder of theanalysis is completed as described in 4.1.

33、 The calibration rangefor metal cyanide complexes using sample preconcentrationmethod is between 0.50 to 200 g/L. This range will differdepending on the specific metal cyanide analyte, with somecomplexes exhibiting greater or lesser detection sensitivitythan others based on their molar absorptivity.

34、 Refer to 12.2 foractual concentration ranges for individual metal cyanide com-plexes.5. Significance and Use5.1 This method directly determines the concentration ofmetal cyanide complexes in environmental waters. The methodis important from an environmental regulatory perspectivebecause it differen

35、tiates metal cyanide complexes of lessertoxicity from metal cyanide complexes of greater toxicity.Previous determinations of strong metal cyanide complexesD6994 152assumed that the concentration of strong metal cyanide com-plexes is equivalent to the difference between the total cyanideand the free

36、cyanide. This approach is subject to error becausedifferent methods used to determine free cyanide often providewidely varying results, thus impacting the strong metal cyanidecomplex concentration that is determined by difference. Thedirect analysis using anion exchange chromatography avoidsthese me

37、thod biases and provides for a more accurate andprecise determination of metal cyanide complexes.6. Interferences6.1 Photodecomposition of some metal cyanide complexessuch as those of iron can reduce their concentration (6-8).Samples shall be collected so as to prevent exposure to light(see 10.2). S

38、amples shall be analyzed in amber bottles andprotected from light whenever possible.6.2 Carbonate is not a method interference but can accumu-late by adherence to the anion exchange resin of the analyticalcolumn. This may eventually lead to unstable baselines and areduction in column capacity and an

39、alyte retention. Care shallbe taken to avoid carbonate contamination when preparing andusing sodium hydroxide eluents (9, 10).(WarningCarbonate is formed in sodium hydroxide solutions by reactionwith atmospheric carbon dioxide. Prepare all eluents usingreagent water degassed by helium sparging or va

40、cuum sonica-tion to prevent carbonate contamination as well as eluentoutgassing during the analysis. Guidelines are provided in thetest method for preparing low-carbonate sodium hydroxideeluent and reagent solutions (see Refs 9, 10).)6.3 Commercial grade sodium cyanide used in the prepara-tion of El

41、uent 1 (see 8.12) often contains metal cyanidecomplex impurities. These impurities can cause noisy, unstablebaselines during the gradient elution profile. The installation ofan anion trap column between the Eluent 1 reservoir and thegradient pump removes the impurities from the eluent streamresultin

42、g in improved chromatographic baselines. Guidelinesfor preparing and installing the anion trap column are providedin the test method (see 7.1.6 and 11.6).6.4 The IonPac4AG5, AG11, AS5 and AS11 chromatogra-phy columns referenced in the test method (see 7.1.7, 7.1.8,and 7.2.4) are polymeric and accord

43、ingly will concentrateneutral organics and polyvalent organic anions at the head ofthe column. Organic species containing a carbonate functionalgroup will absorb at 215 nm. These species can potentiallycause “ghost” peaks when eluted during the analysis. Thiseffect is a function of the quality of th

44、e water used in thepreparation of the eluent solutions as well as the columnequilibration time. Sample preconcentration will enhance thiseffect. High purity reagent water containing as low a concen-tration as possible of organic contaminants should be used inthe preparation of reagents (see 8.2).6.5

45、 Free metal cations present in either the sample matrix oras impurities in the combined eluent stream can combine withthe free cyanide present in Eluent 1 (see 8.12) to formextraneous metal cyanide complexes. Metal free trap columnsshould be installed to prevent positive interference by extrane-ous

46、metal cyanide complexes during the low-level analysisprocedure (see 7.2.5).6.6 The method calibration for iron cyanide is based on itsreduced form, ferrocyanide. Although the alkaline conditionsof the analysis favor the reduction of ferricyanide toferrocyanide, any unreduced species could potentiall

47、y contrib-ute to a bias in the analytical results.6.7 Matrices with relatively high ionic strength or high totaldissolved solids, for example, ocean water, will affect theperformance of the analytical columns, resulting in poorseparation and recovery of the metal cyanide complexes.6.8 When performin

48、g anion exchange chromatographycoupled with on-line sample preconcentration, the silver andcopper cyanide complexes exhibit reduced precision and in-creased bias, especially in high ionic strength matrices, forexample, certain wastewaters. For the silver cyanide complex,large front-end tailing in sa

49、mples containing high total dis-solved solids affects peak resolution. For the copper and silvercyanide complexes possible dissociation during the analysismight also affect quantitation in samples containing high totaldissolved solids. Any matrix with high ionic strength and totaldissolved solids (TDS 1000 mg/L) could affect the perfor-mance of the analytical columns when performing samplepreconcentration, which may result in poor separation andrecovery of metal cyanide complexes.7. Apparatus7.1 Anion Exchange Chromatography Apparatus Require-ments:7.1.1 Pr