EPA-NERL: 330.4:  Total Residual Chlorine by Titration

  • Summary
  • Analytes
  • Revision
  • Data and Sites
Official Method Name
Chlorine, Total Residual (Titrimetric, DPD-FAS)
Current Revision
Issued 1978
Media
WATER
Instrumentation
Titration
Method Subcategory
Inorganic
Method Source
  EPA-NERL
Citation
  Methods for the Chemical Analysis of Water and Wastes (MCAWW) (EPA/600/4-79/020)
Brief Method 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 and Application
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.
Applicable Concentration Range
Greater than 0.1 mg/L.
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.
Quality Control Requirements
None.
Sample Handling
None.
Maximum Holding Time
Analyze Immediately.
Relative Cost
Less than $50
Sample Preparation Methods
None.