Capillary zone electrophoretic separation of alkylbenzyl quaternary ammonium compounds: Effect of organic modifier

Capillary zone electrophoretic separations of alkylphenyl- and alkylbenzyl ammonium compounds with the polar organic solvents acetonitrile, tetrahydrofuran, acetone, and methanol as micelle disrupters were investigated. The results indicate that addition of acetonitrile (30%, v/v), tetrahydrofuran (40%, v/v), or acetone (50%, v/v) to a phosphate buffer is necessary for effective separation of alkylbenzyldimethyl ammonium compounds in a sample (0.01 mM) dissolved in a methanolic solution (60%, v/v). The effectiveness of the organic modifier to disrupt micelles decreases in the order acetonitrile > tetrahydrofuran > acetone > methanol. With a smaller concentration of sample and a sufficient concentration of buffer, less organic modifier is required. The most effective separation was achieved within three minutes with the addition of acetonitrile (30%, v/v) in a phosphate buffer (20 mM, pH 5.0) using a fused-silica capillary at 15 kV for a sample of concentration 0.01 mM. The selectivity and resolution of quaternary ammonium compounds were slightly affected on variation of the concentration and pH of the buffer when electrophoretic conditions with concentrations of the phosphate buffer greater than 20 mM and of the sample less than 0.01 mM were employed.