Effect of mobile phase amine additives on enantioselectivity for phenylalanine analogs

The use of basic mobile phase additives enhances the chiral separation of underivatized phenylalanine analogs on a common amylosic column. These additives appear to exert their effect through differential disruption of hydrogen binding involved in the recognition process. Several examples of amine increasing retention of the second eluting enantiomer while decreasing retention of the other enantiomer were observed. This gave dramatically increased selectivity and was most commonly observed with cyclopropylamine and cyclobutylamine. The effect was attributed to steric factors involved in the elution process.