STACKING OF WEAKLY CATIONIC COMPOUNDS BY ACETONITRILE FOR CAPILLARY-ELECTROPHORESIS

The inclusion of acetonitrile in the sample causes stacking especially in presence of sodium chloride. It is shown here that the type of the separation buffer and the conditions for the stacking of cationic ver sus anionic compounds are quite different. Anionic compounds stacked b etter in high ionic strength inorganic buffers such as berate and phos phate, while the cationic drugs and endogenous substances stacked bett er in amine and zwitterionic buffers. About 10-20% of the capillary vo lume can be loaded with sample. Shielding against the negative charges of the silica is a critical factor in stacking of the cationic compou nds by the acetonitrile in the sample. The ionic strength of the separ ation buffer and the addition of organic modifiers affected the stacki ng to a limited extent. (C) 1998 Elsevier Science B.V. All rights rese rved.