Aurika Janulyte1, Yves Zerega2, Jacques Andre2, Boris Brkic3,4, Stephen Taylor4. 1. Aix-Marseille Université, LISA EA 4672, Campus Etoile - Service 461, Avenue Escadrille Normandie Niémen, 13397, Marseille Cedex 20, France. aurika.janulyte@univ-amu.fr. 2. Aix-Marseille Université, LISA EA 4672, Campus Etoile - Service 461, Avenue Escadrille Normandie Niémen, 13397, Marseille Cedex 20, France. 3. Q-Technologies Ltd, 100 Childwall Road, Liverpool, L15 6UX, UK. 4. University of Liverpool, Department of Electrical Engineering and Electronics, Brownlow Hill, Liverpool, L69 3GJ, UK.
Abstract
RATIONALE: The desire for mass spectrometer portability provides the motivation for simpler, lighter electronics to deliver switched potentials applied to the electrodes of the linear ion trap operated in non-scanning mode. Using a novel method of modelling and theoretical analysis, we simulate the mass analyser performance under these unfavourable operating conditions. METHODS: The electrical fields are simulated using the Charge Particle Optics software which employs the boundary element method. The ion trajectories are computed from the ion cage of the EI source to the interior of the trap where the ions are confined. The spatial/temporal ion distributions during injection are calculated from the individual ion trajectories computed with constant time-steps. Due to geometric non-linearities, βy = 0 lines close to the apex of the stability diagram have been computed for different initial positions with zero initial velocities in order to define the acceptable maximum axial extension. RESULTS: The DC potential well depth has been estimated at about 15 eV from the axial velocity distribution, and the minimum time of ion injection at 120 μs from the temporal ion distribution. To ensure a mass separation of one unit and the confinement of the whole of the injected ions, buffer gas cooling is necessary to reduce the trajectory excursion amplitudes to 0.1 and 15 mm in the radial and axial directions, respectively. CONCLUSIONS: The portable mass spectrometer is predicted to achieve a mass resolution of better than one mass unit providing that helium buffer gas is used. An additional cooling sequence has to be added prior to moving the operating point toward the apex.
RATIONALE: The desire for mass spectrometer portability provides the motivation for simpler, lighter electronics to deliver switched potentials applied to the electrodes of the linear ion trap operated in non-scanning mode. Using a novel method of modelling and theoretical analysis, we simulate the mass analyser performance under these unfavourable operating conditions. METHODS: The electrical fields are simulated using the Charge Particle Optics software which employs the boundary element method. The ion trajectories are computed from the ion cage of the EI source to the interior of the trap where the ions are confined. The spatial/temporal ion distributions during injection are calculated from the individual ion trajectories computed with constant time-steps. Due to geometric non-linearities, βy = 0 lines close to the apex of the stability diagram have been computed for different initial positions with zero initial velocities in order to define the acceptable maximum axial extension. RESULTS: The DC potential well depth has been estimated at about 15 eV from the axial velocity distribution, and the minimum time of ion injection at 120 μs from the temporal ion distribution. To ensure a mass separation of one unit and the confinement of the whole of the injected ions, buffer gas cooling is necessary to reduce the trajectory excursion amplitudes to 0.1 and 15 mm in the radial and axial directions, respectively. CONCLUSIONS: The portable mass spectrometer is predicted to achieve a mass resolution of better than one mass unit providing that helium buffer gas is used. An additional cooling sequence has to be added prior to moving the operating point toward the apex.
Authors: Kiran Iyer; Brett M Marsh; Grace O Capek; Robert L Schrader; Shane Tichy; R Graham Cooks Journal: J Am Soc Mass Spectrom Date: 2019-11-11 Impact factor: 3.109