EPA-NERL: 330.5: Total Residual Chlorine by Spectrophotometer
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Official Method Name
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Chlorine, Total Residual (Spectrophotometric, DPD) |
|---|---|
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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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Spectroscopy (Colorimetry; Photometry) |
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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 liberated iodine reacts with N,N-diethyl-p-phenylene diamine (DPD) to produce a red colored solution. The solution is spectrophotometrically compared to a series of standards, using a graph or a regression analysis calculation. |
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Scope and Application
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The DPD-Colorimetric method is applicable to natural and treated waters at concentrations from 0.2-4 mg/L. |
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Applicable Concentration Range
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0.2-4 mg/L. |
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Interferences
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Any oxidizing agents; these are usually present at insignificant concentrations compared to the residual chlorine concentrations. Turbidity and color will essentially prevent the colorimetric analysis. |
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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. |
