FACTORS THAT CONTROL SUCCESSFUL ENTROPICALLY DRIVEN CHIRAL SEPARATIONS IN SFC AND HPLC

With temperature increases, selectivity of chiral separations decrease s until enantiomers coelute at an isoelution temperature. Above this t emperature, elution order should reverse and selectivity will increase with temperature, In this region, separation is termed ''entropically driven'', Entropically driven chiral separations hold the promise of being able to concurrently increase selectivity and column efficiency by means of increased temperature, The ability to achieve such separat ions is hindered by high isoelution temperatures, The isoelution tempe rature is determined by a balance of enthalpic and entropic contributi ons, A variety of mobile phase modifiers are evaluated for their abili ty to moderate these contributions, Results suggest that more use shou ld be made of nonalcohol modifiers. The major barrier to entropically driven separations was found to be the nonspecific retention increase that is characteristic when the critical temperature is traversed, Use of hexane in place of CO2 shifts the position of the retention increa se away from the temperature range used in this study, and dramaticall y successful entropically driven chiral separations are obtained.