FLOW-INJECTION FOR THE DETERMINATION OF SE(IV) AND SE(VI) BY HYDRIDE GENERATION ATOMIC-ABSORPTION SPECTROMETRY WITH MICROWAVE-OVEN ONLINE PREREDUCTION OF SE(VI) TO SE(IV)

An on-line flow injection system has been developed for the selective determination of Se(IV) and Se(VI) in citric fruit juices and geotherm al waters by hydride generation atomic absorption spectrometry with mi crowave-aided heating prereduction of Se(VI) to Se(IV). The samples an d the prereductant solutions (4 mol l(-1) HCl for Se(IV) and 12 mol l( -1) HCl for Se(VI)) which circulated in a closed-flow circuit were inj ected by means of a time-based injector. This mixture was displaced by a carrier solution of 1% v/v of hydrochloric acid through a PTFE coil located inside the focused microwave oven and mixed downstream with a borohydride solution to generate the hydride. The linear ranges were 0-120 and 0-100 mu g l(-1) of Se(IV) and Se(VI), respectively. The det ection limits were 1.0 mu g l(-1) for Se(IV) and 1.5 mu g l(-1) for Se (VI). The precision (about 2.0-2.5% RSD) and recoveries (96-98% for Se (IV) and 94-98% for Se(VI)) were good. Total selenium values were also obtained by electrothermal atomic absorption spectrometry which agree d with the content of both selenium species. The sample throughput was about 50 measurements per hour. The main advantage of the method is t hat the selective determination of Se(IV) and Se(VI) in citric fruit j uices and geothermal waters is performed in a closed system with a min imum sample manipulation, exposure to the environment, minimum sample waste and operator attention.