EPA Method 330.2

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EPA Method 330.2:
Total Residual Chlorine by Titration. Official Name: Chlorine, Total Residual (Titrimetric, Back, Iodometric (Starch or Amperometric)

Summary:
Chlorine (hypochlorite ion, hypochlorous acid) and chloramines stoichiometrically liberate iodine from potassium iodide at pH 4 or less. The iodine immediately quantitatively oxidizes a standardized reducing agent such as sodium thiosulfate or phenylarsine oxide. The excess reducing agent is then determined by titrating with a standard iodine titrant. The starch endpoint color change is from clear to blue.

Scope:
The iodometric back titration method is applicable to all types of waters but is primarily used for wastewater because it eliminates any contact between the full concentration of liberated iodine and the wastewater.

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

Interferences:
Manganese, iron and nitrite interference may be minimized by buffering to pH 4 before the addition of KI.High concentrations of organics may cause uncertainty in the endpoint. This uncertainty can be reduced by acidifying to pH 1.0 if manganese, iron and nitrite are absent. 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:
None.

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