SPECIATION OF SELENIUM IN AQUEOUS AND BIOLOGICAL MATRICES BY MICROBORE ION CHROMATOGRAPHY COUPLED WITH ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY VIA ULTRA-LOW VOLUME FRACTION COLLECTION

A robust, user-friendly, sensitive and affordable speciation method ba sed on microbore anion-exchange chromatography (IC) for the separation of selenium species and Zeeman-effect ETAAS for element specific dete ction is described. By exploiting the very low flow rates normally emp loyed in microbore chromatography, the analytical usefulness of chroma tography coupled to the sensitive but discontinuous ETAAS detector has been increased in comparison with couplings incorporating normal bore liquid chromatography. The flow rate of the mobile phase in this part icular IC system was 80 mu l min(-1). A highly reproducible and automa ted collection of 20 mu l fractions in sampler cups was used for inter facing the chromatographic separation with ETAAS, The IC-ETAAS results were also directly compared with those obtained by IC-direct injectio n nebulizer ICP-AES for assessing the chromatographic resolution of th e proposed method. It is possible to separate selenomethionine, seleni te, selenate and selenocystine in 6 min. The trade-off in chromatograp hic resolution and time consumption in the detection step using IC-ETA AS is compensated for by a high degree of simplicity and the high spec ificity and sensitivity of the Zeeman-effect ETAAS resulting in relati ve detection limits of 2.8-4.1 ng ml(-1) (42-61 pg absolute). These de tection limits are comparable to those for published HPLC-ICP-MS metho ds, The method was evaluated by injecting aqueous standards, unspiked and spiked sample extracts from the biological certified reference mat erial CRM 402, The eluent was injected along with a palladium-magnesiu m nitrate modifier since the pyrolysis curves for trimethylselenonium, selenomethionine, selenite, selenate and selenocystine revealed a sim ilar response for all species by using this modifier, i.e, all species are thermally stabilized up to 1000 degrees C, Without adding the mod ifier, the species showed very different volatilities during the therm al pre-treatment step.