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Selenium(IV) and tetrahydroborate(III) (borohydride) were simultaneously retained on a strong anion-exchange resin in a packed column. Hydrogen selenide was generated by passage of an injected zone of hydrochloric acid with subsequent detection by AAS with quartz tube atomization. The limits of detection, defined as the concentration giving a signal equal to 3s of the blank, were 0.24, 0.15 and 0.12 mg l 21 of Se for 1, 2 and 3 min preconcentration at a sample flow rate of 3 ml min 21 , respectively. The precision of the procedure, expressed as the RSD of 10 successive determinations of 5, 10, and 20 mg l 21 of Se, varied from 0.41 to 1.32, 0.24 to 0.81 and 0.18 to 0.61% for 1, 2 and 3 min preconcentration, respectively. The system was used for the determination of selenium in river, lake and tap water matrices. No appreciable matrix effects were observed and the system was calibrated with aqueous solutions of a pure selenium salt (Na 2 SeO 3 ). The recoveries of spikes (0.5, 2, and 10 mg l 21 of Se) added to the water samples ranged from 96.0 to 102.0, 96.0 to 107.0 and 98.9 to 108% for river, lake and tap water, respectively.

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