Retention behavior of amino acid enantiomers in reversed-phase liquid chromatography

The work described in this paper tries to demonstrate that the formation of diastereomers, needed for the resolution of enantiomers of amino acids, takes place in the stationary phase, when aspartylalkylamides are used as chiral reagents. The chromatographic behavior of some amino acid enantiomers are studied under various chromatographic conditions. Resolution of the isomers occurs even under extreme conditions, such as low pH or very low resolving agent concentration. The same elution order was observed whether the chiral reagent was in the mobile phase or only in the stationary phase. The temperature dependence of the resolution was studied. it was found that quite frequently the entropy of the D-diastereomer is larger than that of the L-isomer. The behavior of the capacity ratios as a function of the chiral reagent concentration allowed the calculation of the diastereomer formation constant.