Thermospray liquid chromatography/mass spectrometry of quaternary ammonium saltst

Effect of drying on the degradation of cationic surfactants and separation performance in capillary zone electrophoresis of inorganic anions

Tetradecyltrimethylammonium bromide (TTAB) is used in capillary zone electrophoresis (CZE) to control the direction and magnitude of the electroosmotic flow and the migration time of analyte anions. Drying of the hygroscopic TTAB at 100 degrees C overnight has been found to influence the final CZE separation by providing improved resolution, precision of migration times, and enhanced detection response for hydrogenphosphate. Chemical analysis of the dried TTAB using IR and GC-MS indicated the presence of small amounts of an unexpected tertiary alkylamine, tetradecyldimethylamine. This amine appears to contribute to the improved separation, probably by making more effective the masking of silanophilic activity at the capillary surface and/or generating a more stable double-layer.

Identification with liquid chromatography-ionspray mass spectrometry of the metabolites of the enantiomers N-methyl dextrorphan and N-methyl levorphanol after rat liver perfusion

To gather more information on stereochemical factors in the hepatic disposition of organic cations, mass spectrometry coupled to liquid chromatography was used to determine the identity of the metabolites excreted in bile after isolated rat liver perfusions with the quaternary ammonium derivatives of the enantiomeric drugs dextrorphan and levorphanol. Ionspray mass spectrometry was chosen for its soft ionization and absence of thermal degradation of labile compounds. The drugs were labelled with a stable (2H) isotope and mixed with unlabelled drugs to create an artificial isotope pattern in the mass spectrum and facilitate the recognition of unknown metabolites. In mass spectra that were recorded under normal conditions, fragmentation was absent and metabolites of N-methyl dextrorphan and N-methyl levorphanol were visible as parent-ion 'doublets'. Collision-induced fragmentation studies were performed to support the identification of the metabolites. For N-methyl dextrorphan the glucuronide, the glutathione conjugate and the glucuronide of the N-demethylated metabolite were found in bile. For N-methyl levorphanol the glucuronide, the glutathione conjugate, the sulphate conjugate and the glucuronide of a hydroxylated N-methyl levorphanol were excreted in bile. Thus a remarkable stereoselectivity occurs in the metabolism of these quaternary ammonium compounds in the rat liver.

Liquid chromatography-mass spectrometry with ionspray and electrospray interfaces in pharmaceutical and biomedical research

Electrospray and ionspray techniques use samples that exist as ions or ion-molecule complexes in solution. After the dispersion of the solution into an electrically charged aerosol, the sample ions may escape from the solution into the gas phase in a region that is at atmospheric pressure. The sample ions are transported into the mass analyser which is operated under a high vacuum. Liquid chromatographs can be coupled to electrospray and ionspray interfaces. Flow injection or continuous infusion of a sample solution (both without the use of a separating column) may be preferred over on-line liquid chromatography-mass spectometry in certain applications. Electrospray or ionspray is applicable to polar or ionic samples. Weakly polar and apolar samples are not ionized under electrospray or ionspray conditions. Applications of the techniques are in the fields of drug metabolism, natural product analysis and the determination of high molecular weights through the observation of multiply charged ions.