Standard Methods: 4500-S2- F: Sulfide by Iodometry
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Official Method Name
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4500-S2- F. Iodometric Method |
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Current Revision
| Standard Methods 21st Edition (2005); Standard Methods Online |
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Media
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WATER |
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Instrumentation
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Not Applicable |
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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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Iodine oxidizes sulfide in acid solution. A titration based on this reaction is an accurate method for determining sulfide at concentrations above 1 mg/L if interferences are absent and if loss of H2S is avoided. |
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Scope and Application
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The iodometric method is useful for standardizing the methylene blue colorimetric methods (D and E) and is suitable for analyzing samples freshly taken from wells or springs. The method can be used for wastewater and partly oxidized water from sulfur springs if interfering substances are removed first. |
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Applicable Concentration Range
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> 1 mg/L |
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Interferences
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The iodometric method suffers interference from reducing substances that react with iodine, including thiosulfate, sulfite, and various organic compounds, both solid and dissolved. Eliminate interferences due to sulfite, thiosulfate, iodide, and many other soluble substances, but not ferrocyanide, by first precipitating ZnS, removing the supernatant, and replacing it with distilled water. Use the same procedure, even when not needed for removal of interferences, to concentrate sulfide. |
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Quality Control Requirements
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See Section 4020 Quality Assurance/Quality Control. |
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Sample Handling
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Collect water samples with minimum aeration. Either analyze samples immediately after collection or preserve with zinc acetate solution for later analysis. To preserve a sample for a total sulfide determination put zinc acetate and sodium hydroxide solutions into sample bottle before filling it with sample. Use 0.2 mL 2M zinc acetate solution per 100 mL sample. Increase volume of zinc acetate solution if the sulfide concentration is expected to be greater than 64 mg/L. The final pH should be at least 9. Add more NaOH if necessary. Fill bottle completely and stopper. |
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Maximum Holding Time
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28 days |
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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 Section 4500-S2- C |
