ASTM D7284-2008 345 Standard Test Method for Total Cyanide in Water by Micro Distillation followed by Flow Injection Analysis with Gas Diffusion Separation and Amperometric Detecti.pdf

1、Designation: D 7284 08Standard Test Method forTotal Cyanide in Water by Micro Distillation followed byFlow Injection Analysis with Gas Diffusion Separation andAmperometric Detection1This standard is issued under the fixed designation D 7284; the number immediately following the designation indicates

2、 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 is used to determine the conc

3、entrationof total cyanide in an aqueous wastewater or effluent. Themethod detects the cyanides that are free (HCN and CN-) andstrong-metal-cyanide complexes that dissociate and releasefree cyanide when refluxed under strongly acidic conditions.1.2 This method may not be applicable to process solutio

4、nsfrom precious metals mining operations.1.3 This procedure is applicable over a range of approxi-mately 2 to 400 g/L (parts per billion) total cyanide. Higherconcentrations can be measured with sample dilution or lowerinjection volume.1.4 The determinative step of this method utilizes flowinjection

5、 with amperometric detection based on Test MethodD 6888. Prior to analysis, samples must be distilled with amicro-distillation apparatus described in this test method orwith a suitable cyanide distillation apparatus specified in TestMethods D 2036.1.5 This standard does not purport to address all of

6、 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 to use. Specific hazardstatements are given in Note 2 and Section 9.2. Ref

7、erenced Documents2.1 ASTM Standards:2D 1129 Terminology Relating to WaterD 1193 Specification for Reagent WaterD 2036 Test Methods for Cyanides in WaterD 2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD 3856 Guide for Good Laboratory Practice

8、s in Laborato-ries Engaged in Sampling and Analysis of WaterD 5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water AnalysisD 6696 Guide for Understanding Cyanide SpeciesD 6888 Test Method for Available Cyanide with LigandDisplacement and Flow Injection Analysis

9、 (FIA) UtilizingGas Diffusion Separation and Amperometric DetectionD 7365 Practice for Sampling, Preservation and MitigatingInterferences in Water Samples for Analysis of Cyanide3. Terminology3.1 Definitions: For definitions of terms used in this testmethod, refer to Terminology D 1129 and Guide D 6

10、696.3.1.1 total cyanideTotal cyanide is an analytically definedterm that refers to the sum total of all of the inorganic chemicalforms of cyanide that dissociate and release free cyanide whenrefluxed under strongly acidic conditions. Total cyanide isdetermined analytically through strong acid distil

11、lation or UVradiation followed by analysis of liberated free cyanide onaqueous samples preserved with NaOH (pH12). In water,total cyanide includes the following dissolved species: freecyanide, weak acid dissociable metal cyanide complexes andstrong metal cyanide complexes. Also, some of the strongme

12、tal cyanide complexes, such as those of gold, cobalt andplatinum, might not be fully recovered during the total cyanideanalytical procedure. Additionally, total cyanide may alsoinclude some organic forms of cyanide such as nitriles thatrelease free cyanide under the conditions of the analysis.4. Sum

13、mary of Test Method4.1 The samples are distilled with a strong acid in thepresence of magnesium chloride catalyst and captured insodium hydroxide absorber solution.4.2 The absorber solution is introduced into a flow injectionanalysis (FIA) system where it is acidified to form hydrogencyanide (HCN).

14、The hydrogen cyanide gas diffuses through a1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.06 on Methods forAnalysis forOrganic Substances in Water.Current edition approved April 1, 2008. Published April 2008.2For referen

15、ced 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West C

16、onshohocken, PA 19428-2959, United States.hydrophobic gas diffusion membrane, from the acidic donorstream into an alkaline acceptor stream.4.3 The captured cyanide is sent to an amperometric flow-cell detector with a silver-working electrode. In the presence ofcyanide, silver in the working electrod

17、e is oxidized at theapplied potential. The anodic current measured is proportionalto the concentration of cyanide.4.4 Calibrations and data are processed with the instru-ments data acquisition software.5. Significance and Use5.1 Cyanide and hydrogen cyanide are highly toxic. Regu-lations have been e

18、stablished to require the monitoring ofcyanide in industrial and domestic wastes and surface waters.35.2 This test method is applicable for natural waters, indus-trial wastewaters and effluents.6. Interferences6.1 Improper sample collection or pretreatment can result insignificant positive or negati

19、ve bias, therefore it is imperativethat samples be collected and mitigated for interferences asdescribed in Practice D 7365.6.1.1 Sulfide captured in the absorber solution above 50-mg/L S2-will diffuse through the gas diffusion membraneduring flow injection analysis and can be detected in theamperom

20、etric flowcell as a positive response. Refer to Section11.2 for sulfide abatement.6.1.2 Thiocyanate in the presence of oxidants (for example,nitrates, hydrogen peroxide, chlorine or chloramine, Carosacid), can decompose to form cyanide during the distillationresulting in positive interference regard

21、less of the determina-tive step (amperometry, colorimetry, etc.). During acidic dis-tillation, decomposition of thiocyanate in the absence ofoxidants produces elemental sulfur, sulfur(IV) oxide, as well ascarbonyl sulfide which eventually leads to the formation ofsulfite ion (SO32-) in the NaOH abso

22、rbing solution. The sulfiteion slowly oxidizes cyanide to cyanate resulting in a negativeinterference. Therefore, samples that are known to containsignificant amounts of thiocyanate may need to be analyzedwith a method that does not require distillation, for example,available cyanide by Test Method

23、D 6888.6.1.2.1 During the validation study, synthetic samples con-taining up to 15 mg/LSCN-and 25 mg/LNO3as N yielded lessthan 0.5 % of the SCN-to be measurable CN-. For example, asolution that did not contain any known amount of cyanide, butdid contain 15-mg/L SCN-and 25 mg/L NO3as N, wasmeasured a

24、s 53.1 g/L CN-.7. Apparatus and Instrumentation7.1 The instrument should be equipped with a precisesample introduction system, a gas diffusion manifold withhydrophobic membrane, and an amperometric detection sys-tem to include a silver working electrode, a Ag/AgCl referenceelectrode, and a Pt or sta

25、inless steel counter electrode. Theapparatus schematic is shown in Fig. 1, and example instru-ment settings are shown in Table 1.4NOTE 1The instrument settings in Table 1 are only examples. Theanalyst may modify the settings as long as performance of the method hasnot been degraded. Contact the inst

26、rument manufacturer for recommendedinstrument parameters.7.1.1 An autosampler is recommended but not required toautomate sample injections and increase throughput. Autosam-plers are usually available as an option from the instrumentsmanufacturer.7.1.2 Data Acquisition SystemUse the computer hardware

27、and software recommended by the instrument manufacturer tocontrol the apparatus and to collect data from the detector.340 CFR Part 136.4Both the OI Analytical CN Solution and Lachat Instruments QuikChemAutomated Ion Analyzer have been found to be suitable for this analysis.FIG. 1 Flow Injection Anal

28、ysis ApparatusD72840827.1.3 Pump TubingUse tubing recommended by instru-ment manufacturer. Replace pump tubing when worn, or whenprecision is no longer acceptable.7.1.4 Gas Diffusion MembranesA hydrophobic mem-brane which allows gaseous hydrogen cyanide to diffuse fromthe donor to the acceptor strea

29、m at a sufficient rate to allowdetection. The gas diffusion membrane should be replacedwhen the baseline becomes noisy or every 1 to 2 weeks.57.1.5 Use parts and accessories as directed by instrumentmanufacturer.7.2 Distillation ApparatusThe MicroDist System de-scribed below was utilized during the

30、laboratory study todemonstrate precision and bias for this test method. A largerdistillation apparatus such as the MIDI distillation described insection 7 of Test Methods D 2036 can also be used to preparesamples prior to flow injection analysis, but the user isresponsible to determine the precision

31、 and bias.7.2.1 Micro-Distillation Apparatus consisting of a distilla-tion sample tube, stop ring, membrane, and collection vesselcontaining 1.0 M sodium hydroxide and a breakaway collec-tion tube as shown in Fig. 2.67.2.2 Heater block assembly, temperature controlled, ca-pable of heating the MicroD

32、ist tubes to 120C.8. Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of theAmericanChemical Society, where such specifications are available.7Other grades ma

33、y be used, provided it is first ascertained thatthe reagent is of sufficiently high purity to permit its usewithout lessening the accuracy of the determination.8.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water that meetsthe purity specificati

34、ons of Type I or Type II water, presentedin Specification D 1193.8.3 Sodium Hydroxide Solution (1.00 M)Dissolve 40 gNaOH in laboratory water and dilute to 1 L.8.4 Absorber Solution for MIDI Distillations (0.25 MNaOH)Dissolve 10 g NaOH in laboratory water and dilute to1L.8.5 Acceptor Solution (0.10 M

35、 NaOH)Dissolve 4.0 gNaOH in laboratory water and dilute to 1 L.8.6 Stock Cyanide Solution (1000 g/mL CN-)Dissolve2.51 g of KCN and 2.0 g of NaOH in 1 L of water. Standardizewith silver nitrate solution as described in Test Methods5The sole source of supply of the apparatus known to the committee at

36、this timeis PALL Life Sciences Part Number M5PU025, OI Analytical Part NumberA0015200, and Lachat Instruments Part Number 50398. If you are aware ofalternative suppliers, please provide this information to ASTM InternationalHeadquarters. Your comments will receive careful consideration at a meeting

37、of theresponsible technical committee,1which you may attend.6The sole source of supply of the apparatus known to the committee at this timeis Lachat Instruments, PNA17001 (subject to US Reg. Patent No. 5,022,967). If youare aware of alternative suppliers, please provide this information to ASTMInter

38、national Headquarters. Your comments will receive careful consideration at ameeting of the responsible technical committee,1which you may attend.7Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlist

39、ed 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, Inc. (USPC), Rockville,MD.TABLE 1 Flow Injection Analysis ParametersFIA Instrument Parameter Reco

40、mmended Method SettingPump Flow Rates 0.5 to 2 mL/minCycle period (total) Approximately 120 secondsSample load period At least enough timeto completely fill thesample loop priorto injectionInjection valve rinse timebetween samplesAt least enough timeto rinse the sample loopPeak Evaluation Peak heigh

41、t or areaWorking Potential 0.0 V vs Ag/AgClFIG. 2 MicroDist Sample TubeD7284083D 2036, section 16.2. Store the solution under refrigeration andcheck concentration approximately every 6 months and correctif necessary.8NOTE 2Warning: Because KCN is highly toxic, avoid contact orinhalation.8.7 Intermed

42、iate Cyanide Standards:8.7.1 Intermediate Standard 1 (100 g/mL CN-)Pipette10.0 mL of stock cyanide solution (see 8.6) into a 100 mLvolumetric flask containing 1 mL of 1.0 M NaOH (see 8.3).Dilute to volume with laboratory water. Store under refrigera-tion. The standard should be stable for at least 2

43、 weeks.8.7.2 Intermediate Cyanide Solution 2 (10 g/mL CN-)Pipette 10.0 mL of Intermediate Cyanide Solution 1 (see 8.7.1)into a 100 mL volumetric flask containing 1.0 mL of 1.00 MNaOH (see 8.3). Dilute to volume with laboratory water. Thestandard should be stable for at least 2 weeks.8.8 Working Cyan

44、ide Calibration StandardsPrepare freshdaily as described in 8.8.1 and 8.8.2 ranging in concentrationfrom 2 to 400 g/mL CN-.8.8.1 Calibration Standards (50, 100, 200, and 400 g/mLCN-)Pipette 50, 100, 200, 400, and 400 L of IntermediateStandard 1 (see 8.7.1) into separate 100 mL volumetric flasksconta

45、ining 1.0 mL of 1.00 M NaOH (see 8.3). Dilute to volumewith laboratory water.8.8.2 Calibration Standards (2, 5, and 10 g/mL CN-)Pipette 20, 50, and 100 L of Intermediate Cyanide Solution 2(see 8.7.2) into separate 100 mL volumetric flasks containing1.0 mL of 1.00 M NaOH (see 8.3). Dilute to volume w

46、ithlaboratory water.8.9 Potassium Ferricyanide Stock Solution (1000 g/mL asCN-)Weigh 0.2109 g K3Fe(CN)6into a 100-mL volumetricflask containing 1 mL 1 M NaOH, then dilute to volume withlaboratory water.8.9.1 Potassium Ferricyanide Spiking Solution (100 g/mLCN-)Pipette 10.0 mL of potassium ferricyani

47、de stock solu-tion into a 100 mL volumetric flask containing 1.0 mL of 1.00M NaOH, then dilute to volume with laboratory water.8.10 Cyanide Electrode Stabilization Solution (Approxi-mately 2 ppm as CN-)Pipette 200 L of Stock Cyanide (see8.6) into a 100 mL volumetric flask containing 1.0 mL of 1.00M

48、NaOH (see 8.3). Dilute to volume with laboratory water.The solution should be stored under refrigeration.8.11 CarrierWater as indicated in Section 8.2.8.12 Acidification and Sulfide Abatement SolutionWeigh1.00 g bismuth nitrate pentahydrate, Bi(NO3)35H2O, into a 1L volumetric flask. Add 55 mL of wat

49、er then carefully add 55mL of concentrated sulfuric acid to the flask. Gently swirl theflask until the bismuth nitrate pentahydrate has dissolved in theacid solution. Carefully add water to the volumetric flask andfill to volume.8.13 Acetate BufferDissolve 410 g of sodium acetatetrihydrate (NaC2H3O23H2O) in 500 mL of laboratory water.Add glacial acetic acid (approximately 500 mL) to yield a pHof 4.5.8.14 Lead Acetate Test StripsMoisten lead acetate teststrips with acetate buffer prior to use.8.15 Ag/AgCl Reference Electrode Filling Solution