Dr Boris Brkić
Thomas J. Hogan, Stephen Taylor
Quadrupole mass filters (QMFs) and quadrupole ion traps (QITs) are essential components in many mass spectrometer systems e.g. RGA, GC-MS, LC-MS and ICP-MS. A QMF is a highly sensitive device that confines ions in two dimensions and filters them for a specific mass-to-charge ratio (m/z) by changing the voltage values applied to electrodes. In a QIT ion motion is confined to a small volume, set by voltages on the ring electrode and endcap electrodes enabling ions to remain oscillating in the trap. Ion traps have also been used for studying quantum mechanics, optical frequency standards and more recently in quantum computing.
Analytical and numerical modelling of QMFs and QITs is of great importance for analysis, design and fabrication of these devices and for their different applications. Numerical simulations can provide efficient investigation of device electrostatics and ion motion for desired particle control. To enable precise performance predictions, simulation results also need to be very accurate.
We present highly accurate simulation results for miniature QMF and QIT using finite-difference and boundary-element methods. For the larger quadrupole mass spectrometers a prefilter is commonly used. The effects of adding an RF only prefilter to the main QMF will be shown. The results will include ion trajectories, mass spectra and transmission, proposing the optimal prefilter length. Simulations of an endcap ion trap will be presented showing ion trajectories, energies and motional frequencies verified against experimental measurements. The endcap trap is a geometric variant of a quadrupole ion trap and it is easier for fabrication at small sizes than conventional QIT. Modelling of an array of micro ion traps will be shown since such small arrays offer the possibility of hand-held versions of ion trap mass spectrometers. Poster presented at:
28th BMSS Annual Meeting, University of York - 2005