Simultaneous stereoisomeric preconcentration and determination of alkaloids and stereoisomers in Uncariae ramulus cum uncis using field enhanced sample injection and dynamic pH junction sweeping method by cyclodextrin electrokinetic chromatography

Abstract

A rapid and sensitive enrichment technique, field enhanced sample injection-dynamic pH junction-sweeping (FESI-DypH-sweeping) was successfully developed for the simultaneous separation and concentration of alkaloids and stereoisomers of Uncariae ramulus cum uncis (UR) by cyclodextrin electrokinetic chromatography (CDEKC) with diode array detection system. The sample was prepared in a low-conductivity (FESI), low-pH (DypH) sample matrix (4 mM phosphate buffer, 3% methanol, pH=3), and the background electrolyte (BGE) consisted of a high-conductivity, high-pH buffer (40 mM phosphate buffer, pH 7.0, 8 mg/mL carboxymethyl-β-cyclodextrin, and 30% methanol). The crucial parameters influencing separation and enrichment efficiency were systematically optimized using single variable method. Under the optimum conditions, the method provided satisfactory resolution for seven alkaloids within 18 minutes, achieving enrichment factors ranging from 25 to 78 folds. The limits of detections (LODs) ranged from 0.04 to 0.12 μg/mL and limits of quantifications (LOQs) ranged from 0.10 and 0.40 μg/mL respectively. Intra-day and inter-day precision, expressed as relative standard deviations, were all below 3.5%.