ORGANIC AND INORGANIC SELENIUM SPECIATION IN URINE BY ONLINE VESICLE MEDIATED HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY-FOCUSED MICROWAVE DIGESTION-HYDRIDE GENERATION-INDUCTIVELY COUPLED PLASMA-MASS SPECTROMETRY

A vesicle mediated high performance liquid chromatographic (HPLC)-micr owave digestion (MW)-hydride generation (HG) system coupled on-line wi th atomic absorption spectrometry (AAS) and inductively coupled plasma mass spectrometry (ICP-MS) has been assessed for selenium species sep aration and detection, Selenocystine, selenomethionine, selenoethionin e, selenourea, Se-IV and Se-VI are separated by vesicle mediated chrom atography prior to on-line selenocompounds microwave digestion with a KBrO3-HBr mixture to generate Se-IV continuously, which is finally tra nsformed into SeH2, in a continuous manner with a merging flow of sodi um tetrahydroborate(III). Analytical characteristics of this coupling are compared with those obtained coupling HPLC-ICP-MS via conventional nebulisation, Detection limits (DLs) obtained for selenocystine, sele nomethionine, selenoethionine, selenite and selenate in spiked human u rine, when ICP-MS was used as detector, ranged between 1.0 and 5.3 mu g l(-1) (51-267 pg), while precision ranged between +/- 3.4 and +/- 8. 4%. This continuous system, vesicle mediated HPLC-MW-HG-atomic detecti on, allows the separation and detection of selenocystine, selenourea, selenomethionine, selenoethionine, selenite and selenate in human urin e. The analytical versatility of such coupling (with ICP-MS as the ato mic detector) allows basal selenium speciation in urine, Three differe nt normally occurring selenium species in human urine, simply diluted (1 + 1), have been found, The relative sophistication of the vesicle m ediated-HPLC-MW-HG-ICP-MS interface, versus HPLC-ICP-MS via convention al nebulisation, can be justified because of its considerably higher s ensitivity for most of the selenocompounds assayed, lower matrix inter ferences and the possibility of simultaneous interference free Se-77 a nd Se-78 monitoring.