Closed EI Ion Source with Isothermal Shroud for Fast Response
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Solution Overview
Problem
Current Electron Impact ion sources for Time-of-flight mass spectrometers face limitations in sensitivity, immunity to chemical noise, and response time, particularly in GCxGC-TOF analysis, with detection limits around 0.1-1 pg and significant ion losses during transfer interfaces.
Innovation Solution
The proposed solution involves a 'closed' EI source with isothermal design using heat conductive materials, reduced ionization chamber size, molecular separators within the vacuum chamber, electrostatic ion focusing, and tilted ion packet steering to enhance sensitivity and response time, while minimizing chemical noise and ion losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a continuous closed EI source is used, then immunity to chemical noise is improved, but response time deteriorates
Solution Approach 1:
The patent implements periodic pulsed extraction of ions from the continuous closed EI source. The extraction occurs in synchronized pulses with the GCxGC elution peaks, allowing the source to accumulate ions continuously while ejecting them in rapid pulses that match the short chromatographic peaks. This periodic action resolves the contradiction by maintaining the continuous operation benefits for chemical noise immunity while achieving fast response through pulsed ejection.
Solution Approach 2:
The patent performs preliminary ion accumulation within the closed source before ejection. Ions are continuously generated and stored in the ion accumulation region during the interval between chromatographic peaks, then rapidly ejected when a peak arrives. This preliminary accumulation allows the system to be ready for rapid response without sacrificing the continuous operation benefits for chemical noise reduction.
2Speed
If an open EI source with pulsed axial injection is used, then response time is improved, but immunity to chemical noise deteriorates
Solution Approach 1:
The patent introduces an intermediary closed ion accumulation chamber between the continuous electron beam and the TOF MS. This closed source acts as a mediator that shields the ionization process from chemical noise in the vacuum chamber while still allowing rapid ejection of ions to TOF MS. The intermediary structure provides the benefits of both closed and open source configurations.
3Reliability
If orthogonal acceleration is used after closed EI source, then immunity to chemical noise is improved, but ion losses increase
Solution Approach 1:
The patent replaces the traditional orthogonal acceleration interface with direct pulsed extraction of ions along the electron beam axis. Instead of using complex orthogonal acceleration mechanics that cause spatial ion losses, the system uses electrostatic fields to directly extract and accelerate ions along the existing beam path. This substitution eliminates the mechanical interface losses while maintaining chemical noise immunity.
4Loss of substance
If collisional quadrupoles are used to reduce ion losses, then ion losses are reduced, but spectrum quality deteriorates
Solution Approach 1:
The patent extracts ions directly from the closed source along the electron beam axis without introducing collisional quadrupoles into the ion path. By taking out the problematic quadrupole elements from the system and using direct electrostatic extraction instead, the patent avoids both ion losses and the detrimental effects on EI spectrum quality that quadrupoles would introduce.
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 achieves a nearly 100-fold reduction in chemical noise, improved response time, and increased dynamic range, enabling ultrasensitive and reliable analysis with detection limits potentially below 1 fg and improved matching with standard spectra.
Implementation Method 1
Electron impact (EI) ionization is employed for environmental analysis and technological control
Implementation Method 2
improving response time of a 'closed' EI source by making the source isothermal, preferably using an isothermal shroud comprised of heat conductive materials
Implementation Method 3
arranging electrostatic positive plugs along the electron beam to thereby focus ions in the ion storage region while generally removing slow secondary electrons
Implementation Method 4
arranging a 5-10 fold molecular separator within the vacuum chamber and immediately at the entrance of the closed EI ion source
Data Source
AI summary
A closed electron impact ion source with overall opening area of less than 30 mm2 is employed for direct and pulsed extraction into a time-flight mass spectrometer in order to enhance sensitivity and immunity to chemical noise of oil and fumes of the vacuum system. For compatibility with dual stage GCxGC separation, the source may contain an inert liner surrounded by an isothermal cage of thermally conductive material. The source inner surface may be reduced to under 100 mm2. A portion of carrier gas may be pumped down before admitting the sample and carrier gas into the source. A cooled surface may be used to condense fumes at the analysis time.