Stacking Neutral Analytes in Capillary Electrokinetic Chromatography with High-Salt Sample Matrixes

Abstract

We recently described a method to stack neutral analytes in electrokinetic chromatography dependent upon using high-salt sample matrixes (Palmer et al. Anal. Chem. 1999, 71, 1679−1687) The use of a high-mobility co-ion in the sample matrix at a higher concentration than the like-charged electrokinetic vector (e.g., charged micelle) in the separation buffer as we previously suggested induces a single-boundary, discontinuous buffer system which subsequently stacks neutral analytes. Under these conditions, it is possible to electrokinetically inject neutral analytes directly from a high-salt sample matrix via electroosmotic flow, with stacking initiated simultaneously with injection. The correspondence by Quirino et al. (Anal. Chem., previous paper in this issue) suggests the effects of the high-salt sample matrix on stacking of micelles is obviated by a destacking of the micelle zone as it exits the sample zone. They reevaluate the high-salt stacking mode in terms of the γ function. Based on the present data, it is our interpretation that the stacking efficiency is not accurately represented by the γ function and that neither micelle zone nor neutral analyte destacking occurs under conditions we previously described. Low stacking efficiency when low-conductivity sample matrixes are used indicates that the high-salt stacking effect cannot be explained simply as a function of the k value of an analyte/micelle system.