Axial Ion Ejection in Linear Quadrupole Ion Traps
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Solution Overview
Problem
Commercial linear ion traps primarily eject ions radially, causing design difficulties, whereas an axial ejection mechanism would be more suitable for hybrid mass spectrometers with linear ion path geometry.
Innovation Solution
The ion trap design incorporates a first and second electrode set with specific configurations, including dielectric coatings and axial lengths, to create radially dependent axial DC potential barriers that confine and extract ions axially, allowing for axial ejection by varying DC voltages and AC excitation voltages to control ion displacement and extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If commercial linear ion traps eject ions radially, then ion confinement is achieved, but design difficulties arise for hybrid mass spectrometers with linear ion path geometry
Solution Approach 1:
The patent inverts the conventional ejection direction from radial to axial. The linear ion trap is designed to eject ions along the axial direction (parallel to the rod axes) rather than radially outward, matching the linear ion path geometry of hybrid mass spectrometers and eliminating the need for complex radial-to-linear transition components.
Solution Approach 2:
The patent changes the ejection dimension from the radial plane to the axial dimension. By applying DC potentials to the rod electrodes and using AC excitation to modulate ion motion axially, the system achieves mass-selective ejection along the length of the trap rather than perpendicular to it, simplifying integration with linear downstream components.
2Device complexity
If axial ejection is implemented, then design simplicity for linear ion path geometry is achieved, but new electrode configurations and voltage control mechanisms are required
Solution Approach 1:
The rod electrodes serve multiple functions: they provide radial confinement through RF voltages, enable axial transport through DC potentials, and facilitate mass-selective ejection through AC excitation. This multi-functionality reduces the need for separate dedicated electrodes for each function, simplifying the overall device structure despite the advanced control requirements.
Solution Approach 2:
The system uses dynamic voltage control where DC potentials on the rods are modulated by AC excitation voltages at specific frequencies. This dynamic approach allows mass-selective axial ejection without requiring physically different electrode structures for different operational modes, achieving versatility through electrical control rather than structural 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 efficient axial ejection of ions, improving the design of linear ion traps for hybrid mass spectrometers by maintaining high ion transmission efficiency and allowing for mass-selective axial transport, reducing design complexities associated with radial ejection.
Implementation Method 1
a first device arranged and adapted to create a first DC electric field which acts to confine ions having a first radial displacement axially within the ion trap and a second DC electric field which acts to extract or axially accelerate ions having a second radial displacement from the ion trap
Implementation Method 2
a second device arranged and adapted to mass selectively vary, increase, decrease or scan the radial displacement of at least some ions so that the ions are ejected axially from the ion trap
Implementation Method 3
allowing for axial ejection by varying DC voltages and AC excitation voltages to control ion displacement and extraction
Data Source
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AI summary
A mass spectrometer is disclosed comprising a quadrupole rod set ion trap 2,3 wherein a potential field is created at the exit of the ion trap 4,5 which decreases with increasing radius in one radial direction. Ions within the ion trap 2,3 are mass selectively excited in a radial direction. Ions which have been excited in the radial direction experience a potential field which no longer confines the ions axially within the ion trap but which instead acts to extract the ions and hence causes the ions to be ejected axially from the ion trap 2,3.