ASTM D6994-2010 1250 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 10Standard 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 12.1. 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 12.1. 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. No other units of measurement are included in thisstandard.1.7 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-p

11、riate 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 Terminology Relating to WaterD1193 Specification for Reagent WaterD2777 Practice for Determina

12、tion of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD3856 Guide for Good Laboratory Practices in Laborato-ries Engaged in Sampling and Analysis of WaterD5810 Guide for Spiking into Aqueous SamplesD5847 Practice for Writ

13、ing Quality Control Specificationsfor Standard Test Methods for Water AnalysisD6696 Guide for Understanding Cyanide Species3. Terminology3.1 DefinitionsFor a definition of terms used in thismethod, refer to Terminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 anion exchange chr

14、omatography, na type of liquidchromatography in which anionic analytes are separated bydifferential retention on an anion exchange resin and detectedby an appropriate detection mechanism.1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Sub

15、committee D19.05 on Inorganic Constituentsin Water.Current edition approved Sept. 15, 2010. Published November 2010. Originallyapproved in 2004. Last previous edition approved in 2004 as D6994 04. DOI:10.1520/D6994-10.2The boldface numbers in parentheses refer to the list of references at the end of

16、this standard.3For referenced ASTM 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.1*A Summary of Changes section appears at the e

17、nd of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.2 eluent, nthe liquid mobile phase used in anionexchange chromatography to transport the sample through thechromatography system.3.2.3 analytical column, nthe chr

18、omatography 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 characteristics prior to detection.3.2.4 guard column, na short chromatography column

19、that is placed before the analytical column to protect the latterfrom particulates and impurities that may cause fouling.3.2.5 anion trap column, na high-capacity, low-pressureanion exchange column used to remove reagent impuritiesfrom the eluent stream.3.2.5.1 DiscussionThe anion trap column is pla

20、ced 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 the analytes ofinterest prior to detection.3.2.7 gradient pump, na liquid chr

21、omatography pumpthat is 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 metal cyanide complexes.3.2.9 metal cyanide complex, na negatively charged i

22、oniccomplex 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 = transition metal cation,b = number of cyanide groups, andx = ionic charge of the tr

23、ansition 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 complexes are divided into two categories:“weak metal cyanide complexes” and “str

24、ong 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 most stable and least toxicforms of cyanide. Refer to Guide D6696 for a more

25、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 alkalineconditions (1-3).3.2.10 free cyanide, nthe form of cyanide recognized asb

26、eing 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.4. Summary of Test Methods4.1 Dissolved metal cyanide complexes are determ

27、ined 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 differentially retainedon the anion exchange column (4). The concentration r

28、angewill differ depending on the specific metal cyanide analyte,with some complexes exhibiting greater or lesser detectionsensitivity than others based on their molar absorptivity. Referto 12.1 for actual concentration ranges for individual metalcyanide complexes. The metal cyanide complexes are elu

29、tedfrom 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. Under the alkalineconditions of the analysis, ferricyanide (Fe(CN)63-)isre-duc

30、ed 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 complexes are determined by using anionexchange chromatography coupled with on-

31、line sample pre-concentration (4,5). Twenty mL of sample is passed through ananion exchange concentrator column. As the sample passesthrough the column, the metal cyanide complexes are retainedand concentrated on the column while the remainder of thesample matrix is directed to waste. Following conc

32、entration,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. The calibration rangefor metal cyanide complexes using sample preconcentr

33、ationmethod 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. Refer to 12.1 foractual concentration ranges for individual metal cyanide

34、 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 differentiates metal cyanide complexes of lessertoxicity from metal cyanide comple

35、xes of greater toxicity.Previous determinations of strong metal cyanide complexesassumed that the concentration of strong metal cyanide com-plexes is equivalent to the difference between the total cyanideand the free cyanide. This approach is subject to error becausedifferent methods used to determi

36、ne 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 method biases and provides for a more accurate andprecise determination of metal cyan

37、ide complexes.D6994 1026. 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). Samples shall be analyzed in amber bottles andprotected from light whenever

38、 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 analyte retention. Care shallbe taken to avoid carbonate contamination when

39、preparing andusing sodium hydroxide eluents (9,10).NOTE 1Caution: Carbonate is formed in sodium hydroxide solutionsby reaction with atmospheric carbon dioxide. Prepare all eluents usingreagent water degassed by helium sparging or vacuum sonication toprevent carbonate contamination as well as eluent

40、outgassing during theanalysis. Guidelines are provided in the test method for preparinglow-carbonate sodium hydroxide eluent and reagent solutions (see Refs9,10).6.3 Commercial grade sodium cyanide used in the prepara-tion of Eluent 1 (see 8.12) often contains metal cyanidecomplex impurities. These

41、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 streamresulting in improved chromatographic baselines. Guidelinesfor preparing and ins

42、talling the anion trap column are providedin the test method (see 7.1.6 and 11.6).6.4 The IonPact AG5, 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 accordingly will concentrateneutral organics and polyvalent organic anions at

43、 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 the water used in thepreparation of the eluent solutions as well as the c

44、olumnequilibration 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 Free metal cations present in either the sample matrix oras impurities

45、 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 metal cyanide complexes during the low-level analysisprocedure (see 7.2

46、.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 to ferrocya-nide, any unreduced species could potentially contribute to abias in the analytical results.6.7 Matrices with rel

47、atively 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 performing anion exchange chromatographycoupled with on-line sample preconcentra

48、tion, 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 samples containing high total dis-solved solids affects peak resolution.

49、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 Pressurized Eluent ReservoirAccessories must in-clude a gas regulator c