Laser Desorption from a Probe in the Cavity of a Quadrupole Ion Storage Mass Spectrometer

It is possible to trap and mass-analyze ions that have been laser desorbed from a probe within the ion storage volume of a quadrupole ion storage mass spectrometer. A Finnigan ion trap detector was modified to enable a CO₂ laser pulse to strike a probe tip that passed radially through the ring electrode. Molecular and fragment ions from a variety of organic and biochemical compounds have been obtained. These ions are typical of CO₂ laser desorption (LD) processes, while the instrument itself retains tuning characteristics typical of the original electron Impact (El) Ionization performance. Because the El filament assembly was left intact, it has been possible to operate In LD/EI mode and produce additional fragment ions.