On-line solid-phase extraction/thermal desorption for introduction of large volumes of aqueous samples into a capillary gas chromatograph: Part 2

A module for combined solid‐phase extraction and thermal desorption (SPETD) was incorporated into a system for automated GC analysis. Solid‐phase extraction of analytes from water could be carried out after injection of an aqueous sample of 100 μL either by a loop using the carrier gas for sample introduction or manually with a syringe. After drying of the stationary phase by the carrier gas at a high flow rate, thermal desorption could be carried out at temperatures up to 300–350°C. Suitable packing materials for the liner in the SPETD module, i.e., materials which efficiently trap the organic compounds from an aqueous solution and are sufficiently thermostable, include Tenax and carbon‐based phases, as well as a silylated alkylmodified silica. With the latter, however, the problem of efficient drying after sorption still must be solved. Each phase has its own application range which, from among the analytes which are trapped during sorption, is determined at the volatile end by losses occurring during drying by helium purging, and at the nonvolatile end by losses due to incomplete release during thermal desorption. From this study (using n‐alkanes, chlorobenzenes, and chlorophenols as test solutes), it appears that the Tenax phases, Tenax‐TA and Tenax‐GR, have the widest application range; essentially quantitative recoveries were obtained for C10 through C26 n‐alkanes. The carbon‐based phases appear to be useful for relatively volatile compounds, i.e., up to C19 n‐alkanes. Each phase gave good recoveries for two test mixtures containing chlorobenzenes and chlorophenols dissolved in 100 μL of water at the 10 ppb level.