SPECIATION OF SELENOMETHIONINE AND SELENOUREA USING LIVING BACTERIAL-CELLS

A novel and reliable method is proposed for speciation of selenomethio nine (Se-Met) and selenourea (Se-U) combining a time-controlled solid phase extraction by using living bacterial cells and electrothermal at omic absorption spectrometry (ETAAS) for the determination of selenium , The extraction medium consists of a Pseudomonas putida strain cultiv ated in a culture medium based on glucose contaminated with an organos eleno compound. Firstly, equilibrium between the analyte in the soluti on and the retention medium is allowed to be established, and then the concentration of the organoseleno compound is determined directly in the biomass by slurry ETAAS, It is possible to discriminate between di fferent chemical species of selenium by combining the optimization of both the growth conditions and the relative rates of their retention f rom the sample solution. A theoretical model of the retention process, based on a rate-determining step in reaching the adsorption equilibri um, is proposed to describe the experimental adsorption time profiles of the uptake process by the living bacterial cells. This relationship can also provide a feasible quantification of the extraction process before the adsorption equilibrium is reached, whenever the agitation c onditions and the sampling time are under control. The experimental da ta agreed closely with the theoretical model. The study of the adsorpt ion process was derived to develop an analytical procedure to determin e Se-Met and Se-U in matrices containing other selenium species (Se-et hionine, Se-cystamine, Se-cystine and Se-VI). The best detection limit s for the organoseleno compounds at their optimum extraction times are 1.5 ng ml(-1) for Se-Met and 1.2 ng ml(-1) for Se-U. The relative sta ndard deviations of the retention/determination process are 2.2-5.6%.