The unified equation for the evaluation of degenerated first‐order reactions in dynamic electrophoresis

Abstract

An analytical solution for the unified equation for degenerated (pseudo-) first-order reactions, e.g., enantiomerization processes, in dynamic CE is presented, and validated with a dataset of 31 250 elution profiles covering typical experimental parameters. The unified equation was applied to determine the enantiomerization barrier of the hypnotic glutarimide derivative thalidomide (Contergan(R)) by dynamic capillary electrokinetic chromatography (DEKC). The enantiomer separation of thalidomide was performed in an aqueous 50 mM sodium borate buffer at pH 9.3 in the presence of the chiral mobile phase additive carboxymethyl-beta-CD. Interconversion profiles featuring pronounced plateau formation were observed. Activation parameters DeltaH( not equal) and DeltaS( not equal) were obtained from temperature-dependent measurements between 20.0 and 37.5 degrees C in 2.5K steps. From the activation parameters the enantiomerization barrier of thalidomide at 37 degrees C under basic conditions were calculated to be DeltaG( not equal) = 93.2 kJ/mol. Comparison of the kinetic data with results obtained at pH 8.0 reveals the catalytic influence of the base on the enantiomerization barrier.