Chiral separation of mandelic acid and its derivatives by thin-layer chromatography using molecularly imprinted stationary phases

Molecularly imprinted polymers (MIPs) of L-mandelic acid (L-MDA) and its derivatives L-2-chloromandelic acid (L-2-MDA), L-4-chloromandelic acid (L-4-MDA) were prepared. The thin-layer chromatograms were constructed with these MIPs as chiral stationary phases (CSPs) and the mixture of acetonitrile and acetic acid as mobile phase. The effects of acetic acid content on separation were investigated. With the development system of 5% acetic acid in acetonitrile, the MIPs made CSPs separate the template molecules from their racemates with the chiral separation factor α of 1.45, 1.62, and 1.56 for MDA, 2-MDA, and 4-MDA, respectively. In relation to the template, its structural analogues have a lower separation factors on corresponding CSPs. This was attributed to the best compatibility of template molecules with the cavities of MIPs.