A TANDEM QUADRUPOLE ION TRAP MASS-SPECTROMETER

A new tandem mass spectrometer has been constructed by interfacing a Paul ion trap mass spectrometer to a quadrupole mass filter. Ions generated in an EI-CI source are mass-selected using the quadrupole and injected in 50-100 ms pulses into the ion trap at injection energies which range from nominally zero to 150 eV. Helium gas at a pressure of 1 mTorr is used to dampen the ion motion and thus trap the injected ions. Stored ions, as well as their dissociation and ion/molecule reaction products, are detected using the mass-selective instability scan mode of the ion trap. Ions generated from perfluorotributylamine, polycyclic aromatic hydrocarbons, xenon and tungsten hexacarbonyl all show efficient trapping at injection energies ranging from 10 to 110 eV. As the injection energy is raised, the internal energy deposited in the projectile increases, as demonstrated by displaying fragment ion abundances versus injection energy in the form of breakdown curves. Pyrene and other PAH ions undergo extensive fragmentation at injection energies greater-than-or-equal-to 100 eV to give spectra which resemble those recorded using surface-induced dissociation (SID). These and other data suggest that ions injected with sufficient kinetic energies collide with the trap surface during injection. Gas phase ion/molecule reactions also occur and lead to formation of [M + 17]+ from PAH molecular ions and abundant dinuclear ions from tungsten hexacarbonyl. The new instrument is evaluated and compared with other tandem mass spectrometers.