Multidimensional gas chromatography investigation of concentration and temperature effects of oxime interconversion on ionic liquid and poly(ethylene glycol) stationary phases.

This study develops analytical approaches using comprehensive heart-cut multidimensional gas chromatography (H/C MDGC) to experimentally investigate effects of concentration and temperature on peak shapes and on kinetic analysis of E/Z isomerisation of oximes which undergo various extents of interconversion on D and D separation columns. Different stationary phase combinations were investigated. An SLB-IL76 D column results in good separation of the isomers but with negligible interconversion (D). Precise targeted heart-cuts (H/C; 3-15 s windows) and cryogenic trapping of selected sections eluting from this D column allows well controlled E/Z isomer ratios to be delivered to a D poly(ethyleneglycol) (PEG) phase column. This phase catalyses oxime interconversion, with separation; this is termed D. This column set describes a D × D arrangement. The interconversion forward rate constant (k, calculated by using DCXplorer) was found to be independent of the %E isomer (i.e. first order kinetics); k increased at higher temperature (increased Gibbs activation energies, ΔG). In addition, a long D SLB-IL111 column gave oxime separation with interconversion (D). Comprehensive multiple H/C of the zone performed on the D PEG (D) at 40, 60 and 80 °C resulted in a 2D presentation (D × D) with a unique rectangular display of interconversion from each H/C pulse with varied isomer concentration ratios. Data for k from 1DGC analysis suggests underestimation of k on D SLB-IL111 from the 2D result. The k value on D PEG column is more reliably evaluated by summation of all the D profiles rather than that obtained from the average value for the individual H/C pulses.