The design and performance of an 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—RETOF MS) combination have been explored for detection of ions generated from both internal and external ionization sources. Ions were generated inside the trap using laser-induced resonance enhanced multiphoton ionization at 266 nm, while ions were generated external to the trap using eighter an atmospheric pressure or low pressure d.c. plasma souce or an electrospray ionization source. It is demonstrated herein that the ion trap provides an effective means of storing ions from 10 μs up to 10 s prior to mass analysis via pulsed d.c. extraction into the RETOF MS device. In addition, it is shown that the storage capabilities of the device provide enhanced resolution and sensitivity as the storage time is increased. A resolution of nearly 2100 at m/z 93 is demonstrated using external injection from the atmospheric pressure d.c. plasma source when a storage time of 9 s is used before ejection. Further, a resolution of ≈3300 at m/z 1000 is demonstrated using external injection from an electrospray ionization source into the trap with a storage time of 931 ms. 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 of TOF. 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 r.f. 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.