EPA Region 7 ENSV: 3135.2I: Cyanide in Water and Soil by Colorimetry
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Official Method Name
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Cyanide, Total and Amenable, in Aqueous and Soil Samples by Automated Colorimetric With Manual Digestion |
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Current Revision
| May 12, 2008 |
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Media
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VARIOUS |
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Instrumentation
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Colorimeter |
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Method Subcategory
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Inorganic |
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Method Source
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Citation
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Greenlee, Adrienne, 2008, Cyanide, total and amenable in aqueous and soil samples automated colorimetric with manual digestion, RLAB method No. 3135.2I. |
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Brief Method Summary
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The cyanide is released by refluxing the sample with strong acid. The hydrogen cyanide is distilled and collected in an absorber-scrubber containing sodium hydroxide solution. The cyanide ion in the absorbing solution is then determined by automated colorimetry. In the colorimetric measurement, the cyanide is converted to cyanogen chloride. After the reaction is complete, color is formed on the addition of pyridine-barbituric acid reagent. The red colored complex is measured at 570 nm. Cyanide amenable to chlorination is determined by calculating the difference between total cyanide and cyanide remaining after chlorination. |
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Scope and Application
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This method is applicable to the determination of cyanide in drinking, ground, and surface waters, domestic and industrial waste waters, sediments and solid waste. This method detects inorganic cyanides that are present as either simple soluble salts or complex radicals. It is used to determine values for both total cyanide and cyanide amenable to chlorination. It is not intended to determine if a waste is hazardous by the characteristic of reactivity. |
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Applicable Concentration Range
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The applicable range is 0.003 to 0.500 mg/L CN in the distillate. This range can be expanded by sample dilution, either by using less sample for distillation or diluting the distillate. |
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Interferences
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Sulfides adversely affect the colorimetric procedures. False positives may be produced by samples that contain nitrate and/or nitrite greater than 10 PPM. Oxidizing agents such as chlorine, oxygen, and ozone decompose most cyanides. |
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Quality Control Requirements
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A Laboratory Control Sample is run daily and for every 20 unknown samples. A Matrix Spike is run daily for each series of 20 samples or less. |
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Sample Handling
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Oxidizing agents such as chlorine decompose most cyanides. To determine whether oxidizing agents are present, test a drop of the aqueous sample with acidified potassium iodide (KI)-starch test paper at the time the sample is collected; a blue color indicates the need for treatment. Add ascorbic acid a few crystals at a time until a drop of sample produces no color on the indicator. Then add an additional 0.6 gm of ascorbic acid for each liter of water prior to preserving with sodium hydroxide. Preserve aqueous samples with sodium hydroxide pellets to sample pH $12 at the time of collection. Refrigerate samples at 4°C and analyze as soon as possible after collection. |
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Maximum Holding Time
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The maximum holding time is 14 days for aqueous samples. |
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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