Enantiomeric separation of seven β-agonists by NACE—Study of chiral selectivity with diacetone-d-mannitol–boric acid complex
A rapid and effective nonaqueous capillary electrophoresis (NACE)–ultraviolet (UV) method was developed for the enantiomeric separation of seven β-agonists. Diacetone-d-mannitol–boric acid complex was used as a new chiral selector. It was in situ synthesized by the reaction of diacetone-d-mannitol and boric acid in methanol medium containing triethylamine. The effects of diacetone-d-mannitol, boric acid, and triethylamine concentrations on the enantioseparation were carefully investigated. Under the optimized conditions, baseline enantioseparation could be obtained for six of the tested β-agonists within 12 min. These results were better than that obtained with d-mannitol–boric acid complex in previous work. 11B nuclear magnetic resonance (11B NMR) was applied to determine the fraction of boron species and confirm the formation of diacetone-d-mannitol–boric acid complex. Validation of the established NACE method was also carried out according to ICH guidelines. Calibration curves showed good linearity with correlation coefficients (r) ≥ 0.9992 over a certain concentration range for each enantiomer of the tested five β-agonists. The relative standard deviations (RSDs) of intra-day precisions and inter-day precisions of migration times were ≤1.4% (n = 6), and ≤6.3% (n = 10), respectively. That of peak areas were ≤3.7% (n = 6), and ≤5.6% (n = 10), respectively. The limits of detection (LODs) and the limits of quantitation (LOQs) based on the signal-to-noise ratios of 3 and 10 were found below 1.25 μg mL−1 and 5.00 μg mL−1, respectively. The proposed method was successfully applied to the determination of clenbuterol enantiomers in a multi-component pharmaceutical dosage form called “Ambroxol Hydrochloride and Clenbuterol Hydrochloride Oral Solution”.