Influence of Mobile Phase Composition on the Apparent Thermodynamic Characteristics in Liquid Chromatographic Enantioseparation on a Tartardiamide-Based Stationary Phase

Four amino acid derivatives and two binaphthyl compounds were enantioseparated successfully by HPLC with a chiral stationary phase commercially named Kromasil CHI-DMB, which contains an immobilized network polymer derived from L-tartaric acid. Chromatographic experiments were performed under normal phase conditions. n-Hexane/2-propanol was used as mobile phase. The effects of the content of 2-propanol and the column temperature on the retention and enantioseparation were studied systematically. Associated apparent thermodynamic parameters were calculated from the van’t Hoff plots. It was found that the enantioseparations of these amino acid derivatives were typical enthalpy driven, but for binaphthyl compounds the entropy term was also favorable to enantioselectivity in most cases. From the changes of the thermodynamic parameters and the isoenantioselective temperatures with the variety of mobile phase polarity, it was deduced that the CSP underwent remarkable conformational change when the content of 2-propanol was below 3%.