Standard Methods: 4500-CN-E: Colorimetric Method for Cyanide in Distillate
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Official Method Name
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Cyanide: Colorimetric Method |
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Current Revision
| Standard Methods Online |
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Media
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WATER |
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Instrumentation
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Spectroscopy (Colorimetry; Photometry) |
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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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Brief Method Summary
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Cyanide in the alkaline distillate from preliminary treatment is converted to CNCl by reaction with chloramine-T at pH < 8 without hydrolyzing to CNO-. After reaction, CNCl forms a red-blue color on addition of a pyridine-barbituric acid reagent. Maximum color absorbance in aqueous solution is between 575 and 582 nm. |
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Scope and Application
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This method allows for determination of free cyanides in an alkaline distillate. The treatment and distillation preceding measurment determine what cyanide complexes are included in the measurement (complex cyanides release free cyanides that are measured with this method). |
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Applicable Concentration Range
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0.02 - 0.2 mg-CN/L |
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Interferences
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All known interferences are eliminated or reduced by distillation and interfence removal steps used during distillation. The distillation procedure 4500-CN- B lists known interferences and removal procedures; see also ASTM D2036 for information. |
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Quality Control Requirements
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See Standard Methods Section 1020. |
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Sample Handling
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Add 0.1 g sodium arsenite in the presence of oxidizing agents. Add lead acetate or lead carbonate in the presence of sulfide. Filter sample before raising pH for stabilization. If samples cannot be analyzed immediately, add NaOH pellets or a strong NaOH solution to raise sample pH to 12 to 12.5. Store in a closed, dark bottle in a cool place. |
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Maximum Holding Time
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24 hours after raising pH to > 12 |
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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Various (e.g., 4500-CN- B Distillation) |
