The design and performance of a quadrupole ion trap storage/reflectron time-of-flight mass spectrometer.

Abstract

The design and performance of an ion trap storage/reflectron time-of-flight mass spectrometer (IT/RETOFMS) combination has been explored. This device combines the storage capabilities of the ion trap with the relatively high resolution, speed and high mass capabilities of the TOF to potentially produce a hybrid instrument with unique capabilities. Ions were generated internally using resonance enhanced multiphoton ionization (REMPI) or matrix-assisted laser desorption/ionization (MALDI), while ions were generated external to the trap using atmospheric pressure chemical ionization (APCI), low pressure glow discharge ionization (LPGDI), electrospray ionization (ESI) and inductively coupled plasma ionization (ICPI). It is demonstrated herein that the ion trap provides an effective means of storing ions from 10 $\mu$s up to 10 sec prior to mass analysis via pulsed DC extraction into the RETOFMS device. A resolution of $\sim$6200 at m/z 1347 is demonstrated with the MALDI method. A resolution of $\sim$3300 at m/z 1060 is demonstrated using external injection from an electrospray ionization source into the trap. It is shown that the storage capabilities of the device provide enhanced resolution and sensitivity as the storage time is increased. The IT/RETOF storage capabilities are shown to provide the potential for nearly 100% duty cycle in converting a continuous ion beam into a pulsed source for TOF with no dependence on the scan rate. The detection limit of the device is demonstrated with liquid injection techniques for a typical sample and found to be in the low femtomole range. In addition, the RF voltage was shown to be an effective means of eliminating low mass background ions from the trap and, thus, from the TOF mass spectra obtained. The collisional induced dissociation (CID) of peptide ions produced from an electrospray ionization source in the differentially pumped region is shown to be an effective means of performing structural analysis and the resolution of the fragment ions produced by CID were found to be comparable to those of the molecular ions. Overall, it is shown that this novel quadrupole ion trap storage/reflectron time-of-flight mass spectrometer has enormous potential to evolve into a powerful but inexpensive device for mass analysis.