Low-Pressure Electron Ionization Mass Spectrometry Source
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Solution Overview
Problem
Conventional high-pressure chemical ionization (CI) sources in mass spectrometry are limited by contamination, restricted reagent gas choices, and reduced ionization yield due to high pressure, while internal ionization at low-pressure ion traps requires heating the entire electrode assembly, leading to inaccurate spectral data and increased operational complexity.
Innovation Solution
Implementing low-pressure electron ionization (EI) and CI by flowing a sample and reagent gas into an ion source at pressures below 0.1 Torr, where the reagent gas is ionized to produce reagent ions that react with the sample, and the resulting product ions are transmitted to an ion trap for mass analysis, allowing for efficient ionization without heating the ion trap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If high-pressure CI is used in external ion sources, then ionization can be achieved, but contamination increases due to pyrolysis of reagent gas at high temperature
Solution Approach 1:
The patent changes the pressure parameter from conventional high pressure (1-5 Torr) to low pressure (10^-3 to 10^-6 Torr) in the ion source. This parameter change allows the ion source to be kept at lower temperature while maintaining ionization capability, thereby preventing pyrolysis of reagent gas and reducing contamination in the filament area.
Solution Approach 2:
The patent creates a vacuum environment (inert atmosphere) in the ion source by maintaining low pressure. This vacuum environment prevents unwanted chemical reactions and pyrolysis of reagent gas, reducing contamination while still allowing controlled chemical ionization to occur when reagent gas is introduced.
2Ease of manufacture
If high-pressure CI is used, then ionization can be achieved, but the choice of reagent gases is restricted
Solution Approach 1:
By changing the pressure parameter to low pressure conditions, the patent expands the range of suitable reagent gases. Gases that would condense or react undesirably at high pressure can now be used at low pressure, increasing versatility in reagent gas selection while maintaining ionization capability.
3Ease of manufacture
If high-pressure CI is used, then ionization can be achieved, but ionization yield is reduced due to limited residence time
Solution Approach 1:
The patent changes the pressure parameter to low pressure, which reduces gas flow rate and increases the residence time of sample molecules in the ionization region. This allows more time for reactions between sample molecules and reagent ions, thereby increasing ionization yield while maintaining ionization capability.
Solution Approach 2:
The low pressure environment allows for continuous interaction between sample molecules and reagent ions over an extended period. The reduced gas flow rate ensures that sample molecules remain in the ionization region long enough to undergo complete ionization reactions, maximizing the continuity and effectiveness of the ionization process.
4Stress or pressure
If internal ionization at low-pressure ion traps is used, then pressure is reduced, but the entire electrode assembly must be heated to prevent sample condensation
Solution Approach 1:
The patent segments the mass spectrometer into two distinct pressure regions: an external ion source at low pressure and an ion trap at very low pressure. This segmentation allows the ion source to be heated for ionization without requiring the ion trap electrodes to be heated, preventing sample condensation on electrodes while maintaining low pressure conditions.
Solution Approach 2:
The patent introduces an intermediary component - the external ion source - that performs the heating and ionization function separately from the ion trap. This intermediary allows the ion trap to remain cool and at low pressure while still achieving efficient ionization of samples through the external source, avoiding the need to heat the entire electrode assembly.
5Stress or pressure
If internal ionization at low-pressure ion traps is used, then pressure is reduced, but spectral accuracy decreases due to sample adsorption on electrodes
Solution Approach 1:
By segmenting the system into an external ion source and an ion trap, the patent prevents sample adsorption on ion trap electrodes. The ionization occurs in the external source where samples are already ionized, so neutral sample molecules that could adsorb on cold electrodes are minimized, thereby maintaining spectral accuracy while operating at low pressure.
Solution Approach 2:
The external ion source acts as an intermediary that performs ionization before samples enter the ion trap. This ensures that most sample molecules are already ionized when they enter the ion trap region, reducing the amount of neutral sample that could adsorb on electrodes and compromise spectral accuracy, while maintaining the benefits of low pressure operation.
6Temperature
If external ion sources are used, then ion trap heating is avoided, but high pressure operation increases contamination
Solution Approach 1:
The patent changes the pressure parameter in the external ion source from conventional high pressure to low pressure. This allows the ion source to operate at lower temperature without causing pyrolysis of reagent gas, thereby reducing contamination while still achieving effective ionization. The ion trap remains at low temperature and low pressure, avoiding both contamination and the need for heating.
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 reduces contamination, increases the choice of reagent gases and reaction pathways, enhances ionization yield, and maintains the ion trap at a lower temperature, preventing sample condensation and adsorption, thus improving spectral accuracy and simplifying operation.
Implementation Method 1
a beam of energetic electrons is formed by emission from a suitable filament and accelerated by a voltage potential (typically 70 V) into the ion source to bombard the sample molecules
Implementation Method 2
The sample is then ionized by collisions between the resulting reagent ions and the sample
Data Source
AI summary
A sample is ionized by chemical ionization by flowing the sample and a reagent gas into an ion source at a pressure below 0.1 Torr. While maintaining the ion source at a pressure below 0.1 Torr, the reagent gas is ionized in the ion source by electron ionization to produce reagent ions. The sample is reacted with the reagent ions at a pressure below 0.1 Torr to produce product ions of the sample. The product ions are transmitted into an ion trap for mass analysis.