SIMULTANEOUS ISOLATION OF 2 DIFFERENT M/Z IONS IN AN ION-TRAP MASS-SPECTROMETER AND THEIR TANDEM MASS-SPECTRA USING FILTERED-NOISE FIELDS

For the first time, molecular ions from two different compounds have been simultaneously isolated in an ion-trap mass spectrometer and their subsequent tandem mass spectra (MS/MS) obtained. Isolation was achieved by applying a filtered-noise field (FNF) to the end-caps of a FinniganMAT ion-trap mass spectrometer (ITMS) using the Teledyne MEC/Hitachi HST-1000 Enhancement Kit. The HST-1000 generates a broadband waveform that would normally eject all ions from the trap. However, by setting notches in the waveform that correspond to certain resonant frequencies, individual masses can be isolated and stored in the trap without the need for the conventional DC voltage on the ring electrode. Using this FNF technique, the molecular ions of p-dichlorobenzene (m/z 146) and 1,3,5-trimethylbenzene (m/z 120) were simultaneously isolated from a 42-component mixture of volatile organic compounds. Each molecular ion was collisionally dissociated by applying a resonance excitation ('tickle') voltage from the HST-1000, and the spectrum for each molecular ion was obtained by scanning the RF voltage to the ring electrode.