Identification of Drugs Containing a Tertiary Amine Side Chain via Oxidation and LC-MS Analysis

Tamar Shamai Yamin, Analytical Chemistry, IIBR, Ness Ziona, Israel
Hagit Prihed, Analytical Chemistry, Iibr, Ness Ziona, Israel
Avital Shifrovitch, Analytical Chemistry, Iibr, Ness Ziona, Israel
Shai Dagan, Analytical Chemistry, Iibr, Ness Ziona, Israel
Avi Weissberg, Analytical Chemistry, Iibr, Ness Ziona, Israel

Identification of drugs containing tertiary amine side chains, is an important analytical challenge. The GC-MS and LC-MS/MS spectra of these compounds exhibit fragments and product ions mostly representing the amine-containing residue, while ions representing the main core are infrequently observed. This lack of information leads to unavoidable ambiguity in the identification process. We developed a novel analytical approach for the structural elucidation of drugs containing a tertiary amine side chain via simple oxidation followed by liquid chromatography-mass spectrometry (LC-MS) analysis. A series of lidocaine and benzimidazole derivatives, featuring a major/single amine-representative base peak, both in their EI-MS and ESI-MS/MS spectra, were “in-vial” oxidized utilizing hydrogen peroxide and instantaneously analyzed by LC-ESI-MS/MS, employing a quadrupole linear ion trap (QTRAP) mass spectrometer and a Q-Exactive Orbitrap-MS. HR-MS was utilized to assign product ion formulae and to suggest structures. While the fragmentation pattern of the original compounds exhibited poor quality uninformative mass spectra, their N-oxide counterparts promoted extensive fragmentation patterns with a complete coverage of all parts of the molecule. The highly informative mass spectra were used for structural elucidation and allowed unambiguous identification of the un-oxidized analytes at low ppb levels.