Simultaneous determination of metal ions by capillary electrophoresis with contactless conductivity detection and insights into the effects of BGE component

Abstract

A capillary electrophoresis method integrated with capacitively coupled contactless conductivity detection (CE-C4D) using lactic acid (Lac) (providing background conductivity) and β-alanine (β-Ala) (maintaining stable ionic strength) as the components of background electrolyte (BGE) was developed for the simultaneous determination of eight metal ions (Mg2+, Mn2+, Cd2+, Co2+, Pb2+, Ni2+, Zn2+, Cu2+). The effects of the concentration and composition of BGE and other CE separation conditions in CE-C4D were comprehensively investigated and carefully optimized. It was observed that the optimal BGE consisted 25.0 mmol/L Lac and 25.0 mmol/L β-Ala (at pH 3.6). Under such conditions, all metal ions were successfully separated in less than 10 min. In comparison with two general used BGE systems (2-(N-morpholino) ethanesulfonic acid with histidine, Lac with histidine), the developed BGE has higher sensitivity and better resolution for the certain analytes of Co2+ and Zn2+. Here, the linear ranges of metal ions are within 1.5–3000 μmol/L with high correlation coefficients over 0.994 and the obtained limits of detection (S/N = 3) were in the range of 0.66–8.62 μmol/L. The repeatability with respect to migration times and peak areas, expressed as relative standard deviations, is better than 0.39% and 4.54% (n = 5), respectively. Subsequently, this method was utilized to analyze metal ions in Forsythiae Fructus (FF), a Chinese herbal medicine. The studied recoveries of all metal ions in FF ranged from 82.0% to 103.5%. It was observed that the content of Mg2+ and Mn2+ in FF detected by CE-C4D was similar with that of inductively coupled plasma atomic emission spectrometry (ICP-AES), which demonstrated that the developed CE-C4D had promising in the analysis of metal ions.