ASTM D7237-2018 Standard Test Method for Free Cyanide and Aquatic Free Cyanide with Flow Injection Analysis (FIA) Utilizing Gas Diffusion Separation and Amperom.pdf

1、Designation: D7237 15aD7237 18Standard 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 indic

2、ates 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 is used to establish the

3、concentration of free cyanide in an aqueous wastewater, effluent and in-stream freecyanide concentrations after mixing treated water with receiving water. The test conditions of this test method are used to measurefree cyanide (HCN and CN-) and cyanide bound in the metal-cyanide complexes that are e

4、asily dissociated into free cyanide ionsat the pH of 6. Free cyanide is determined at pH 6 at room temperature. The aquatic free cyanide can be determined by matchingthe pH to the water in the receiving environment in the range of pH 6 to 8. The extent of HCN formation is less dependent ontemperatur

5、e than the pH; however, the temperature can be regulated if deemed necessary for aquatic free cyanide to furthersimulate the actual aquatic environment.1.2 The free cyanide test method is based on the same instrumentation and technology that is described in Test Method D6888,but employs milder condi

6、tions (pH 68 buffer versus HCl or H2SO4 in the reagent stream), and does not utilize ligand displacementreagents.1.3 The aquatic free cyanide measured by this procedure should be similar to actual levels of HCN in the original aquaticenvironment. This in turn may give a reliable index of toxicity to

7、 aquatic organisms.1.4 This procedure is applicable over a range of approximately 5 to 500 g/L (parts per billion) free cyanide. Sample dilutionmay increase cyanide recoveries depending on the cyanide speciation; therefore, it is not recommended to dilute samples. Higherconcentrations can be analyze

8、d by increasing the range of calibration standards or with a lower injection volume. In accordancewith Guide E1763 and Practice D6512 the lower scope limit was determined to be 9 g/L for chlorinated gold leaching barreneffluent water and the IQE10 % is 12 g/L in the gold processing detoxified revers

9、e osmosis permeate waste water sample matrix.1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.6 This test method is not recommended for samples that contain reduced sulfur compounds such as sulfides.1.7 This standard does

10、 not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine theapplicability of regulatory limitations prior to use. Specific

11、hazard statements are given in 8.6 and Section 9.1.8 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the

12、World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD1193 Specification for Reagent WaterD1293 Test Methods for pH of WaterD2036 Test Methods for Cyanides in Water1 This test method is under the jurisdicti

13、on of ASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.06 on Methods for Analysis forOrganic Substances in Water.Current edition approved June 1, 2015Dec. 1, 2018. Published June 2015January 2019. Originally approved in 2006. Last previous edition approved in 2015 asD

14、7237 15.D7237 15a. DOI: 10.1520/D7237-15A.10.1520/D7237-18.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standardsstandards Document Summary page on the ASTM w

15、ebsite.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult pr

16、ior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19

17、428-2959. United States1D2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on WaterD3856 Guide for Management Systems in Laboratories Engaged in Analysis of WaterD4658 Test Method for Sulfide Ion in WaterD4841 Practice for Estimation of Holding Time fo

18、r Water Samples Containing Organic and Inorganic ConstituentsD5847 Practice for Writing Quality Control Specifications for Standard Test Methods for Water AnalysisD6512 Practice for Interlaboratory Quantitation EstimateD6696 Guide for Understanding Cyanide SpeciesD6888 Test Method for Available Cyan

19、ides with Ligand Displacement and Flow Injection Analysis (FIA) Utilizing GasDiffusion Separation and Amperometric DetectionD7365 Practice for Sampling, Preservation and Mitigating Interferences in Water Samples for Analysis of CyanideD7728 Guide for Selection of ASTM Analytical Methods for Implemen

20、tation of International Cyanide Management CodeGuidanceE691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test MethodE1601 Practice for Conducting an Interlaboratory Study to Evaluate the Performance of an Analytical MethodE1763 Guide for Interpretation and Use of

21、Results from Interlaboratory Testing of Chemical Analysis Methods (Withdrawn2015)33. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this standard, refer to Terminology D1129 and Guide D6696.3.2 Definitions of Terms Specific to This Standard:For definitions of terms used in this te

22、st method, refer to TerminologyD1129 and Guide D6696.3.2.1 aquatic free cyanide, nfree cyanide measured when the buffer or temperature is adjusted to mimic the receiving-waterenvironment.3.2.2 free cyanide, nsum of the free cyanide (HCN and CN-) and cyanide bound in the metal-cyanide complexes that

23、areeasily dissociated into free cyanide under the test conditions described in this test method at pH 6 and room temperature.4. Summary of Test Method4.1 The test is generally performed at room temperature, but temperature of the sample and flow injection reagents can beregulated to match the aquati

24、c environment if necessary to measure aquatic free cyanide.4.2 The sample is introduced into a carrier solution of the flow injection analysis (FIA) system via an injection valve andconfluence downstream with a phosphate buffer solution at pH 6 to measure free cyanide or in the range of pH 6 to 8 to

25、 measureaquatic free cyanide. The released hydrogen cyanide (HCN) gas diffuses through a hydrophobic gas diffusion membrane into analkaline acceptor stream where the CN- is captured and sent to an amperometric flowcell detector with a silver-working electrode.In the presence of cyanide, silver in th

26、e working electrode is oxidized at the applied potential. The anodic current measured isproportional to the concentration of cyanide in the standard or sample injected.4.3 Calibrations and sample data are processed with the instrumentsinstruments data acquisition software.5. Significance and Use5.1

27、Cyanide and hydrogen cyanide are highly toxic. Regulations have been established to require the monitoring of cyanide inindustrial and domestic wastes and surface waters.45.2 It is useful to determine the aquatic free cyanide to establish an index of toxicity when a wastewater is introduced into the

28、natural environment at a given pH and temperature.5.3 This test method is applicable for natural water, saline waters, and wastewater effluent.5.4 Free cyanide measured using this test method is applicable for implementation of the International Cyanide Code Guidancein accordance with Guide D7728.6.

29、 Interferences6.1 Sulfide will diffuse through the gas diffusion membrane and can be detected in the amperometric flowcell. Oxidizedproducts of sulfide can also rapidly convert CN- to SCN- at a high pH. Refer to 11.3 for sulfide removal.6.2 Refer to 6.1 of Test Method D6888 and Test Methods D2036 fo

30、r elimination of cyanide interferences.3 The last approved version of this historical standard is referenced on www.astm.org.4 40 CFR Part 136.D7237 1826.1 Residual Sulfide, as H2S, will diffuse through the gas diffusion membrane and can be detected in the amperometric flowcell.Also, residual flotat

31、ion reagents have been shown to interfere, which is indicated by failure of the amperometric signal to returnto baseline compared to the standards.This effect is attributed to the formation of volatile carbon disulfide. If sulfides are suspected,confirm by means of Test Method D4658this interference

32、 is encountered, verify by comparing with analysis using Test Method.Aside from this method, ion chromatography may be used as a reliable means for D6888 including bismuth nitratedeterminingsulfide interference. See Appendix X1in the acidification reagent on a solution without sodium hydroxide prese

33、rvation, whichshould provide confirmation due to lower results For National Pollutant Discharge Elimination System reporting, however, theuser is advised to analyze the sample using Test Method D6888 for samples containing reduced sulfur compounds.6.2 Oxidants can continue to react with free cyanide

34、 if present, lowering the concentration, if not immediately treated with areducing reagent during sampling.7. Apparatus7.1 The instrument must be equipped with a precise sample introduction system, a gas diffusion manifold with hydrophobicmembrane, and an amperometric detection system to include a

35、silver working electrode, a Ag/AgCl reference electrode, and a Ptor stainless steel counter electrode. An example of the apparatus schematic is shown in Fig. 1. Example instrument settings areshown in Table 1.NOTE 1The instrument and settings in Fig. 1 and Table 1 are shown as examples. The analyst

36、may modify these settings as long as performance ofthe method has not been degraded. Contact the instrument manufacturer for recommended instrument parameters.7.2 An autosampler is recommended but not required to automate sample injections and increase throughput.Autosamplers areusually available as

37、 an option from the instrumentsinstruments manufacturer. If the sample is to be analyzed at a constanttemperature other than the temperature of the room, manual injections may be required unless the autosampler is equipped tomaintain constant temperature.7.3 If aquatic free cyanide at a temperature

38、other than room temperature is required, a constant temperature bath capable ofmaintaining the temperature of the aquatic environment within 60.5C should be used to regulate the temperature of the flowinjection reagents and samples.7.4 Data Acquisition SystemUse the computer hardware and software re

39、commended by the instrument manufacturer tocontrol the apparatus and to collect data from the detector.7.5 Pump TubingUse tubing recommended by instrument manufacturer. Replace pump tubing when worn, or when precisionis no longer acceptable.7.6 Gas Diffusion MembranesA hydrophobic membrane which all

40、ows gaseous hydrogen cyanide to diffuse from the donorto the acceptor stream at a sufficient rate to allow detection. The gas diffusion membrane should be replaced when the baselinebecomes noisy, or every 1 to 2 weeks.C = carrier (water), R = reagent buffer (variable: pH 6 for free cyanide and pH 6-

41、868 for aquatic free cyanide, 0.2 M phosphate buffer), A = acceptor solution (0.1 MNaOH), S = sample, PPP = peristaltic pump (flow rates in mL/min), I = injection valve (200 L sample loop), MC = mixing coolcoil (3060 cm 0.5 mm i.d.),ID), positionedin optional constant temperature manifold, D = gas-d

42、iffusion cell, FC = amperometric flow cell, PO/DAT = potentiostat/data collection device running data acquisitionsoftware, W = waste flows.FIG. 1 Example of Flow Injection Manifold for the Determination of Aquatic Free CyanideD7237 1837.7 Use parts and accessories as directed by instrument manufactu

43、rer.8. Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that allreagents shall conform to the specifications of the American Chemical Society, where such specifications are available.5 Othergrades may be used,

44、provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lesseningthe accuracy of the determination.8.2 Purity of WaterUnless otherwise indicated, references to water shall be understood to mean reagent water that meets thepurity specifications of Ty

45、pe I or Type II water, presented in Specification D1193.8.3 Sodium Hydroxide Solution (1.00M (1.00 M NaOH)Dissolve 40 g NaOH in laboratory water and dilute to 1 L.8.4 Sodium Hydroxide and Acceptor Solution (0.10 M NaOH)Dissolve 4.0 g NaOH in laboratory water and dilute to 1 L.NOTE 2Acceptor solution

46、 concentration of 0.025 M NaOH has also been found to be acceptable.8.5 CarrierWater, as described in 8.2.NOTE 3Carrier solution containing 0.025 M NaOH has also been found to be acceptable.8.6 Stock Cyanide Solution (1000 g/mL CN-)Dissolve 2.51 g of KCN and 2.0 g of NaOH in 1 L of water. Standardiz

47、e withsilver nitrate solution as described in Test Methods D2036, 16.2. Store the solution under refrigeration and check concentrationapproximately every 6 months and correct if necessary.6 (WarningBecause KCN is highly toxic, avoid contact or inhalation.)5 Reagent Chemicals, American Chemical Socie

48、ty Specifications, Am.American Chemical Soc.,Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American chemicalChemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United StatesPharmacopeia.Pharmacopeia and Nation

49、al Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.6 Commercial Solutions of Stock Cyanide may be substituted.TABLE 1 Flow Injection Analysis ParametersFIA InstrumentParameterRecommendedMethod SettingFIA InstrumentParameterRecommendedMethod SettingPump Flow Rates 0.5 to 2.0 mL/minPump flow rates 0.5 to 2.0 mL/minCycle period (total) Approximately 120 secondsSample load period At least enough time to completely fill thesample loop prior to injectionInjection valve rinse timebetween samplesAt least enough time to rinse the