UV-photochemical vapour generation with in situ trapping in a graphite tube atomizer for ultratrace determination of selenium

A very sensitive method has been developed for the determination of selenium (Se(IV)) utilizing continuous UV-photochemical vapour generation followed by in situ trapping and atomization of the generated volatile compounds in the graphite tube atomizer. Formic acid was chosen as a photochemical agent for the UV-assisted conversion of the analyte from the condensed to the gaseous phase. The only other chemical added to the liquid reaction mixture was nitric acid, which significantly increased the analytical signal. Introduction of selenium volatile products into the graphite tube covered with an iridium permanent modifier was done automatically. Optimum experimental conditions for generation, collection and atomization of volatile compounds were found and the analytical characteristics of the method were subsequently determined. A very low concentration limit of detection 4.1 ng L-1 of Se(IV) (corresponding to an absolute LOD 18 pg) was achieved. The repeatability expressed as % RSD was 3.0% at 0.5 mu g L-1 Se(IV). The figures of merit were compared with those obtained by chemical vapour generation using a borohydride/acid system; lower LODs were attained for UV-photochemical vapour generation. An overall efficiency of all the processes from generation to collection of volatile compounds of more than 80% was estimated. The effect of various concomitants on the selenium signal was also investigated. Finally, the accuracy of the studied method was successfully verified by the analysis of the certified reference material NIST SRM 1643e and two spiked river water samples.