Microemulsion electrokinetic chromatography for the separation of carbamazepine, oxcarbazepine, and their metabolites

Microemulsion electrokinetic capillary chromatography was applied to separate two dibenzo[b,f]azepine-Derived antiepileptic drugs from their metabolites, namely carbamazepine from 10,11-dihydro-10,11-epoxycarbamazepine, 10,11-dihydro-10,11-dihydroxycarbamazepine, 2-hydroxycarbamazepine and 3-hydroxycarbamazepine; and oxcarbazepine from 10,11-dihydro-10-hydroxycarbamazepine and 10,11-dihydro-10,11-dihydroxycarbamazepine. Different separation parameters were varied in order to modify the mobilities of the compounds to be separated: the type of the co-surfactant (homologous series of 1-alkanols), the pH and salinity of the aqueous background electrolyte, the concentration of the organic constituents of the microemulsion system (n-octane, SDS, 1-alkanol). The potential for selectivity changes was highly restricted. However, favourable separation conditions were found at 1.98% SDS, 0.48% n-octane, and 3.96% 1-butanol (all w/w), 93.6% aqueous borate buffer consisting of 10 mM borate/boric acid at pH 9.7. With an uncoated fused-silica capillary of 36.5 cm total length (effective length 28 cm; 50 μm ID), a running voltage of 10 kV, and a thermostating temperature of 20.0°C baseline separation of all analytes was obtained within less than 13 min.