1、Designation: D7237 15Standard Test Method forFree Cyanide and Aquatic Free Cyanide with Flow InjectionAnalysis (FIA) Utilizing Gas Diffusion Separation andAmperometric Detection1This standard is issued under the fixed designation D7237; the number immediately following the designation indicates the
2、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 is used to establish the concentra
3、tion offree cyanide in an aqueous wastewater, effluent and in-streamfree cyanide concentrations after mixing treated water withreceiving water. The test conditions of this test method are usedto measure free cyanide (HCN and CN-) and cyanide bound inthe metal-cyanide complexes that are easily dissoc
4、iated intofree cyanide ions at the pH of 6. Free cyanide is determined atpH 6 at room temperature. The aquatic free cyanide can bedetermined by matching the pH to the water in the receivingenvironment in the range of pH 6 to 8. The extent of HCNformation is less dependent on temperature than the pH;
5、however, the temperature can be regulated if deemed necessaryfor aquatic free cyanide to further simulate the actual aquaticenvironment.1.2 The free cyanide test method is based on the sameinstrumentation and technology that is described in TestMethod D6888, but employs milder conditions (pH 6-8 buf
6、ferversus HCl or H2SO4in the reagent stream), and does notutilize ligand displacement reagents.1.3 The aquatic free cyanide measured by this procedureshould be similar to actual levels of HCN in the originalaquatic environment. This in turn may give a reliable index oftoxicity to aquatic organisms.1
7、.4 This procedure is applicable over a range of approxi-mately 5 to 500 g/L (parts per billion) free cyanide. Sampledilution may increase cyanide recoveries depending on thecyanide speciation; therefore, it is not recommended to dilutesamples. Higher concentrations can be analyzed by increasingthe r
8、ange of calibration standards or with a lower injectionvolume. In accordance with Guide E1763 and Practice D6512the lower scope limit was determined to be 9 g/L forchlorinated gold leaching barren effluent water and the IQE10 %is 12 g/L in the gold processing detoxified reverse osmosispermeate waste
9、 water sample matrix.1.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 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 stand
10、ard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. Specific hazardstatements are given in 8.6 and Section 9.2. Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD1193 Specification for Reagent Wa
11、terD1293 Test Methods for pH of WaterD2036 Test Methods for Cyanides in WaterD2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD3856 Guide for Management Systems in LaboratoriesEngaged in Analysis of WaterD4841 Practice for Estimation of Holdin
12、g Time for WaterSamples Containing Organic and Inorganic ConstituentsD5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water AnalysisD6512 Practice for Interlaboratory Quantitation EstimateD6696 Guide for Understanding Cyanide SpeciesD6888 Test Method for Availab
13、le Cyanide with LigandDisplacement and Flow InjectionAnalysis (FIA) UtilizingGas Diffusion Separation and Amperometric DetectionD7365 Practice for Sampling, Preservation and MitigatingInterferences in Water Samples for Analysis of CyanideD7728 Guide for Selection ofASTMAnalytical Methods forImplemen
14、tation of International Cyanide ManagementCode Guidance1This 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 Feb. 1, 2015. Published March 2015.
15、Originallyapproved in 2006. Last previous edition approved in 2010 as D7237 10. DOI:10.1520/D7237-15.2For 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 D
16、ocument 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 States1E691 Practice for Conducting an Interlaboratory Study toDetermine the Precision o
17、f a Test MethodE1601 Practice for Conducting an Interlaboratory Study toEvaluate the Performance of an Analytical MethodE1763 Guide for Interpretation and Use of Results fromInterlaboratory Testing of Chemical Analysis Methods(Withdrawn 2015)33. Terminology3.1 DefinitionsFor definitions of terms use
18、d in this testmethod, refer to Terminology D1129 and Guide D6696.3.1.1 aquatic free cyanide, nfree cyanide measured whenthe buffer or temperature is adjusted to mimic the receiving-water environment.3.1.2 free cyanide, nsum of the free cyanide (HCN andCN-) and cyanide bound in the metal-cyanide comp
19、lexes thatare easily dissociated into free cyanide under the test condi-tions described in this test method at pH 6 and room tempera-ture.4. Summary of Test Method4.1 The test is generally performed at room temperature, buttemperature of the sample and flow injection reagents can beregulated to matc
20、h the aquatic environment if necessary tomeasure aquatic free cyanide.4.2 The sample is introduced into a carrier solution of theflow injection analysis (FIA) system via an injection valve andconfluence downstream with a phosphate buffer solution at pH6 to measure free cyanide or in the range of pH
21、6 to 8 tomeasure aquatic free cyanide. The released hydrogen cyanide(HCN) gas diffuses through a hydrophobic gas diffusionmembrane into an alkaline acceptor stream where the CN-iscaptured and sent to an amperometric flowcell detector with asilver-working electrode. In the presence of cyanide, silver
22、 inthe working electrode is oxidized at the applied potential. Theanodic current measured is proportional to the concentration ofcyanide in the standard or sample injected.4.3 Calibrations and sample data are processed with theinstruments data acquisition software.5. Significance and Use5.1 Cyanide
23、and hydrogen cyanide are highly toxic. Regu-lations have been established to require the monitoring ofcyanide in industrial and domestic wastes and surface waters.45.2 It is useful to determine the aquatic free cyanide toestablish an index of toxicity when a wastewater is introducedinto the natural
24、environment at a given pH and temperature.5.3 This test method is applicable for natural water, salinewaters, and wastewater effluent.5.4 Free cyanide measured using this test method is appli-cable for implementation of the International Cyanide CodeGuidance in accordance with Guide D7728.6. Interfe
25、rences6.1 Sulfide will diffuse through the gas diffusion membraneand can be detected in the amperometric flowcell. Oxidizedproducts of sulfide can also rapidly convert CN-to SCN-at ahigh pH. Refer to 11.3 for sulfide removal.6.2 Refer to 6.1 of Test Method D6888 and Test MethodD2036 for elimination
26、of cyanide interferences.6.3 Residual flotation reagents have been shown tointerfere,5which is indicated by failure of the amperometricsignal to return to baseline compared to the standards. Thiseffect is attributed to the formation of volatile carbon disulfide.If this interference is encountered, v
27、erify by comparing withanalysis using Test Method D6888 including bismuth nitrate inthe acidification reagent on a solution without sodium hydrox-ide preservation, which should provide confirmation due tolower results.7. Apparatus7.1 The instrument must be equipped with a precise sampleintroduction
28、system, a gas diffusion manifold with hydropho-bic membrane, and an amperometric detection system toinclude a silver working electrode, a Ag/AgCl referenceelectrode, and a Pt or stainless steel counter electrode. Anexample of the apparatus schematic is shown in Fig. 1.Example instrument settings are
29、 shown in Table 1.NOTE 1The instrument and settings in Fig. 1 and Table 1 are shownas examples. The analyst may modify these settings as long as perfor-mance of the method has not been degraded. Contact the instrumentmanufacturer for recommended instrument parameters.7.2 An autosampler is recommende
30、d but not required toautomate sample injections and increase throughput. Autosam-plers are usually available as an option from the instrumentsmanufacturer. If the sample is to be analyzed at a constanttemperature other than the temperature of the room, manualinjections may be required unless the aut
31、osampler is equippedto maintain constant temperature.7.3 If aquatic free cyanide at a temperature other than roomtemperature is required, a constant temperature bath capable ofmaintaining the temperature of the aquatic environment within60.5C should be used to regulate the temperature of the flowinj
32、ection reagents and samples.7.4 Data Acquisition SystemUse the computer hardwareand software recommended by the instrument manufacturer tocontrol the apparatus and to collect data from the detector.7.5 Pump TubingUse tubing recommended by instrumentmanufacturer. Replace pump tubing when worn, or whe
33、nprecision is no longer acceptable.7.6 Gas Diffusion MembranesA hydrophobic membranewhich allows gaseous hydrogen cyanide to diffuse from thedonor to the acceptor stream at a sufficient rate to allowdetection. The gas diffusion membrane should be replacedwhen the baseline becomes noisy, or every 1 t
34、o 2 weeks.3The last approved version of this historical standard is referenced onwww.astm.org.440 CFR Part 136.5Solujic, L., and Milosavljevic, E., Flotation Reagents Testing and Analyses ofCyanide Spiked Samples, Report to Newmont Mining Corporation, July 30, 2011.D7237 1527.7 Use parts and accesso
35、ries as directed by instrumentmanufacturer.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 a
36、vailable.6Other grades may 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 me
37、etsthe purity specifications of Type I or Type II water, presentedin D1193.8.3 Sodium Hydroxide Solution (1.00M NaOH)Dissolve40 g NaOH in laboratory water and dilute to 1 L.8.4 Sodium Hydroxide and Acceptor Solution (0.10 MNaOH)Dissolve 4.0 g NaOH in laboratory water and diluteto1L.NOTE 2Acceptor so
38、lution concentration of 0.025 M NaOH has alsobeen found to be acceptable.8.5 CarrierWater, as described in 8.2.NOTE 3Carrier solution containing 0.025 M NaOH has also beenfound to be acceptable.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. Standar
39、dizewith silver nitrate solution as described in Test MethodsD2036, 16.2. Store the solution under refrigeration and checkconcentration approximately every 6 months and correct ifnecessary.7(WarningBecause KCN is highly toxic, avoidcontact or inhalation.)8.7 Intermediate Cyanide Standards:8.7.1 Inte
40、rmediate 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 weeks.8.7.2 Intermediate Cyanide
41、 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 Cyanide Calibration StandardsPrepare
42、freshdaily as described in 8.8.1 and 8.8.2 ranging in concentrationfrom 2 to 500 g/L CN-.6Reagent Chemicals, American Chemical Society Specifications, Am. ChemicalSoc., Washington, DC. For suggestions on the testing of reagents not listed by theAmerican chemical Society, see Analar Standards for Lab
43、oratory Chemicals, BDHLtd., Poole, Dorset, U.K., and the United States Pharmacopeia.7Commercial Solutions of Stock Cyanide may be substituted.C = carrier (water), R = reagent buffer (variable: pH 6 for free cyanide and pH 6-8 for aquatic free cyanide, 0.2 M phosphate buffer),A= acceptor solution (0.
44、1 M NaOH),S = sample, P = peristaltic pump (flow rates in mL/min),I=injectionvalve(200Lsample loop), MC = mixing cool (3060 cm 0.5 mm i.d.), positioned in optional constanttemperature manifold, D = gas-diffusion cell, FC = amperometric flow cell, PO/DAT = potentiostat/data collection device running
45、data acquisition software, W = waste flows.FIG. 1 Example of Flow Injection Manifold for the Determination of Aquatic Free CyanideTABLE 1 Flow Injection Analysis ParametersFIA InstrumentParameterRecommendedMethod SettingPump Flow Rates 0.5 to 2.0 mL/minCycle period (total) Approximately 120 secondsS
46、ample load period At least enough time to completely fill thesample loop prior to injectionInjection valve rinse timebetween samplesAt least enough time to rinse thesample loopPeak Evaluation Peak height or areaWorking Potential 0.0 V vs. Ag/AgClD7237 1538.8.1 Calibration Standards (20, 50, 100, 200
47、, and 500 g/LCN-)Pipette 20, 50, 100, 200, and 500 L of IntermediateStandard 1 (see 8.7.1) into separate 100 mL volumetric flaskscontaining 1.0 mL of 0.10 M NaOH (see 8.4). Dilute to volumewith laboratory water.8.8.2 Calibration Standards (2, 5, and 10 g/L CN-)Pipette 20, 50, and 100 L of Intermedia
48、te Cyanide Solution 2(see 8.7.2) into separate 100 mL volumetric flasks containing1.0 mL of 0.10 M NaOH (see 8.4). Dilute to volume withlaboratory water.8.9 Cyanide Electrode Stabilization Solution (Approxi-mately 5 ppm as CN-)Pipette 500 L of Stock Cyanide (see8.6) into a 100 mL volumetric flask co
49、ntaining 1.0 mL of0.10M M NaOH (see 8.4). Dilute to volume with laboratorywater. The solution should be stored under refrigeration.8.10 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 4.5.8.11 Buffer Solution A, 2M Sodium phosphate monobasicsolutionWeigh 276 g sodium phosphate monobasic monohy-drate (NaH2PO4H2O)ina1Lvolumetric flask. Dissolve anddilute to volume with water.8.12 Buffer Solution B, 2 M Sodium phosphate dib
