Online concentration by head-column field-amplified with large-volume sample stacking using flow injection-capillary...

A simple, effective, and sensitive online concentration method for the detection of dextromethorphan hydrobromide (Dex), chlorphenamine hydrogen maleate (Chl), pseudoephedrine hydrochloride (Pse) and paracetamol (Par) based on flow injection-capillary electrophoresis (FI-CE) analysis with head-column field-amplified sample stacking and large-volume sample stacking was developed. The background electrolyte (BGE) was a solution composed of 55 mM borate-15% (v/v) acetonitrile (ACN) (pH 9.3). The sample was injected electrokinetically between plugs of water. Under the optimum conditions, about a 30-fold improvement in the concentration sensitivity relative to normal CE methods was achieved, giving low limits of detection (LOD) of 1.94 x 10(-5), 0.64 x 10(-5), 1.16 x 10(-5) and 2.84 x 10(-5) mg/mL for Dex, Chl, Pse and Par, respectively. The repeatability (defined as RSD) was 1.01, 1.91, 0.89 and 0.92% with the peak-area evaluation and 1.94, 3.98, 2.66 and 3.27% with the peak-height evaluation for Dex, Chl, Pse and Par, respectively. This method has been successfully applied to the analysis of commercial pharmaceutical preparations containing Dex, Chl, Pse and Par.