Ion trap mass analysis at high pressure: A theoretical view

Abstract. Secular frequency scanning is implemented and characterized using both a benchtop linear ion trap and a miniature rectilinear ion trap mass spectrometer. Separation of tetraalkylammonium ions and those from a mass calibration mixture and from a pesticide mixture is demonstrated with peak widths approaching unit resolution for optimized conditions using the benchtop ion trap. The effects on the spectra of ion trap operating parameters, including waveform amplitude, scan direction, scan rate, and pressure are explored, and peaks at black holes corresponding to nonlinear (higher-order field) resonance points are investigated. Reverse frequency sweeps (increasing mass) on the Mini 12 are shown to result in significantly higher ion ejection efficiency and superior resolution than forward frequency sweeps that decrement mass. This result is accounted for by the asymmetry in ion energy absorption profiles as a function of AC frequency and the shift in ion secular frequency at higher amplitudes in the trap due to higher order fields. We also found that use of higher AC amplitudes in forward frequency sweeps biases ions toward ejection at points of higher order parametric resonance, despite using only dipolar excitation. Higher AC amplitudes also increase peak width and decrease sensitivity in both forward and reverse frequency sweeps. Higher sensitivity and resolution were obtained at higher trap pressures in the secular frequency scan, in contrast to conventional resonance ejection scans, which showed the opposite trend in resolution on the Mini 12. Mass range is shown to be naturally extended in secular frequency scanning when ejecting ions by sweeping the AC waveform through low frequencies, a method which is similar, but arguably superior, to the more usual method of mass range extension using low q resonance ejection.

Section: Resultssupporting

confidence: 87%

Experimental Characterization of Secular Frequency Scanning in Ion Trap Mass Spectrometers

Snyder

Pulliam

Wiley

et al. 2016

“…With condensed ion distributions, the ion reaction rate could be increased by increasing the buffer gas pressure (Figure 6a). As shown in Figure 6b, the size of the cation cloud would decrease as the buffer gas pressure increases, and it reaches a plateau when the pressure reaches to~7 mTorr, which agrees well with previous simulation and experimental results [44][45][46]. In conventional ion trap mass spectrometers, the increase of buffer gas pressure would cause degraded mass resolution.…”

Section: Buffer Gas Pressuressupporting

confidence: 89%

GPU Assisted Simulation Study of Ion–Ion Reactions within Quadrupole Ion Traps

Guo

Wang

et al. 2015

Self Cite

Abstract. In this study, a gas-phase ion-ion reaction model was developed, and it was integrated into an ion trajectory simulation program. GPU parallel computation techniques were also applied to accelerate the simulation process. With this simulation tool, the dependence of ion-ion reaction rate within 3D quadrupole ion traps on both ion trap operation parameters and the characteristics of reaction pair were investigated. It was found that the m/z values and charge states of ions have significant influences on the reaction rate. Moreover, higher ion-ion reaction rate was achieved under higher trapping voltages and higher buffer gas pressures. Furthermore, secondary reaction and/or neutralization of ETD fragment ions were observed from simulation. The reaction and/or neutralization rate depends on the charge state and m/z of each fragment ion.

“…In this simulation, 10 4 ions of m/z 500 are placed in the 3D ion trap with an RF voltage of 400 V p-p . As expected, the ion cloud size decreases by increasing the buffer gas pressure from 0.1 to 5 mTorr [64][65][66]. However, not much change is observed when the pressure was increased from 5 to 10 mTorr.…”

Section: Space Charge Effects On Ion Trappingsupporting

confidence: 56%

“…Although the reason is still under investigation, interestingly, measurements of the ion trapping efficiency of externally generated ions are also found to be optimal at~5 mTorr for linear ion traps [64,67]. On the other hand, mass analysis resolution of an ion trap depends not only on the ion cloud size but also the ion motion frequency peak width [65]. Buffer gas can cool the ion cloud but also broaden the ion motion frequency peak width.…”

Section: Space Charge Effects On Ion Trappingmentioning

confidence: 99%

Accelerated Simulation Study of Space Charge Effects in Quadrupole Ion Traps Using GPU Techniques

Xiong

Fang

et al. 2012

Self Cite

Space charge effects play important roles in the performance of various types of mass analyzers. Simulation of space charge effects is often limited by the computation capability. In this study, we evaluate the method of using graphics processing unit (GPU) to accelerate ion trajectory simulation. Simulation using GPU has been compared with multi-core central processing unit (CPU), and an acceleration of about 390 times have been obtained using a single computer for simulation of up to 10 5 ions in quadrupole ion traps. Characteristics of trapped ions can be investigated at detailed levels within a reasonable simulation time. Space charge effects on the trapping capacities of linear and 3D ion traps, ion cloud shapes, ion motion frequency shift, mass spectrum peak coalescence effects between two ion clouds of close m/z are studied with the ion trajectory simulation using GPU.