Mass-selective instability and resonance ejection modes for DIT with rectangular asymmetric wave shape.

We consider the operation of a digital linear ion trap with resonance radial ejection and mass selective instability modes. Periodic wave shape has a positive part with amplitude and duration and negative part with amplitude and duration , where is the period. The mapping of the stability diagram, calculations of the well's depth and ion oscillations spectra are presented.

Modeling of a linear ion trap with driving rectangular waveforms.

We consider the operation of a digital linear ion trap with resonant radial ejection. A sequence of rectangular voltage pulses with a dipole resonance signal is applied to the trap electrodes. The periodic waveform is piecewise constant, has zero mean, and is determined by an asymmetry parameter : one value is taken on interval and another on , where is the RF period.

Modelling some rod set imperfections of a quadrupole mass filter.

The problem of modeling the mass peak shape of a quadrupole mass filter (QMF) with round rods is considered. A number of factors leading to the degradation of the mass peak shape are studied, namely, displacement of the electrodes with respect to their original position, changes in the diameter of the electrodes, and asymmetry of the supply potentials. Decomposition of the rod set field on multipole fields allows to obtain an analytical representation of the ion motion equations.

Dipole and quadrupole resonance excitation in linear quadrupoles.

In the development of commercial quadrupole mass spectrometers, there is an interest in improving the performance characteristics such as transmission, resolution, and mass range. In particular, parametric and dipolar resonance excitation of trapping ions are used for linear quadrupole mass filters. Theoretical methods and numerical simulation of ion trajectories were applied for study of ion-optical properties.

Modelling of a linear ion trap operation in the second stability region.

Ion trajectory numerical simulation is used to find the linear ion trap excitation contour in the second stability region. The effects of initial conditions, the ejection Mathieu parameter, scan speed, dipole excitation voltage and gas damping are studied. Modeling shows that in the stability region center the resolution power is (at full width half height of a peak, FWHM) at pressure 0.

Modeling dipolar excitation for quadrupole mass filter.

The results of modeling AC and DC dipole excitation of ion oscillations in a quadrupole mass filter are presented. The simulation is done by numerical integration of the ion motion equations, ions' initial coordinates and velocities are distributed normally. For AC dipole excitation the instability bands on the (, stability diagram follow along the isolines and , creating regular dips on the transmission contour.

A simulation study of excitation contour of a linear trap with spatial harmonics.

The process of nonlinear resonant excitation of ion oscillations in a linear trap is studied. There is still no detailed simulation of the resonance peak in the literature. We propose to use the excitation contour to describe the collective ion resonance.

Stable -islands of quadrupole mass filter.

Quadrupole mass filters are normally operated as narrow band pass filters by appropriate choices of rf and DC voltages corresponding to Mathieu and values near the apex of the first stability region. We add an auxiliary quadrupole excitation potential to the main drive voltage. As a result, stability islands appear on the () plane.

Quadrupole mass filter operation with dipole direct current and quadrupole radiofrequency excitation.

Rationale: For mass analysis, a quadrupole mass filter (QMF) usually operates at the upper tip of the first stability region. We introduce a new mode of QMF operation with dipole direct current (dc) and with auxiliary quadrupole excitation. Before experimental investigation of this mode, we have carried out numerical simulations of this process.

Quadrupole mass filter acceptance in stability island created by double-frequency quadrupole excitation.

Increase in quadrupole mass filter resolution at separation in narrow band stability island (X-band) formed by biharmonic resonance excitation of ion oscillation is discussed. X-band and the normal working quadrupole mass filter modes are compared at theoretical resolution of 10,000 and different separation times. Transmission curves, acceptance ellipses parameters, and acceptance characteristics are obtained by numerical simulation.

Simulation of the simultaneous dual-frequency resonance excitation of ions in a linear ion trap.

The process of ion resonance dipolar excitation in a linear ion trap by 2 ejection waveforms with close frequencies is studied. The physical mechanism of increasing the resolving power using the ion excitation is a nonlinearity of the electric radio frequency fields caused by space charge. Using 2 resonance forces with 2 close frequencies leads to the completion of 2 excitation processes.

4D phase-space acceptance of the quadrupole mass filter.

Simulations of the four-dimensional (4D) phase-space acceptance volume of a quadrupole mass filter (QMF) are discussed. The 4D acceptance is considered since the ion trajectories in the X and Y phase planes are dependent via the initial RF phase at ion entry into QMF. The QMF parameters are set up for resolution equal to the ion mass number M.

Dipolar excitation in the third stability region.

Dipole resonant excitation of ions creates instability bands which follow iso-β lines where β is the characteristic exponent (stability parameter). Instability bands are exited most effectively on the fundamental frequency π= βΩ/2. Here π is the angle resonance frequency of the dipolar voltage applied to x or y pair rods of the analyzer, and Ω is the angle frequency of the main drive voltage.

Linear ion trap mass selectivity with impulse power supply and sinusoidal dipolar excitation.

Rationale: An ion trap mass analyzer can be operated by either a sinusoidal waveform power supply or an impulse waveform power supply. The optimal conditions for the performance of ion trap which is driven by an impulse waveform power supply with sinusoidal dipolar voltage were investigated theoretically, and further verified by experiments.

Methods: The analytical relationship between β and q values is derived theoretically for optimal performance, and the dependencies β(q) for different trapezoidal waveforms are studied.

Dipole Excitation: A New Method for Mass Analysis with a Quadrupole Mass Filter.

Trajectory calculations are used to investigate peak shapes and ion transmission with a proposed new method of mass analysis with a quadrupole mass filter. Dipole excitation is applied to either the x or the y electrodes, or both, to create bands of instability within the first stability region. With excitation between the y electrodes (near β y  = 0), ions are removed from the low mass side of a peak, and with ion excitation in x (near β x  = 1), ions are removed from the high mass side.

Mass resolution of linear quadrupole ion traps with round rods.

Rationale: Auxiliary dipole excitation is widely used to eject ions from linear radio-frequency quadrupole ion traps for mass analysis. Linear quadrupoles are often constructed with round rod electrodes. The higher multipoles introduced to the electric potential by round rods might be expected to change the ion ejection process.

Quadrupolar ion excitation for radiofrequency-only mass filter operation.

Trajectory calculations are used to model a mass filter based on the radiofrequency (rf)-only operation of a linear quadrupole with resonant quadrupole excitation of ions (resonant excitation applied with the same spatial electric field as the main quadrupole rf field). Ions are not trapped, but pass continuously through the quadrupole. Excited ions gain axial kinetic energy in the fringe field at the quadrupole exit, overcome a stopping potential and are transmitted to an external detector.

Mass selectivity of dipolar resonant excitation in a linear quadrupole ion trap.

Rationale: For mass analysis, linear quadrupole ion traps operate with dipolar excitation of ions for either axial or radial ejection. There have been comparatively few computer simulations of this process. We introduce a new concept, the excitation contour, S(q), the fraction of the excited ions that reach the trap electrodes when trapped at q values near that corresponding to the excitation frequency.

Ion cloud model for a linear quadrupole ion trap.

If large numbers of ions are stored in a linear quadrupole ion trap, space charge causes the oscillation frequencies of ions to decrease. Ions then appear at higher apparent masses when resonantly ejected for mass analysis. In principle, to calculate mass shifts requires calculating the positions of all ions, interacting with each other, at all times, with a self-consistent space charge field.

Trajectory calculations of space-charge-induced mass shifts in a linear quadrupole ion trap.

Rationale: If too many ions are stored in a linear quadrupole ion trap, space charge causes the oscillation frequencies to decrease. Ions therefore appear at higher apparent mass-to-charge ratios in a mass spectrum. To further understand this process, we have used trajectory calculations of ions to determine mass shifts.

Space-charge effects with mass-selective axial ejection from a linear quadrupole ion trap.

Methods to reduce mass shifts caused by space charge with mass-selective axial ejection from a linear quadrupole ion trap are investigated. For axial ejection, dipole excitation is applied to excite ions at q ≈ 0.85.

Two stability islands of quadrupole mass filter near q = 0.9 created by auxiliary radio frequency voltage.

We report the numerical investigations of quadrupole mass filters concerning stability islands created by auxiliary radio frequency (RF) voltage with high and low frequencies near q = 0.9. The islands are located along the q axis near boundary value q = 0.

Mass peak shape improvement of a quadrupole mass filter when operating with a rectangular wave power supply.

Numeric experiments were performed to study the first and second stability regions and find the optimal configurations of a quadrupole mass filter constructed of circular quadrupole rods with a rectangular wave power supply. The ion transmission contours were calculated using ion trajectory simulations. For the first stability region, the optimal rod set configuration and the ratio r/r(0) is 1.

Mass analysis in islands of stability with linear quadrupoles with added octopole fields.

Mass analysis with linear quadrupole mass filters is possible by forming "islands" in the stability diagram with auxiliary quadrupole excitation. In this work, computer simulations are used to calculate stability boundaries, island positions, and peak shapes and ion transmission for mass analysis with linear quadrupole mass filters that have added octopole fields of about 2 to 4%. Rod sets with exact geometries that have quadrupole and octopole fields only in the potential, and round rod sets, with multipoles up to N = 10 (the twenty pole term) included in the calculations, show the same stability boundaries, island positions, and peak shapes.