COMPARISON OF ONLINE SPE-HPLC AND SPME-GC FOR THE ANALYSIS OF MICROCONTAMINANTS IN WATER

Solid-phase preconcentration coupled on-line with liquid chromatograph y, and solid-phase microextraction coupled with gas chromatography hav e been applied to the determination of trace-level concentrations of b enzene and sulfur compounds (tetrahydrothiophene (THT), t-butyl mercap tan (TBM), and n-butyl mercaptan (nBM)) in aqueous media. The first te chnique uses a microcolumn packed with a styrene-divinylbenzene copoly mer. Retention values for THT, TBM, and benzene on this sorbent, expre ssed as the capacity factors, are 1100, 1600, and 4000, respectively. It is, therefore, possible to preconcentrate them efficiently and this method enables minimum concentrations of 0.05, 0.7, and 0.8 mu g L(-1 ), respectively, to be reached. In microextraction, a fine silica fibe r coated with a thin layer of polydimethylsiloxane is used. The partit ion coefficients of the analytes between the polymeric coating and wat er have been determined to be 40, 115, and 110 for THT, TBM, and benze ne, respectively. When sampling is performed from the liquid phase, pa rtition equilibrium is reached within 5 to 20 minutes, or more quickly when the solution is agitated. Using a flame ionization detector, det ection limits for THT, TBM, and benzene were 3, 5, and 0.2 mu g L(-1), respectively. Extraction of volatile or semi-volatile analytes can al so be performed from the headspace with very similar detection limits. In addition, the extraction time is shorter since equilibrium is reac hed within 1 to 1.5 minute, which can again be reduced by agitation of the sample. The advantages and drawbacks of both techniques are gathe red and discussed in this paper, which also underlines their complemen tarity.