EPA Method 330.5

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EPA Method 330.5:
Total Residual Chlorine by Spectrophotometer. Official Name: Chlorine, Total Residual (Spectrophotometric, DPD)

Summary:
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.

Scope:
The DPD-Colorimetric method is applicable to natural and treated waters at concentrations from 0.2-4 mg/L.

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

Interferences:
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.

QC Requirements:
None.

Maximum Holding Time:
Analyze Immediately.

Media:
WATER

Subcategory:
Inorganic

Concentration:
0.2-4 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