Unusual Regularity in GC Retention of Simple Amino Acid Derivatives
Anzor I. Mikaia, Nino G. Todua, Zenkevich G. Igor
Background. Application of simple regularities and the general principles along with direct use of reference retention index data is a useful approach for reliable structure determination of compounds by GC-MS. Objective. Interpretation of anomaly in elution order of alkyl esters of alkoxycarbonyl derivatives of glycine and alanine. Method. Preliminary derivatization to alkyl esters of N-alkoxycarbonyl analogs for GC-MS analysis of amino acids. Results. Alkyl es¬ters of N-alkoxycarbonyl derivatives of alanine (Alkyl = C2H5, n- and iso- C3H7) elute prior to the same deri¬va¬tives of glycine, despite the presen¬ce of addi¬tional methyl group at C(2). Elution order is reversed for methyl es¬ters of N-methoxycarbonyl derivatives. Conclusion. The peculiar behavior of alkyl esters of N-alkoxycarbonyl derivatives of glycine and alanine agrees with the concepts of gas chromatography and the known retention index regularities of organic compounds. Decrease of retention index values is a result of an introduction of additional methyl group to a carbon atom connected to two polar fragments in a molecule CH2XY. The dependence of the difference of retention index values for homologs of the types of CH3-CHXY and CH2XY vs. the total mass of fragments (X + Y) is similar to those for other sub-groups of analytes.