Radial-Ejection Ion Trap Electrode Geometry for Mass Accuracy
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Solution Overview
Problem
Two-dimensional radial-ejection ion traps face performance issues due to field distortions caused by apertures, leading to ion frequency shifting and degradation of mass accuracy, and existing solutions to balance the RF field are complex and costly to implement.
Innovation Solution
The ion trap is constructed with four elongated electrodes, each with a hyperbolic surface and an aperture, equally spaced from the centerline, creating a balanced RF field that reduces m/z dependence and eliminates significant octopolar field components, allowing for phase-locked resonance experiments and operation as either a radial-ejection ion trap or a quadrupole mass filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If X-electrodes are outwardly displaced to compensate for aperture field distortion, then mass accuracy is improved, but RF field becomes unbalanced causing m/z-dependent ion acceptance
Solution Approach 1:
The patent employs parameter changes by adjusting the RF voltage amplitudes applied to different electrode pairs. Specifically, when X-electrodes are outwardly displaced to compensate for aperture distortion, the RF voltage amplitude applied to the X-electrode pair is modified relative to the Y-electrode pair. This parameter adjustment rebalances the RF field, ensuring that ion acceptance becomes independent of m/z values while maintaining the mass accuracy benefits of the displaced electrode configuration.
2Reliability
If asymmetric electrode displacement is used to cancel aperture distortion, then field balance is improved, but device complexity increases
Solution Approach 1:
The patent manages device complexity through parameter changes in the voltage application scheme. Rather than requiring complex mechanical adjustment mechanisms for electrode positioning, the invention achieves RF field balance by modifying the electrical parameters (voltage amplitudes and phases) applied to the electrodes. This approach maintains the simplified mechanical structure while achieving the desired field balance, thereby reducing overall device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enables balanced ion injection across a wide m/z range, enhances space charge capacity, and facilitates higher resolution and frequency dispersion, while maintaining a symmetric RF field that approximates a conventional round-rod quadrupole mass filter.
Implementation Method 1
Ions are radially confined within the ion trap interior by applying opposite phases of a radio-frequency (RF) trapping voltage to the electrode pairs
Implementation Method 2
To perform an analytical scan, a dipole resonant excitation voltage is applied across the electrodes of the apertured electrode pair... This causes the trapped ions to come into resonance with the applied excitation voltage
Data Source
AI summary
A two-dimensional radial-ejection ion trap is constructed from four apertured electrodes having inwardly facing hyperbolic surfaces, with each electrode being spaced from the centerline by a distance r that is greater than the hyperbolic radius r0 defined by the hyperbolic surfaces. This geometry produces a balanced symmetrical trapping field that has a negligible octopole field component and a relatively large dodecapole or icosapolar field component. In one specific implementation, the ion trap is selectably operable as a quadrupole mass filter by applying a filtering DC voltage to the electrodes.