Micellar electrokinetic chromatography–electrospray ionization mass spectrometry for the identification of drug impurities

Previously, we have presented a system hyphenating continuous micellar electrokinetic chromatography (MEKC) with electrospray ionization mass spectrometry (ESI-MS). Here we evaluate this technique for its applicability in impurity profiling of drugs using galantamine and ipratropium as test samples. A background electrolyte (BGE) of 10 mM sodium phosphate (pH 7.5), 12.5–15% acetonitrile and 20 mM sodium dodecylsulfate (SDS) was used for the MEKC–MS analysis of a galantamine sample containing a number of related impurities, and a heat-treated solution of ipratropium containing a number of unknown degradation products. MEKC provided efficient separation of all sample constituents. Despite the presence of non-volatile BGEs, all impurities in the galantamine sample could be detected by ESI-MS in their respective extracted ion traces (XICs) with a detection sensitivity in the sub-μg/ml range (full-scan mode). MS/MS detection provided useful product spectra allowing the structural characterization of the respective galantamine impurities. With the MEKC–MS/MS system, two degradation products could be revealed and identified in the heat-stressed ipratropium sample. The presented method shows good potential for the detection and structure elucidation of minor impurities in drug substances.