Computer simulation of the gap-tripole ion trap with linear injection, 3D ion accumulation, and versatile packet ejection

Abstract

The behavior of a completely new ion trap is shown with SIMION 7.0 simulations. The simulated trap, which was a mix of a linear and a 3D trap, was made by axially setting two ion guides with a gap between them. Each guide consisted of three rods with three symmetrically delayed radio frequency (rf) voltages (tripole). The "injected" ions were linearly contained by pulsed potentials on the entrance and exit plates. Then the three-dimensional (3D) rf field in the gap, which was created by the tripole special rod arrangement, could trap the ions when the translational energy was dampened by collisions with low-pressure nitrogen. Because the injected ions were trapped in the small gap, the trapping cycle could be repeated many times before ion ejection, so a high concentrated ion cloud could be obtained. This trapping and accumulation methodology is not possible in most conventional multipole linear traps with even number of poles. Compared with quadrupole linear trap at the same rf amplitude, tripole lost more ions due to strong charge repulsion in the ion cloud. However, tripole could catch up the ions at higher voltage. Radial and axial mass-independent ejection of the ions localized in the tripole gap was very simple, compared with conventional linear ion traps that need extra and complicated electrodes for effective axial ejection. F or analytical sciences, high sensitivity is one of the key points for success. In many types of mass spectrometers, the signal-to-noise ratio increases considerably by analyte accumulation, and the linear ion trap (LIT) concept has been widely used for ion accumulation in hybrid instruments [1][2][3][4][5][6][7]. The LIT has been suitable for the construction of miniature mass analyzers, gas-phase reactions, atomic spectroscopy, precursor fragmentation, and beam physics experiments [8][9][10][11][12][13][14][15][16]. In the case of quadrupole LIT, it can perform ion trapping and mass analysis, all in a single package [17]. The LIT is considered to have higher trapping efficiency and capacity than conventional 3D quadrupole ion trap (3D QIT or Paul Trap). The trapping efficiency for LIT is very high (~100%) compared with the 5% range for QIT when high-speed ions are externally injected [2,18,19]. Compared with the 3D QIT, space-charge repulsion is minimized in LIT because the charges can be dispersed in its big central volume.We have proposed a new ion optics, called "tripole" which consists of three parallel rods, carrying three rf voltages with symmetrically delayed phase shifts [20]. The rotating electric field of the tripole showed stable ion guiding for wide ranges of AC amplitude, better Address reprint requests to Dr. T. Masujima, Analytical Molecular Medicine and Devices Laboratory, Faulty of Frontier Medical Sciences, Graduate School of Hiroshima University, 1-2-3 Kasumi, Minarni-ku, Hiroshima 734-8551, Japan. E-mail: tsutomufehiroshima-u.ac.jp collisional focusing than hexapole and octapole, and similar focusing as quadrupole (rod pole). Also, the ion optic showed interest...

Ion trap mass analysis at high pressure: A theoretical view

“…In simulations, hypothetical scenarios are created in which trapped ions experience realistic features of an ion trap electrical field and operating conditions, which are close to experiments [4,5,[35][36][37][38][39][40][41]. Discrete ion-molecule collision [4,39,41] and space charge effects [35,36] are included in the simulation settings.…”