Multivariate approach for the enantioselective analysis in MEKC-MS: II. Optimization of 11′-binaphthyl-22′-diamine in positive ion mode

摘要

Enantiomeric separation and detection of 1,1′-binaphthyl-2,2′-diamine (BNA) has been successfully optimized by micellar electrokinetic chromatography coupled to electrospray ionization mass spectrometry (MEKC-ESI-MS) using a polymeric surfactant polysodium N-undecenoxycarbonyl-L-leucinate (poly-L-SUCL) as a pseudostationary phase. In the first step, MEKC conditions were optimized by a five-factor three-level central composite design (CCD) of experiment. All five MEKC factors (buffer pH, percentage of acetonitrile in the running buffer, concentration of surfactant, concentration of NH4OAc, and voltage) were found significant to the responses (measured as the chiral resolution and analysis time). The interactions between MEKC factors were further evaluated using a quadratic model equation which allowed the generation of 3-D response surface image to reach the optimum conditions. To obtain the best signal to noise (S/N) ratio, sheath liquid composition and spray chamber parameters were successfully optimized using the same strategy. Baseline enantiomeric resolution in less than 20 min and optimum mass spectrometry signal of BNA enantiomers (S/N = 45 at 0.4 mg/mL) were ultimately achieved at the optimized conditions. The adequacy of the model was validated by experimental runs at the optimal predicted conditions. The predicted results were found to be in good agreement with the experimental data.