Compound screening for the presence of the primary N-oxide functionality via ion-molecule reactions in a mass spectrometer

A mass spectrometry method is presented for the identification of compounds that contain the primary N-oxide functional group. This method utilizes a gas-phase ion-molecule reaction with dimethyl disulfide that rapidly and selectively derivatizes the protonated primary N-oxide functional group in a mass spectrometer to yield an ionic reaction product (with 31 Da higher mass than that of the protonated molecule) that is diagnostic for the presence of a primary N-oxide functionality. A variety of protonated analytes containing different functional groups were tested in Fourier transform ion-cyclotron resonance and triple quadrupole mass spectrometers to probe the selectivity of the reaction. Only molecules containing the protonated primary N-oxide functional group yielded the diagnostic reaction product; all other protonated molecules gave protonated dimethyl disulfide or no reaction products. The feasibility of this method for compound screening was tested by examining six analytes with the same molecular formula but different atom connectivity. The one analyte that contained the primary N-oxide functional group was readily differentiated from the other analytes.