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 alpha 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.