1、Designation: D7237 10Standard Test Method forFree Cyanide with Flow Injection Analysis (FIA) UtilizingGas Diffusion Separation and Amperometric Detection1This standard is issued under the fixed designation D7237; the number immediately following the designation indicates the year oforiginal adoption
2、 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 concentration offree cyanide in a
3、n aqueous wastewater or effluent. The testconditions of this method are used to measure free cyanide(HCN and CN-) and cyanide bound in the metal-cyanidecomplexes that are easily dissociated into free cyanide ions atthe pH of 6. Free cyanide is determined at pH 6 at roomtemperature. The aquatic free
4、cyanide can be determined bymatching the pH to the water in the receiving environment inthe range of pH 6 to 8. The extent of HCN formation is lessdependent on temperature than the pH; however, the tempera-ture can be regulated if deemed necessary for aquatic freecyanide to further simulate the actu
5、al aquatic environment.1.2 The free cyanide method is based on the same instru-mentation and technology that is described in standard testmethod D6888, but employs milder conditions (pH 6-8 bufferversus HCl or H2SO4in the reagent stream), and does notutilize ligand displacement reagents.1.3 The aqua
6、tic 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.1.4 This procedure is applicable over a range of approxi-mately 2 to 500 g/L (parts per billion) free cyanid
7、e. Sampledilution may increase cyanide recoveries depending on thecyanide speciation; therefore, it is not recommended to dilutesamples. Higher concentrations can be analyzed by increasingthe range of calibration standards or with a lower injectionvolume. In accordance with Guide E1763 and Practice
8、D6512the lower scope limit was determined to be 9 g/L forchlorinated gold leaching barren effluent water.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
9、, 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 8.6 and Section 9.2. Referenced Documents2.1 A
10、STM Standards:2D1129 Terminology Relating to WaterD1193 Specification for Reagent WaterD1293 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 Good Laboratory P
11、ractices in Laborato-ries Engaged in Sampling and Analysis of WaterD4841 Practice for Estimation of Holding Time for WaterSamples Containing Organic and Inorganic ConstituentsD5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water AnalysisD6512 Practice for Inter
12、laboratory Quantitation EstimateD6696 Guide for Understanding Cyanide SpeciesD6888 Test Method for Available Cyanide with LigandDisplacement and Flow Injection Analysis (FIA) UtilizingGas Diffusion Separation and Amperometric DetectionD7365 Practice for Sampling, Preservation and MitigatingInterfere
13、nces in Water Samples for Analysis of CyanideE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE1763 Guide for Interpretation and Use of Results fromInterlaboratory Testing of Chemical Analysis Methods3. Terminology3.1 Definitions For definitions of term
14、s used 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
15、 complexes that1This 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 May 1, 2010. Published June 2010. Originallyapproved in 2006. Last previous
16、edition approved in 2006 as D7237 06. DOI:10.1520/D7237-10.2For 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 Document Summary page onthe ASTM website.1*
17、A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.are easily dissociated into free cyanide under the test condi-tions described in this method at pH 6 and room temperature
18、.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 match the aquatic environment if necessary tomeasure aquatic free cyanide.4.2 The sample is introduced into a carrier solution of theflow inj
19、ection 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 6 to 8 tomeasure aquatic free cyanide. The released hydrogen cyanide(HCN) gas diffuses through a hydrophobic gas diffusionmembrane into a
20、n alkaline acceptor stream where the CN-iscaptured and sent to an amperometric flowcell detector with asilver-working electrode. In the presence of cyanide, silver inthe working electrode is oxidized at the applied potential. Theanodic current measured is proportional to the concentration ofcyanide
21、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 and hydrogen cyanide are highly toxic. Regu-lations have been established to require the monitoring ofcyanide in industrial and domestic
22、wastes and surface waters.35.2 It is useful to determine the aquatic free cyanide toestablish an index of toxicity when a wastewater is introducedinto the natural environment at a given pH and temperature.5.3 This test method is applicable for natural water, salinewaters, and wastewater effluent.6.
23、Interferences6.1 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 section 6.1 of Test Method D6888 and TestMethod D2036 f
24、or elimination of cyanide interferences.7. Apparatus7.1 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 o
25、r stainless steel counter electrode. Anexample of the apparatus schematic is shown in Fig. 1.Example instrument settings are 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
26、not been degraded. Contact the instrumentmanufacturer for recommended instrument parameters.7.2 An autosampler is recommended 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
27、be analyzed at a constanttemperature other than the temperature of the room, manualinjections may be required unless the autosampler is equippedto maintain constant temperature.7.3 If aquatic free cyanide at a temperature other than roomtemperature is required, a constant temperature bath capable of
28、maintaining the temperature of the aquatic environment within6 0.5C should be used to regulate the temperature of the flowinjection reagents and samples.7.4 Data Acquisition SystemUse the computer hardwareand software recommended by the instrument manufacturer tocontrol the apparatus and to collect
29、data from the detector.340 CFR Part 136.C = carrier (water),R=reagent buffer (variable: pH 6 for free cyanide and pH 6-8 for aquatic free cyanide, 0.2M phosphate buffer), A = acceptor solution (0.1M NaOH),S = sample, P = peristaltic pump (flow rates in mL/min), I = injection valve (200L sample loop)
30、, MC = mixing cool (30-60 cm 3 0.5mm i.d.), positioned in optional constanttemperature manifold, D = gas-diffusion cell, FC = amperometric flow cell, PO/DAT = potentiostat/data collection device running data acquisition software, W = waste flows.FIG. 1 Example of flow injection manifold for the dete
31、rmination of aquatic free cyanide.D7237 1027.5 Pump TubingUse tubing recommended by instrumentmanufacturer. Replace pump tubing when worn, or whenprecision is no longer acceptable.7.6 Gas Diffusion MembranesA hydrophobic membranewhich allows gaseous hydrogen cyanide to diffuse from thedonor to the a
32、cceptor stream at a sufficient rate to allowdetection. The gas diffusion membrane should be replacedwhen the baseline becomes noisy, or every 1 to 2 weeks.7.7 Use parts and accessories as directed by instrumentmanufacturer.8. Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall
33、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.4Other grades may be used, provided it is first ascertained thatthe reagent is of sufficiently high purity to p
34、ermit 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 specifications of Type I or Type II water, presentedin D1193.8.3 Sodium Hydroxide Solution (1.00M NaOH)Dis
35、solve40 g NaOH in laboratory water and dilute to 1 L.8.4 Sodium Hydroxide and Acceptor Solution (0.10MNaOH)Dissolve 4.0 g NaOH in laboratory water and diluteto1L.8.5 CarrierWater, as described in section 8.2.8.6 Stock Cyanide Solution (1000 g/mL CN-)Dissolve2.51 g of KCN and 2.0 g of NaOH in 1 L of
36、water. Standardizewith silver nitrate solution as described in Test MethodsD2036, section 16.2. Store the solution under refrigeration andcheck concentration approximately every 6 months and correctif necessary.5(WarningBecause KCN is highly toxic, avoidcontact or inhalation.)8.7 Intermediate Cyanid
37、e 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 weeks.8.7.
38、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 Cyanide Calibra
39、tion StandardsPrepare freshdaily as described in 8.8.1 and 8.8.2 ranging in concentrationfrom 2 to 500 g/L CN-.8.8.1 Calibration Standards (20, 50, 100, 200, 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
40、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 Intermediate 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 withlaborato
41、ry 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 containing 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
42、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 mono-hydrate (NaH2PO4H2O)ina1Lvolumetri
43、c flask. Dissolveand dilute to volume with water.8.12 Buffer Solution B, 2M Sodium phosphate dibasicsolutionWeigh 284 g sodium phosphate dibasic, anhydrous(Na2HPO4)ina1Lvolumetric flask. Dissolve and dilute tovolume with water. If necessary, warm to approximately 40Con a hot plate and stir to comple
44、tely dissolve the sodiumphosphate dibasic into the water. Allow the solution to coolprior to use.8.13 1M Phosphate Buffer pH 7.0 Stock SolutionAdd 97.5mL Buffer SolutionAand 152.5 mL Buffer Solution B to a 500mL volumetric flask. Dilute to volume with water.8.14 0.2 M Phosphate Buffer pH 7.0Ina1Lvol
45、umetricflask, add 200 mL 1M Phosphate Buffer Solution pH 7.0 anddilute to volume with water. The pH should be pH 7.0 6 0.1.Verify the pH as described in D1293 (Test Method A) andadjust if necessary with dilute sodium hydroxide or sulfuricacid. This buffer solution is to be used in the FIA system whe
46、naquatic free cyanide is to be determined at pH 7.0.8.15 1M Phosphate Buffer pH 6.0 Stock SolutionAdd219.25 mL Buffer Solution A and 30.75 mL of Buffer SolutionB to a 500 mL volumetric flask. Dilute to volume with water.8.16 0.2 M Phosphate Buffer pH 6.0Ina1Lvolumetricflask, add 200 mL 1M Phosphate
47、Buffer Solution pH 6.0 and4Reagent 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 Laboratory Chemicals, BDHLtd., Poole, Dorset, U.K., and the Unite
48、d States Pharmacopeia.5Commercial Solutions of Stock Cyanide may be substituted.TABLE 1 Flow Injection Analysis ParametersFIA InstrumentParameterRecommendedMethod SettingPump Flow Rates 0.5 to 2.0 mL/minCycle period (total) Approximately 120 secondsSample load period At least enough time to complete
49、ly 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 103dilute to volume with water. The pH should be pH 6.0 6 0.1.Verify the pH as described in D1293 (Test Method A) andadjust if necessary with dilute sodium hydroxide or sulfuricacid. This buffer solution is to be used in the FIA system whenfree cyanide or aquatic free cyanide is to be determined at pH6.0 or if the pH of the aquatic enviro
