INDIVIDUAL AND SIMULTANEOUS CLASS SEPARATIONS OF CATIONIC AND ANIONICSURFACTANTS USING CAPILLARY ELECTROPHORESIS WITH INDIRECT PHOTOMETRICDETECTION

Various chromophoric cationic and anionic reagents and combinations th ereof are evaluated for individual and simultaneous class separations of nonchromophoric cationic and anionic surfactants using capillary el ectrophoresis (CE) with indirect photometric detection (IPD). Optimiza tion results indicated a pH of 6-7 with at least 50% methanol is neces sary for separations of long-chain cationic (tetrahexylammonium, didod ecyl dimethylammonium) or anionic (C-14-C18SO3- or C-14-C18SO4-) compo unds along with medium- to short-chain ionic surfactants of each class . For individual class separations, benzylamine (BA) or 1-ephedrine (E P) are recommended electrolytes for cationic surfactants, and naphthal enemonosulfonate (NMS) provided better detectability than p-toluenesul fonate (PTS) for anionic surfactants. Using an electroosmotic flow dri ven approach, a combined; separation of a five-component tetraalkylamm onium cationic and 10-component anionic (C-4-C18SO3-) surfactant mixtu re is possible in about 45 min using either BA-MMS or BA-PTS electroly tes. The BA-NMS mixture will provide better detectability of anionic s urfactants with some loss of sensitivity for cationic surfactants, whe reas the reverse is true with the BA-PTS combination. The commercially available pyridinium (PY)-PTS reagent in the absence of methanol coul d separate a three-component tetralkylammonium cationic and a 10-compo nent anionic (C-1-C-14-SO3-) surfactant mixture in less than 7 min.