SPECTROCHIMICA ACTA PART B ELSEVIER Spectrochimica Acta Part B 51 (1996) 1837-1847 Flow injection for the determination of Se(IV) and Se(VI) by hydride generation atomic absorption spectrometry with microwave oven on-line prereduction of Se(VI) to Se(IV) 1 J.L. Burguera*, P. Carrero, M. Burguera, C. Rondon, M.R. Brunetto, M. Gallignani IVAIQUIM (Venezuelan Andean Institute for Chemical Research), Faculty of Sciences, University of Los Andes, P.O. Box 542, 5101-A Merida, Venezuela Received 26 July 1995; accepted 8 March 1996 Abstract An on-line flow injection system has been developed for the selective determination of Se(IV) and Se(VI) in citric fruit juices and geothermal waters by hydride generation atomic absorption spectrometry with microwave-aided heating prereduction of Se(VI) to Se(IV). The samples and the prereductant solutions (4 tool 1-1 HCI for Se(IV) and 12 tool 1-1 HC1 for Se(VI)) which circulated in a closed-flow circuit were injected 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 ~g 1-1 of Se(IV) and Se(VI), respectively. The detection limits were 1.0 ttg 1-1 for Se(IV) and 1.5/~g 1 -l 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 agreed with the content of both selenium species. The sample throughput was about 50 measurements per hour. The main advantage of the method is that the selective determination of Se(IV) and Se(VI) in citric fruit juices and geothermal waters is performed in a closed system with a minimum sample manipulation, exposure to the environ- ment, minimum sample waste and operator attention. Keywords: Citric fruit juices; Geothermal waters; Hydride generation; On-line flow injection; Se(IV); Se(VI) 1. Introduction Selenium has received much attention as an essen- tial and also as a very toxic element [1]. Thus, food and water must be monitored for trace amounts of this element. An estimated safe and adequate daily dietary intake has been established as 10-200 ~g day -1, depending on age [2]. Specifically, the Food and * Corresponding author. 1This paper was published in the Special Issue of Spectrochimica Acta, Part B, devoted to Flow Analysis. Nutrition Board of the US National Research Council [3] has recommended a dietary selenium allowance of 0.87 #g kg -1 or, with rounding, 55 and 70 #g day-1 for the reference North American adult female and male, respectively. Although selenium levels in ground and surface waters are generally low (less than 10/zg 1-1), high concentrations of this element may occur in asso- ciation with geological features or due to the corrosion of household plumbing by soft, acidic water [4]. The concentration of selenium in fruits is also low, usually below the 100 ttg 1-1 levels [5]. However, the levels of selenium in individual foods of plant origin are highly 0584-8547/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved PII S0584-8547(96)01521-2