Salting-out solvent extraction for the off-line preconcentration of benzalkonium chloride in capillary electrophoresis

The use of salting-out effect for the off-line preconcentration of charged analytes in capillary electrophoresis is demonstrated for the first time. U sing benzalkonium chloride (BAK) as model compound, a mixture of cationic s urfactants consisting of even-numbered alkylbenzyl quaternary ammonium homo logues (C-8-C-18), the addition of appropriate amounts of sodium chloride a nd acetonitrile in the sample solution (2 mL sample volume) was found to be capable of providing ca. 40-fold enhancement in detection sensitivity. In addition to affording a preconcentrating effect due to the extraction of BA K in the smaller volume water-miscible organic solvent phase (acetonitrile) , the organic solvent also serves to improve the peak area and shape of the longer chain surfactants. Optimal experimental conditions, such as volume of acetonitrile and concentration of sodium chloride, for the preconcentrat ion of BAK with good preconcentration factors and reproducibility were inve stigated. The usefulness of the present method was demonstrated for the imp roved determination of BAK present in commercially available industrial and pharmaceutical products.