SWITCHING VALVE WITH INTERNAL MICRO PRECOLUMN FOR ONLINE SAMPLE ENRICHMENT IN CAPILLARY ZONE ELECTROPHORESIS

The design of a switching valve containing a micro precolumn for on-line sample enrichment in capillary electrophoresis is described. Samples are loaded on to the precolumn with a micro liquid chromatographic pump, while desorption is performed by means of the electroosmotic flow. The influence of the precolumn on the capillary zone electrophoretic separation process was investigated. A zone-cutting procedure was introduced, by means of valve switching, to prevent excessive band broadening and shifting of the migration times. Using papaverine as a model compound, it was shown that sample volumes of up to 100 mul can be enriched on the precolumn. Calibration plots are linear over a concentration range of two orders of magnitude. The detection limit of papaverine is 5 . 10(-8) M (5 pmol injected; UV detection at 254 nm). The potential of the sample-enrichment valve for on-line coupling to micro liquid chromatography is discussed.