ASTM D6994-2004 Standard Test Method for Determination of Metal Cyanide Complexes in Wastewater Surface Water Groundwater and Drinking Water Using Anion Exchange Chromatography wit.pdf

1、Designation: D 6994 04Standard 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 D 6994; the number immediately following the des

2、ignation 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the

3、determination 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

4、 all 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 gr

5、eater 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 t

6、han 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 specifi

7、c 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.

8、4 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 ot

9、herthan those in 1.1.1.5 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 t

10、o use. For specific hazardstatements, refer to Section 9.2. Referenced Documents2.1 ASTM Standards:3D 1129 Terminology Relating to WaterD 1192 Specification for Equipment for Sampling Waterand Steam in Closed ConduitsD 1193 Specification for Reagent WaterD 2777 Practice for Determination of Precisio

11、n and Bias ofApplicable Methods of Committee D-19 on WaterD 3370 Practices for Sampling Water from Closed ConduitsD 3856 Guide for Good Laboratory Practices in Laborato-ries Engaged in Sampling and Analysis of WaterD 5810 Guide for Spiking into Aqueous SamplesD 5847 Practice for Writing Quality Cont

12、rol Specificationsfor Standard Test Methods for Water AnalysisD 6696 Guide for Understanding Cyanide Species3. Terminology3.1 DefinitionsFor a definition of terms used in thismethod, refer to Terminology D 1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 anion exchange chromatographya t

13、ype of liquidchromatography in which anionic analytes are separated bydifferential retention on an anion exchange resin and detectedby an appropriate detection mechanism.3.2.2 eluentthe liquid mobile phase used in anion ex-change chromatography to transport the sample through thechromatography syste

14、m.3.2.3 analytical columnthe chromatography column thatcontains the stationary phase for separation by ion exchange.The column is packed with anion exchange resin that separatesthe analytes of interest based on their retention characteristicsprior to detection.1This test method is under the jurisdic

15、tion of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.05 on Inorganic Constituentsin Water.Current edition approved March 1, 2004. Published April 2004.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For referenced AS

16、TM 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshoh

17、ocken, PA 19428-2959, United States.3.2.4 guard columna short chromatography column thatis placed before the analytical column to protect it fromparticulates and impurities that may cause fouling.3.2.5 anion trap columna high-capacity, low-pressureanion exchange column used to remove reagent impurit

18、iesfrom the eluent stream. The anion trap column is placedbetween the eluent reservoir and the gradient pump.3.2.6 gradient elutiona type of elution in which the eluentcomposition is steadily altered throughout the analysis in orderto provide for an adequate separation of the analytes of interestpri

19、or to detection.3.2.7 gradient pumpa liquid chromatography pump that iscapable of performing gradient elutions.3.2.8 total cyanidethe sum total of all of the inorganicchemical forms of cyanide. Total cyanide thus includes bothfree cyanide and anionic metal cyanide complexes.3.2.9 metal cyanide compl

20、exa negatively charged ioniccomplex consisting of one or more cyanide ions bound to asingle transition metal cation. Also referred to as metal-complexed cyanides, these complexes have the general for-mula:MCN!b#x2(1)where:M = transition metal cation,b = number of cyanide groups, andx = ionic charge

21、of the transition metal complex.3.2.9.1 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”

22、 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 most stable and least toxicforms of cyanide. Refer to Guide D 6696 f

23、or a more detaileddiscussion of aqueous cyanide species.3.2.9.2 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 cyanidethe form of cyanide recogni

24、zed asbeing bioavailable and toxic. Free cyanide may be present aseither molecular HCN or the anion CN- depending on the pHconditions. Refer to Guide D 6696 for a more detailed discus-sion of aqueous cyanide species.4. Summary of Test Methods4.1 Dissolved metal cyanide complexes are determined byani

25、on 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 rangewill d

26、iffer 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 elutedfrom th

27、e 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-duced to ferr

28、ocyanide (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-line sampl

29、e 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 concentration,

30、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 preconcentrationmetho

31、d 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 com-plexe

32、s.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 complexes of gre

33、ater 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 determine free cy

34、anide 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 cyanide comple

35、xes.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). Samples shall be analyzed in amber bottles andprotected from light whenever possible.6.2 Carbo

36、nate 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 preparing andusing

37、sodium hydroxide eluents (9,10).D6994042NOTE 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 outgassing

38、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 impurities

39、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 installing the

40、 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 the head o

41、fthe 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 columnequili

42、bration 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 in the com

43、bined 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 7.2.5).6.6 The

44、 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 relatively hig

45、h 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 preconcentration, the s

46、ilver 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. For the cop

47、per 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 perform

48、ing 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 capable of maintaininga2to10psiheadpressure on the

49、eluent solutions using helium gas.7.1.2 Pressurizable Eluent BottlesBottles must be capableof withstanding an internal pressure of 7 to 10 psi. The bottlesmust be made of a chemically inert plastic such as polypropy-lene, suitable for use with sodium hydroxide-based eluents.7.1.3 TubingTo be used with the eluent reservoir andmade of a material that is compatible with the eluent solutions.7.1.4 Gradient PumpHigh performance liquid chroma-tography (HPLC) or ion chromatography (IC) pump capable ofdelivering a constant flow in the range of 1 to 5 mL/min at apressur