Computerized optimization of selectivity for direct capillary gas chromatographic multicomponent separations of enantiomers

Abstract

A computer-assisted procedure was elaborated for optimization of selectivity of two capillary columns coupled in series for direct gas chromatographic multicomponent separations of enantiomers. Two fused-silica capillary columns (column A coated with permethyl-β-cyclodextrin (ChirasilDex) and column B coated with a mixture of heptakis(6- O-tert.-butyl-dimethylsilyl-2,3- O-diacetyl)-β-cyclodextrin and polysiloxane OV-1701 in 1:1 ratio (TBDMSDAC) were coupled in series via a T-piece. Each column was placed in an independently heated oven. Selectivity was tuned by variation of temperatures of the two columns ( T A, T B) and carrier gas pressure in the column coupling point ( p m) under a constant inlet and outlet pressure. The chromatograms were recorded under working conditions ( T A, T B and p m) calculated using the Doehlert experimental design. Optimization procedure was based on mathematical models. A new threshold criterion for optimization of selectivity suitable for multicomponent sample separation was introduced. The elaborated optimization procedure was verified by separating d- and l-enantiomers of N-trifluoroacetyl/ O-alkyl derivatives of alanine, valine, 2-aminobutanoic acid and proline.