Dynamic Micellar Electrokinetic Chromatography. Determination of the Enantiomerization Barriers of Oxazepam, Temazepam, and Lorazepam

摘要

The temperature-dependent enantiomerization barriers of oxazepam, temazepam, and lorazepam have been deter-mined between 0 and 30 0C by dynamic miceliar electro-kinetic chromatography (DMEKC) in an aqueous 20 mM borate/phosphate buffer system at pH 8 with 60 mM sodium cholate as chiral surfactant. Interconversion profiles featuring plateau formation and peak broadening were observed, and simulated by the new program ChromWin based on the theoretical plate as well as on the stochastic model using the experimental data plateau height, h91~~, peak width at half-height, Wh, total reten-tion times, tR, and electroosmotic breakthrough time, to. Peak form analysis yielded rate constants k and kinetic activation parameters, AG8, AW, and AS8, of the enan-tiomerization of oxazepam, temazepam, and lorazepam. At 25 0C, the enantiomerization barrier, AG8, was deter-mined to be ~90 ki moL1 and the half-lives, r, were determined to be approximately 21 mm. The new ap-proach allows the fast and precise determination of enantiomerization barriers in a biogenic environment and it mimics physiological conditions, as no organic modi-fiers or abiotic chiral stationary phases (CSP) are em-ployed.