On-line concentration by head-column field amplified sample injection for the analysis of berberine, palmatine and jatrorrhizine in herbal medicine by flow injection-micellar electrokinetic chromatography

A simple, sensitive and continuous on-line stacking technique using head-column (HC)-field amplified sample injection (FASI) and sweeping was developed by combination of flow injection with micellar electrokinetic chromatography. Berberine, palmatine and jatrorrhizine were selected as model mixture to demonstrate this stacking method. Based on the characteristic of a 16-way injection valve (16-V), a sample was injected electrokinetically into a capillary after the introduction of a plug of water. Under optimum conditions, 64-86-fold improvement in the detection sensitivity was obtained for the analytes and the sample throughput can reach up to 24 h(-1) using the background electrolyte containing 240 mM ammonium acetate ( pH 4.7), 30% (v/v) ethanol, and 2% (v/v) polyoxyethylene sorbitan monolaurate ( Tween 20). The repeatabilities ( n = 4) reached relative standard deviation values of 1.2, 2.7 and 3.1% for the peak areas and 1.6, 3.3 and 3.8% for peak heights of berberine, palmatine and jatrorrhizine, respectively. The limit of detection for the berberine, palmatine and jatrorrhizine was found to be 27, 26, 22 ng mL(-1) (S/N=3).