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 spectrophotometric detection for As(V) following ion chromatographic separation was developed. The color-developing system was based on the ion-association complex formed by heteropolymolybdoarsenic acid with bismuth in the presence of Triton X-100. Experimental conditions for electrochemical 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 eluent of 2.0 mM sodium hydrogencarbonate-5.5 mM sodium carbonate with a 175 μl sample loop for ion chromatographic separation, the detection limits, which are defined as the concentrations that give the peak intensity twice the baseline noise, are found to be 2.9 μg/l for As(III) and 13 μg/l for As(V), respectively. The spiked waste water samples were analyzed and recoveries were found to be 97.5–104% for As(III) and 93.5–103% for As(V), respectively.