EPA-NERL: 410.3: Chemical Oxygen Demand in Saline Waters by Titrimetry
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Official Method Name
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Chemical Oxygen Demand (Titrimetric, High Level for Saline Waters) |
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Current Revision
| Issued 1971; Editorial Revision 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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Organic |
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Method Source
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Citation
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Brief Method Summary
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Organic and oxidizable inorganic substances in an aqueous sample are oxidized by potassium dichromate solution in sulfuric acid solution. The excess dichromate is titrate with standard ferrous ammonium sulfate using orthophenanthroline ferrous complex (ferroin) as an indicator. |
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Scope and Application
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This method determines chemical oxygen demand in saline waters. |
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Applicable Concentration Range
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Greater than 250 mg/L when chloride levels exceed 1000 mg/L. |
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Interferences
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(A) Contamination: Trace organics from glassware or the atmosphere can cause gross positive error. Run blanks through glassware to eliminate trace organics. (B) Volatiles: Volatile organics may be lost when the temperature rises during the addition of sulfuric acid. (C) Chlorides: Chlorides are quantitatively oxidized by dichromate and represent a positive interference. A chloride correction procedure is provided in the method. |
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Quality Control Requirements
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None. |
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Sample Handling
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Glass bottles are preferred; use plastic containers only if they are know to contain no organic contaminant. Analyze biologically active samples as soon as possible, and thoroughly homogenize all samples. Preserve samples at pH < 2 with sulfuric acid and refrigerate at 4oC. |
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Maximum Holding Time
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28 Days (MCAWW, Table 1). |
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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. |
