Planar RF Ion Guide With Overhanging Electrodes
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Solution Overview
Problem
Existing RF ion guides for mass spectrometry face challenges such as cumbersome assembly, dielectric charging, and neutral species collisions, which affect ion motion and performance, particularly in constructing deep potential wells and robust designs for ion confinement and collisional cooling.
Innovation Solution
A planar RF ion guide design featuring electrodes arranged on a dielectric surface with exposed portions shadowed by overhanging electrodes, reducing dielectric charging and neutral species collisions, and enabling effective ion confinement and separation, manufactured using mass-production techniques like printed circuit boards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional machining methods are used to construct RF ion guides with additional axial fields, then ion motion control is improved, but device complexity and assembly difficulty increase due to massive metal rods and numerous parts
Solution Approach 1:
The ion guide is divided into multiple rod electrodes (typically 4 rods for quadrupole configuration) arranged in a specific geometric pattern. Each rod can be independently manufactured and then assembled, simplifying the overall construction while maintaining effective ion motion control through the combined electric field of all rods
Solution Approach 2:
The same rod electrode structure serves multiple functions: it generates the RF field for ion confinement, provides structural support, and can be configured to create additional axial fields when needed. This multi-functionality reduces the number of separate components required
2Ease of manufacture
If planar designs are used to simplify manufacturing by standard mass-production techniques, then ease of manufacture is improved, but the ability to construct deep potential wells for mass spectrometry is reduced
Solution Approach 1:
The design parameters of the rod electrodes (radius, spacing, length) are optimized to generate sufficiently strong electric fields that create deep potential wells. By carefully selecting these parameters, the planar design achieves the necessary confinement depth for mass spectrometry applications while maintaining manufacturing simplicity
3Ease of manufacture
If dielectric gaps between electrodes are used in planar designs, then ease of manufacture is improved, but dielectric charging occurs that affects ion motion
Solution Approach 1:
The dielectric material is completely removed from the electrode structure. Instead of having dielectric gaps between electrodes, the design uses direct metal-to-metal spacing with vacuum or gas filling, eliminating the source of dielectric charging while preserving the planar manufacturing approach
4Reliability
If conventional multipoles are positioned near the ion source, then ion guide functionality is achieved, but neutral species collisions with multipole rods increase and affect performance over time
Solution Approach 1:
The rod electrodes are positioned asymmetrically relative to the ion source, with larger spacing between the rods and the ion source compared to the spacing between opposing rods. This asymmetric configuration reduces the solid angle subtended by the rods as seen from the ion source, thereby reducing neutral species collisions while maintaining effective ion confinement
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 design provides a robust, efficient, and cost-effective RF ion guide with reduced dielectric charging and neutral species collisions, enabling effective ion confinement and separation, suitable for mass spectrometry applications including collisional cooling and ion fragmentation.
Implementation Method 1
RF ion guides, such as RF multipoles, are widely used in mass spectrometry in ion optical devices
Implementation Method 2
These ion guides typically consist of massive metal or resistive RF rods, usually of circular section, and different means to provide an additional DC distribution along the axis of the guide
Implementation Method 3
RF ion guides with additional axial fields have been developed for better control of ion motion
Data Source
AI summary
An ion guide for mass spectrometry comprising an electrode arrangement of at least two electrodes, at least one of which is an RF electrode, arranged adjacent to each other but spaced apart on a planar surface of a dielectric material and arranged at a distance from an ion flow path, wherein a portion of the dielectric surface is exposed between an adjacent pair of the spaced apart electrodes and wherein at least one electrode of said adjacent pair of electrodes is arranged to overhang the exposed portion of surface between them such that there is no direct line of sight from the ion flow path to the exposed portion of dielectric surface. The device enables RF guiding of ions accompanied by much reduced charging-up of dielectric surfaces and reduced amount of collisions of neutral species with electrodes.