Trapping and detection of ions generated in a high magnetic field electrospray ionization fourier transform ion cyclotron resonance mass spectrometer

Abstract

The trapping and detection parameters employed with a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer that is interfaced to a high magnetic field electrospray ionization (ES11 source are presented. ES1 occurs at atmospheric pressure in a 1.5-T field, and FTICR detection occurs 25 cm away at 3.0 T in either one of two cells separated by a conductance limit and maintained at pressure differentials of 5 × 10(5) and 2 × 10(7) torr, respectively. The continuous electrospray ion current traversing the high- and low-pressure cells is 350 and 100 pA, respectively. Retarding grid studies at the high-pressure cell indicate electrospray ion kinetic energies are controllable from less than an electronvolt to more than 10 eV. These kinetic energies are a function of desolvating capillary-skimmer assembly distance and the skimmer potential. Efficient accumulation of injected ions is accomplished only when the trap-plate potential matches the ion kinetic energy. If this condition is satisfied, the trapped ion cell fills to the ion space charge limit within a few hundred milliseconds. It is concluded that even at the high pressures used, the primary trapping mechanism cannot be solely collision dependent because the rate of ion accumulation is independent of background pressure. However, optimized FTICR excitation conditions for peptides and proteins in the mass range from 10(3) to more than 10(6) kDa are found to vary strongly with pressure; this is attributed to large mass- and charge-dependent differences in ion-molecule collision frequency.

Transformative effects of higher magnetic field in Fourier transform ion cyclotron resonance mass spectrometry

“…Initially electrospray source and transfer parameters were optimized for maximum signal magnitude. Static trapping[24] at a relatively low trapping potential (1.0 V/0.8 V for 4.7 T, 0.9 V/0.8 V for 7.0 T and 1.2 V/1.2 V for 9.4 T for front/rear trapping plates) were used. These trapping potentials were roughly ~30% greater than potential where no signal was observed (and presumably little trapping occurred).…”

Fast, generic gradient high performance liquid chromatography coupled to Fourier transform ion cyclotron resonance mass spectrometry for the accurate mass analysis of mixtures

“…Traditionally, the external source FTICR experiment has been relatively slow, owing mainly to lengthy ion accumulation methods. Techniques such as gated trapping23,, 24 and accumulated trapping25,, 26 require the use of long ion relaxation or gas pump‐down delays (2–20 s), thereby making such schemes incompatible with fast LC methods. An alternative approach, known as SideKick,15 utilises a pulsed electrostatic gradient for the collection of externally generated ions.…”

ELECTROSPRAY IONIZATION FOURIER TRANSFORM ION CYCLOTRON RESONANCE MASS SPECTROMETRY

“…Methods of injection include multipole ion guides (60)(61)(62)(63), electrostatic lenses (64)(65)(66), and the wire ion guide (a type of electrostatic lens different enough to warrant special mention) (59,67). Finally, Laude and coworkers have demonstrated ESI inside the magnet bore, thereby eliminating the magnetic mirror effect (68,69).…”