EPA Method 330.4

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EPA Method 330.4:
Total Residual Chlorine by Titration. Official Name: Chlorine, Total Residual (Titrimetric, DPD-FAS)

Summary:
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.

Scope:
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.

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

Interferences:
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.

QC Requirements:
None.

Maximum Holding Time:
Analyze Immediately.

Media:
WATER

Subcategory:
Inorganic

Concentration:
Greater than 0.1 mg/L.

Sample Prep:
None.

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

Detection:
None.

Revision Number:
Issued 1978

Test Description:
Chlorine, Total Resi

Report Number:
600/4-79-020

Instrument used for this test:
Buret