Comparison of two derivatizing agents for the simultaneous determination of selenite and organoselenium species by gas chromatography and atomic emission detection after preconcentration using solid-phase microextraction

Two methods for the simultaneous determination of selenite and two organoselenium compounds, dimethylselenide (DMSe) and dimethyldiselenide (DMDSe), are proposed. Both methods involve sample preconcentration by solid-phase microextraction (SPME) and capillary gas chromatography coupled to atomic emission detection (GC-AED). The main difference between the methods is the derivatizing agent used to complex the inorganic species: sodium tetraethylborate and 4,5-dichloro-1,2-phenylenediamine. The parameters affecting the derivatization and preconcentration steps, chromatographic separation as well as detection of the compounds were optimized. Direct immersion (DI) mode and a relatively long extraction time were selected for the method involving the formation of the piazselenol complex, better sensitivity being achieved for the three analytes under study. In this case, detection limits ranged between 3 and 25 ng L(-1), depending on the compound. Headspace mode (HS) and extraction times of 20 min were selected for the method involving tetraalkylborate, and detection limits of between 7.3 and 55 ng L(-1) were obtained. DMSe and Se(IV) were found in several of the water samples analyzed at concentrations of 0.07-1.0 ng mL(-1).