1、Designation: D 7237 06Standard Test Method forAquatic Free Cyanide with Flow Injection Analysis (FIA)Utilizing Gas Diffusion Separation and AmperometricDetection1This standard is issued under the fixed designation D 7237; the number immediately following the designation indicates the year oforiginal
2、 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 establish the concentration ofaquatic
3、“free” cyanide in an aqueous wastewater or effluent.The test conditions of this method are used to measure freecyanide (HCN and CN-) and cyanide bound in the metal-cyanide complexes that are easily dissociated into free cyanideions at the pH of the aquatic environment ranging from pH 6to pH 8. The e
4、xtent of HCN formation is less dependent ontemperature than the pH; however, the temperature can beregulated if deemed necessary to further simulate the actualaquatic environment.1.2 The aquatic free cyanide method is based on the sameinstrumentation and technology that is described in standardtest
5、method D 6888, but employs milder conditions (pH 6-8buffer versus HCl in the reagent stream), and does not utilizeligand 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
6、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) aquatic free cyanide.Sample dilution may increase cyanide recoveries depending onthe cyanide speciation; therefore, it is not recommended todilute samples.
7、Higher concentrations can be analyzed byincreasing the range of calibration standards or with a lowerinjection volume. In accordance with Guide E 1763 andPractice D 6512 the lower scope limit was determined to be 9g/L for chlorinated gold leaching barren effluent water.1.5 This standard does not pur
8、port 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 to use. Specific hazardstatements are given in Secti
9、on 8.6 and Section 9.2. Referenced Documents2.1 ASTM Standards:2D 1129 Terminology Relating to WaterD 1193 Specification for Reagent WaterD 1293 Test Methods for pH of WaterD 2036 Test Methods for Cyanides in WaterD 2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of C
10、ommittee D19 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 4841 Practice for Estimation of Holding Time for WaterSamples Containing Organic and Inorganic ConstituentsD 5847 Practi
11、ce for Writing Quality Control Specificationsfor Standard Test Methods for Water AnalysisD 6512 Practice for Interlaboratory Quantitation EstimateD 6696 Guide for Understanding Cyanide SpeciesD 6888 Test Method for Available Cyanide with LigandDisplacement and Flow Injection Analysis (FIA) Utilizing
12、Gas Diffusion Separation and Amperometric DetectionE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE 1763 Guide for Interpretation and Use of Results fromInterlaboratory Testing of Chemical Analysis Methods3. Terminology3.1 Definitions For definitions
13、 of terms used in this testmethod, refer to Terminology D 1129 and Guide D 6696.3.1.1 aquatic free cyanideSum of the free cyanide (HCNand CN-) and cyanide bound in the metal-cyanide complexes1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of
14、 Subcommittee D19.06 on Methods for Analysis ofOrganic Substances in Water.Current edition approved Feb. 1, 2006. Published February 2006.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume
15、information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.that are easily dissociated into free cyanide under the testconditions described in this method.4. Summary o
16、f 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.4.2 The sample is introduced into a carrier solution of theflow injection analysis (FIA) system via an injectio
17、n valve andconfluenced downstream with a phosphate buffer solution atpH in the 6-8 range. The released hydrogen cyanide (HCN) gasdiffuses through a hydrophobic gas diffusion membrane into analkaline acceptor stream where the CN-is captured and sent toan amperometric flowcell detector with a silver-w
18、orking elec-trode. In the presence of cyanide, silver in the workingelectrode is oxidized at the applied potential. The anodiccurrent measured is proportional to the concentration ofcyanide in the standard or sample injected.4.3 Calibrations and sample data are processed with theinstruments data acq
19、uisition 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 wastes and surface waters.35.2 It is useful to determine the aquatic free cyanide toestablish an index of toxi
20、city when a wastewater is introducedto the pH and temperature of the natural environment.5.3 This test method is applicable for natural water, salinewaters, and wastewater effluent.6. Interferences6.1 Sulfide will diffuse through the gas diffusion membraneand can be detected in the amperometric flow
21、cell. Oxidizedproducts of sulfide can also rapidly convert CN-to SCN-at ahigh pH. Refer to 11.2 for sulfide removal.6.2 Refer to section 6.1 of Test Method D 6888 and TestMethod D 2036 for elimination of cyanide interferences.7. Apparatus7.1 The instrument should be equipped with a precisesample int
22、roduction 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 stainless steel counter electrode. Anexample of the apparatus schematic is shown in Fig. 1.Example instrument se
23、ttings 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 not been degraded. Contact the instrumentmanufacturer for recommended instrument parameters.7.2 An autosampler is
24、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 be analyzed at a constanttemperature other than the temperature of the room, manualinjections may be required unle
25、ss 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 ofmaintaining the temperature of the aquatic environment within6 0.5C should be used to regulate the temperature of
26、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 data from the detector.7.5 Pump TubingUse tubing recommended by instrumentmanufacturer. Replace pump tubing when w
27、orn, or whenprecision is no longer acceptable.340 CFR Part 136.C = carrier (water),R=reagent buffer (variable: pH 6-8, 0.2M phosphate buffer), A = acceptor solution (0.1M NaOH), S = sample, P = peristaltic pump (flow rates inmL/min),I=injectionvalve(200L sample loop), MC = mixing cool (30-60 cm 3 0.
28、5mm i.d.), positioned in optional constant temperature 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 determination of aquatic free cyanide
29、.D72370627.6 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 to 2 weeks.7.7 Use parts an
30、d accessories 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 specificati
31、ons are available.4Other 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 wate
32、r that meetsthe purity specifications of Type I or Type II water, presentedin D 1193.8.3 Sodium Hydroxide Solution (1.00M NaOH)Dissolve40 g NaOH in laboratory water and dilute to 1 L.8.4 Sodium Hydroxide and Acceptor Solution (0.10MNaOH)Dissolve 4.0 g NaOH in laboratory water and diluteto1L.8.5 Carr
33、ierWater, 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 water. Standardizewith silver nitrate solution as described in Test MethodsD 2036, section 16.2. Store the solution under refrigeration andcheck concentration approximate
34、ly every 6 months and correctif necessary.5(WarningBecause KCN is highly toxic, avoidcontact or inhalation.)8.7 Intermediate 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 (s
35、ee 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 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 MNa
36、OH (see 8.3). Dilute to volume with laboratory water. Thestandard should be stable for at least 2 weeks.8.8 Working Cyanide Calibration 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/L
37、CN-)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 Intermediate Cyanide So
38、lution 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 containing 1.0
39、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 Buf
40、fer Solution A, 2M Sodium phosphate monobasicsolutionWeigh 276 g sodium phosphate monobasic mono-hydrate (NaH2PO4H2O)ina1Lvolumetric flask. Dissolveand dilute to volume with water.8.12 Buffer Solution B, 2M Sodium phosphate dibasicsolutionWeigh 284 g sodium phosphate dibasic, anhydrous(Na2HPO4)ina1L
41、volumetric flask. Dissolve and dilute tovolume with water. If necessary, warm to approximately 40Con a hot plate and stir to completely 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 Solution
42、Aand 152.5 mL Buffer Solution B to a 500mL volumetric flask. Dilute to volume with water.8.14 0.2 M Phosphate Buffer pH 7.0Ina1Lvolumetricflask, 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 D 1293 (Test Met
43、hod A) andadjust if necessary with dilute sodium hydroxide or sulfuricacid. This buffer solution is to be used in the FIA system whenaquatic 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 5
44、00 mL volumetric flask. Dilute to volume with water.8.16 0.2 M Phosphate Buffer pH 6.0Ina1Lvolumetricflask, add 200 mL 1M Phosphate Buffer Solution pH 6.0 anddilute to volume with water. The pH should be pH 6.0 6 0.1.Verify the pH as described in D 1293 (Test Method A) andadjust if necessary with di
45、lute sodium hydroxide or sulfuric4Reagent 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 th
46、e United States Pharmacopeia.5Commerical 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 c
47、ompletely 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/AgClD7237063acid. This buffer solution is to be used in the FIA system whenaquatic free cyanide is to
48、be determined at pH 6.0 or if the pHof the aquatic environment has not been specified.8.17 1M Phosphate Buffer pH 8.0 Stock SolutionAdd 10.0mL Buffer Solution A and 240 mL Buffer Solution B to a 500mL volumetric flask. Dilute to volume with water.8.18 0.2 M Phosphate Buffer pH 8.0Ina1Lvolumetricflas
49、k, add 200 mL 1 M Phosphate Buffer Solution pH 8.0 anddilute to volume with water. The pH should be pH=8.0 6 0.1.Verify the pH as described in D 1293 (Test Method A) andadjust if necessary with dilute sodium hydroxide or sulfuricacid. This buffer solution is to be used in the FIA system whenaquatic free cyanide is to be determined at pH 8.0.8.19 Ag/AgCl Reference Electrode Filling SolutionFillthe reference electrode as recommended by the instrumentmanufacturer.9. Hazards9.1 WarningBecause of the toxicity of cyanide, greatcare must be exer
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