title: Performance evaluation of a Loeb-Eiber mass filter at 1 Torr.
abstract: The Loeb-Eiber mass filter is best operated at relatively high pressures-such as 1 Torr-where collisional dampening of ions up to the mass filter thermalizes the ions' kinetic energy, which is a requirement for effective filtering. The inter-electrode gaps of ~8 μm require rf amplitudes on the order of 0-5 V p-p at approximately 50 MHz to achieve mass filtering up to m/z 40. Mass filtering between the 25-μm diameter wires, therefore, takes place on time frames less than the collision frequency at ~1 Torr. The low power and high pressure capabilities of the Loeb-Eiber mass filter make it ideally suited for miniaturization, where power and space are a premium. In the present work, a Loeb-Eiber mass filter was constructed using commercial silicon-on-insulator (SOI) microfabrication techniques. Ions transmitting through the chip-based Loeb-Eiber mass filter were characterized in real time using a traditional linear quadrupole mass analyzer in series with the Loeb-Eiber mass filter. The new hybrid instrument has enabled us to verify several important claims regarding the operation of the Loeb-Eiber mass filter: (1) that ions can be effectively filtered at ~1 Torr, (2) that for ions of a fixed mass-to-charge ratio, the ion transmission current decreases linearly with increasing rf amplitude on the Loeb-Eiber mass filter, (3) that the cutoff voltage at which all ions of a particular m/z value are effectively blocked is linearly related to mass-to-charge, and (4) that square waveforms can filter ions more effectively than sinusoidal waveforms for a given peak-to-peak rf amplitude.
authors.affiliation: Department of Forensic and Investigative Science, West Virginia University, Morgantown, WV, 26506, USA.
authors.forename: William D
authors.initials: WD
authors.lastname: Hoffmann
authors.forename: Feng
authors.initials: F
authors.lastname: Jin
authors.forename: Randall E
authors.initials: RE
authors.lastname: Pedder
authors.forename: Christopher
authors.initials: C
authors.lastname: Taormina
authors.forename: Glen P
authors.initials: GP
authors.lastname: Jackson