EPA Method 330.3

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EPA Method 330.3:
Total Residual Chlorine by Titration. Official Name: Chlorine, Total Residual (Titrimetric, Iodometric)

Chlorine (hypochlorite ion, hypochlorous acid) and chloramines stoichiometrically liberate iodine from potassium iodide at pH 4 or less. The iodine is titrated with a standard reducing agent such as sodium thiosulfate or phenylarsine oxide using a starch 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.

The iodometric titration method is applicable to natural and treated waters at concentrations greater than 0.1 mg/L.

Methods for the Chemical Analysis of Water and Wastes (MCAWW) (EPA/600/4-79/020)

Ferric, manganic and nitrite ions interfere, the neutral titration minimizes these interferences. Acetic acid is used for the acid titration. Sulfuric acid may be used if no interferences are present. Hydrochloric acid should never be used. Turbidity and color may make the endpoint difficult to detect. Practice runs with spiked samples may be necessary.

QC Requirements:

Maximum Holding Time:
Analyze Immediately.



Greater than 0.1 mg/L.

Sample Prep:

Precision and accuracy values were calculated using interlaboratory data from EPA-managed Water Pollution (WP) performance evaluation studies.


Revision Number:
Issued 1978

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Examples:  8260

Examples:  Dioxin
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