Comparison of ion chromatography and flow injection analysis methods for monitoring chlorite and chlorate ions in drinking water

Abstract

Up-coming regulations on chlorine dioxide in drinking water treatment require low level measurement of chlorite ion (CI0₂-) and chlorate ion (CI0₃-). This research investigated analysis of CI0₂- and CI0₃-; in drinking water by flow injection analysis with iodometric detection (FIA) and ion chromatography with conductivity detection (IC).

Both the FIA and IC methods were accurate for the determination of CIO₂-; and CIO₃-; in reagent water. The IC method was accurate in drinking water, however, FIA responded to chloramines and other oxidants present in drinking water causing inaccurate analysis of CIO₂-; and CIO₃-; by FIA.

The two IC eluants investigated, a carbonate/bicarbonate mixture and a borate/boric acid mixture, performed well. By taking advantage of the slightly different separation abilities of each eluant, the IC method can be modified to maximize resolution of CIO₂-; and CIO₃-; in different drinking water matrices.

Chlorite was unstable in chlorinated drinking water but was stable for up to three days when sodium oxalate was added and stable up to eighteen days when ethylene diamine was added as a preservative. Chlorate was stable in drinking water for up to eighteen days with or without a preservative.

The propagation of errors method for determining detection limits yielded limits of detection for CIO₂- (mg/L) of 0.05 for FIA, 0.03 for the IC carbonate eluant and 0.01 for the IC borate eluant. For CIO₃- the limits of detection (mg/L) were 0.24 for FIA; 0.11 for the IC carbonate eluant and 0.02 for the borate eluant.