Pyrolytic methylation assisted enantioseparation of chiral hydroxycarboxylic acids

Abstract

Quaternary ammonium salts and dialkylformamide acetals have been demonstrated to be effective reactants for the injector port gas phase derivatization of organic compounds which have insufficient chromatographic properties. A derivatization method is described, in which dimethylformamide dimethylacetal is used as a methylating reagent for hydroxycarboxylic acids in the heated insert zone directly before their gas chromatographic enantioseparation. The results show that the chiral lactic, malic, mandelic, and tartaric acids or mixtures thereof were transformed into their methyl esters very quickly; these esters could easily be resolved into their enantiomers by gas chromatography employing chiral stationary phases. The amount of required samples depends on the analyte and could be limited to a few nanomoles; the entire derivatization procedure could be performed in less than 1 min. We examined the potential reagents systematically to select one of them for application in the COSAC experiment within ESA's ROSETTA mission, where solvent chemistry should be avoided because the transformation of polar organic compounds into derivatives suitable for chromatographic separation has to be performed on the surface of a cometary nucleus under near-zero gravity.