QUANTITATIVE EXTRACTION USING AN INTERNALLY COOLED SOLID-PHASE MICROEXTRACTION DEVICE

Solid phase microextraction (SPME) is a new extraction technique which uses a fused silica fiber coated with polymeric coating to extract organic compounds from their matrix and directly transfer analytes into a gas chromatograph (GC) by thermal desorption in a GC injector. SPME has been proven to be simple, time efficient, and sensitive. By sampling from the headspace above sample matrices, SPME can be used to extract target analytes from very complex matrices such as sludge, wastewater, and soil. In this paper, we develop a new approach for headspace SPME sampling. By heating the sample matrix while simultaneously cooling the fiber coating, we not only facilitate the mass transfer and the release of analytes into the headspace but also create a temperature gap between the cold fiber coating and the hot headspace which significantly increases the partition coefficients of analytes. With this method, quantitative extraction has been achieved for toluene, ethylbenzene, and xylene isomers from gas, water, or soil in less than 5 min. A thermodynamic theory has been developed to calculate coating/gas phase partition coefficients of analytes under these extraction conditions. The experimental data indicate that the predictions based on theoretically calculated partition coefficients are quite accurate when analyte molecules are released from their matrix during extraction. This internally cooled SPME device, in combination with simultaneous heating of samples, enables us to achieve sub-parts per trillion detection limit for analytes in difficult matrices such as clay.