Enantioselective discrimination of menthone enantiomers by using achiral liquid chromatography with circular dichroism detection and penicillamine-coated gold nanoparticles

A simple and rapid method is described for enantioselective discrimination of menthone enantiomers in peppermint oil samples. The method includes a quick and simple preparation procedure, followed by achiral liquid chromatography with circular dichroism detection (ALC-CD) with an on-line penicillamine-coated gold nanoparticles (Pen-AuNPs) derivatization. The method involves the enantioselective discrimination of menthone enantiomers by ALC-CD, as well as an enhancement of their optical rotation signal was achieved in the presence Pen-AuNPs. Under the optimal experimental conditions menthone enantiomers present a maximum ellipticity between the two optically active forms at a wavelength of 305 nm. The calibration curve of anisotropy factor (g) versus the enantiomeric excess was linear with a correlation coefficient (R2) of 0.9984. The precision evaluated by UV and circular dichroism (CD) signals was suitable in all cases (RSD < 5%). The developed method was validated, showing interesting advantages in terms of simplicity, rapidity and precision in the enantiomeric resolution. Additionally, the method avoids the use of expensive chiral columns and more sophisticated instrumentation, as it is the case of discrimination using liquid chromatography alternatives. It is suitable for both, the simultaneous determination of menthone enantiomers and for the analytical control of the chemical purity of menthone.