Coelectroosmotic separations of anions in non-aqueous capillary electrophoresis

Abstract The suitability of hexadimethrine bromide (HDB) as electroosmotic flow (EOF) modifier in non-aqueous capillary electrophoresis was investigated. Using HDB as EOF modifier a reversed EOF resulted, which allows very fast separations of anionic compounds in the coelectroosmotic mode. This is demonstrated for the separation of hydroxy- and dihydroxybenzoic acids in various acetonitrile–methanol mixtures. According to the decreasing ratio of dielectric constant and viscosity the EOF mobility showed a linear decrease with increasing methanol concentration in the electrophoresis medium, whereas the analytes showed non-uniform behaviour on addition of methanol. The EOF reproducibility of EOF migration time was excellent, if the concentration of HDB in the running electrolyte was 0.001% (w/v). With this concentration a reproducibility of