ONLINE SOLID-PHASE EXTRACTION THERMAL-DESORPTION FOR INTRODUCTION OF LARGE VOLUMES OF AQUEOUS SAMPLES INTO A CAPILLARY GAS-CHROMATOGRAPH .2.

A module for combined solid-phase extraction and thermal desorption (S PETD) was incorporated into a system for automated GC analysis. Solid- phase extraction of analytes from water could be carried out after inj ection of an aqueous sample of 100 muL either by a loop using the carr ier gas for sample introduction or manually with a syringe. After dryi ng of the stationary phase by the carrier gas at a high flow rate, the rmal desorption could be carried out at temperatures up to 300-350-deg rees-C. Suitable packing materials for the liner in the SPETD module, i.e., materials which efficiently trap the organic compounds from an a queous Solution and are sufficiently thermostable, include Tenax and c arbon-based phases. as well as a silylated alkyl-modified silica. With the latter, however, the problem of efficient drying after sorption s till must be solved. Each phase has its own application range which, f rom among the analytes which are trapped during sorption, is determine d at the volatile end by losses occurring during drying by helium purg ing, and at the nonvolatile end by losses due to incomplete release du ring thermal desorption. From this study (using n-alkanes, chlorobenze nes, and chlorophenols as test solutes), it appears that the Tenax pha ses, Tenax-TA and Tenax-GR, have the widest application range; essenti ally quantitative recoveries were obtained for C-10 through C26 n-alka nes. The carbon-based phases appear to be useful for relatively volati le compounds, i. e., up to C19 n-alkanes. Each phase gave good recover ies for two test mixtures containing chlorobenzenes and chlorophenols dissolved in 100 muL of water at the 10 ppb level.