SEQUENTIAL DETERMINATION OF ARSENITE AND ARSENATE BY ION CHROMATOGRAPHY

A procedure for the sequential determination of arsenite [As(III)] and arsenate [As(V)] based on electrochemical detection for As(III) and s pectrophotometric detection for As(V) following ion chromatographic se paration was developed. The color-developing system was based on the i on-association complex formed by heteropolymolybdoarsenic acid with bi smuth in the presence of Triton X-100. Experimental conditions for ele ctrochemical detection and color-developing conditions were optimized for As(III) and As(V), respectively. The optimal applied potential for electrochemical detection of As(III) was + 0.35 V and the wavelength for spectrophotometric detection of As(V) was 700 nm. By using an elue nt of 2.0 mM sodium hydrogencarbonate-5.5 mM sodium carbonate with a 1 75 mu l sample loop for ion chromatographic separation, the detection limits, which are defined as the concentrations that give the peak int ensity twice the baseline noise, are found to be 2.9 mu g/l for As(III ) and 13 mu g/l for As(V), respectively. The spiked waste water sample s were analyzed and recoveries were found to be 97.5-104% for As(III) and 93.5-103% for As(V), respectively.