SOLUTE TRAPPING IN OFF-LINE SUPERCRITICAL-FLUID EXTRACTION USING CONTROLLED MODIFIER CONDENSATION

A new approach to solvent trapping, based on controlled modifier conde nsation, is presented. The trapping system consists of a fused-silica capillary (30 cm x 500 mu m I D.) equipped with a cryofocusing device. As a trapping mechanism, nebulization of expanding supercritical mixt ure with condensing modifier, followed by analyte trapping into moving liquid layer is assumed. In spiking experiments a urea-based herbicid e, flufenoxuron, was extracted with 10% methanol-modified CO2 and reco veries of over 90% were found. The resulting solvent volumes needed fo r quantitive trapping are much lower (ca. 0.3 ml) than in the case of direct bubbling through bulk liquid.