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

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-beta-cyclodextrin (ChirasilDex) and column B coated with a mixture of heptakis(6-O-tert.-butyl dimethylsilyl-2,3-O-diacetyl)-beta-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. (C) 1997 Elsevier Science B.V.