Ion Pusher Device for Time-of-Flight Mass Spectrometers
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Solution Overview
Problem
Time-of-flight mass spectrometers with orthogonal injection suffer from mass discrimination due to the dilution of light ions when heavy ions are present, and existing solutions for improving ion ejection methods are either complex or result in low mass resolution.
Innovation Solution
A simplified ion pusher device using four electrodes arranged as two parallel plates, with RF voltages forming a two-dimensional quadrupole field for storage and DC voltages creating a homogeneous dipole field for ion ejection, allowing for precise acceleration and focusing of ions without significant mass discrimination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a linear RF ion trap with lens-type accelerator is used to generate fine ion beams, then ion beam quality is improved, but mass discrimination occurs due to dilution of light ions when heavy ions are present
Solution Approach 1:
The device is segmented into two distinct functional regions: an RF quadrupole storage field region for ion confinement and a dipole ejection field region for ion acceleration. This segmentation allows independent optimization of each region's characteristics, enabling homogeneous dipole fields for non-discriminatory ejection while maintaining effective quadrupole storage
Solution Approach 2:
The invention transitions from conventional linear ion trap geometry to a planar configuration with parallel plates separated by a gap. This dimensional change enables the creation of a homogeneous dipole field across the gap region, fundamentally improving mass resolution by eliminating field inhomogeneities that cause mass discrimination
2Reliability
If dipolar ejection is used to push ions directly into the flight tube, then mass discrimination is avoided, but mass resolution is degraded due to non-homogeneous fields
Solution Approach 1:
Different regions of the device are assigned different field characteristics: the storage region uses inhomogeneous quadrupole fields for ion confinement, while the ejection region between parallel plates uses homogeneous dipole fields for mass-resolving acceleration. This local differentiation of field quality resolves the contradiction between avoiding mass discrimination and maintaining mass resolution
3Manufacturing precision
If many electrodes are used around the storage volume to achieve ideal quadrupole and dipole fields, then field homogeneity is improved, but device complexity increases
Solution Approach 1:
The invention merges the functions of multiple electrodes into just four planar electrodes arranged as two parallel plates with slits. These four electrodes can generate both the quadrupole storage field and the dipole ejection field by appropriate voltage application, dramatically simplifying the device while maintaining field homogeneity where critical for mass resolution
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
The solution provides improved mass resolution and reduced complexity in ion ejection, enabling efficient and precise pulsing of ions into the flight tube while maintaining a non-mass discriminating acceleration process.
Implementation Method 1
The four half plates can be supplied with RF voltages to form a two-dimensional quadrupole field along the center between the slits
Implementation Method 2
or with direct current (DC) voltages to form an ideal dipole field to eject the ions
Implementation Method 3
After the RF has been switched off, a short delay time without any field allows the ion cloud to expand, so that switching on the accelerating dipole field results in the well-known time focusing of ions of the same mass according to Wiley-McLaren
Data Source
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AI summary
The invention provides methods and devices to pulse ions from an RF ion storage into the flight tube of a time-of-flight mass spectrometer. The pusher cell comprises essentially two parallel plates, both plates completely slotted into two electrically insulated halves. The four half plates can be supplied with RF voltages to form a two-dimensional quadrupole field in the center between the slits, or with DC voltages to form a homogeneous acceleration field to eject ions. The RF quadrupole field is not ideal, but sufficiently good to store ions, to damp the ions by an additional collision gas, and to form a fine thread of ions in the axis of the quadrupole field. The DC acceleration field is extremely homogeneous; slight distortions near the slits can be corrected by external electrodes. The ideal acceleration field results in a high mass resolution and the device does not show any mass discrimination.