Capillary electrophoresis separation and native laser-induced fluorescence detection of metallotexaphyrins

Methods based on capillary zone electrophoresis (CZE) and electrokinetic chromatography (EKC) are developed for the separation of motexafin gadolinium (MGd, Xcytrin®), a novel redox-active drug, under development for cancer therapy, and two closely related metallotexaphyrin impurities, called PCI-0400 and PCI-0430. The three metallotexaphyrins are baseline resolved using EKC in a separation solution containing 400-mM cetyltrimethyl ammonium bromide, 50-mM phosphoric acid, and 20% methanol. Detection is achieved using native laser-induced fluorescence (LIF) by exciting at 488 nm and collecting emission at 750 nm. Analysis of a representative clinical batch of MGd using EKC combined with native LIF allowed for the detection of PCI-0400 and PCI-0430 along with nine other possible MGd impurities, each of which is present at approximately 0.1% (total weight of the sample).