効率的なSe測定のためのTiO₂触媒光化学気相生成法

TiO₂-assisted photochemical vapor generation (PVG) elegantly solves the inertness of selenate to PVG allowing on-line prereduction of this species and sensitive determination of the element. Overall efficiency of TiO₂-assisted photochemical generation depends on the efficiency of electron transfer from the photocatalyst to the dissolved analyte, which is affected by the characteristics of the photocatalyst as well as by the chemical conditions. Up to date, the overall PVG efficiency of the Se TiO₂ assisted-PVG system has not been known and the effect of particle size and crystal phase on the efficiency has not been studied.

Two types of TiO₂ photocatalyst were characterized and tested showing that smaller particle plays more important role than crystal phase. Optimization of the chemical conditions including addition of transition metal mediators led to the development of photochemical vapor generation method having overall vapor generation efficiency of 63 % (selenite) or 67 % (selenate). The limits of detection were 1.2 μg dm^-3 (selenite) and 1.1 μg dm^-3 (selenate) with quartz furnace atomic absorption spectrometry detection or 0.15 μg dm^-3 (selenite) and 0.14 μg dm^-3 (selenate) with inductively coupled plasma mass spectrometry detection on mass 78 Da (not using polyatomic interference suppression). The method shows unusually good tolerance toward dissolved salts and inorganic acids including HNO₃. The method's accuracy was successfully verified on spiked freshwater and seawater samples and water reference materials.

The overall PVG efficiency of a benchmark photocatalysis approach to the on-line prereduction of selenate has been determined. The importance of particle size and corresponding larger surface area over crystal phase was demonstrated. The developed method for determination of Se is suitable for seawater matrix and can be used without modification with various detection techniques.