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

The concept of sweeping neutral analytes using a high-conductivity matrix o r 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 th e micelles at the cathodic interface between the sample solution (S) and ba ckground solution (BGS) zones is identified. This is then followed by the s weeping of analyte molecules by the stacked micelles that enter the S zone. Finally, the destacking of the stacked micelles at the anodic interface be tween 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 o f 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 compar ed 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 propo sed by another group (Palmer, J.; Munro, N. J.; Landers, J. P. Anal. Chem. 1999, 71, 1679-87).