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

The on-line reduction of Se(VI) to Se(IV) and subsequent determination of Se(IV) by flow injection-hydride generation atomic absorption spectrometry are proposed. To reduce Se(VI) quantitatively to Se(IV), the sample is acidified with concentrated HCI and the sample coil is heated to 140-degrees-C. Hydride generation is performed in an ice-bath to prevent decomposition of the NaBH4. The sensitivity of the proposed method is about twice that of the traditional method without heating, the relative standard deviation is below 5%, the recovery is 95-105% and the selectivity is significantly increased. No Se losses occur because the reduction system is closed until the selenium hydride reaches the phase separator. The method has been successfully applied to the determination of Se(IV) and Se(VI) in sea water.