The solid-phase microextraction (SPME) technique Involves exposing a fused silica fiber that has been coated with a stationary phase to an aqueous solution containing organic contaminants. The analytes partition Into the stationary phase until an equilibrium has been reached, after which the fiber Is removed from the solution and the analytes are thermally desorbed In the Injector of a gas chromatograph. The method has been automated by adapting a Varían Model 8100 autosampler. Factors affecting sample throughput, precision, and accuracy of the method have been Investigated and optimized. Precision was affected by the location of the fiber In the Injector and the oven cryofocus temperature. The relative standard deviation has Improved to an average of 4 %, allowing further studies on factors affecting the accuracy. Quantitative desorption occurred with an Injector temperature slightly above the maximum boiling point In the analyte mix. Accuracy was not affected by methanol or sodium chloride concentrations below 1% and pH In the range of 4-10 for benzene, toluene, ethylbenzene and the xylene Isomers (BTEX). If equilibrium has been reached, temperature has no significant effect on the accuracy between 0 and 40 °C. Small sample volumes can be significantly depleted after one Injection for analytes with high distribution constants.The limit of detection ranges from 0.3 to 3 µg/L for the BTEX compounds using a 56-µ poly(dlmethylsiloxane) coating and a flame Ionization detector. The linear dynamic range of the method was tested over 4 orders of magnitude.

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