Investigation of the effects of cyclodextrins and organic solvents on the separation of cationic surfactants in capillary electrophoresis

The use of alpha- and beta-cyclodextrin (CD) to understand and to improve the separation of a series of cationic surfactants, homologues of alkylbenzyldimethyl ammonium compounds (ABDACs) with an alkyl chain of varying length (C-10-C-18), in capillary electrophoresis (CE) is reported for the first time. Similar to the effects of organic solvents, the presence of alpha- or beta-CD in the running buffer was found to reduce peak tailing/loss for the longer-chain ABDACs. Based on fluorescence measurements, it was found that formation of host-guest complexes occurred between alpha- or beta-CD and various ABDACs, with the likelihood that the hydrophobic alkyl chain including into the CD cavity and the positively charged ammonium group remaining outside the cavity. The effects of alpha- or beta-CD can be interpreted in terms of a shift away from the formation of (1) micelles in the buffer system and (2) surfactant aggregates at the fused-silica capillary walls, as a result of the formation of inclusion complexes between alpha- or beta-CD and ABDACs. (C) 2000 Elsevier Science BN. All rights reserved.