Performance Evaluation of a Loeb-Eiber Mass Filter at 1 Torr

Abstract

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.

Improvement in ionization efficiency of direct analysis in real time-mass spectrometry (DART-MS) by corona discharge

“…These conditions promote Penning ionization of He* with not only H 2 O (reaction (14)) but also N 2 and O 2 (reactions (16) and (17)), having ionization energies of 14.5 and 13.6 eV, respectively. These conditions promote Penning ionization of He* with not only H 2 O (reaction (14)) but also N 2 and O 2 (reactions (16) and (17)), having ionization energies of 14.5 and 13.6 eV, respectively.…”

“…This feature allows DART to be used for the direct analysis of narcotics, 6 addictive drugs, 7 counterfeit drugs, 8 microorganisms, 9 warfare agents, 10 pesticides, 11 for quality control, 12 in organic syntheses monitoring, 13 and for the surface analysis of living organisms. Thus, DART makes direct and highly sensitive analyte measurements feasible, as compared to typical low-pressure plasma ion sources using glow discharge 16 or dielectric barrier discharge. The desorption is carried out using hot helium gas, whereas the ionization goes through an atmospheric pressure chemical ionization (APCI)-like process involving ion-molecule reactions with excited helium.…”

“…These conditions lead to a significantly long reaction time for analyte ionization, resulting in the generation of a large number of thermal analyte ions, without the occurrence of excessive ion kinetic energy. Thus, DART makes direct and highly sensitive analyte measurements feasible, as compared to typical low-pressure plasma ion sources using glow discharge 16 or dielectric barrier discharge. 17 The broad range of DART applications has necessitated a continual development and refinement of techniques to enhance sensitivity.…”

High Pressure Mass Spectrometry: The Generation of Mass Spectra at Operating Pressures Exceeding 1 Torr in a Microscale Cylindrical Ion Trap

“…Many current fieldable mass spectrometry systems push boundaries of MS miniaturization, such as the MMS 100 and OEM-100 from 1 st Detect and the Griffin 400 series and Griffin 844 from FLIR, , but all of these systems require turbo pumps for operation. With the development of a discontinuous atmospheric pressure interface (DAPI), ion trapping has been performed at elevated pressures (∼1 Torr), but a turbo pump is still needed to reach lower pressures for mass analysis (<10 mTorr). , Hoffman et al have shown high-pass mass filtering for ions of low m / z (<40) at 1 Torr with a MEMS based Loeb-Eiber mass filter . The Loeb-Eiber filter shows promise as a filter for ions at 1 Torr but was only used for relatively low m / z species, and mass analysis was still performed at low pressures with a linear quadrupole.…”

High pressure mass spectrometry of volatile organic compounds with ambient air buffer gas

“…A discontinuous atmospheric pressure interface (DAPI) has been used to trap ions at 1 Torr with air as the background gas, but mass analysis was performed at low pressures (<10 mTorr) . A Loeb‐Eiber mass filter has been used to high‐pass filter ions of low m/z at 1 Torr of air, but mass spectra were collected with a linear quadrupole operating at 10 −5 Torr after filtering . The studies mentioned above demonstrate that ion trap based mass analysis with air buffer gas is possible, but the authors were unable to perform both trapping/filtering and mass analysis at 1 Torr.…”