Time of Flight Mass Analyzer Ion Guide Radial Confinement
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Solution Overview
Problem
The existing Time of Flight mass analyzers suffer from low ion transmission efficiency due to poor radial confinement of ions, significant initial velocity and position spreads leading to poor resolution, and are limited to operating with Electron Impact ion sources at low pressure, not accommodating atmospheric pressure ionization.
Innovation Solution
The implementation of a Time of Flight mass analyzer with a multipole rod set, ion tunnel, or segmented electrodes, utilizing RF and DC voltages to create radial pseudo-potentials and axial electric fields that confine and propel ions, enabling improved radial confinement and mass separation across a wider range of pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a known reflectron Time of Flight mass analyser is used, then the mass analysis function is provided, but ion transmission efficiency is low due to poor radial confinement of ions
Solution Approach 1:
A buffer gas is introduced as an intermediary medium between the ions and the vacuum environment. The buffer gas molecules collide with ions to provide radial confinement through gas kinetic pressure, enabling effective ion guidance without direct contact with physical walls or electrodes that would cause ion loss.
Solution Approach 2:
The patent employs a pneumatic approach by using buffer gas flow to create a virtual wall effect. The gas pressure gradient and flow dynamics provide radial confinement forces on ions, replacing traditional mechanical or electrostatic confinement structures.
2Measurement precision
If a known reflectron Time of Flight mass analyser is used, then the mass analysis function is provided, but resolution is poor due to large spread of initial velocities and initial positions of ions
Solution Approach 1:
Ions undergo preliminary cooling and velocity matching through collisions with buffer gas molecules before entering the flight region. This preliminary thermalization reduces the spread of initial velocities and positions, improving resolution without requiring complex ion source modifications.
Solution Approach 2:
The buffer gas pressure and flow rate are optimized to achieve optimal ion cooling and velocity matching. By adjusting these parameters, the system balances ion confinement effectiveness with velocity spread reduction, thereby improving mass resolution.
3Adaptability or versatility
If a known reflectron Time of Flight mass analyser is used, then operation with Electron Impact ion source is enabled, but operation with atmospheric pressure ionisation ion source is not possible
Solution Approach 1:
The mass analyser is designed with universal compatibility for multiple ion source types by incorporating a buffer gas system that can handle both vacuum and atmospheric pressure conditions. The same analytical chamber and detection system work with both Electron Impact and atmospheric pressure ionisation sources.
Solution Approach 2:
The system allows dynamic adjustment of buffer gas pressure to match the operating conditions of different ion sources. For Electron Impact, the pressure is maintained at vacuum levels, while for atmospheric pressure ionisation, the buffer gas pressure is increased to enable operation at atmospheric conditions.
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 transmission efficiency, improves mass resolution, and allows the mass analyzer to operate with atmospheric pressure ionization sources, effectively addressing the limitations of existing systems.
Implementation Method 1
A RF voltage and a static DC voltage are applied across the ends of the potential divider or resistor chain so that a static axial DC voltage gradient and an inhomogenous axial RF voltage are maintained along the length of the mass analyser
Implementation Method 2
The axial electric field which is maintained along the length of the mass analyser is such that it propels ions in an axial direction through the mass analyser
Implementation Method 3
The time of flight of the ions from the time that the voltage pulse is applied to the acceleration grid to the subsequent detection of the ions by the ion detector is related to the mass to charge ratio of the ions and the field parameters within the Time of Flight mass analyser
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
A mass spectrometer is disclosed comprising a time of flight mass analyser (7). The time of flight mass analyser (7) comprises an ion guide comprising a plurality of electrodes (1) which are interconnected by. a series of resistors (2) forming a potential divider. Ions are confined radially within the ion guide by the application of a two-phase RF voltage to the electrodes (1). A single phase additional RF voltage is applied across the potential divider so that an inhomogeneous pseudo-potential force is maintained along the length of the ion guide.