The effect of cyclodextrin modifiers on separation of aromatic hydrocarbons

Cyclodextrin-modified capillary electrophoresis has been developed for separation and analysis of benzene and its derivatives. The procedure used a mixture of negatively charged sulfobutyl ether-beta-cyclodextrin (SB beta CD) and neutral hydroxypropyl-beta-cyclodextrin (HP beta CD) to effect differential distribution (partitioning) of the aromatic hydrocarbons between the buffer and CD phases. In 80 mM phosphate buffer, containing 15 mM SB beta CD and 5 mM HP beta CD, benzene, toluene, ethyl benzene and three xylene isomers (BTEXs) were well resolved with a number of theoretical plates well above 100 000, for 50 cm of effective length. Some halogenated benzenes were also observed to separate well from the BTEX components to indicate their suitability as an internal standard for BTEX analyses. Equilibrium complexation models were used for investigating the effect of the cyclodextrin(s) at different concentrations and temperature on the electrophoretic mobility.