EPA-NERL: 410.1: Chemical Oxygen Demand by Titrimetry
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Official Method Name
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Chemical Oxygen Demand (Titrimetric, Mid-Level) |
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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 substances in the sample are oxidized by potassium dichromate in 50% sulfuric acid solution at reflux temperature. Silver sulfate is used as a catalyst and mercuric sulfate is added to remove chloride interference. The excess dichromate is titrated with standard ferrous ammonium sulfate using orthophenanthroline ferrous complex as an indicator. |
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Scope and Application
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This method determines chemical oxygen demand; the quantity of oxygen required to oxidize organic matter in a waste sample. |
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Applicable Concentration Range
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50 mg/L or higher. |
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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. To minimize loss, cool the sample flask during the addition of sulfuric acid. (C) Chlorides: Chlorides are quantitatively oxidized by dichromate and represent a positive interference. Mercuric sulfate is added to the digestion flask to complex chlorides and eliminate the interference. |
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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. |
