Determination of volatile mercury species at the picogram level by low-temperature gas chromatography with cold-vapour atomic fluorescence detection

Alkylmercury compounds were preconcentrated from air on a Carbotrap (graphitized carbon black) column at room temperature. The species were then transferred by thermal desorption to a U-tube chromatographic column packed with 15% OV-3 on Chromosorb WAW-DMSC, held at ?196°C in liquid nitrogen. The compounds were clearly separated and eluted in order of increasing polarity using a simple, ramped heating step to 180°C over 20 min. After thermal decomposition of the eluant, the resultant mercury vapour was detected by cold-vapour atomic fluorescence spectrometry. The detection limits (as Hg) for the system were approximately 0.3 pg for mercury and dimethylmercury, 0.4 pg for diethylmercury, and 2.0 pg for methylmercury chloride. A study of the Long Island Sound atmosphere showed Hg⁰ to account for 95–100% of the total mercury present, with the remainder being monomethylmercury.