ENHANCEMENT OF SELECTIVITY AND CONCENTRATION SENSITIVITY IN CAPILLARYZONE ELECTROPHORESIS BY ONLINE COUPLING WITH COLUMN LIQUID-CHROMATOGRAPHY AND UTILIZING A DOUBLE STACKING PROCEDURE ALLOWING FOR MICROLITERINJECTIONS

A double stacking procedure based on field enhancement is described as a means to increase the concentration sensitivity in capillary electr ophoresis. Microliter volumes of sample are concentrated directly in t he electrophoresis capillary without significant loss of separation pe rformance. The whole procedure can be performed with a high degree of precision. A sensitivity gain of ca. 400 can easily be obtained by con centration of a 3-mu l sample as compared with a 7-nl sample. The effe ct of experimental parameters on the final separation was studied for the enantiomers of rac-terbutaline, using alkyl substituted beta-cyclo dextrins as chiral selectors. Other enantiomers of chiral drugs can al so be separated using the same procedure. Column liquid chromatography was used on-line with capillary electrophoresis for sample pre-treatm ent and concentration of the sample which allowed for injection of mic roliter volumes into the electrophoresis capillary. The selectivity an d sensitivity gain of combining column liquid chromatography with capi llary electrophoresis for determination of low concentrations of drugs in biosamples is exemplified.