Standard Methods: 3500-Cu B: Copper by Neocuproine
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Official Method Name
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3500-Cu B. Neocuproine 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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Cuprous ion (Cu+) in neutral or slightly acidic solution reacts with 2,9-dimethyl-1,10-phenanthroline (neocuproine) to form a complex which is then extracted by a number of organic solvents, including a chloroform-methanol mixture, to give a yellow solution with a molar absorptivity of about 8000 at 457 nm. Full color development is obtained when the pH of the aqueous solution is between 3 and 9; the color is stable in CHCl3-CH3OH for several days. The sample is treated with hydroxylamine-hydrochloride to reduce cupric ions to cuprous ions. Sodium citrate is used to complex metallic ions that might precipitate when the pH is raised. The pH is adjusted to 4 to 6 with NH4OH, a solution of neocuproine in methanol is added, and the resultant complex is extracted into CHCl3. After dilution of the CHCl3 to an exact volume with CH3OH, the absorbance of the solution is measured at 457 nm. |
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Scope and Application
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Useful for a variety of waters, the method is recommended because of its freedom from most interferences. |
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Applicable Concentration Range
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Interferences
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Large amounts of chromium and tin may interfere. Avoid interference from chromium by adding sulfurous acid to reduce chromate and complex chromic ion. In the presence of much tin or excessive amounts of other oxidizing ions, use up to 20 mL additional hydroxylamine-hydrochloride solution. Cyanide, sulfide, and organic matter interfere but can be removed by a digestion procedure. |
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Quality Control Requirements
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See Section 3020 Quality Assurance/Quality Control. |
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Sample Handling
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Copper ion tends to be adsorbed on the surface of sample containers. Therefore, analyze samples as soon as possible after collection. If storage is necessary, use 0.5 mL 1 + l HCl/100 mL sample, or acidify to pH 2 with HNO3, to prevent this adsorption. |
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Maximum Holding Time
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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