Waveform activated rearrangement of n-butylbenzene molecular ions during tandem mass spectrometry in the quadrupole ion trap

The "molecular thermometer," n-butylbenzene, when analyzed by tandem mass s pectrometry, produced an unusual product ion mass spectrum. Instead of the expected tandem mass spectrum containing fragments at m/z 91 and m/z 92, an unexpected base peak at m/z 119 was observed. Tandem parameters such as q( z), collision-induced dissociation (CID) voltage, trap temperature, and spa ce charge were examined. When n-butylbenzene was analyzed by other ion trap mass spectrometers in our laboratory and other laboratories, analogous res ults were obtained. This phenomenon was investigated and found to be associ ated with the Varian protocol used in ion isolation during the tandem mass spectrometry experiment on commercial instruments. Studies were performed i n an attempt to cool the precursor ion prior to activation with no change i n the mass spectrum. Comparison of n-butylbenzene with other butylbenzene i somers gave evidence that rearrangement was taking place during the isolati on of the precursor in the tandem experiment. Thorough investigation of the commercial protocol was undertaken that linked the cause of the rearrangem ent to the broadband waveform used in the precursor ion isolation step of t he tandem mass spectrometry experiment. (Int J Mass Spectrom 190/191 (1999) 265-279) (C) 1999 Elsevier Science B.V.