Sweeping of neutral analytes in electrokinetic chromatography with high-salt-containing matrixes.

The concept of sweeping neutral analytes using a high-conductivity matrix or under a reduced electric field in micellar electrokinetic chromatography (MEKC) using anionic micelles and in the presence of electroosmotic flow is presented. Three important processes are identified. First, stacking of the micelles at the cathodic interface between the sample solution (S) and background solution (BGS) zones is identified. This is then followed by the sweeping of analyte molecules by the stacked micelles that enter the S zone. Finally, the destacking of the stacked micelles at the anodic interface between the S and BGS zones occurs. The stacking of the micelles improves the focusing effect of sweeping by a factor approximately equal to the ratio of conductivities between the S and BGS zones (ratio = enhancement factor = gamma'). However, the destacking of the stacked micelles broadens the swept zones by a factor approximately equal to 1/gamma'. In effect, the focusing effect of sweeping using a matrix with equal or higher conductivity compared to the BGS will be roughly the same. The micelle stacking and destacking mechanisms are verified experimentally. This paper also provides comments on the mechanism of neutral analyte focusing under similar conditions proposed by another group.