NEMI Method Summary

Method Summary

Method Source	U.S. EPA National Exposure Research Laboratory (NERL) [formerly EMSL]
Method Number	330.5
Revision Information	Issued 1978
Method Name	Descriptive Name: Total Residual Chlorine by Spectrophotometer Official Name: Chlorine, Total Residual (Spectrophotometric, DPD)
Media	Media: WATER
Subcategory	Inorganic
Citation	Methods for the Chemical Analysis of Water and Wastes (MCAWW) (EPA/600/4-79/020)
Method Download	Download full method now (PDF file)
Summary of Method	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 and Application	The DPD-Colorimetric method is applicable to natural and treated waters at concentrations from 0.2-4 mg/L.
Applicable Concentration Range	0.2-4 mg/L.
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.
Sample Handling	None.
Max Holding Time	Analyze Immediately.
Relative Cost/Effort	Less than $50
Sample Prep Method(s)	None.

Analyte	Detection Level	Bias	Precision	Pct False Positive
Chlorine, Total Residual (N-50060)	.2 mg/L	105.38 % Rec (ML)	11.1 % RSD (ML)	.5 mg/L

Precision Descriptor Notes	Precision and accuracy values were calculated using interlaboratory data from EPA-managed Water Pollution (WP) performance evaluation studies.
Detection Level Note	None.