ASTM D4282-02(2015)
(Test Method)Standard Test Method for Determination of Free Cyanide in Water and Wastewater by Microdiffusion
Standard Test Method for Determination of Free Cyanide in Water and Wastewater by Microdiffusion
SIGNIFICANCE AND USE
5.1 This test method is useful in distinguishing between the potentially available free cyanide (total cyanide) and the free cyanide actually present.
5.2 This test method provides a convenient technique for making on-site free cyanide determinations.
SCOPE
1.1 This test method covers the determination of free cyanides in waters and wastewaters. Free cyanide is here defined as the cyanide which diffuses as cyanide (HCN), at room temperature, from a solution at pH 6.2
1.2 This test method does not include complexes that resist dissociation, such as hexacyanoferrates and gold cyanide, nor does it include thiocyanate and cyanohydrin.
1.3 This test method may be applied to water and wastewater samples containing free cyanide from 10 to 150 μg/L. Greater concentrations may be determined by appropriate dilution.
1.4 This test method has been fully validated by collaborative testing as specified by Practice D2777.
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 standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific hazard statements, see 8.6, 8.9, Section 9, and 12.2.1.
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Designation: D4282 − 02(Reapproved 2015)
Standard Test Method for
Determination of Free Cyanide in Water and Wastewater by
Microdiffusion
This standard is issued under the fixed designation D4282; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope D1192Guide for Equipment for Sampling Water and Steam
in Closed Conduits (Withdrawn 2003)
1.1 This test method covers the determination of free
D1193Specification for Reagent Water
cyanides in waters and wastewaters. Free cyanide is here
D2777Practice for Determination of Precision and Bias of
defined as the cyanide which diffuses as cyanide (HCN), at
2 Applicable Test Methods of Committee D19 on Water
room temperature, from a solution at pH 6.
D3370Practices for Sampling Water from Closed Conduits
1.2 This test method does not include complexes that resist
D3856Guide for Management Systems in Laboratories
dissociation, such as hexacyanoferrates and gold cyanide, nor
Engaged in Analysis of Water
does it include thiocyanate and cyanohydrin.
D4210Practice for Intralaboratory Quality Control Proce-
dures and a Discussion on Reporting Low-Level Data
1.3 This test method may be applied to water and wastewa-
ter samples containing free cyanide from 10 to 150 µg/L. (Withdrawn 2002)
D5788Guide for Spiking Organics into Aqueous Samples
Greater concentrations may be determined by appropriate
dilution. D5789Practice for Writing Quality Control Specifications
for Standard Test Methods for Organic Constituents
1.4 This test method has been fully validated by collabora-
(Withdrawn 2002)
tive testing as specified by Practice D2777.
D5847Practice for Writing Quality Control Specifications
1.5 The values stated in SI units are to be regarded as
for Standard Test Methods for Water Analysis
standard. No other units of measurement are included in this
E275PracticeforDescribingandMeasuringPerformanceof
standard.
Ultraviolet and Visible Spectrophotometers
1.6 This standard does not purport to address all of the
3. Terminology
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
3.1 Definitions—For a definition of terms used in this test
priate safety and health practices and determine the applica-
method, refer to Terminology D1129.
bility of regulatory limitations prior to use. For specific hazard
3.2 Definitions of Terms Specific to This Standard:
statements, see 8.6, 8.9, Section 9, and 12.2.1.
3.2.1 free cyanide—refers to those simple cyanides or
looselyheldcomplexesofcyanidethatdiffuseatpH6,atroom
2. Referenced Documents
temperature.
2.1 ASTM Standards:
D1129Terminology Relating to Water
4. Summary of Test Method
4.1 The reactions are carried out in a microdiffusion cell.
This test method is under the jurisdiction ofASTM Committee D19 on Water
4.2 The sample is treated with cadmium ion to precipitate
andisthedirectresponsibilityofSubcommitteeD19.06onMethodsforAnalysisfor
the hexacyanoferrates.
Organic Substances in Water.
Current edition approved Feb. 1, 2015. Published March 2015. Originally
4.3 The sample is buffered at pH 6 and allowed to stand for
approved in 1983. Last previous edition approved in 2010 as D4282–02 (2010).
4h.
DOI: 10.1520/D4282-02R15.
The paper by J. M. Kruse and L. E. Thibault “Determination of Free Cyanide
4.4 The HCN diffuses into sodium hydroxide solution.
in Ferro- and Ferricyanides,”Analytical Chemistry, 45(13): 2260–2261; 1973 Nov.,
recommendsadiffusionatpH7.TheANSImodification(ANSIPH4.41-1978)uses 4.5 An aliquot of the sodium hydroxide solution is treated
pH 6. Using the conditions of the ANSI method, diffusion is completed within 4
with chloramine-T, and the cyanogen chloride formed is
hoursatpH6.LongerdiffusiontimewasrequiredatpH7onthesamplesanalyzed.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4282 − 02 (2015)
reacted with barbituric acid in pyridine. The absorbance of the 8.3 Cadmium Chloride Solution (10 g/L), CdCl —Dissolve
color formed is measured using a spectrophotometer at a 10.0 g of anhydrous cadmium chloride in 750 mL of water in
wavelength of 580 nm. a 1 L volumetric flask. Dilute to volume with water.
8.4 Chloramine-T Reagent (10 g/L)—Dissolve 1.00 g of
5. Significance and Use
chloramine-Tin 50 mLof water in a 100 mLvolumetric flask.
5.1 This test method is useful in distinguishing between the
Dilute to volume with water. Make this reagent fresh daily.
potentially available free cyanide (total cyanide) and the free
−
8.5 Cyanide Solution, Standard (1.00 mL=2 µg CN )
cyanide actually present.
—Pipet 2.00 mL of cyanide stock solution (approximately 1.0
−
5.2 This test method provides a convenient technique for
g/LCN )intoa1Lvolumetricflaskanddilutetovolumewith
making on-site free cyanide determinations.
sodium hydroxide solution (2.05 g/L).
8.6 Cyanide Solution Stock—Dissolve 2.51 g of potassium
6. Interferences
cyanide, KCN, in 500 mL of sodium hydroxide solution (2.05
6.1 Decomposition of Hexacyanoferrates During Diffusion:
g/L) ina1L volumetric flask. Dilute to volume with sodium
6.1.1 This decomposition is virtually eliminated by allow-
hydroxide solution (2.05 g/L). This solution contains approxi-
ing the sample to diffuse in the dark, and by precipitating the
−
mately 1.0 g/L cyanide (CN ). (Warning—KCN is highly
hexacyanoferrates with cadmium ion.
toxic, avoid contact or inhalation. Prepare and standardize this
6.2 Instability of Free Cyanide in Effluents—The reactivity
solution weekly.)
of free cyanide with such chemicals as aldehydes or oxidizing
8.6.1 Standardizing Cyanide Stock Solution:
agents, is not really a method interference. However, because
8.6.1.1 Using a silver electrode and a reference electrode,
of this instability, it is important for the diffusion to begin as
titrate 20.0 mL of the cyanide stock solution (in a beaker also
soon after sampling as possible. It is beyond the scope of this
containing 50 mL of sodium hydroxide solution (2.05 g/L))
testmethodtolistallthepossiblecyanidereactionsthatmaybe
with the silver nitrate standard solution.
encountered.
8.6.1.2 Record the mLof titration for use in the calculation
(see Fig. 1 for an example of a typical titration curve).
7. Apparatus
8.6.1.3 Calculate the concentration of the cyanide stock
7.1 Diffusion Cell, microdiffusion cell, Conway type, 68
solution using the following equation:
mm outside diameter.
50 3 mLsilvernitrate 5mg/L CN instocksolution
~ !
7.2 Micropipets, 0.10 mL, 1.00 mL.
1.00mLofsilvernitratesolutionisequalto1 mgofCN .
7.3 Spectrophotometer, conforming to Practice E275. 8.7 Potassium Phosphate Buffer Solution (Acidified)—Add
8.0mLofconcentratedphosphoricacid(spgr1.69),H PO,to
3 4
7.4 Spectrophotometer Cell, 1 cm equipped with a stopper.
100 mL of potassium phosphate solution.
7.5 Pipet or Syringe, adjustable (to deliver 1.30 mL).
8.8 Potassium Phosphate Solution, 190 g/L—Add 400 mL
7.6 Calomel Reference Electrode, with saturated KNO
of water toa2L beaker. Add and dissolve 14.5 g of sodium
electrolyte, or the equivalent.
hydroxide, NaOH. Add and dissolve 190 g of potassium
7.7 pH Meter. phosphate, monobasic, KH PO . Add water to 950 mL to aid
2 4
dissolution. Adjust the pH of the solution to pH 5.9 to 6.1,
7.8 Silver Electrode.
using100g/Lsodiumhydroxidesolution.Transferthesolution
toa1L volumetric flask, and dilute to volume with water.
8. Reagents
8.1 Purity of Reagents—Reagent grade chemicals shall be
used in all tests. Unless otherwise indicated, it is intended that
reagents shall conform to the specifications of the Committee
on Analytical Reagents of the American Chemical Society
where such specifications are available. Other grades may be
used provided it is first ascertained that the reagent is of
sufficient purity to permit its use without lessening the accu-
racy of the determination.
8.2 Purity of Water—Unless otherwise indicated, reference
towatershallbeunderstoodtomeanreagentwaterconforming
to Type II of Specification D1193.
One source of supply for these cells is Arthur H. Thomas, No. 3806-F-10.
Reagent Chemicals, American Chemical Society Specifications, American
Chemical Society, Washington, DC. For Suggestions on the testing of reagents not
listed by the American Chemical Society, see Annual Standards for Laboratory
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
NOTE 1—Twenty millilitres of 2.51 g/L KCN titrated with AgNO .
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
MD. FIG. 1 Typical Titration Curve Standardizing KCN Solution
D4282 − 02 (2015)
8.9 Pyridine-Barbituric Acid Reagent—Add 15.0 g of bar- 10. Sampling and Sample Preservation
bituricacidtoa250mLvolumetricflask.Washdownthesides
10.1 Collect the sample in accordance with Guide D1192
of the flask with just enough water to moisten the barbituric
and Practices D3370.
acid. Add 75 mL of pyridine and swirl to mix. Slowly add 15
10.2 A satisfactory preservation technique is not available.
mLof concentrated hydrochloric acid (sp gr 1.19) and swirl to
−
Reactions between CN and aldehydes, oxidizing agents, or
mix. Cool the solution to room temperature. Dilute to volume
sulfides will continue. However, if the sample cannot be
and mix. It is recommended that this reagent be prepared fresh
analyzed immediately, some steps can be taken to slow down
weekly and stored in a dark place. (Warning—Pyridine is
the reactions taking place.
toxic; avoid contact or inhalation. Prepare this reagent in an
10.2.1 Adjust the sample to pH 12 or more.This minimizes
exhaust hood.)
−
CN losses due to vaporization.
8.10 Silver Nitrate Solution, Standard (1 mL=1 mg of
10.2.2 Store the samples in the dark to prevent hexacyano-
−
CN )—Weigh 3.2647 g of silver nitrate on an analytical
ferrate breakdown.
balance. Quantitatively transfer the silver nitrate toa1L
10.2.3 Keepthesamplecool(forexample,inarefrigerator).
volumetric flask. Dissolve and dilute to volume with water.
Store in a dark glass bottle.
11. Calibration
8.11 Sodium Hydroxide Solution (4.1 g/L), NaOH—Add
11.1 Calibration Standards—Pipet 0.00 (Note 2), 5.00,
4.10 g of sodium hydroxide to 800 mL of water ina1L
10.0, and 15.0 mL of the 2.00 mg/L cyanide standard solution
volumetric flask. Stir until dissolved, and cool the solution to
intofour200mLvolumetricflasks.Diluteeachoftheflasksto
room temperature before adjusting the final volume to 1 L.
volume with sodium hydroxide solution (2.05 g/L). These
dilutions yield calibration standards that are approximately 0,
8.12 Sodium Hydroxide Solution (2.05 g/L), NaOH—Add
−
50, 100, and 150 µg/L of CN , respectively.
2.05 g of sodium hydroxide to 800 mL of water ina1L
volumetric flask. Stir until dissolved, and cool the solution to
NOTE 1—The 0.00 sample can also be considered the blank.
roomtemperaturebeforeadjustingthefinalvolumeto1L.(An
11.2 To establish the calibration curve, analyze the calibra-
alternative preparation is to dilute 0.10 N sodium hydroxide
tion standards in accordance with the procedure in Section 12.
solution with an equal volume of water.)
−
Plot a calibration curve of concentrations of CN versus
absorbance (see Fig. 2). Standards should be run daily for
9. Hazards
calibration, until it is established that the calibration curve will
9.1 Safety Precautions:
apply for a longer period of time. Then it is only necessary to
−
9.1.1 Because of the toxicity of cyanide, exercise great care
run two standards (such as 0 and 100 µg/L CN ) with each
in its handling. Acidification of cyanide solutions produces
batch of samples as a check on the existing calibration curve.
toxic gaseous hydrocyanide acid (HCN). Perform all manipu-
lations in the hood so that any HCN that might volatilize is
12. Procedure
safely vented.
12.1 Microdiffusion of Free Cyanide:
9.1.2 Some of the reagents used in these methods, such as
12.1.1 Pipet 3.00 mLof sample or calibration standard into
cyanide solutions, are highly toxic. Dispose of these reagents
the outer ring of a clean, dry, microdiffusion cell (see Fig. 3).
and their solutions properly.
12.1.2 Usingacalibratedsyringe(oradjustablepipet),pipet
9.1.3 Do not pipet by mouth.
1.30 mL of sodium hydroxide solution (4 g/L) into the center
9.2 Operational Precautions—This test method requires
of the chamber of the microdiffusion cell.
practice and manual dexterity. The following practices have
been found necessary to obtain reliable test results:
9.2.1 Keep the samples in the dark because light can
dissociate complex cyanides and lead to high values.
9.2.2 Run the samples at least in duplicate.
9.2.3 Use calibrated syringes or equivalent for delivering
thesample.Theforceofthesampleejectionaidsinthemixing
in the microdiffusion cell.
9.2.4 Exercise great care during mixing of solutions by
tilting and rotating the microdiffusion cell to avoid spilling or
splashing liquid from one compartment to another.
9.2.5 Make the seal between the microdiffusion cell and lid
airtight.
9.2.6 It is important to observe the specified time periods in
those steps where such is noted. In particular, make the
spectrophotometer measurements in the 3 to 6 min interval.
9.2.7 Full color development in the spectrophotometer cell
requires that after each addition, mix the solution thoroughly
−
without loss of material. FIG. 2 Example of Calibration Curve for CN
D4282 − 02 (2015)
Typical Cell
(a)
Filling Inner Compartment Filling Outer Compartment
(b) (c)
FIG. 3 Microdiffusion Cell
12.1.3 At this time, smear the ground glass side of a glass microdiffusion cell, inject at an angle in order to force the
cell cover plate with a sufficiently heavy layer of petroleum
solutionaroundthechamber,andquicklysealwiththegreased
jelly or stopcock grease to achieve an airtight seal.
glass plate.
12.1.4 Usingamicropipet,pipet0.5mLof10g/Lcadmium
12.1.6 Tilt and rotate the cell for 15 s to ensure proper
chloridesolution(10g/L)intothesampleintheoutsideringof
mixing.
themicrodiffusioncell.Tiltandrotatethecellfor15stoensure
12.1.7 Keep the covered cell in the dark for a period of not
mixing.
less than 4 h a
...
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. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D4282 − 02 (Reapproved 2010) D4282 − 02 (Reapproved 2015)
Standard Test Method for
Determination of Free Cyanide in Water and Wastewater by
Microdiffusion
This standard is issued under the fixed designation D4282; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers the determination of free cyanides in waters and wastewaters. Free cyanide is here defined as the
cyanide which diffuses as cyanide (HCN), at room temperature, from a solution at pH 6.
1.2 This test method does not include complexes that resist dissociation, such as hexacyanoferrates and gold cyanide, nor does
it include thiocyanate and cyanohydrin.
1.3 This test method may be applied to water and wastewater samples containing free cyanide from 10 to 150 μg/L. Greater
concentrations may be determined by appropriate dilution.
1.4 This test method has been fully validated by collaborative testing as specified by Practice D2777.
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 standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use. For specific hazard statements, see 8.6, 8.9, Section 9, and 12.2.1.
2. Referenced Documents
2.1 ASTM Standards:
D1129 Terminology Relating to Water
D1192 Guide for Equipment for Sampling Water and Steam in Closed Conduits (Withdrawn 2003)
D1193 Specification for Reagent Water
D2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
D3370 Practices for Sampling Water from Closed Conduits
D3856 Guide for Management Systems in Laboratories Engaged in Analysis of Water
D4210 Practice for Intralaboratory Quality Control Procedures and a Discussion on Reporting Low-Level Data (Withdrawn
2002)
D5788 Guide for Spiking Organics into Aqueous Samples
D5789 Practice for Writing Quality Control Specifications for Standard Test Methods for Organic Constituents (Withdrawn
2002)
D5847 Practice for Writing Quality Control Specifications for Standard Test Methods for Water Analysis
E275 Practice for Describing and Measuring Performance of Ultraviolet and Visible Spectrophotometers
3. Terminology
3.1 Definitions—For a definition of terms used in this test method, refer to Terminology D1129.
3.2 Definitions of Terms Specific to This Standard:
This test method is under the jurisdiction of ASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.06 on Methods for Analysis for
Organic Substances in Water.
Current edition approved June 15, 2010Feb. 1, 2015. Published December 2010March 2015. Originally approved in 1983. Last previous edition approved in 20022010
as D4282 – 02.D4282 – 02 (2010). DOI: 10.1520/D4282-02R10. 10.1520/D4282-02R15.
The paper by J. M. Kruse and L. E. Thibault “Determination of Free Cyanide in Ferro- and Ferricyanides,” Analytical Chemistry, 45(13): 2260–2261; 1973 Nov.,
recommends a diffusion at pH 7. The ANSI modification (ANSI PH 4.41-1978) uses pH 6. Using the conditions of the ANSI method, diffusion is completed within 4 hours
at pH 6. Longer diffusion time was required at pH 7 on the samples analyzed.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4282 − 02 (2015)
3.2.1 free cyanide—refers to those simple cyanides or loosely held complexes of cyanide that diffuse at pH 6, at room
temperature.
4. Summary of Test Method
4.1 The reactions are carried out in a microdiffusion cell.
4.2 The sample is treated with cadmium ion to precipitate the hexacyanoferrates.
4.3 The sample is buffered at pH 6 and allowed to stand for 4 h.
4.4 The HCN diffuses into sodium hydroxide solution.
4.5 An aliquot of the sodium hydroxide solution is treated with chloramine-T, and the cyanogen chloride formed is reacted with
barbituric acid in pyridine. The absorbance of the color formed is measured using a spectrophotometer at a wavelength of 580 nm.
5. Significance and Use
5.1 This test method is useful in distinguishing between the potentially available free cyanide (total cyanide) and the free
cyanide actually present.
5.2 This test method provides a convenient technique for making on-site free cyanide determinations.
6. Interferences
6.1 Decomposition of Hexacyanoferrates During Diffusion:
6.1.1 This decomposition is virtually eliminated by allowing the sample to diffuse in the dark, and by precipitating the
hexacyanoferrates with cadmium ion.
6.2 Instability of Free Cyanide in Effluents—The reactivity of free cyanide with such chemicals as aldehydes or oxidizing
agents, is not really a method interference. However, because of this instability, it is important for the diffusion to begin as soon
after sampling as possible. It is beyond the scope of this test method to list all the possible cyanide reactions that may be
encountered.
7. Apparatus
7.1 Diffusion Cell, microdiffusion cell, Conway type, 68 mm outside diameter. diameter.
7.2 Micropipets, 0.10 mL, 1.00 mL.
7.3 Spectrophotometer, conforming to Practice E275.
7.4 Spectrophotometer Cell, 1 cm equipped with a stopper.
7.5 Pipet or Syringe, adjustable (to deliver 1.30 mL).
7.6 Calomel Reference Electrode , Electrode, with saturated KNO electrolyte, or the equivalent.
7.7 pH Meter.
7.8 Silver Electrode.
8. Reagents
8.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that
reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where
such specifications are available. Other grades may be used provided it is first ascertained that the reagent is of sufficient purity
to permit its use without lessening the accuracy of the determination.
8.2 Purity of Water—Unless otherwise indicated, reference to water shall be understood to mean reagent water conforming to
Type II of Specification D1193.
8.3 Cadmium Chloride Solution (10 g/L), CdCl —Dissolve 10.0 g of anhydrous cadmium chloride in 750 mL of water in a 1
L volumetric flask. Dilute to volume with water.
8.4 Chloramine-T Reagent (10 g/L)—Dissolve 1.00 g of chloramine-T in 50 mL of water in a 100 mL volumetric flask. Dilute
to volume with water. Make this reagent fresh daily.
− −
8.5 Cyanide Solution, Standard (1.00 mL = 2 μg CN ) —Pipet 2.00 mL of cyanide stock solution (approximately 1.0 g/L CN )
into a 1 L volumetric flask and dilute to volume with sodium hydroxide solution (2.05 g/L).
One source of supply for these cells is Arthur H. Thomas, No. 3806-F-10.
Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington, DC. For Suggestions on the testing of reagents not listed by
the American Chemical Society, see Annual Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and National
Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.
D4282 − 02 (2015)
8.6 Cyanide Solution Stock—Dissolve 2.51 g of potassium cyanide, KCN, in 500 mL of sodium hydroxide solution (2.05 g/L)
in a 1 L volumetric flask. Dilute to volume with sodium hydroxide solution (2.05 g/L). This solution contains approximately 1.0
−
g/L cyanide (CN ). (Warning—KCN is highly toxic, avoid contact or inhalation. Prepare and standardize this solution weekly.)
8.6.1 Standardizing Cyanide Stock Solution:
8.6.1.1 Using a silver electrode and a reference electrode, titrate 20.0 mL of the cyanide stock solution (in a beaker also
containing 50 mL of sodium hydroxide solution (2.05 g/L)) with the silver nitrate standard solution.
8.6.1.2 Record the mL of titration for use in the calculation (see Fig. 1 for an example of a typical titration curve).
8.6.1.3 Calculate the concentration of the cyanide stock solution using the following equation:
50 3 mL silver nitrate 5 mg/L CN in stock solution
~ !
1.00 mL of silver nitrate solution is equal to 1 mg of CN .
8.7 Potassium Phosphate Buffer Solution (Acidified)—Add 8.0 mL of concentrated phosphoric acid (sp gr 1.69), H PO , to 100
3 4
mL of potassium phosphate solution.
8.8 Potassium Phosphate Solution, 190 g/L—Add 400 mL of water to a 2 L beaker. Add and dissolve 14.5 g of sodium
hydroxide, NaOH. Add and dissolve 190 g of potassium phosphate, monobasic, KH PO . Add water to 950 mL to aid dissolution.
2 4
Adjust the pH of the solution to pH 5.9 to 6.1, using 100 g/L sodium hydroxide solution. Transfer the solution to a 1 L volumetric
flask, and dilute to volume with water.
8.9 Pyridine-Barbituric Acid Reagent—Add 15.0 g of barbituric acid to a 250 mL volumetric flask. Wash down the sides of the
flask with just enough water to moisten the barbituric acid. Add 75 mL of pyridine and swirl to mix. Slowly add 15 mL of
concentrated hydrochloric acid (sp gr 1.19) and swirl to mix. Cool the solution to room temperature. Dilute to volume and mix.
It is recommended that this reagent be prepared fresh weekly and stored in a dark place. (Warning—Pyridine is toxic; avoid
contact or inhalation. Prepare this reagent in an exhaust hood.)
−
8.10 Silver Nitrate Solution, Standard (1 mL = 1 mg of CN )—Weigh 3.2647 g of silver nitrate on an analytical balance.
Quantitatively transfer the silver nitrate to a 1 L volumetric flask. Dissolve and dilute to volume with water. Store in a dark glass
bottle.
8.11 Sodium Hydroxide Solution (4.1 g/L), NaOH—Add 4.10 g of sodium hydroxide to 800 mL of water in a 1 L volumetric
flask. Stir until dissolved, and cool the solution to room temperature before adjusting the final volume to 1 L.
8.12 Sodium Hydroxide Solution (2.05 g/L), NaOH—Add 2.05 g of sodium hydroxide to 800 mL of water in a 1 L volumetric
flask. Stir until dissolved, and cool the solution to room temperature before adjusting the final volume to 1 L. (An alternative
preparation is to dilute 0.10 N sodium hydroxide solution with an equal volume of water.)
9. Hazards
9.1 Safety Precautions:
9.1.1 Because of the toxicity of cyanide, exercise great care in its handling. Acidification of cyanide solutions produces toxic
gaseous hydrocyanide acid (HCN). Perform all manipulations in the hood so that any HCN that might volatilize is safely vented.
9.1.2 Some of the reagents used in these methods, such as cyanide solutions, are highly toxic. Dispose of these reagents and
their solutions properly.
9.1.3 Do not pipet by mouth.
NOTE 1—Twenty millilitres of 2.51 g/L KCN titrated with AgNO .
FIG. 1 Typical Titration Curve Standardizing KCN Solution
D4282 − 02 (2015)
9.2 Operational Precautions—This test method requires practice and manual dexterity. The following practices have been found
necessary to obtain reliable test results:
9.2.1 Keep the samples in the dark because light can dissociate complex cyanides and lead to high values.
9.2.2 Run the samples at least in duplicate.
9.2.3 Use calibrated syringes or equivalent for delivering the sample. The force of the sample ejection aids in the mixing in the
microdiffusion cell.
9.2.4 Exercise great care during mixing of solutions by tilting and rotating the microdiffusion cell to avoid spilling or splashing
liquid from one compartment to another.
9.2.5 Make the seal between the microdiffusion cell and lid airtight.
9.2.6 It is important to observe the specified time periods in those steps where such is noted. In particular, make the
spectrophotometer measurements in the 3 to 6 min interval.
9.2.7 Full color development in the spectrophotometer cell requires that after each addition, mix the solution thoroughly without
loss of material.
10. Sampling and Sample Preservation
10.1 Collect the sample in accordance with SpecificationGuide D1192 and Practices D3370.
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10.2 A satisfactory preservation technique is not available. Reactions between CN and aldehydes, oxidizing agents, or sulfides
will continue. However, if the sample cannot be analyzed immediately, some steps can be taken to slow down the reactions taking
place.
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10.2.1 Adjust the sample to pH 12 or more. This minimizes CN losses due to vaporization.
10.2.2 Store the samples in the dark to prevent hexacyanoferrate breakdown.
10.2.3 Keep the sample cool (for example, in a refrigerator).
11. Calibration
11.1 Calibration Standards—Pipet 0.00 (Note 2), 5.00, 10.0, and 15.0 mL of the 2.00 mg/L cyanide standard solution into four
200 mL volumetric flasks. Dilute each of the flasks to volume with sodium hydroxide solution (2.05 g/L). These dilutions yield
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calibration standards that are approximately 0, 50, 100, and 150 μg/L of CN , respectively.
NOTE 1—The 0.00 sample can also be considered the blank.
11.2 To establish the calibration curve, analyze the calibration standards in accordance with the procedure in Section 12. Plot
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a calibration curve of concentrations of CN versus absorbance (see Fig. 2). Standards should be run daily for calibration, until
it is established that the calibration curve will apply for a longer period of time. Then it is only necessary to run two standards
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(such as 0 and 100 μg/L CN ) with each batch of samples as a check on the existing calibration curve.
12. Procedure
12.1 Microdiffusion of Free Cyanide:
12.1.1 Pipet 3.00 mL of sample or calibration standard into the outer ring of a clean, dry, microdiffusion cell (see Fig. 3).
12.1.2 Using a calibrated syringe (or adjustable pipet), pipet 1.30 mL of sodium hydroxide solution (4 g/L) into the center of
the chamber of the microdiffusion cell.
12.1.3 At this time, smear the ground glass side of a glass cell cover plate with a sufficiently heavy layer of petroleum jelly or
stopcock grease to achie
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