ASTM D7237-06

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Designation: D7237 – 06
Standard Test Method for
Aquatic Free Cyanide with Flow Injection Analysis (FIA)
Utilizing Gas Diffusion Separation and Amperometric
Detection
This standard is issued under the fixed designation D7237; 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 bility of regulatory limitations prior to use. Specific hazard
statements are given in Section 8.6 and Section 9.
1.1 Thistestmethodisusedtoestablishtheconcentrationof
aquatic “free” cyanide in an aqueous wastewater or effluent.
2. Referenced Documents
The test conditions of this method are used to measure free
- 2.1 ASTM Standards:
cyanide (HCN and CN ) and cyanide bound in the metal-
D1129 Terminology Relating to Water
cyanide complexes that are easily dissociated into free cyanide
D1193 Specification for Reagent Water
ions at the pH of the aquatic environment ranging from pH 6
D1293 Test Methods for pH of Water
to pH 8. The extent of HCN formation is less dependent on
D2036 Test Methods for Cyanides in Water
temperature than the pH; however, the temperature can be
D2777 Practice for Determination of Precision and Bias of
regulated if deemed necessary to further simulate the actual
Applicable Test Methods of Committee D19 on Water
aquatic environment.
D3370 Practices for Sampling Water from Closed Conduits
1.2 The aquatic free cyanide method is based on the same
D3856 Guide for Good Laboratory Practices in Laborato-
instrumentation and technology that is described in standard
ries Engaged in Sampling and Analysis of Water
test method D6888, but employs milder conditions (pH 6-8
D4841 Practice for Estimation of Holding Time for Water
buffer versus HCl in the reagent stream), and does not utilize
Samples Containing Organic and Inorganic Constituents
ligand displacement reagents.
D5847 Practice for Writing Quality Control Specifications
1.3 The aquatic free cyanide measured by this procedure
for Standard Test Methods for Water Analysis
should be similar to actual levels of HCN in the original
D6512 Practice for Interlaboratory Quantitation Estimate
aquatic environment. This in turn may give a reliable index of
D6696 Guide for Understanding Cyanide Species
toxicity to aquatic organisms.
D6888 Test Method for Available Cyanide with Ligand
1.4 This procedure is applicable over a range of approxi-
Displacement and Flow InjectionAnalysis (FIA) Utilizing
mately 2 to 500 µg/L (parts per billion) aquatic free cyanide.
Gas Diffusion Separation and Amperometric Detection
Sample dilution may increase cyanide recoveries depending on
E691 Practice for Conducting an Interlaboratory Study to
the cyanide speciation; therefore, it is not recommended to
Determine the Precision of a Test Method
dilute samples. Higher concentrations can be analyzed by
E1763 Guide for Interpretation and Use of Results from
increasing the range of calibration standards or with a lower
Interlaboratory Testing of Chemical Analysis Methods
injection volume. In accordance with Guide E1763 and Prac-
tice D6512 the lower scope limit was determined to be 9 µg/L
3. Terminology
for chlorinated gold leaching barren effluent water.
3.1 Definitions For definitions of terms used in this test
1.5 This standard does not purport to address all of the
method, refer to Terminology D1129 and Guide D6696.
safety concerns, if any, associated with its use. It is the
3.1.1 aquatic free cyanide—Sum of the free cyanide (HCN
responsibility of the user of this standard to establish appro-
-
and CN ) and cyanide bound in the metal-cyanide complexes
priate safety and health practices and determine the applica-
that are easily dissociated into free cyanide under the test
conditions described in this method.
This test method is under the jurisdiction of ASTM Committee D19 on Water
and is the direct responsibility of Subcommittee D19.06 on Methods forAnalysis of For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Organic Substances in Water. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved Feb. 1, 2006. Published February 2006. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
D7237-06. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D7237 – 06
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 in
mL/min),I=injectionvalve(200µL sample loop), MC = mixing cool (30-60 cm 3 0.5mm 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.
4. Summary of Test Method 6.2 Refer to section 6.1 of Test Method D6888 and Test
Method D2036 for elimination of cyanide interferences.
4.1 Thetestisgenerallyperformedatroomtemperature,but
temperature of the sample and flow injection reagents can be
7. Apparatus
regulated to match the aquatic environment if necessary.
4.2 The sample is introduced into a carrier solution of the
7.1 The instrument should be equipped with a precise
flow injection analysis (FIA) system via an injection valve and sample introduction system, a gas diffusion manifold with
confluenced downstream with a phosphate buffer solution at
hydrophobic membrane, and an amperometric detection sys-
pHinthe6-8range.Thereleasedhydrogencyanide(HCN)gas tem to include a silver working electrode, aAg/AgCl reference
diffusesthroughahydrophobicgasdiffusionmembraneintoan
electrode, and a Pt or stainless steel counter electrode. An
-
alkaline acceptor stream where the CN is captured and sent to example of the apparatus schematic is shown in Fig. 1.
an amperometric flowcell detector with a silver-working elec-
Example instrument settings are shown in Table 1.
trode. In the presence of cyanide, silver in the working
NOTE 1—The instrument and settings in Fig. 1 and Table 1 are shown
electrode is oxidized at the applied potential. The anodic
as examples. The analyst may modify these settings as long as perfor-
current measured is proportional to the concentration of
mance of the method has not been degraded. Contact the instrument
cyanide in the standard or sample injected.
manufacturer for recommended instrument parameters.
4.3 Calibrations and sample data are processed with the
7.2 An autosampler is recommended but not required to
instrument’s data acquisition software.
automate sample injections and increase throughput.Autosam-
plers are usually available as an option from the instrument’s
5. Significance and Use
manufacturer. If the sample is to be analyzed at a constant
5.1 Cyanide and hydrogen cyanide are highly toxic. Regu-
temperature other than the temperature of the room, manual
lations have been established to require the monitoring of
injections may be required unless the autosampler is equipped
cyanide in industrial and domestic wastes and surface waters.
to maintain constant temperature.
5.2 It is useful to determine the aquatic free cyanide to
7.3 If aquatic free cyanide at a temperature other than room
establish an index of toxicity when a wastewater is introduced
temperature is required, a constant temperature bath capable of
to the pH and temperature of the natural environment.
maintaining the temperature of the aquatic environment within
5.3 This test method is applicable for natural water, saline
6 0.5°C should be used to regulate the temperature of the flow
waters, and wastewater effluent.
injection reagents and samples.
7.4 Data Acquisition System—Use the computer hardware
6. Interferences
and software recommended by the instrument manufacturer to
6.1 Sulfide will diffuse through the gas diffusion membrane
control the apparatus and to collect data from the detector.
and can be detected in the amperometric flowcell. Oxidized
7.5 Pump Tubing—Use tubing recommended by instrument
- -
products of sulfide can also rapidly convert CN to SCN at a
manufacturer. Replace pump tubing when worn, or when
high pH. Refer to 11.2 for sulfide removal.
precision is no longer acceptable.
7.6 Gas Diffusion Membranes—A hydrophobic membrane
40 CFR Part 136. which allows gaseous hydrogen cyanide to diffuse from the
D7237 – 06
-
TABLE 1 Flow Injection Analysis Parameters
8.7.2 Intermediate Cyanide Solution 2 (10 µg/mL CN )—
FIA Instrument Recommended Pipette 10.0 mLof Intermediate Cyanide Solution 1 (see 8.7.1)
Parameter Method Setting
into a 100 mL volumetric flask containing 1.0 mL of 1.00 M
Pump Flow Rates 0.5 to 2.0 mL/min
NaOH (see 8.3). Dilute to volume with laboratory water. The
standard should be stable for at least 2 weeks.
Cycle period (total) Approximately 120 seconds
8.8 Working Cyanide Calibration Standards—Prepare fresh
Sample load period At least enough time to completely fill the
daily as described in 8.8.1 and 8.8.2 ranging in concentration
sample loop prior to injection
-
from 2 to 500 µg/L CN .
Injection valve rinse time At least enough time to rinse the
8.8.1 Calibration Standards (20, 50, 100, 200, and 500 µg/L
between samples sample loop
-
CN )—Pipette 20, 50, 100, 200, and 500 µL of Intermediate
Peak Evaluation Peak height or area Standard 1 (see 8.7.1) into separate 100 mL volumetric flasks
containing1.0mLof0.10MNaOH(see8.4).Dilutetovolume
Working Potential 0.0 V vs Ag/AgCl
with laboratory water.
-
8.8.2 Calibration Standards (2, 5, and 10 µg/L CN )—
Pipette 20, 50, and 100 µL of Intermediate Cyanide Solution 2
donor to the acceptor stream at a sufficient rate to allow
(see 8.7.2) into separate 100 mL volumetric flasks containing
detection. The gas diffusion membrane should be replaced
1.0 mL of 0.10 M NaOH (see 8.4). Dilute to volume with
when the baseline becomes noisy, or every 1 to 2 weeks.
laboratory water.
7.7 Use parts and accessories as directed by instrument
8.9 Cyanide Electrode Stabilization Solution (Approxi-
-
manufacturer.
mately 5 ppm as CN )—Pipette 500 µL of Stock Cyanide (see
8.6) into a 100 mL volumetric flask containing 1.0 mL of
8. Reagents and Materials
0.10M M NaOH (see 8.4). Dilute to volume with laboratory
8.1 Purity of Reagents—Reagent grade chemicals shall be
water. The solution should be stored under refrigeration.
used in all tests. Unless otherwise indicated, it is intended that
8.10 Acetate Buffer—Dissolve 410 g of sodium acetate
all reagents shall conform to the specifications of theAmerican
trihydrate (NaC H O ·3H O) in 500 mL of laboratory water.
2 3 2 2
Chemical Society, where such specifications are available.
Add glacial acetic acid (approximately 500 mL) to yield a pH
Other grades may be used, provided it is first ascertained that
of 4.5.
the reagent is of sufficiently high purity to permit its use
8.11 Buffer Solution A, 2M Sodium phosphate monobasic
without lessening the accuracy of the determination.
solution—Weigh 276 g sodium phosphate monobasic mono-
8.2 Purity of Water—Unless otherwise indicated, references
hydrate (NaH PO ·HO)ina1L volumetric flask. Dissolve
2 4 2
to water shall be understood to mean reagent water that meets
and dilute to volume with water.
the purity specifications of Type I or Type II water, presented
8.12 Buffer Solution B, 2M Sodium phosphate dibasic
in D1193.
solution—Weigh 284 g sodium phosphate dibasic, anhydrous
8.3 Sodium Hydroxide Solution (1.00M NaOH)—Dissolve
(Na HPO)ina1L volumetric flask. Dissolve and dilute to
2 4
40 g NaOH in laboratory water and dilute to 1 L.
volume with water. If necessary, warm to approximately 40°C
8.4 Sodium Hydroxide and Acceptor Solution (0.10M
on a hot plate and stir to completely dissolve the sodium
NaOH)—Dissolve 4.0 g NaOH in laboratory water and dilute
phosphate dibasic into the water. Allow the solution to cool
to1L.
prior to use.
8.5 Carrier—Water, as described in section 8.2.
-
8.13 1MPhosphateBufferpH7.0StockSolution—Add97.5
8.6 Stock Cyanide Solution (1000 µg/mL CN )—Dissolve
mLBuffer SolutionAand 152.5 mLBuffer Solution B to a 500
2.51 g of KCN and 2.0 g of NaOH in 1 Lof water. Standardize
mL volumetric flask. Dilute to volume with water.
with silver nitrate solution as described in Test Methods
D2036, section 16.2. Store the solution under refrigeration and 8.14 0.2 M Phosphate Buffer pH 7.0—Ina1L volumetric
flask, add 200 mL 1M Phosphate Buffer Solution pH 7.0 and
check concentration approximately every 6 months and correct
if necessary. (Warning—Because KCN is highly toxic, avoid dilute to volume with water. The pH should be pH 7.0 6 0.1.
Verify the pH as described in D1293 (Test Method A) and
contact or inhalation.)
8.7 Intermediate Cyanide Standards: adjust if necessary with dilute sodium hydroxide or sulfuric
-
acid. This buffer solution is to be used in the FIAsystem when
8.7.1 Intermediate Standard 1 (100 µ g/mL CN )—Pipette
10.0 mL of stock cyanide solution (see 8.6) into a 100 mL aquatic free cyanide is to be determined at pH 7.0.
volumetric flask containing 1 mL of 1.0 M NaOH (see 8.3).
8.15 1M Phosphate Buffer pH 6.0 Stock Solution—Add
Dilute to volume with laboratory water. Store under refrigera-
219.25 mLBuffer SolutionAand 30.75 mLof Buffer Solution
tion. The standard should be stable for at least 2 weeks.
B to a 500 mL volumetric flask. Dilute to volume with water.
8.16 0.2 M Phosphate Buffer pH 6.0—Ina1L volumetric
flask, add 200 mL 1M Phosphate Buffer Solution pH 6.0 and
Reagent Chemicals, American Chemical Society Specifications ,Am. Chemical
dilute to volume with water. The pH should be pH 6.0 6 0.1.
Soc., Washington, DC. For suggestions on the testing of reagents not listed by the
Verify the pH as described in D1293 (Test Method A) and
American chemical Society, see Analar Standards for Laboratory Chemicals, BDH
adjust if necessary with dilute sodium hydroxide or sulfuric
Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia.
Commerical Solutions of Stock Cyanide may be substituted. acid. This buffer solution is to be used in the FIAsystem when
D7237 – 06
aquatic free cyanide is to be determined at pH 6.0 or if the pH powdered lead carbonate to avoid significantly reducing the
of the aquatic environment has not been specified. pH. Repeat this test until a drop of treated sample no longer
8.17 1MPhosphateBufferpH8.0StockSolution—Add10.0 darkens the acidifi
...