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 b een simultaneously isolated in an ion-trap mass spectrometer and their subsequent tandem mass spectra (MS/MS) obtained. Isolation was achiev ed by applying a filtered-noise field (FNF) to the end-caps of a Finni ganMAT ion-trap mass spectrometer (ITMS) using the Teledyne MEC/Hitach i HST-1000 Enhancement Kit. The HST-1000 generates a broadband wavefor m that would normally eject all ions from the trap. However, by settin g notches in the waveform that correspond to certain resonant frequenc ies, 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 molecul ar ion was obtained by scanning the RF voltage to the ring electrode.