Magnetic Electron Guidance for Ionization Efficiency
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Solution Overview
Problem
Current electron impact ion sources for mass spectrometers, particularly in benchtop GCMS instruments, face inefficiencies in ionization due to limited ionization areas and the need for high electron emission currents, which can lead to filament deformation and space charge issues, making them unsuitable for small, high-efficiency applications.
Innovation Solution
The electron impact ion source employs a counter flow arrangement where electrons enter the gas beam head-on, with a portion being slowed and scattered, allowing unreacted electrons to interact with gas molecules multiple times, increasing ionization efficiency while avoiding magnetic traps and space charge issues by using the far fringe field of a magnet for electron guidance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high electron emission currents are used to improve ionization efficiency, then ionization efficiency is improved, but filament deformation and space charge issues occur
Solution Approach 1:
The invention transitions from a single-pass linear electron path to a multi-dimensional spiral trajectory using magnetic fields. Electrons spiral around magnetic field lines, increasing their path length and interaction opportunities with sample molecules without requiring higher electron currents, thus maintaining filament stability while improving ionization efficiency.
Solution Approach 2:
The magnetic field configuration creates a continuous spiral electron path that maximizes the utilization of each electron through multiple passes around the ionization region. This continuous action allows electrons to interact with sample molecules repeatedly, improving ionization efficiency without increasing electron emission current.
2Productivity
If a solenoid magnet is used to confine electrons into the jet area, then ionization efficiency is improved, but large current requirements and heat management complications arise
Solution Approach 1:
The invention extracts only the essential function of electron confinement from the solenoid magnet system. Instead of using a full solenoid, it employs a simplified magnet assembly with permanent magnets arranged to create the necessary magnetic field geometry, eliminating unnecessary complexity and heat generation while maintaining electron confinement.
Solution Approach 2:
The invention replaces expensive, high-power electromagnet systems with simpler permanent magnet assemblies. This substitution reduces power consumption, eliminates cooling requirements, and simplifies the overall system while achieving the same electron confinement function.
3Productivity
If electrons are accelerated toward the axis where the field is denser, then electron confinement is improved, but a magnetic trap is created leading to space charge issues
Solution Approach 1:
Instead of creating a magnetic trap that accumulates electrons, the invention inverts the approach by using magnetic field lines to guide electrons through a continuous spiral path that exits the interaction region. This prevents electron accumulation by ensuring electrons continuously flow through rather than being trapped in the magnetic field.
Solution Approach 2:
The magnetic field configuration is designed to be dynamic in its action on electrons, creating a spiral trajectory that continuously changes the electron path. This dynamic field geometry ensures electrons remain confined to the ionization region during their passage while maintaining forward momentum and preventing accumulation.
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 enhances ionization efficiency by utilizing electrons more effectively and preventing electron accumulation, making it suitable for small, high-efficiency applications in benchtop GCMS instruments without the need for large magnetic fields or complex cooling systems.
Implementation Method 1
The magnet assembly (46, 47, 48) generates a magnetic field that causes electrons to spiral along magnetic field lines
Implementation Method 2
a magnet assembly comprising two magnets (46) and (47) and a magnetic yoke (48) guides the electrons
Implementation Method 3
The EI source uses a filament assembly (42) with a straight filament that generates electrons
Implementation Method 4
electrons are accelerated to typically seventy electron volts toward the ionization region where they collide with sample molecules and ionize
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The invention relates to a mass spectrometer having an electron impact ionization source which comprises an ejector for forming a beam of sample gas being driven in a first direction through an interaction region; a magnet assembly configured and arranged such that its magnetic field lines pass through the interaction region substantially parallel to the first direction; an electron emitter assembly for directing electrons toward the interaction region in a second direction being aligned substantially opposite to the first direction, wherein the electrons propagate along and are confined about the magnetic field lines until reaching the interaction region and forming sample gas ions therein; and a mass analyzer located downstream from the interaction region to which the sample gas ions are guided for mass analysis.