Tubular Ion Guide with Offset Electrodes for High-Pressure Confinement
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Solution Overview
Problem
Conventional ion guides face challenges in efficiently focusing and confining ions from a diffuse source without increasing RF voltage, and they suffer from gas streaming and contaminant issues, especially when dealing with high-pressure gases and mixed gas-ion streams.
Innovation Solution
A tubular or mesh ion guide with offset electrodes and a combination of DC and RF voltages is used to create a radial potential well, preventing ions from striking the electrodes and allowing orthogonal extraction, thereby focusing and confining ions effectively while minimizing gas streaming and contaminant transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the ion guide is operated at a relatively high pressure, then collisional cooling reduces ion radial density distribution, but this requires increased RF voltage to maintain ion confinement
Solution Approach 1:
The patent changes the operational parameters by operating the ion guide at relatively high pressure (e.g., 1-100 mbar) to enable collisional cooling of ions. This pressure regime allows gas molecules to thermalize ion kinetic energy through collisions, reducing ion radial density distribution without requiring proportionally increased RF voltage as would be needed in vacuum conditions
2Area of stationary object
If the ion guide radius is increased to capture ions from a diffuse source, then ion capture efficiency improves, but the RF voltage must be increased in proportion to the square of the radius
Solution Approach 1:
The patent operates at elevated gas pressure to enable collisional cooling, which modifies the ion dynamics and allows for reduced RF voltage requirements. This parameter change (pressure) decouples the relationship between ion guide radius and RF voltage, enabling larger aperture ion guides to capture diffuse ion sources without the RF voltage increasing proportionally to the square of the radius
Solution Approach 2:
The patent utilizes gas pressure (pneumatics) as a medium to achieve collisional cooling of ions. By introducing a controlled pressure of background gas into the ion guide, the gas molecules act as a thermalizing medium that reduces ion kinetic energy through collisions, thereby enabling ion confinement with reduced RF voltage requirements in larger aperture guides
3Productivity
If a direct line of sight is provided between ion entrance and exit apertures, then ion transmission efficiency improves, but gas streaming increases pumping requirements
Solution Approach 1:
The patent operates at relatively high pressure (1-100 mbar) where the mean free path of gas molecules is short compared to the ion guide dimensions. This pressure regime enables ions to be guided through the aperture while gas molecules undergo frequent collisions that randomize their trajectories, allowing the ion guide to maintain ion transmission efficiency without requiring a direct line of sight, thereby reducing gas streaming effects
4Reliability
If neutral species or droplets are present in the gas-ion mixture, then they pass through the ion guide and contaminate subsequent vacuum chambers, but filtering them out reduces ion transmission
Solution Approach 1:
The patent utilizes gas pressure and collisional dynamics to separate ions from neutral species and droplets. At the operating pressure (1-100 mbar), ions undergo collisional cooling and are confined by the ion guide fields, while neutral species and droplets follow different trajectories due to their lack of charge and different interaction cross-sections with the background gas, allowing selective transmission of ions while filtering out contaminants
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 enables efficient focusing and confinement of ions from a diffuse source without excessive voltage requirements, reduces gas streaming, and minimizes contaminant build-up in subsequent vacuum chambers, improving the overall performance of mass spectrometry systems.
Implementation Method 1
A known multipole rod set ion guide comprises four, six or eight parallel rods which are equi-spaced about a circular circumference. Opposite phases of a two-phase RF voltage are applied to adjacent rods. The RF voltage applied to the rods generates a symmetrical pseudo-potential well within the ion guide which acts to confine ions radially within the ion guide.
Implementation Method 2
A DC and/or AC or RF voltage may be applied to the upper and lower planar electrodes in order to confine ions within the ion guide.
Implementation Method 3
If the ion guide is operated at a relatively high pressure then the ion radial density distribution may also be reduced due to the effect of collisional cooling wherein ions lose kinetic energy after colliding with gas molecules.
Implementation Method 4
A DC and/or AC or RF voltage may be applied to the upper and lower planar electrodes in order to confine ions within the ion guide.
Implementation Method 5
The preferred embodiment relates to an ion guide or ion transport device which preferably uses a combination of a DC voltage and an AC or RF voltage in order to focus and/or transport ions through the ion guide or ion transport device
Data Source
AI summary
A mass spectrometer is disclosed comprising an ion guide. The ion guide comprises a hollow tubular conductor having a wall. One or more electrodes are provided in the wall of the tubular conductor. An exit aperture is provided in the wall of the tubular conductor downstream of the one or more electrodes. An AC or RF voltage is applied to the one or more electrodes and a DC potential difference is maintained between the wall of the tubular conductor and the one or more electrodes. The combination of a DC voltage gradient and applying an AC or RF voltage to the electrodes is that ions are confined radially to a region which is preferably close to the one or more electrodes. Ions are preferably extracted from the ion guide via the exit aperture.