Quadrupole Ion Trap RF Voltage Control for Mass Resolving Power
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Solution Overview
Problem
Existing quadrupole ion traps face challenges in minimizing the velocity spread of ions during ejection, which limits the mass resolving power of mass spectrometers due to the difficulty in rapidly terminating RF trapping potentials at their maximum amplitude, causing ions to disperse and acquire increased velocity spreads at zero crossing points.
Innovation Solution
The method involves reducing the amplitude of RF voltages for one half cycle after a zero crossing point and turning them off at the next zero crossing point, allowing for the application of an extraction field when the ions have a minimum velocity spread, thereby minimizing the velocity spread and enabling efficient ion ejection with reduced capacitance challenges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If RF trapping potentials are terminated at maximum amplitude to minimize ion velocity spread, then mass resolving power is improved, but the large capacitance of trap electrodes prevents rapid termination causing ions to disperse and acquire increased velocity spreads
Solution Approach 1:
The patent applies preliminary action by reducing the RF amplitude to a lower level before termination at the zero crossing point. This preparatory step allows the RF potential to be switched off more rapidly without causing significant ion dispersion, thereby maintaining mass resolving power while achieving faster termination than would be possible at maximum amplitude.
Solution Approach 2:
The patent changes the parameter of RF amplitude from maximum to a reduced level before termination. By operating at a reduced RF amplitude just prior to ejection, the system enables faster voltage switching while maintaining effective ion confinement, thus resolving the contradiction between rapid termination capability and mass resolving power.
2Speed
If RF trapping potentials are terminated at zero crossing point to enable rapid switching, then termination speed is improved, but ion velocity spread increases due to dispersion during the termination period
Solution Approach 1:
The patent applies preliminary action by reducing the RF amplitude before termination at the zero crossing point. This preparatory step allows the RF potential to be switched off more rapidly without causing significant ion dispersion, thereby maintaining mass resolving power while achieving faster termination than would be possible at maximum amplitude.
3Ease of manufacture
If RF amplitude is reduced for one half cycle before termination, then capacitance challenges are minimized enabling efficient ejection, but ejection timing must be precisely synchronized with the next zero crossing point
Solution Approach 1:
The patent applies periodic action by utilizing the periodic nature of the RF waveform. The RF amplitude is reduced for one complete half-cycle period, and termination is synchronized with the subsequent zero crossing point. This periodic approach naturally provides optimal ejection conditions while maintaining manageable control complexity through synchronization with the inherent RF oscillation period.
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 approach results in ions being ejected with a minimum velocity spread, enhancing the mass resolving power by synchronizing the ion ejection with the next zero crossing point, where the RF trapping potentials are at a lower amplitude, and allowing for precise control of ion trajectories within the quadrupole ion trap.
Implementation Method 1
collisions between ions and the gas molecules cause the ions to lose energy progressively with each collision and thereby cool to approximately the gas temperature
Data Source
AI summary
A method of ejecting ions to be analyzed from a quadrupole ion trap in which a trapping field is created by one or more RF voltages applied to one or more electrodes of the trap, the method comprising the steps of cooling the ions to be analyzed within the quadrupole ion trap until the ions are thermalized, reducing the amplitude of one or more RF voltages applied to the quadrupole ion trap and applying the reduced amplitude RF voltages for one half cycle after the one or more RF voltages have reached a zero crossing point, turning off the RF voltages applied to the quadrupole ion trap, and ejecting the ions to be analyzed from the quadrupole ion trap.