Segmented Ion-Optical Lens for Time-of-Flight Mass Spectrometers
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Solution Overview
Problem
Current time-of-flight mass spectrometers with stationary sample supports face limitations in scanning large areas due to non-uniform movement and oscillations, restricting mass resolution and efficiency in acquiring mass spectra, especially for high-density samples like tissue samples.
Innovation Solution
The method involves subdividing ion-optical lenses into segments with independently adjustable voltages to deflect the desorption beam and adjust the focusing center, allowing ions off-axis to be accelerated in phase and focused into a parallel beam, enabling efficient scanning of larger areas without phase shifts and maintaining high mass resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the laser spot is deflected from the axis to scan large areas, then the scanning area is improved, but the mass resolution deteriorates due to phase shifts in ion acceleration
Solution Approach 1:
The ion-optical lens is divided into multiple independently controllable segments (e.g., 4 quadrants or 8 octants). Each segment can be adjusted individually to create a virtual focusing center that tracks the deflected laser spot position, allowing large area scanning while maintaining mass resolution by ensuring ions are always focused through the correct virtual center point.
Solution Approach 2:
The voltages applied to the lens segments are dynamically adjusted in real-time based on the laser spot position. As the laser spot moves across the sample, the lens segments are reconfigured to shift the virtual focusing center accordingly, maintaining optimal ion focusing conditions throughout the scanning area and preventing phase shifts that would degrade mass resolution.
2Area of stationary object
If the sample support is moved to scan large areas, then the scanning area is improved, but the stability deteriorates due to non-uniform movement and oscillations
Solution Approach 1:
The mechanical sample support movement system is replaced with an optical beam deflection system. Instead of physically moving the heavy sample support plate (which causes oscillations and non-uniform movement), a fast mirror or galvanometer deflects the laser spot across the stationary sample, achieving large area scanning with high speed and stability while eliminating mechanical instability.
Solution Approach 2:
The system changes from mechanical position control to optical parameter control. By adjusting the deflection angles and positions of optical elements (mirrors, beam splitters), the laser spot can be rapidly repositioned across the sample without any physical movement of the sample support, achieving both large scanning area and high stability simultaneously.
3Productivity
If the laser shot frequency is increased to improve productivity, then the acquisition rate is improved, but the time for position control is reduced
Solution Approach 1:
The mechanical position control system is replaced with an optical deflection system that can change laser spot position virtually instantaneously. Galvanometer mirrors or acousto-optic deflectors can reposition the laser spot in microseconds, matching the high laser shot frequency (10,000 shots/second) without becoming a limiting factor, thus maintaining both high productivity and adequate position control time.
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 the acquisition of mass spectra over larger areas with improved mass resolution and reduced oscillation-induced losses, enabling efficient analysis of high-density samples by shifting the effective focusing center and compensating for deflection-induced energy differences in ions, thus enhancing scanning efficiency and resolution.
Implementation Method 1
pulsed ionization of a sample deposited on a sample support in an ion source using a desorption beam, e.g. a laser beam (for MALDI in particular)
Implementation Method 2
or a primary ion beam (for SIMS in particular)
Implementation Method 3
acceleration of ions onto a flight path by means of diaphragms which act as ion-optical lenses, where at least one of the diaphragms is subdivided into a plurality of segments and the segments are supplied with asymmetrical voltages
Implementation Method 4
at least one of the diaphragms is subdivided into a plurality of segments (e.g. halves, quadrants, or octants) and the segments are supplied with asymmetrical voltages... such that ions which are produced in a desorption beam spot off axis are accelerated in phase into an ion beam by a lens center off the axis
Data Source
AI summary
The invention relates to time-of-flight mass spectrometers with pulsed ionization of samples, for example by matrix-assisted laser desorption (MALDI), where the samples are located on a sample support and are irradiated and ionized one after the other in a grid by a position-controlled desorption beam. An ion-optical puller lens arrangement is positioned in front of the sample support, with at least one of the lens diaphragms in the arrangement being subdivided into segments, and a voltage supply being able to supply the segments, or some of them, with different voltages, depending on the impact position of the desorption beam on the support plate. It is then possible to virtually shift the effective ion-optical focusing center of the lens away from the axis, and to focus an ion beam, which is generated off the real lens axis, into a beam which runs essentially parallel to the real lens axis, with no time phase shift for ions of the same mass. This beam can be brought back onto the axis by an x/y deflection unit, for example for operating the time-of-flight mass spectrometer with a reflector.