Enantiomeric separation of phenoxy acid methyl esters by gas chromatography using alpha-and gamma-cyclodextrin derivatives as stationary phases

Abstract

Enantiomeric separation of 46 phenoxy acid methyl esters (PAMs) were studied by capillary gas chromatography using two derivatized cyclodextrins as stationary phases: hexakis (2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl)-alpha-cyclodextrin (ASiAc). Analytes of interest included mainly mono- and di-substituted PAMEs with different type and position of substitution on the aromatic ring All gas chromatographic separations were done on capillary columns of 15 meter long, 0.25 millimeter i.d., and 0.25 micrometer film thickness. Hydrogen was used as a carrier gas at the average linear velocity of 50 cm/s. A split injector and a flame ionization detector were used. The retention factors and enantioselectivities were studied as a function of temperature and analyte structures. The effect of cyclodextrin ring size was also observed as GSiAc column could separate enantiomers of 34 PAMEs while ASiAc column could not separate any enantiomeric pair of PAMEs For GSiAc column, type and position of substitution of the aromatic ring affected enantioseparation of mono- and di-substituted PAMEs. as all fluoro-substituted PAMEs and most meta-substituted PAMEs could be enantioseparated. The effect of number of substitution was not clear. However, all substituted PAMEs showed lower enantioseparation than methyl 2-phenoxypropanoate, an unsubstituted PAME