On-line enrichment of neutral analytes by the sweeping technique in micellar electrokinetic chromatography is presented. The equations for describing the effet of sample injection length and the difference between the nature of the sample zone and that of the buffer zone on enhancement factors were obtained on the basis of the relaxation theory. With the further study of sample injection length and the relationship between the capacity factors of solutes in two different zones and enhancement factors, it can be proved that the solubility of solutes in the micelle is the most important factor to affect the enhancement factors. The appropriate increase in the sample injection length could be favorable to the enrichment without loss in resolution.

Key words: RELAXATION, CHROMATOGRAPHIC COLUMN, CONCENTRATION, CAPILLARY ZONE ELECTROPHORESIS, HIGH SPEED LIQUID CHROMATOGRAPHY