Standard Methods: 3500-Pb B: Lead by Dithizone
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Official Method Name
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3500-Pb B. Dithizone 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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An acidified sample containing microgram quantities of lead is mixed with ammoniacal citrate-cyanide reducing solution and extracted with dithizone in chloroform (CHCl3) to form a cherry-red lead dithizonate. The color of the mixed color solution is measured photometrically. Sample volume taken for analysis may be 2 L when digestion is used. |
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Scope and Application
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The dithizone method is sensitive and specific as a colorimetric procedure. |
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Applicable Concentration Range
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Interferences
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In a weakly ammoniacal cyanide solution (pH 8.5 to 9.5) dithizone forms colored complexes with bismuth, stannous tin, and monovalent thallium. In strongly ammoniacal citrate-cyanide solution (pH 10 to 11.5) the dithizonates of these ions are unstable and are extracted only partially. This method uses a high pH, mixed color, single dithizone extraction. Interference from stannous tin and monovalent thallium is reduced further when these ions are oxidized during preliminary digestion. A modification of the method allows detection and elimination of bismuth interference. Excessive quantities of bismuth, thallium, and tin may be removed. |
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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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Plastic or glass containers. Add HNO3 to pH <2. See Section 3010 for more details. |
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Maximum Holding Time
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6 months (See Section 1060) |
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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See 3500-Pb B.1.c. |
