Effect of ionic liquids and deep eutectic solvents on the enantiomeric separation of clopidogrel by cyclodextrin-electrokinetic chromatography. Quantitative analysis in pharmaceutical formulations using tetrabutylammonium l-aspartic acid combined with carboxymethyl-γ-cyclodextrin

Abstract

The effect of ionic liquids (ILs) and deep eutectic solvents (DESs) on the chiral separation of clopidogrel by Cyclodextrin-Electrokinetic Chromatography (CD-EKC) was investigated in this work. Experiments were conducted at two pH values (100 mM formate buffer at pH 3.0 and 100 mM borate buffer at pH 9.0). Preliminary work was carried out to select the optimal CDs as chiral selectors. A screening with thirteen neutral CDs was achieved at pH 3.0 at which clopidogrel is positively charged and thirteen charged CDs were assayed at pH 9.0 at which the drug is neutral. Carboxymethyl-γ-CD (CM-γ-CD) (at pH 3.0) and sulfobutylated-β-CD (SB-β-CD) (at pH 9.0) were chosen as the most advantageous selectors. In both cases, the enantiomeric impurity (R)-clopidogrel was the first-migrating enantiomer, which is the most desirable situation. After the optimization of the CD concentration, the temperature and the separation voltage at each working pH (12.5 mM CM-γ-CD, 25 °C and 30 kV at pH 3.0 and 5 mM SB-β-CD, 20 °C and 20 kV at pH 9.0), an enantiomeric resolution of 2.1 was obtained in both cases. Under these optimized conditions, the effect of the addition of five DESs and sixteen ILs on the chiral separation of clopidogrel enantiomers was studied. The dual system formed by 12.5 mM CM-γ-CD + 10 mM [TBA][L-Asp] at pH 3.0 was selected as a compromise among resolution, analysis time and peak area. A resolution of 3.4 in 17.5 min was obtained showing the existence of a synergistic effect originating an increase in the chiral resolution with respect to the use of the single CD chiral system. The developed method was applied to the enantiomeric determination of clopidogrel in commercial pharmaceutical formulations marketed as enantiomerically pure in (S)-clopidogrel after evaluating its analytical characteristics. LODs of 0.47 mg L−1 were obtained for both enantiomers allowing the detection of up to a 0.1% of the enantiomeric impurity as established by the International Council on Harmonization.