AUTOMATED-SYSTEM FOR THE TRACE ANALYSIS OF ORGANIC-COMPOUNDS WITH SUPPORTED LIQUID MEMBRANES FOR SAMPLE ENRICHMENT

Supported liquid membranes, mounted in flow systems, can be used for selective and efficient extraction and enrichment of various types of analytes. The basic principle is a continuous extraction from an aqueous phase into an organic solvent, immobilized in a porous hydrophobic membrane, followed by a continuous back-extraction to a stagnant aqueous acceptor phase on the other side of the membrane. The entire acceptor phase is then used for further analysis. The ASTED (Gilson) automated sample preparation system was modified by exchanging the dialysis unit for a supported liquid membrane unit. This permits a direct connection to a liquid chromatographic column with minimal sample losses. The instrument can be loaded with up to 60 samples, which are automatically processed before the final chromatographic analysis. With this equipment, the same sample can pass the membrane extractor several times (while the acceptor phase remains stagnant) to give a higher recovery. When one sample is chromatographed the next one is enriched simultaneously. The technique was evaluated for the extraction of a basic drug and its metabolite from water solutions with the purpose to be applied to brood plasma samples. The recovery depends on the time used for the enrichment. With enrichment times similar to the chromatographic run, or ca. 15 min, the recovery was ca. 35%.