SIMULTANEOUS DETERMINATION OF ARSENITE, ARSENATE, SELENITE, AND SELENATE BY SUPPRESSED ION CHROMATOGRAPHY

Studies of chemical processes involving As and Se in soil solution require accurate determination of arsenite, arsenate, selenite, and selenate. Many of the currently used speciation techniques rely on indirect measurement of one or more species. Direct, simultaneous measurement of these As and Se ionic species was achieved using a commercially available suppressed ion chromatography system and a Na2CO3-NaHCO3 eluant. Electrochemical and conductivity detectors were used in series with a dual-channel integrator to quantify arsenite, arsenate, selenite, and selenate. Resolution of the As and Se ionic species from the other ions depended on the nature of the eluant. An eluant containing 2 mM Na2CO3 and 1.7 mM NaHCO3 provided a good compromise between analyte resolution and time of analysis. Concentrations of 1 mg L-1 each of arsenite, arsenate, selenite, and selenate were measured in the presence of 50 mg L-1 each of F, Cl, NO3-N, SO4-S, and PO4-P. Detection limits ranged from 0.016 mg L-1 for selenite to 0.120 mg L-1 for arsenate. The detection limits for arsenate and selenite obtained using this suppressed ion chromatographic technique were lower than values reported in the literature using nonsuppressed ion chromatography. Precision of analysis decreased with decreasing analyte concentration. The ion chromatographic method was compared to spectroscopic methods using analyses of soil solution, receiving As and Se spikes, and analyses of adsorption equilibrium solutions. The results of this study show that suppressed ion chromatography is a reliable method for determination of the As and Se oxyanions in soil solution.