Retention and selectivity of amino acid ester derivatives on (R)-N-(3,5-dinitrobenzoyl)-phenylglycine column

The effect of the size of alkyl substituent (ethyl, 2-propyl, 1-butyl or 2- butyl) in the ester group of benzoyl derivatives of amino acids on the sepa ration factor and retention of enantiomers was examined. Pirkle type chiral stationary phase (R)-3,5-dinitrobenzoylphenylglycine) and binary nonaqueou s eluents were used. The Snyder-Soczewinski linear equation was applied for presentation of retention vs. eluent composition relationships, which perm its the evaluation of separation selectivity in a wide range of concentrati ons of the more polar component in the binary mobile phase. It was found that, in the majority of cases, the best separation was obtain ed for 2-propyl derivatives of amino acids, although some exceptions from t his rule were also observed. Similarly, in some cases, the ethyl derivative s of amino acids do not exhibit the strongest retention. Both selectivity, as well as retention, depended on the type and concentrat ion of the more polar component of the eluent.