DETERMINATION OF ULTRA-TRACE AMOUNTS OF SELENIUM(IV) BY FLOW-INJECTION HYDRIDE GENERATION ATOMIC-ABSORPTION SPECTROMETRY WITH ONLINE PRECONCENTRATION BY COPRECIPITATION WITH LANTHANUM HYDROXIDE

A flour injection procedure for the determination of ultratrace amounts of selenium(IV) in water samples is described, which combines hydride generation atomic absorption spectrometry (HGAAS) with on-line preconcentration of the analyte by coprecipitation. The samples, each spiked with lanthanum nitrate (20 mg l(-1)), are introduced into the flow injection system using time-based injection, and mixed with an ammonium buffer (pH 9.1). Selenium(IV) is preconcentrated by coprecipitation with the generated lanthanum hydroxide precipitate. The precipitate is quantitatively collected on the inner walls of an incorporated knotted Microline reactor, and subsequently eluted with 1 mol l(-1) hydrochloric acid and directed into the HGAAS system. At a sample consumption of 6.7 ml, an enrichment factor of 24 was obtained at a sampling frequency of 33 samples h(-1). The detection limit (3 sigma) was 0.001 mu g l(-1) and the precision (relative standard deviation) was 0.7% (n = 11) at the 0.5 mu g l(-1) level. Satisfactory results were obtained for the analysis of selenium(IV) in tap- and well-water samples.