Effect of column temperature on enantioseparation of dihydropyrimidinones using alcohol solvated Chiralpak AS and AS-H columns

In this study we report the application of column temperature programs to compare the chromatographic behaviors of four commercially available dihydropyrimidinone (DHP) compounds on Chiralpak AS and AS-H phases under different alcohol solvation conditions such as 1-propanol (1-PrOH), 2-methyl-1-PrOH (2-Me-1-PrOH), 1-butanol (1-BuOH), 2-BuOH, and tert-BuOH (t-BuOH) in n-hexane (n-Hex). It was observed that the apparent retention factors of the DHP compounds on the AS phase in t-BuOH/n-Hex mobile phase had the largest reduction (>27%) among the mobile phases studied after a heating and cooling temperature cycle (10 to 50 back to 10°C). However, the average reduction of the apparent retention factors of the compounds on t-BuOH solvated AS-H was less than 4%. No clear trend of changes in the apparent retention factors on AS and AS-H columns was observed in other alcohol modified mobile phases. Step-temperature programs showed that alcohol solvated AS phase had larger changes in the apparent retention factors with time than those of AS-H phase at the elevated temperature step (50°C). Both t-BuOH solvated AS and AS-H phases showed kinetic behaviors in chromatographic processes at the elevated temperature.