Field determination of volatile selenium species at ultra trace levels in environmental waters by on-line purging, cryofocusing and detection by atomic fluorescence spectroscopy
Résumé
The field determination of selenium species was obtained after stripping 1 l of water, removal of the water vapour by a water trap, and cryofocusing in a small packed chromatographic column hyphenated to a non dispersive atomic fluorescence detector. Water trap and purging conditions were carefully studied. Under routine operating conditions, absolute detection limits of 4 and 4.5 pg of Se for Me2Se and Me2Se2 were obtained, respectively. Under routine conditions, linearity extended up to 1 ng as Se for the different species studied. The selectivity of the system is discussed in the presence of carbon-containing species. This system was applied to the determination of volatile selenium species in the Gironde estuarine environment (France). Me2Se was found to be the main volatile selenium species in concentrations ranging from 0.8 to 6.3 pmol l-1. Seasonal variations have been observed and commented upon. Correlation with water temperature and salinity is also discussed.