On-column preconcentration and determination of inorganic anions in cigarette samples with capillary electrophoresis

An on-column dual-preconcentration method combining anion-selective exhaustive injection with base stacking and capillary electrophoresis was proposed for preconcentration and determination of inorganic anions in cigarette samples.' In the first place; the separation capillary was filled with tris ( hydroxymethyl) aminomethane ( Tris) buffer solution containing 0. 4 mmol/L trimethyl ( tetradecyl) ammonium bromide TTAB) to suppress. electroosmotic flow ( EOF). Water plug was introduced and TTAB on the capillary inner wall could be dissolved into the water plug, which enhanced negative zeta potential of the capillary section. Then sample solution was injected electrokinetically. The anions in sample cell migrated quickly into the capillary and were stacked at, the boundary between the buffer solution and water plug, meanwhile, the water plug moved back to the capillary inlet by EOF. Sequencially, the soluiton of NaOH zone was injected electrokinetically. The fast migrating hydroxide ions reacted with Tris(+) from buffer solution to form a low conductive sample zone, and made the zone be condensed further. The preconcentration method achieved an enhancement factor of (0. 8 similar to 1. 3) x 10(5) compared with the normally electrokinetic sample injection. The proposed method has been applied successfully to determine six anions ( Cl-, NO2- NO3- SO42- F- HPO42-) in cigarette samples with the detection limits lower than 6..2 ng/L.