Collision Cell Geometry for Mass Spectrometer Pressure Control
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Solution Overview
Problem
Mass spectrometer systems face challenges in managing gas pressures and gas flow, particularly in collision-induced-fragmentation cells, where high internal pressures are needed for efficient ion fragmentation, but conventional designs struggle to attain optimal pressures while minimizing gas flow and preventing collision gas from entering other components.
Innovation Solution
The design of collision cells with specific geometries, including a gas containment vessel with a central chamber and gas outlet apertures, optimized to reduce combined gas conductance to less than 95% of the apertures' conductance, exploiting the phenomenon of Lambertian reflection to increase internal pressure while minimizing gas flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If conventional collision cell designs are used, then gas flow is minimized and vacuum pump burden is reduced, but internal pressure cannot reach optimal levels for efficient ion fragmentation
Solution Approach 1:
The patent changes the geometric parameters of the collision cell, specifically optimizing the ratio of chamber cross-sectional area to aperture cross-sectional area and adjusting chamber length, to control gas conductance and achieve optimal internal pressure for ion fragmentation while managing gas flow
2Productivity
If high internal pressure is achieved in collision cells, then ion fragmentation is enhanced, but collision gas may enter other mass spectrometer components
Solution Approach 1:
The patent applies different geometric characteristics to different parts of the collision cell system - the chamber has optimized dimensions for pressure buildup while the apertures are sized and positioned to control gas flow direction, creating local quality variations that simultaneously achieve high internal pressure and prevent gas leakage to other components
Solution Approach 2:
The patent controls gas flow by managing the three-dimensional geometry of the chamber and apertures, using spatial arrangement and dimensional relationships (area ratios, length-to-diameter ratios) to direct gas flow patterns that contain collision gas within the chamber while allowing ion transmission
3Stress or pressure
If chamber volume is increased to maintain pressure, then gas conductance increases and pressure control becomes difficult, but smaller chambers cannot achieve optimal pressure levels
Solution Approach 1:
The patent creates an asymmetric relationship between chamber volume and aperture size, optimizing the ratio of chamber cross-sectional area to aperture cross-sectional area to be greater than 10:1, which allows the chamber to maintain pressure effectively while the small aperture restricts gas conductance and flow
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 allows for higher internal pressures in collision cells, enhancing ion fragmentation during tandem mass spectrometry while reducing the burden on vacuum pumps and minimizing collision gas entry into other mass spectrometer components.
Implementation Method 1
exploiting the phenomenon of Lambertian reflection to increase internal pressure while minimizing gas flow
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
A mass spectrometer collision cell system, comprising: a gas containment vessel comprising an internal chamber having ion inlet and ion outlet ends and a cross-sectional area, Achamber; a gas inlet aperture; first and second gas outlet apertures that are disposed at or proximal to the ion inlet and outlet ends, respectively, and that have respective outlet aperture cross-sectional areas, Aaperture1 and Aaperture2, and an average outlet aperture cross-sectional area, Aapertureave, a longitudinal axis of the chamber extending from the ion inlet end to the ion outlet end and having a length, Lchamber; and a set of multipole rod electrodes, at least a portion of each multipole rod electrode being within the chamber, wherein the values of Achamber, Lchamber and Aapertureave are such that the combined gas conductance of the chamber and the gas outlet apertures is not greater than 95 percent of the gas conductance of the gas outlet apertures alone