Experimental Validation of the Digital Tandem Mass Filter.

This work presents the experimental evaluation of a digital tandem mass filter that is composed of two digitally operated low-resolution mass filters in series whose mass windows are shifted with respect to each other. The overlap of the mass windows allows the resolution (Δ) of ions to be narrowed to provide better resolving power, while the acceptance of the tandem mass filter is defined by the acceptance of the first low-resolution quadrupole. Our experiments show that digital operation fulfills the promise of the tandem mass filter for providing better ion transmission at the same or better resolving power as a single quadrupole mass filter.

Peak structure with a quadrupole mass filter operated in the first stability region.

Rationale: In the development of commercial quadrupole mass spectrometers, there is an interest in understanding the factors that affect the transmission and peak shape of ions passing through the mass filter. These include the ion collection effects of the ion optics that lead to the presence of a peak structure.

Methods: The peak structure can be observed by increasing the ion's axial kinetic energy and reducing the mass step size in a mass spectrum.

Reducing ion reflections at the quadrupole pre-filter/mass filter boundary: Simulation and experiment.

Rationale: Ion reflections at the quadrupole pre-filter/mass filter boundary lead to the trapping of ions within the pre-filter. The trapped ions lead to space charge effects on the transmission of ions through this region which become more of an issue with the development of high sensitivity mass spectrometers which have bright ions beams.

Methods: Simulations were carried out matching the effective potentials at the pre-filter/mass filter boundary to reduce the field gradients across the boundary by reducing the field radius of the pre-filter.

Quadrupole pre-filter/mass filter transmission profiles: Experiment and simulation.

Rationale: Quadrupole pre-filter transmission profiles are shown to be affected by the presence of trapped ions within the pre-filter of a quadrupole mass spectrometer. Trapped ions are the result of ions reflected at the pre-filter/mass filter boundary and lead to space charge effects that can affect the shape of the pre-filter transmission profile, ion beam stability, peak width and peak intensity. The development of high sensitivity mass spectrometers with bright ion beams leads to greater numbers of trapped ions.

A high dynamic range pulse counting detection system for mass spectrometry.

Rationale: A high dynamic range pulse counting system has been developed that demonstrates an ability to operate at up to 2e8 counts per second (cps) on a triple quadrupole mass spectrometer. Previous pulse counting detection systems have typically been limited to about 1e7 cps at the upper end of the systems dynamic range. Modifications to the detection electronics and dead time correction algorithm are described in this paper.

MS/MS of ions in a low pressure linear ion trap using a pulsed gas.

A pulsed valve was used to increase the pressure within the trapping region of a low-pressure linear ion trap by situating the pulsed valve close to the ion trapping region. The pressure was estimated to increase from a background pressure of 3.5e-5 Torr of nitrogen to 0.

Fragmentation of ions in a low pressure linear ion trap.

The efficiency of in-trap fragmentation in a low-pressure linear ion trap (LIT), using dipolar excitation, is dependent upon the choice of both the excitation q and the drive frequency of the quadrupole. In the work presented here, fragmentation efficiencies have been measured as a function of excitation q for drive frequencies of 816 kHz and 1.228 MHz.