Ion Guide for Mass Spectrometer Magnetic Field Introduction
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Solution Overview
Problem
Current ion cyclotron resonance mass spectrometry systems face challenges in accurately and efficiently introducing ions of a wide mass range into strong magnetic fields due to magnetic fringe field distortions and cyclotron frequency resonance issues, leading to incomplete ion capture and mass dispersion, especially for light ions.
Innovation Solution
The use of coaxial ring diaphragm ion guides connected alternately to RF voltages, with optional axial DC fields, to guide ions along the magnetic field lines, avoiding cyclotron motion excitation and enabling mass-selective extraction to ensure simultaneous arrival of ions at the measuring cell.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If ions are introduced into a strong magnetic field with a steep field increase, then the magnetic field strength is improved, but ion capture efficiency deteriorates due to fringe field reflections
Solution Approach 1:
An ion guide consisting of multipole rods (quadrupole, hexapole, or octopole) is introduced as an intermediary device between the ion source and the strong magnetic field. This ion guide creates a pseudopotential well that guides ions along the magnetic field lines through the steep field increase region, preventing fringe field reflections and enabling efficient ion capture in the measuring cell.
2Stability of the object's composition
If asymmetric distortions of the fringe field are present, then magnetic field homogeneity is improved, but ion injection capability deteriorates
Solution Approach 1:
The ion guide acts as a mediator that compensates for asymmetric fringe field distortions. By creating a controlled pseudopotential field through the multipole rods, the system can guide ions even when the fringe field is asymmetric, maintaining ion injection capability while preserving magnetic field homogeneity in the measuring cell.
Solution Approach 2:
RF voltages are applied alternately to the multipole rods to dynamically create and maintain the pseudopotential well. This dynamic application of voltages allows the ion guide to adapt to varying ion trajectories and fringe field conditions, maintaining effective ion guidance despite asymmetric distortions.
3Ease of operation
If cyclotron frequency resonance occurs with RF voltage applied to multipole rods, then ion guidance is improved, but light ion transport deteriorates
Solution Approach 1:
The system uses multipole rod configurations (quadrupole, hexapole, octopole) with different pole numbers to change the pseudopotential distribution parameters. By selecting appropriate multipole orders and adjusting RF voltage parameters, the system can guide ions of different masses effectively, including light ions, without resonant excitation problems.
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 true-to-quantity introduction of ions across a wide mass range into the measuring cell, reducing mass dispersion and improving ion capture efficiency, particularly for light ions, by aligning ion trajectories with the magnetic field and controlling pseudopotential distributions.
Implementation Method 1
In whose interior a radially focusing pseudopotential is produced
Implementation Method 2
The two phases of an RF voltage are applied alternately to the pole rods of the quadrupole system, in whose interior a radially focusing pseudopotential is produced
Implementation Method 3
an axial DC electric field to drive the ions forward
Implementation Method 4
The aim of the investigations is usually to determine the mass of the ions, which is obtained by measuring the circular cyclotron motions which an ion assumes after appropriate excitation
Implementation Method 5
measuring the circular cyclotron motions which an ion assumes
Implementation Method 6
all other ions injected either at a slight angle or slightly off-axis are reflected by the fringe field as if they were in a magnetic bottle
Data Source
AI summary
In a mass spectrometer that uses a space-restricted magnetic field, such as an ion cyclotron resonance mass spectrometer, ions with a wide mass range generated in an ion supply located outside the magnetic field are transported in the direction of the magnetic field lines to an ion storage device located inside the magnetic field without losing ions by guiding the ions through the region in which the magnetic field strength increases with a special ion guide. This ion guide consists of an arrangement of coaxial ring diaphragms which are alternately supplied with the phases of an RF voltage. In an alternative embodiment, the ion guide uses two wires wound in a double helix where each wire is supplied with one phase of a two-phase RF voltage.