Laser Ion Source Asymmetry for Mass Spectrometry Contamination
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Solution Overview
Problem
Mass spectrometry systems using laser desorption/ionization face contamination issues due to neutral molecules and matrix deposits, leading to decreased sensitivity and resolution over time, particularly in high-throughput applications.
Innovation Solution
An ion source with a sample plate positioned at an angle relative to the mass analyzer's ion optical axis and laser pulses striking at an angle, combined with an electric field, is used to direct analyte ions into the mass analyzer while minimizing the entry of neutral contaminants by optimizing the distance between the sample plate and the inlet aperture, leveraging gas drag and electric field forces to separate ions from neutrals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the sample plate is positioned close to the inlet aperture to maximize ion transmission, then ion detection sensitivity is improved, but neutral contaminants are drawn into the mass analyzer causing deposits and performance degradation
Solution Approach 1:
The sample plate is positioned at an asymmetric angle (e.g., 45 degrees) relative to the ion optical axis, creating an asymmetric plume geometry where the plume center is directed away from the inlet aperture. This asymmetric configuration allows ions to be extracted effectively while neutral contaminants are directed away from the sensitive regions of the mass analyzer
Solution Approach 2:
The problem is solved by adding a spatial dimension - tilting the sample plate in the vertical dimension relative to the horizontal ion optical axis. This creates a three-dimensional plume structure where the plume center is offset from the inlet aperture path, allowing separation of ion transmission from neutral contaminant entry
2Object-affected harmful factors
If the sample plate is positioned far from the inlet aperture to reduce neutral contaminant entry, then contaminant deposits are reduced, but ion transmission efficiency decreases
Solution Approach 1:
By positioning the sample plate at an angle and optimizing the distance, the plume geometry becomes asymmetric with the center directed away from the inlet. This allows the plate to be positioned farther from the aperture without sacrificing ion transmission, as ions are still effectively extracted along the optical axis while neutrals are directed away
3Power
If laser pulses strike the sample at normal incidence to maximize ion production, then ion generation efficiency is improved, but plume direction cannot be controlled to avoid contaminants
Solution Approach 1:
The laser pulses strike the tilted sample plate at an angle, creating an asymmetric plume that is directed away from the inlet aperture. The angle of incidence is optimized to balance ion generation efficiency with plume direction control, ensuring the plume center does not intersect with the inlet region
Solution Approach 2:
By tilting the sample plate, the problem is moved from a one-dimensional (normal incidence) to a three-dimensional configuration. The laser still effectively ionizes the sample, but the plume is now directed in a different spatial dimension, away from the inlet aperture path
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 significantly reduces contamination, maintaining high sensitivity and resolution over a large number of samples, with experiments showing a 50% signal reduction after 200,000 samples compared to 30,000 samples in prior art systems, and reduces the need for frequent cleaning.
Implementation Method 1
a laser configured to generate laser pulses striking at least a portion of the sample. Upon laser desorption, a plume that can contain analyte ions of the sample and neutral contaminants is produced
Implementation Method 2
an electric field is applied to draw analyte ions into the inlet region of the mass analyzer
Implementation Method 3
gas drag forces resulting from the pressure difference between the ion source and the mass analyzer result in the effect of such gas drag forces being considerably reduced so as not to draw a substantial proportion of the neutral contaminants through the inlet aperture
Data Source
AI summary
An apparatus and method is disclosed for reducing contamination in a mass spectrometer instrument system. The system includes an ion source at a first pressure for generating ions by laser desorption/ionization and an inlet aperture to a vacuum chamber at a second, lower pressure than the first pressure of the ion source. A sample plate within the ion source supports a sample deposited thereon and a laser can be configured to generate laser pulses striking at least a portion of the sample at an angle of incidence from about 0 to about 80 degrees to the center line of a first ion optical axis of a mass analyzer, producing a plume. A combination of the angle of incidence of the laser pulses and the distance between the sample plate and the inlet region aperture can reduce neutral contaminants in the plume from being drawn into the inlet aperture.