ENHANCEMENT OF SELECTIVITY AND CONCENTRATION SENSITIVITY IN CAPILLARY ZONE ELECTROPHORESIS BY ONLINE COUPLING WITH COLUMN LIQUID-CHROMATOGRAPHY AND UTILIZING A DOUBLE STACKING PROCEDURE ALLOWING FOR MICROLITER INJECTIONS

A double stacking procedure based on field enhancement is described as a means to increase the concentration sensitivity in capillary electrophoresis. Microliter volumes of sample are concentrated directly in the electrophoresis capillary without significant loss of separation performance. The whole procedure can be performed with a high degree of precision. A sensitivity gain of ca. 400 can easily be obtained by concentration of a 3-mu l sample as compared with a 7-nl sample. The effect of experimental parameters on the final separation was studied for the enantiomers of rac-terbutaline, using alkyl substituted beta-cyclodextrins as chiral selectors. Other enantiomers of chiral drugs can also be separated using the same procedure. Column liquid chromatography was used on-line with capillary electrophoresis for sample pre-treatment and concentration of the sample which allowed for injection of microliter volumes into the electrophoresis capillary. The selectivity and sensitivity gain of combining column liquid chromatography with capillary electrophoresis for determination of low concentrations of drugs in biosamples is exemplified.