Mobile phase effects on enantiomer resolution using molecularly imprinted polymers

Abstract

The aim of this study was to rationalise retention behaviour of a chiral solute on molecularly imprinted polymer (MIP) HPLC stationary phases in terms of variation of the mobile phase. It is generally held that the most important interaction governing the separation of enantiomers on such materials is H-bonding, and that retention times increase with decreasing H-bonding potential of the mobile phase. Previous studies have largely concerned mobile phases containing chloroform with acetic acid as a polar modifier. Boc-L-Phenylalanine (Boc-L-Phe-OH) MIPs were prepared, processed, and packed into HPLC columns, which were then used to investigate the retention characteristics of Boc-L-Phe-OH and Boc-D-Phe-OH with a range of mobile phases. The main observations were as follows: (1) in chloroform-based mobile phases there was generally a linear relationship between the H-bond donator factor of the polar modifier and capacity (K′). Results also indicated a hydrogen bond donor parameter value for a polar modifier at which retention became concentration independent; (2) For given values of K′L, K′D varied depending on the polar modifier, indicating that enantiomer resolution was solvent dependent; (3) Using mobile phases based on solvents of lower polarity/H-bonding potential than chloroform, substantial increases in K′ were observed, although enantioselectivity was greatly reduced. Chirality 9:238–242, 1997. © 1997 Wiley-Liss, Inc.