USGS-NWQL: I-3840: Sulfide, total, iodometric
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Official Method Name
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Sulfide, titrimetric, iodometric |
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Current Revision
| 1985 |
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Media
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WATER |
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Instrumentation
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Titration |
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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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Methods for the Determination of Inorganic Substances in Water and Fluvial Sediments, Techniques of Water-Resources Investigations of the United States Geological Survey, Book 5, Chapter A1 Edited by Marvin J. Fishman and Linda C. Friedman |
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Brief Method Summary
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This iodometric method does not differentiate the forms of the sulfide ion in solution. Sulfide is reacted with an excess of iodine in acid solution, and the remaining iodine is then determined by titration with sodium thiosulfate, using starch as an indicator (Kolthoff and others, 1969). A blank is treated exactly the same as the samples. The sulfide concentration is calculated from the difference between the volume of thiosulfate required for the blank and the volume used for the sample. This method is similar to that in an article published by the American Public Health Association (1980). |
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Scope and Application
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This method may be used to analyze water and water-suspended sediment containing more than 0.5 mg/L of sulfide. Water-suspended sediment may be analyzed by this method if sample is shaken vigorously and a suitable aliquot of well-mixed sample is rapidly withdrawn. Water containing dissolved sulfides readily loses hydrogen sulfide, particularly if the pH of the sample is low. Oxygen destroys sulfides by oxidation, particularly if the pH of the sample is high. Aeration and agitation of the sample should, therefore, be avoided. The addition of 2 g of zinc acetate per liter of water will fix the sample for several days. Acidic water must be neutralized before addition of zinc acetate. |
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Applicable Concentration Range
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NA |
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Interferences
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Reducing substances such as sulfites and heavy-metal ions react with iodine, which con-tributes to positive errors. Oxygen and other oxidants may react with hydriodic acid to liberate iodine, which contributes to negative errors. |
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Quality Control Requirements
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Laboratory Blanks (LB) |
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Sample Handling
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Container Description: 250 or 500 mL polyethylene bottle. Handling and Treatment: Use unfiltered sample to rinse bottle. Addition zinc acetate at a rate of 2 grams of zinc acetate to a liter of water will fix the sample for several days |
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Maximum Holding Time
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NA |
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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