Determination of Barbiturates by Solid-Phase Microextraction and Capillary Electrophoresis

The solid phase microextraction device is based on plasticized poly(vinyl chloride) (PVC) as an extraction solvent, which is coated on a primed steel rod. The plasticizer is a phosphate triester. A simple device for back-extraction of analytes into a few microliters of back-extraction solution is described. A Teflon tube, with an inside diameter just larger than the PVC-coated extraction rod, is terminated at one end by a syringe. A few microliters of back-extraction solution is placed into the open end of the tube. Because the Teflon does not wet, the drop remains together. After exposure to sample, the PVC-coated extraction rod containing the analytes is inserted into the back-extraction solution-containing tube. The aqueous back-extraction solvent spreads out in the narrow annular space thus formed. After a suitable period, the rod is removed, and the droplet re-forms. It can be ejected into a sample vial with the syringe. The device has been used in a CE-based determination of barbiturates. Extraction, back-extraction, and separation of 10 barbiturates takes less than 30 min. Extraction and preconcentration of benzoates is also briefly considered.