RF Multipole Ion Guide for TOF MS Duty Cycle
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Solution Overview
Problem
Current mass spectrometry techniques face challenges in achieving high duty cycle efficiency and sensitivity over a wide range of mass-to-charge (m/z) values, particularly in Time-Of-Flight (TOF) Mass Spectrometry (MS), due to trade-offs between resolving power, sensitivity, and m/z range, and inefficient ion transport from atmospheric pressure to vacuum.
Innovation Solution
The use of a radio-frequency (RF) multipole ion guide with a configuration of RF and electrostatic fields to create a pseudo potential well for ion trapping and manipulation, allowing for improved ion storage, transport, and analysis by controlling ion trajectories and energy through a combination of RF and DC voltages, and integrated multipole ion guides for efficient ion transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If orthogonal pulse-acceleration is used to couple continuous ionization sources to TOF MS, then mass-to-charge resolving power greater than 10,000 FWHM can be achieved, but sensitivity and duty cycle efficiency are reduced due to trade-offs between angular and spatial distributions of sampled ions
Solution Approach 1:
Ions are pre-cooled and pre-focused in the ion guide before being pulsed into the TOF analyzer. This preliminary cooling and focusing action allows ions to be bunched into tight packets with reduced kinetic energy spread, enabling high resolving power while maintaining high duty cycle efficiency by analyzing continuous ion beams without sacrificing angular or spatial distributions.
Solution Approach 2:
The ion guide acts as an intermediary device between the continuous ionization source and the pulsed TOF analyzer. It provides a transition region where continuous ion beams are transformed into pulsed, cooled, and focused ion packets, resolving the contradiction between continuous ion production and pulsed analysis requirements.
2Adaptability or versatility
If the repetition rate is reduced to accommodate long flight times of high-m/z ions, then m/z range is extended, but duty cycle efficiency decreases
Solution Approach 1:
Ions are pre-cooled and pre-bunched in the ion guide before being pulsed into the TOF analyzer. This preliminary action allows ions of different m/z values to be prepared in advance, enabling the system to maintain high repetition rates even when analyzing high-m/z ions with long flight times, thus preserving duty cycle efficiency while extending m/z range.
3Productivity
If a multipole ion guide with electrostatic electrode is used to trap and store ions, then duty cycle efficiency approaches 100% for selected m/z range, but duty cycle decreases for m/z values outside the selected range due to m/z separation
Solution Approach 1:
The patent replaces the electrostatic field-based ion trapping mechanism with a radio-frequency (RF) field-based trapping mechanism. The RF ion guide uses time-varying electromagnetic fields rather than static electrostatic fields to confine and manipulate ions. This substitution allows for dynamic control of ion trajectories and energy without the m/z separation limitations of electrostatic fields, enabling high duty cycle efficiency across a broader m/z range.
4Quantity of substance
If continuous ion beams are transferred into a three-dimensional RF-quadrupole ion trap, then ion accumulation is achieved, but duty cycle is reduced because ions can only overcome RF fields during a short segment of the RF cycle time
Solution Approach 1:
The patent replaces the three-dimensional RF-quadrupole ion trap with a linear RF ion guide configuration. Instead of using a quadrupole field that requires ions to overcome RF barriers during specific phases, the linear RF guide uses a continuous RF field along the ion transport path, allowing continuous ion loading without duty cycle limitations while still achieving ion accumulation through controlled potential wells.
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 TOF MS duty cycle efficiency and resolving power over a broader m/z range, improves ion transport efficiency from atmospheric pressure to vacuum, and enables more effective ion manipulation and analysis, including fragmentation and reaction capabilities.
Implementation Method 1
The use of a radio-frequency (RF) multipole ion guide with a configuration of RF and electrostatic fields to create a pseudo potential well for ion trapping and manipulation
Implementation Method 2
controlling ion trajectories and energy through a combination of RF and DC voltages
Implementation Method 3
The application of electric fields, and in particular the combination of radio-frequency (RF) and direct current (DC) voltages to ion guides and ion trapping surfaces
Implementation Method 4
Ions are cooled by collisional damping with background gas molecules
Implementation Method 5
improves ion transport efficiency from atmospheric pressure to vacuum
Implementation Method 6
The application of electric fields, and in particular the combination of radio-frequency (RF) and direct current (DC) voltages to ion guides
Data Source
AI summary
Apparatus and methods are provided for trapping, manipulation and transferring ions along RF and DC potential surfaces and through RF ion guides. Potential wells are formed near RF-field generating surfaces due to the overlap of the radio-frequency (RF) fields and electrostatic fields created by static potentials applied to surrounding electrodes. Ions can be constrained and accumulated over time in such wells. During confinement, ions may be subjected to various processes, such as accumulation, fragmentation, collisional cooling, focusing, mass-to-charge filtering, spatial separation ion mobility and chemical interactions, leading to improved performance in subsequent processing and analysis steps, such as mass analysis. Alternatively, the motion of ions may be better manipulated during confinement to improve the efficiency of their transport to specific locations, such as an entrance aperture into vacuum from atmospheric pressure or into a subsequent vacuum stage.