Determination of selenite and selenate in drinking water:a fully automatic on-line spearation/pre-concentration system coulped to electrothermal atomic spectrometry with permanent chemical modifiers

摘要

A time-based flow injection(FI)spearation pre-concentration system coupled to an electrothermal atomic absorption spectrometer(graphite furnace)has been developed for the direct ultra-trace determination of selenite and selenate in drinking ware.The pre-concentration of both forms of selenium is carried out onto a micro-column packed with an anionic resin(Dowex 1X8)that is placed in the robotic arm of the autosampling device.Selenite and selenate are sequentially eluted with HCI 0.1 M and HCI 4M,respectively.The interference of large quantities of chloride during selenium atomisation is prevented by using iridium as a "permanent"chemical modifier.The feautres of the pre-concentration separation system for both species are:53% efficiency of retention and an enhancement factor of 82 for a pre-concentration time of 180s(sample flow rate-31 ml min~-1) with HCI elution volumes of 100 mul.The detection limit(3s)is 10 ng l~1) for the two species and the relative standard deviation(n-10)at the 200 ng l~-1 level is 3.5% for selenite and 5.6% for selenate.The addition of selenite and selenate stock standard solutions to tap water samples yields a 97-103% recovery of both species.