EPA-NERL: 330.4: Total Residual Chlorine by Titration
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Official Method Name
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Chlorine, Total Residual (Titrimetric, DPD-FAS) |
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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 is titrated with FAS using DPD as the indicator. The results are calculated as mg/L Cl even though the actual measurement is of total oxidizing power because chlorine is the dominant oxidizing agent present. |
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Scope and Application
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The N,N-diethyl-p-phenylene diamine (DPD) - ferrous ammonium sulfate (FAS) titration method is applicable to natural and treated waters at concentrations above 0.1 mg/L Cl. |
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Applicable Concentration Range
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Greater than 0.1 mg/L. |
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Interferences
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Bromine, bromamine, and iodine are interferences which are normally present in insignificant amounts. Oxidized manganese interferes but can be corrected by subtraction after performing a titration in the presence of sodium arsenite (NaAsO2). Copper interferes but is accounted for (up to approximately 10 mg/L copper) by incorporation of EDTA. The EDTA also retards deterioration of DPD due to oxidation and completely suppresses dissolved oxygen errors by preventing trace metal catalysis. 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. |
