Analysis of some β-Lactam antibiotics using ionic liquids as mobile phase additives by RP-HPLC

Abstract

The retentions of five β-Lactam antibiotics were analyzed by reversed-phased high-performance liquid chromatography. The mobile phase was acetonitrile/water (15/85, v/v) and the absorption wavelength was determined at 254 nm. When 1-butyl-3-methylimidazolium tetrafluoroborate was added into the mobile phase as additive, the samples were well separated with sharper peaks. The optimal concentration of 1-butyl-3-methylimidazolium tetrafluoroborate at pH 3 was 1.0 mM. The pH has large effect on the retention that the retention factor increasing with the pH of the mobile phase increasing. Three types of 1-alkyl-3-methylimidazolium-based ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate, and 1-octyl-3-methylimidazolium tetrafluoroborate) were used and compared as additives in the mobile phase. The results showed that the retention time increased with increasing alkyl chain length. Among the three ionic liquids, the optimal effective additive was 1-butyl-3-methylimidazolium tetrafluoroborate.