EPA-NERL: 330.2: Total Residual Chlorine by Titration
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Official Method Name
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Chlorine, Total Residual (Titrimetric, Back, Iodometric (Starch or Amperometric) |
|---|---|
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Current Revision
| Issued 1978 |
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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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Brief Method Summary
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Chlorine (hypochlorite ion, hypochlorous acid) and chloramines stoichiometrically liberate iodine from potassium iodide at pH 4 or less. The iodine immediately quantitatively oxidizes a standardized reducing agent such as sodium thiosulfate or phenylarsine oxide. The excess reducing agent is then determined by titrating with a standard iodine titrant. The starch endpoint color change is from clear to blue. |
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Scope and Application
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The iodometric back titration method is applicable to all types of waters but is primarily used for wastewater because it eliminates any contact between the full concentration of liberated iodine and the wastewater. |
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Applicable Concentration Range
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None. |
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Interferences
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Manganese, iron and nitrite interference may be minimized by buffering to pH 4 before the addition of KI. High concentrations of organics may cause uncertainty in the endpoint. This uncertainty can be reduced by acidifying to pH 1.0 if manganese, iron and nitrite are absent. Turbidity and color may make the endpoint difficult to detect. Practice runs with spiked samples may be necessary. |
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Quality Control Requirements
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None. |
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Sample Handling
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None. |
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Maximum Holding Time
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Analyze Immediately. |
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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None. |
