Field sampling and analysis of volatile reduced sulphur compounds in air, water and wet sediments by cryogenic trapping and gas chromatography

Abstract

A method for the simultaneous analysis of volatile reduced sulphur species such as hydrogen sulphide, carbonyl sulphide, methanethiol, dimethyl sulphide, carbon disulphide and dimethyl disulphide in air, water and wet sediments is described. In the atmosphere these compounds are preconcentrated by pumping air through a U-shaped cryogenic trap cooled with liquid argon. In waters and sediment pore waters they are concentrated by nitrogen purging and cryo-trap condensation. The trap is then connected on-line to a field-portable gas chromatograph provided with a secondary cryofocusing trap and a flame photometric detector. Detection limits less than or equal to 10 pg S/1 (air), 1 ng S/1 (water) and 10 pg S/g (wet sediment) are achieved for individual compounds. The variation in the quantitative results for water analyses is less than 7%, with the only exception being methanethiol (20%). Examples of application to air, water and wet sediment samples from a stratified karstic lake and a coastal saltern pond are shown.