Linear Ion Trap Fragmentation via Pulsed RF Excitation
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Solution Overview
Problem
Traditional ion trap methods require high collision gas pressures and RF excitation amplitudes to achieve efficient ion fragmentation, which can lead to ion loss and inefficient fragmentation processes, especially at lower pressures and amplitudes.
Innovation Solution
The introduction of a pulsed collision gas and an auxiliary alternating electrical field with lower amplitudes and longer excitation times in a linear ion trap with circular cross-section electrodes, allowing for fragmentation at pressures below 5×10−4 Torr and amplitudes below 500 mV, while maintaining fragmentation efficiencies above 80%.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high collision gas pressures and RF excitation amplitudes are used, then fragmentation efficiency is improved, but ion loss increases and the process becomes less efficient at lower pressures
Solution Approach 1:
The patent applies periodic pulsed RF excitation to the ions in the linear ion trap. By delivering RF energy in periodic pulses rather than continuously, the system achieves efficient ion fragmentation through repeated collision cycles with the collision gas, while allowing the ion population to be replenished and maintained between pulses. This periodic action enables high fragmentation efficiency without the continuous high-energy input that causes ion loss.
Solution Approach 2:
The patent changes the operational parameters by using lower collision gas pressures (below 5×10^-4 Torr) combined with optimized pulsed RF excitation parameters (amplitudes below 500 mV and extended pulse durations). This parameter change allows the system to achieve efficient fragmentation through multiple low-energy collision events rather than requiring high-pressure, high-amplitude conditions that lead to ion loss.
2Productivity
If high RF excitation amplitudes are used, then ion fragmentation is achieved, but ions collide with trap elements or are ejected from the trap
Solution Approach 1:
The patent uses periodic pulsed RF excitation with controlled amplitude and duration. The pulsed nature allows ions to be accelerated and collide with collision gas molecules during the pulse, then coast and stabilize between pulses. This periodic modulation prevents continuous high-amplitude excitation that would push ions onto unstable trajectories leading to trap element collisions or ejection.
Solution Approach 2:
The patent dynamically controls the RF excitation parameters, adjusting amplitude and pulse duration based on the specific ion mass and desired fragmentation efficiency. This dynamic adjustment optimizes the excitation trajectory for each ion type, ensuring sufficient energy transfer for fragmentation while maintaining trajectory stability and preventing ion loss to trap elements.
3Loss of substance
If low collision gas pressures are used, then ion loss is reduced, but fragmentation efficiency decreases
Solution Approach 1:
The patent compensates for low collision gas pressure by using periodic pul RF excitation with optimized pulse durations (5-200 ms). The extended pulse duration allows multiple collision opportunities at lower pressure, accumulating sufficient energy transfer for fragmentation without requiring high instantaneous pressure that would increase ion loss through excessive collisions with trap elements.
Solution Approach 2:
The patent maintains continuous useful action during the RF pulse duration, keeping ions confined and repeatedly exposing them to the collision gas. The continuous confinement and repeated collision opportunities during extended pulses ensure that even at low pressures, ions accumulate sufficient energy for fragmentation through multiple incremental collision events rather than requiring a single high-pressure event.
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 enables efficient ion fragmentation at reduced pressures and amplitudes, increasing fragmentation efficiency and reducing ion loss, allowing for faster production and detection of fragment ions, including those below the typical low-mass cut-off.
Implementation Method 1
applying an alternating electric potential (RF potential) to electrodes of the trap to impart kinetic energy to the ions in the trap
Implementation Method 2
creating a non-steady-state pressure increase within the ion-confinement region by delivering a neutral gas into the ion trap
Implementation Method 3
The accelerated ions can collide with other molecules within the trap, resulting in fragmentation of the ions for sufficiently high collision energies
Data Source
AI summary
Methods for fragmenting ions retained in an ion trap are described. In various embodiments, a non-steady-state pressure of a neutral collision gas of less than about 5×10−4 Torr and an excitation amplitude of less than about 500 mV (peak to ground) is used to fragment ions with greater than about 80% fragmentation efficiency. In various embodiments, duration of ion excitation is greater than about 25 ms.