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Total Cyanide Analysis of

NPDES Wastewater Samples

by ASTM D 7511-09e2

Introduction

The Federal Water Pollution Control Act Amendments of 1972 directed the U.S. EPA to complete a list of toxic

pollutants in water for which effluent standards were subsequently proposed.(1) Cyanide was included on the list oftoxic pollutants.

The first generation of U.S. EPA cyanide analysis methods from the 1970s employ an acid distillation samplepretreatment step to dissociate cyanide from metal-cyanide complexes and separate cyanide from the matrix. Aciddistillation is known to cause either negative or positive analytical biases depending upon the composition of thesample matrix being tested. In fact, the U. S. EPA Solutions to Analytical Chemistry Problems with Clean Water

and Methods(2) (Pumpkin Guide) notes; Next to oil and grease, cyanide is the pollutant for which the mostmatrix interferences have been reported. Table 1 provides a summary of cyanide analysis interferences associated

with acid distillation of samples.

ASTM D 7511-09e2

ASTM D 7511-09 e2(3) defines a method for the determination of total cyanide in various types of water (such asground, municipal waste, industrial effluent, leachate, and surface water). This automated method is applicable to amass concentration range of 3500 g/L CN, however, higher concentrations can be determined by eitherperforming dilutions or changing the operating conditions.

ASTM D 7511-09e2 was validated according to the U.S. EPA ATP protocol for EPA Approval of New Methods for

Organic and Inorganic Analytes in Wastewater and Drinking Water (4) and complies with ASTM D 2777-08e1

Standard Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 onWater(5). ASTM D 7511-09e2 was specifically developed to mitigate interferences commonly encountered withother cyanide methods, especially those that utilize a high temperature acid distillation step.

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Total Cyanide Analysis of NPDES Wastewater Samples by ASTM D 7511-09e2Publication 36871010 2

ASTM D 7511-09e2 uses narrow-band, low- watt UV irradiation to decompose cyanide complexes in samples atambient temperature in a continuously flowing acidic stream. Reducing and complexing reagents, combined withambient temperature UV digestion minimizes the formation of matrix interferences. Elimination of the sampledistillation step enables measurement of cyanide at lower concentrations with improved precision.

Table 1: Summary of Known Cyanide Analysis Interferences from Acid Distillation of Samples

* These cyanide interferences are specifically cited in the U.S. EPA Pumpkin Guide.(2)

Regulatory Status of ASTM D 7511-09e2 within the U.S.

On August 6th, 2010, the U.S. EPA Administrator signed a Methods Update Rule (MUR) proposing approval of

new analytical methods for testing of pollutants in wastewater under the Clean Water Act.(6) The proposed rule was

published in the Federal Register(7)

on September 23, 2010. Six ASTM methods (including ASTM D 7511-09e2)covering sampling, preservation, and analysis of free, available and total cyanide species were included in theMUR. Facilities with National Pollutant Discharge Elimination System (NPDES) permits can now use ASTM D7511-09e2 to test wastewater samples for regulatory compliance reporting.

Compound Description of Interference

Oxidizers*(chlorine and hypochlorite)

React with cyanide decreasing its concentration

Sulfur/Sulfide*Distills into absorber solution and reacts with CN formingthiocyanate.

Sulfite* (or Sulfur Dioxide)Reacts with cyanide decreasing its concentration. Distills intoabsorber solution and reacts with cyanide decreasing itsconcentration.

Thiosulfate* and other

oxidized sulfur species(except sulfate)

Decompose to form native sulfur and sulfur dioxide. React

with cyanide decreasing its concentration. Sulfur dioxidedistills into absorber solution and reacts with cyanidedecreasing its concentration.

Thiocyanate*Decomposes to sulfur dioxide and reacts with cyanidedecreasing its concentration. Sulfur dioxide distills intoabsorber solution.

Thiocyanate + Nitrate orNitrite

Decompose to form cyanide

Misc. Organics + Nitrate orNitrite

Decompose to form cyanide

Carbonate*Excessive foaming and possible violent release of carbondioxide in distillation flask. Can reduce pH of absorbersolution and cause incomplete cyanide recovery.

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Principle of Operation

A flow diagram for performing total cyanide analysis by ASTM D 7511-09e2 is shown in Figure 1. In operation asample is injected into a carrier stream, segmented, and acidified. Under acidic conditions the weak aciddissociable cyanide complexes convert to HCN (1) and the strong metal-cyanide complexes are irradiated byultraviolet light in the UV digestion module (2) where they break down and release HCN. The HCN gas from allcyanide species present in the sample diffuses across a hydrophobic membrane into a basic acceptor solution (3),

where it converts back to CN- and is carried into a flow cell of an amperometric detector. Cyanide ions react with asilver electrode and generate current proportional to the cyanide ion concentration (4). The detector response isdisplayed as a peak. The resulting peak height is proportional to the cyanide concentration present in the sample.

Figure 1. Flow Diagram for Total Cyanide Analysis by ASTM Method D 7511-09e2

Instrumentation for Cyanide Analysis by ASTM D 7511-09e2

ASTM D 7511-09e2 defines design and performance characteristics a flow injection analysis (FIA) instrumentshould possess to perform the method. Among the design features needed for this in-line UV digestion, gas-diffusion amperometry method are a UV digestion module with a 312-nm lamp, a gas diffusion manifold with ahydrophobic membrane, an amperometric detector equipped with a silver working electrode, an AgCl referenceelectrode, and a Pt or stainless steel counter electrode.

The CNSolution Cyanide Analyzer (Figure 2) is a compact, modular, laboratory instrument that meets therequirements stated in ASTM D 7511-09e2.

UV Digestion

Module

.................

1

2 3

4

Waste

Acid

Air

Total Acid 2

Base

Carrier

Inj. Loop

Valve

PumpSample Gas

Diffusion

ModuleWaste

Membrane Detector Waste

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Figure 2. OI Analytical CNSolution Cyanide Analyzer for ASTM D 7511-09e2

Advantages of ASTM D 7511-09e2 for Lab Operation

Laboratories gain a number of operational benefits by employing ASTM D 7511-09e2 for cyanide analysis beyond

a reduction in matrix interferences and improved analytical performance(8).

ASTM D 7511-09e2 does not require the preliminary acid distillation step specified in method 335.4. Eliminating

the distillation step provides laboratories the following operational advantages.

Higher sample throughput

Lower labor costs

Lower cost per analysis for reagents and consumables

Eliminates analyst exposure to hazardous reagents (boiling, concentrated sulfuric acid and pyridine)

Sample Throughput

Figure 3 illustrates the maximum capacity possible when performing manual distillation and analysis by 335.4compared to in-line UV digestion and gas-diffusion amperometry per ASTM D 7511-09e2. The maximum capacityis based on the samples possible to distill in an 8 hour work day using a 10-position midi distillation block, a 21-

position MICRO DIST apparatus, or a CNSolution cyanide analyzer configured to run ASTM D 7511-09e2.Data for the midi and MICRO DIST distillations are from a supplier website and probably overstate potentialcapacity by not taking into account factors such as operator fatigue, coffee breaks, etc. Data for the CNSolutionanalyzer is based on the number of samples it can run in an 8 hour period at 1 minute per injection withsimultaneous UV-digestion and analysis of samples by ASTM D 7511-09e2.

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Figure 3. Sample throughput in an 8-hour shift for manual distillation and analysis by Method 335.4 versusin-line UV digestion and analysis by ASTM D7511-09e2

Labor Costs

Figure 4 illustrates the estimated annual labor costs required for manual distillation and analysis of 40 samples permonth by method 335.4 versus in-line UV digestion and analysis by ASTM D 7511-09e2. A cost of $15.00 perhour for technician time was used in these estimates.

Figure 4. Estimated annual labor cost for distilling and analyzing 40 samples per month by Method 335.4 versusASTM D 7511-09e2

The labor involved in performing midi distillations includes estimated time spent on glassware setup, disassemblyand washing. Labor also includes hands-on labor associated with pipetting samples and reagents (MgCl

2,

0

25

50

100

125150

200

225

250

Midi-Dist MICRO DIST CNSolution

NumberofSa

mples

$0.00

$1,000.00

$2,000.00

$3,000.00

$4,000.00

$5,000.00

$6,000.00

$7,000.00

Midi Dist MICRO DIST CNSolution

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NaOH, etc.). The MICRO DIST apparatus uses disposable polypropylene distillation tube, which eliminates someof the labor costs associated with re-usable Midi distillation glass tubes/flasks.

ASTM D 7511-09e2 uses automated in-line UV digestion instead of a manual distillation step so there are no laborcosts for sample distillation.

Reagent and Consumables Cost Per Analysis

Figure 5 presents the estimated cost per analysis of reagents and consumable items to perform cyanide analysis bymethod 335.4 versus ASTM D 7511-09e2. While the MICRO Dist apparatus uses reduced amounts of reagents, thepotential savings is offset by the high cost of disposable polypropylene distillation tubes. The larger volume ofreagents required to perform Midi distillations increases its cost per analysis. The cost per analysis for performingASTM D 7511-09e2 on a CNSolution cyanide analyzer is less than $1.00 because no distillation reagents orconsumables are required.

Figure 5. Estimated reagent and consumable cost per analysis for cyanide analysis by Method 335.4 versusASTM D 7511-09e2

Comparison of U.S. EPA 335.4 and ASTM D 7511-09e2

U.S. EPA 335.4

U.S. EPA Method 335.4(9) utilizes a manual reflux-distillation to release hydrocyanic acid (HCN) from cyanide

complexes, which is absorbed in a sodium hydroxide scrubber solution and transferred to a continuous flowanalyzer for colormetric measurement.

In operation, the NaOH scrubber solution from the distillation step is injected into a carrier stream and reacted withchloramine-T, converting the cyanide ion to cyanogen chloride. A pyridine and barbituric acid reagent is thenreacted with cyanogen chloride producing a red-colored complex that passes through a 37 C heater and into theflow cell of a photometric detector for measurement of 570 nm.

0

1

2

3

4

5

6

7

8

Dollars

Midi-Dist MICRO DIST CNSolution

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Analytical Interferences Encountered with Method 335.4

The U.S. EPA identified a potential drawback of Method 335.4 in the Pumpkin Guide(2) stating; If sulfite andthiosulfate are present there is no way to accurately determine cyanide if heat is applied. In these situations a non-distillation method such as D 6888-04, or method OIA-1677 may be used. This guidance document alsorecommended use of a UV digestion or ligand exchange method (OIA-1677) instead of an acid distillation methodif thiocyanate is known or suspected to be present.

Section 4.0 of Method 335.4 identifies interferences related to both the acid distillation step and colorimetricdeterminative step. Samples containing nitrate and/or nitrite may yield high results attributable to acid distillation.An explanation in section 4.3 states; During the distillation nitrate and nitrite will form nitrous acid that will reactwith some organic compounds to form oximes. These oximes will decompose under test conditions to generateHCN.

ASTM D 7511-09e2

ASTM D 7511-09e2 is a non-distillation method that operates on a principle similar to ASTM D 6888-09(10) and

U.S. EPA OIA-1677.(11) ASTM D 7511-09e2 was developed in conjunction with OIA-1677 as a non-distillation

methods for analysis of total cyanide and free/available cyanide respectively.

Mitigation of Analytical Interferences Encountered with Method 335.4

ASTM D 7511-09e2 mitigates sulfide interference at concentrations up to 50 mg/L. This concentration of sulfideapproximates the concentration that is detected by commonly used lead acetate test strips. The ASTM alsoexperimentally determined that concentrations greater than 50 mg/L S rapidly deplete cyanide concentrations fromthe time of sampling to the time of analysis. ASTM D7511-09e2 recommends testing for sulfide when samplingand only treating the sample if the lead acetate paper detects sulfide. ASTM D 7511-09e2 uses UV irradiation at312 nm to dissociate cyanide as HCN from metal cyanide complexes. In environmental samples the complexes thatcomprise total cyanide are usually complexes of ferrous and ferric iron.

ASTM D 7511-09e2 minimizes recovery of cyanide from thiocyanate to

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ASTM D 7511-09e2 evaluated nine very complex matrices known, and demonstrated, to be problematic foranalysis by conventional cyanide methods. These nine matrices were first thoroughly tested in a single lab study,and then the same samples were distributed and evaluated in a multiple laboratory trial. This data is also available

in the standard(3) and the supporting research report.

A direct comparison of ASTM D 7511-09e2 and EPA 335.4 methods for total cyanide analysis is presented inTable 2.

Table 2: Comparison of ASTM D 7511-09e2 and 335.4

* Inter-laboratory study did not evaluate samples below 20ppb.

Parameter ASTM D 7511-09e2 335.4

NPDES/CWA compliance Yes Yes

Measurement Range (g/L) 3500 5500*

UV irradiation >295nm Yes N/A

Separation of HCN Gas diffusion Distillation

Measurement of CN Amperometry ColorimetryMatrices evaluated 9 1

Types of matrices tested

Drum handling facility, municipalwastewater, petroleum refinery effluent,coke plant effluent, rolling mill effluent,

metals forming plant effluent, diecasting plant effluent, precious metals

operation reclaim water, water treatmentplant filter effluent

Reagent water

Interferences evaluated

Sulfide, nitrite, nitrate, nitrate plus

thiocyanate, thiocyanate, thiosulfate,sulfite, formaldehyde, ammonium,chloride, bromide, iodide, sulfate,

carbonate, cyanate, glycerol, glucose,ascorbic acid citric acid

No data

Metal cyanide speciesevaluated for recovery

Cadmium, copper, zinc, silver, mercury,iron (II), iron (III), palladium, gold,

cobalt, platinum, and rutheniumNo data

Metal cyanide speciesevaluated in multi-laboratory

studyIron (II), iron (III), nickel, and mercury No data

Recovery Data (Total Cyanide)from multi-laboratory study

>10 g/L 80107%20 g/L 9198%

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Summary and Conclusions

ASTM D 7511-09e2 and 335.4 are test methods for total cyanide analysis in wastewater samples. ASTM D 7511-09e2 was included in the proposed Methods Update Rule (MUR) published in the Federal Register on September23, 2010. This action allows facilities with NPDES permits to use ASTM D 7511-09e2 to test wastewater samplesfor Clean Water Act compliance reporting.

The principal differences between these two U.S. EPA approved methods can be summarized as follows.

U.S. EPA Method 335.4:

1. Requires a time-consuming manual acid distillation step that delays availability of the first test result forhours.

2. Limits sample throughput to the number of positions available on the distillation apparatus. Typical samplethroughput is 10-20 samples every 3-4 hours.

3. Utilizes hazardous chemicals including boiling sulfuric acid and pyridine, and requires use of barbituric acid,which is a controlled substance in many states within the United States.

4. Is subject to significant false positive and/or false negative results. If the composition of sample matrices isnot well characterized for interferences the test results cannot be trusted.

ASTM Method D 7511-09e2:

1. Measures total cyanide without a preliminary 2-hour acid distillation step providing results in minutes.

2. Employs automated in-line UV digestion to dissociate cyanide complexes, which supports a sample through-put of 30 samples per hour.

3. Determined the recovery of cyanide from 15 metal cyanide complexes at two different concentrations, andcompared the results to distillation methods.

4. Evaluated over 20 different potential interferences at two different concentrations with and without cyanidepresent.

5. Accurately determines cyanide in solutions containing up to 50 ppm Sulfide. Provides details on testing andtreatment of samples containing higher sulfide concentrations.

6. Does not suffer from sulfite interference.

7. Was evaluated in nine very complex matrices known to be problematic with conventional cyanide methods.

8. Recovers less cyanide when thiocyanate is present in samples than any other cyanide method, avoidingpositive analytical interference and bias.

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Publication 36871010

References

1. U.S. EPA, Proposed Toxic Pollution Effluent Standards, 40 CFR Part 129, Federal Register, Vol. 38, 35388,1973.

2. Solutions to Analytical Chemistry Problems with Clean Water Act Methods, U. S. EPA Office of Science andTechnology, March 2007.

3. ASTM D 7511-09e2 Standard Test Method for Total Cyanide by Segmented Flow Injection Analysis, In-lineUltraviolet Digestion and Amperometric Detection, ASTM International.

4. Protocol for EPA Approval of New Methods for Organic and Inorganic Analytes in Wastewater and DrinkingWater, www.epa.gov/waterscience/methods/atp/EPA821B98003.pdf.

5. ASTM D 2777-08e1 Standard Practice for Determination of Precision and Bias of Applicable Test Methodsof Committee D19 on Water, ASTM International.

6. U.S. EPA Clean Water Act Analytical Methods Recent Regulatory Changes;http://www.epa.gov/waterscience/methods/update.

7. Federal Register, Vol. 75, No. 184, September 23, 2010, Guidelines Establishing Test Procedures forAnalysis of Pollutants Under the Clean Water Act; Analysis and Sampling Procedures; Proposed Rule,http://edocket.access.gpo.gov/2010/pdf/2010-20018.pdf.

8. OI Analytical Application Note #3515, Cyanide Analysis - Reducing Laboratory Operating Costs withoutCompromising Data Quality or Regulatory Compliance, 2010.

9. USEPA Method 335.4: Determination of Total Cyanide by Semi-Automated Colorimetry, in Methods for theChemical Analysis of Water and Wastes, EPA-60014-79-020, U.S. Environmental Protection Agency,National Exposure Research Laboratory, Cincinnati, Ohio, 1979.

10. ASTM D 6888-09 Standard Test Method for Available Cyanide with Ligand Displacement and FlowInjection Analysis (FIA) Utilizing Gas Diffusion Separation and Amperometric Detection, ASTMInternational.

11. U.S. EPA Method OIA-1677 Available Cyanide by Flow Injection, Ligand Exchange, and Amperometry,EPA-821-R-99-013, August 1999.

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