Application of 1-Alkyl-3-methylimidazolium-Based Ionic Liquids as Background Electrolytes in Nonaqueous Capillary Electrophoresis for the Analysis of Coptidis Alkaloids

Abstract

Interest in ionic liquids (ILs) for their potential in analytical chemistry is increasing because they are environmentally benign and are good separation solvents. The aim of the presented investigation was to verify whether ILs would be a suitable background electrolyte (BGE) in nonaqueous capillary electrophoresis (NACE) for organic cations analysis of the closely related analogues. In this study, a novel and very simple NACE method has been established for analyzing seven quaternary alkaloids in Coptis rhizome using 1-alkyl-3-methylimidazolium tetrafluoroborate-based ionic liquid as BGE. The effects of the alkyl group, imidazolium counterion (anionic part), along with the concentration of IL, are investigated and discussed. Baseline separation, high efficiencies, and symmetrical peaks of the seven alkaloids were obtained. The separation mechanism could be hydrophobic and hydrogen-bonding interactions between the alkaloids and the imidazolium cations. The optimum conditions were 70 mM 1-decyl-3-methylimidazolium tetrafluoroborate (1D-3MI-TFB) methanol solution (apparent pH 2.66) and 30 kV applied voltage. The detection was performed at 254 nm. Seven quaternary alkaloids in Coptis rhizome were separated within 14 min. The proposed NACE separation procedure is highly reproducible and can be applied in the qualitative and quantitative analysis of Coptidis alkaloids.

Keywords:

• Alkaloid
• Coptidis
• Ionic liquid
• Nonaqueous capillary electrophoresis

Acknowledgments

This paper is part of a special issue organized by Dr. Nikolaos Thomaidis and Dr. Antony C. Calokerinos from research presented at the Aegean Analytical Chemistry Days Conference in Lesvos, Greece on 29 September–3 October 2010.

This work was financially supported by a grant from the National Science Fund for Distinguished Young Scholars (50725825), the National Natural Science Foundation of China (50978132), the Scientific Research Fund of Jiangxi Provincial Education Department (GJJ08200), and the Opening Fund of Key Laboratory of Chemical Biology and Traditional Chinese Medicine Research (Ministry of Education of China), Hunan Normal University (KLCBTCMR2008-6).

Notes

^a Y and X are the peak areas and the concentration of the analytes, respectively.

^b The limit of detection was defined as the concentration where the signal-to-noise ratio is 3.

^c The limit of quantification was defined as the concentration where the signal-to-noise ratio is 10.