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Enantiomer separation of mandelates and their analogs, which are important intermediates in asymmetric synthetic and pharmaceutical chemistry, was investigated by capillary gas chromatography using different cyclodextrin derivative chiral stationary phases (CD CSPs). The used cyclodextrin derivatives included permethylated beta-CD (PMBCD), permethylated gamma-CD, heptakis(2,6-di-O-butyl-3-O-butyryl)-beta-CD, heptakis(2,6-di-O-pentyl-3-O-acetyl)-beta-CD and heptakis(2,6-di-O-nonyl-3-O-trifluoroacetyl)-beta-CD (DNTBCD), respectively. Among all the CSPs used, PMBCD and DNTBCD exhibited the broadest and best enantioselectivity for all the racemates investigated. Some thermodynamic parameters were evaluated and an enthalpy-entropy compensation effect was observed in enantiomer separation processes of mandelates and their analogs. Based on thermodynamic data and molecular mechanics calculations, the chiral recognition mechanism of mandelate derivatives on CD CSPs is discussed.

By utilizing the combination of frontal chromatography at ambient temperature, back-flushing and temperature gradient thermal desorption, a prototype of a dynamic pre-concentration system has been designed and evaluated. It realized the enrichment for gas samples of boiling point higher than - 103 degrees C without cryogenic facilities. To reduce the sample volume and enhance enrichment factor, the technique of momentarily non-steady state produced at the beginning of back-flushing, and the negative temperature gradient generated during thermal desorption were utilized, resulting a very sharp desorption band. Standard samples were tested to demonstrate the applicability of the method. At 10 mL sample volume, the enrichment factor was 100.