Temperature and nano-TiO2 controlled photochemical vapor generation for inorganic selenium speciation analysis by AFS or ICP-MS without chromatographic separation

Abstract

A simple yet ultrasensitive UV photochemical vapor generation (photo-CVG) is proposed for the speciation analysis of Se(IV) and Se(VI). The new photo-CVG, which is based on Se(IV) or Se(VI) reacting with an organic acid under different reaction conditions, can be coupled to AFS or ICP-MS for the speciation analysis of Se(IV) and Se(VI) in real samples such as table salt and water samples without chromatographic separation. At low temperature, only Se(IV) can be photochemically converted to selenium volatile species, and this is used for its selective determination; however, by using boiling water bath together with nano-TiO₂ as a catalyst, both Se(IV) and Se(VI) can be photochemically converted to selenium volatile species, thus determining the total of Se(IV) and Se(VI). Therefore, Se(VI) concentration can be calculated from the difference between the total and Se(IV) concentration. Optimal reaction conditions and instrumental parameters are investigated; and the interferences from transition metals and other ions, as well as the photo-CVG mechanism, are discussed. The limits of detection range from 0.02 to 0.1 ng mL⁻¹, depending on the kind of organic acid and the detector. The accuracy of the method is validated by determining Se(IV) in certified reference water sample. Real samples including commercial table salt, waste water and mineral water were successfully analyzed. This is a simple, relatively green, highly selective and sensitive, yet inexpensive method for the speciation analysis of Se(IV) and Se(VI).