OPTIMIZATION OF THE GAS STRIPPING AND CRYOGENIC TRAPPING METHOD FOR CAPILLARY GAS CHROMATOGRAPHIC ANALYSIS OF TRACES OF VOLATILE HALOGENATED COMPOUNDS IN DRINKING WATER

摘要

A simple laboratory-made gas stripping and cryogenic trapping system coupled to a gas chromatograph with flame ionization detector as a universal detector has been developed for the determination of traces of volatile halogenated compounds (VHCs) in drinking water. The effects of inert gas velocity, stripping time, temperature and salting out on the extraction efficiency and the efficacy of different adsorbents for water vapour elimination were studied. The VHCs were trapped in a stainless-steel coil (50 cm x 1.5 mm I.D.) placed in liquid nitrogen. The trapped compounds were released by thermal desorption and injected in the capillary column. To prevent peak tailing arising from the injection of the sample spread in a large volume of the carrier gas,VHCs were retrapped in the beginning of the capillary column with a cryofocusing system. The chromatographic analyses were run with a suitable temperature program. The present method allows the determination of 0.1-10 ppb of each VHC. The relative standard deviation of 5-10% (n = 5) was obtained at 2 ppb for different VHCs. The detection limits (signal-to-noise ratio 3) were 0.01-0.05 ppb for the studied compounds which are comparable with US Environmental Protection Agency method 502.2. [References: 32]