FIELD DETERMINATION OF VOLATILE SELENIUM SPECIES AT ULTRA-TRACE LEVELS IN ENVIRONMENTAL WATERS BY ONLINE PURGING, CRYOFOCUSING AND DETECTION BY ATOMIC FLUORESCENCE SPECTROSCOPY

The field determination of selenium species was obtained after strippi ng 1 l of water, removal of the water vapour by a water trap, and cryo focusing in a small packed chromatographic column hyphenated to a non dispersive atomic fluorescence detector. Water trap and purging condit ions were carefully studied. Under routine operating conditions, absol ute detection limits of 4 and 4.5 pg of Se for Me2Se and Me2Se2 were o btained, respectively. Under routine conditions, linearity er;tended u p 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 spec ies 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 comme nted upon. Correlation with water temperature and salinity is also dis cussed.