Identification of aliphatic and aromatic tertiary N-oxide functionalities in protonated analytes via ion/molecule and dissociation reactions in an FT-ICR mass spectrometer.

A mass spectrometric method is presented for the identification of compounds that contain the aliphatic or aromatic N-oxide functional group. This method utilizes gas-phase ion/molecule reactions of tri(dimethylamino)borane (TDMAB), which rapidly derivatizes protonated aliphatic and aromatic tertiary N-oxides, amides, and some amines via loss of dimethylamine in a Fourier transform ion cyclotron resonance mass spectrometer. The mechanism involves proton transfer from the protonated analyte to the borane, followed by addition of the analyte to the boron center and elimination of dimethylamine. The derivatized analytes are readily identified on the basis of their m/z value which is 98 Th (thomson) greater than that of the protonated analyte, and the characteristic boron isotope patterns. SORI-CAD of the product ions (adduct-(CH3)2NH) yields different fragment ions for aliphatic tertiary N-oxides, aromatic tertiary N-oxides, amides, and pyridines. Therefore, these analytes can be identified based on their characteristic fragment ions. This method was tested by examining two drug samples, Olanzapine and Olanzapine-4' N-oxide.