Off-Axis Electron Beam Ion Source for Stable Mass Spectrometry
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Solution Overview
Problem
The sensitivity of mass spectrometers is limited by the efficiency of the ion source, ion losses, and detector sensitivity, necessitating improved ion sources for enhanced detection limits and stability.
Innovation Solution
An ion source configuration including an electron generator, ionization chamber, magnetic field, and ion optic, where the electron beam is directed off-axis to reduce charging near the ion exit aperture, increasing ion production and stability through chemical ionization and electron dispersion mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If electrons are directed axially through the ionization chamber, then ion production efficiency is improved, but charging accumulates near the ion exit aperture causing ion losses
Solution Approach 1:
The electron beam is deliberately offset from the chamber axis by approximately 0.5 mm, creating an asymmetric configuration where electrons traverse a diagonal path through the ionization chamber. This asymmetry prevents direct axial accumulation of charging at the ion exit aperture while maintaining effective ionization throughout the chamber volume, thereby resolving the contradiction between ion production efficiency and ion losses from charging.
Solution Approach 2:
The electron beam trajectory is shifted from the one-dimensional axial path to a two-dimensional diagonal path through the ionization chamber. This dimensional change allows electrons to ionize analyte molecules effectively while avoiding direct convergence at the ion exit aperture, thus preventing charging accumulation and associated ion losses.
2Productivity
If electrons are directed axially through the ionization chamber, then ionization efficiency is improved, but stability deteriorates due to charging accumulation
Solution Approach 1:
The asymmetric offset of the electron beam (approximately 0.5 mm from the chamber axis) prevents direct axial accumulation of charging at the ion exit aperture. This asymmetric configuration maintains stable ionization efficiency over time by eliminating the charging buildup that would otherwise cause drift and instability in ion source performance.
3Device complexity
If an on-axis electron beam is used, then device complexity is reduced, but ion losses increase due to charging near the exit aperture
Solution Approach 1:
The electron beam configuration is modified from a simple on-axis arrangement to an off-axis configuration with approximately 0.5 mm offset. This relatively simple asymmetric adjustment effectively prevents charging accumulation and ion losses without requiring complex additional components or mechanisms.
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 ion production and stability, improving detection limits and enabling quantitative comparisons by reducing ion losses and charging, thus increasing the sensitivity of mass spectrometers.
Implementation Method 1
The magnetic field can be arranged to confine electrons in a beam directed through the electron entrance aperture, in a direction within 45 degrees of parallel to the axis, and towards a location displaced from the ion exit aperture
Implementation Method 2
The ionization chamber can be configured to produce ions by chemical ionization
Implementation Method 3
The ion optic can be configured to direct ions exiting the ion exit aperture in an ion beam along the axis
Data Source
AI summary
An ion source includes an electron generator, an ionization chamber, and a magnetic field. The electron generator is configured to produce electrons. The ionization chamber has an electron entrance aperture through a first wall, an ion exit aperture through a second wall, and an axis. The ionization chamber is configured to produce ions. The magnetic field is arranged to confine electrons in a beam directed through the electron entrance aperture, in a direction within 45 degrees of parallel to the axis, and towards a location displaced from the ion exit aperture.