Determination of selenite and selenate in drinking water: A Fully Automatic On-line Separation/Pre-concentration System coupled to Electrothermal Atomic Spectrometry with Permanent Chemical Modifiers

J. STRIPEIKIS; J. PEDRO; A. BONIVARDI; M. TUDINO

ANALYTICA CHIMICA ACTA

Año: 2004 vol. 502 p. 99 - 105

0003-2670

A time-based flow injection (FI) separation 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 water. 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 HCl 0.1M and HCl 4M, respectively. The interference of large quantities of chloride during selenium atomisation is prevented by using iridium as a “permanent” chemical modifier. The features 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 180 s (sample flow rate = 3 ml min-1) with HCl elution volumes of 100ml. The detection limit (3 s) 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.