Supersonic Nozzle Photoionization Mass Spectrometer
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Solution Overview
Problem
Photoionization methods, such as atmospheric pressure photoionization, often produce both molecular and fragment ions, especially for larger compounds, making it difficult to achieve pure molecular ion spectra necessary for mixture characterization in mass spectrometry, and existing ionization methods like field ionization are unstable and costly.
Innovation Solution
A mass spectrometer system with a supersonic molecular beam photoionization ion source that uses high flow rates of carrier gases for vibrational cooling of sample compounds, combined with continuous vacuum ultra-violet photon sources, to produce nearly exclusive molecular ions with less than 3% fragment ions for hydrocarbons, and optionally includes a fly-through electron ionization source for complementary analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If photoionization is used for ionization of sample compounds, then molecular ions are produced with higher abundance compared to electron ionization, but fragment ions are also generated especially for larger compounds
Solution Approach 1:
The patent changes the temperature parameter by cooling the sample compounds to cryogenic temperatures (below -150°C, preferably below -180°C) before photoionization. This temperature reduction decreases the internal vibrational energy of the molecular ions, preventing fragmentation and achieving near-exclusive molecular ion production with fragment ions below 3% intensity
Solution Approach 2:
The patent applies preliminary cooling action by passing the sample compounds through a cooled region (using liquid nitrogen or liquid helium cooling) before they enter the photoionization zone. This pre-cooling step ensures that when photoionization occurs, the molecules are in a cold state that produces minimal fragmentation
2Object-generated harmful factors
If field ionization is used to produce molecular ions without fragment ions, then pure molecular ion spectra are achieved, but the ion source becomes unstable and requires extensive service
Solution Approach 1:
The patent replaces the complex, expensive, and unstable field ionization source with a simpler, more reliable photoionization source using deuterium or krypton lamps. These lamp-based sources are more stable, require less maintenance, and when combined with cryogenic cooling, achieve the same pure molecular ion spectra as field ionization
Solution Approach 2:
The patent changes the physical state parameter by cooling samples to cryogenic temperatures, which when combined with photoionization, achieves the pure molecular ion spectra that previously required field ionization, but with improved source stability and reduced maintenance
3Quantity of substance
If in-vacuum photoionization is used for GC-MS analysis, then soft ionization is achieved producing more molecular ions, but the method does not provide molecular ions alone and fragmentation increases with compound size
Solution Approach 1:
The patent introduces cryogenic temperature control as a new parameter, cooling samples to below -150°C before photoionization. This temperature parameter change suppresses fragmentation across all compound sizes, enabling accurate mixture characterization through pure molecular ion spectra even for large molecules
Solution Approach 2:
The patent applies preliminary cryogenic cooling to the sample compounds before they undergo photoionization. This pre-cooling action ensures that even large compounds produce minimal fragmentation, enabling the mass spectrometer to provide accurate averaged mass spectra for mixture separation and quantitation
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 significantly enhances the abundance of molecular ions and reduces fragment ions, enabling effective characterization and quantitation of complex mixtures like fuels and oils, while being more stable and cost-effective than traditional methods.
Implementation Method 1
expanding the sample compounds with a carrier gas from the supersonic nozzle into a supersonic nozzle vacuum chamber proximate the supersonic nozzle to enable the sample compounds to expand from the supersonic nozzle with carrier gas flow rate greater than 20 ml/min for vibrationally cooling the sample compounds
Implementation Method 2
continuously ionizing the sample compounds by illuminating them with vacuum ultra-violet photons produced by a continuously operated vacuum ultra-violet photon source to produce ions
Data Source
AI summary
Method for producing ions for mass spectrometry analysis, including introducing vaporized sample compounds behind a supersonic nozzle and expanding the sample compounds with a carrier gas from the supersonic nozzle into a supersonic nozzle vacuum chamber proximate thereto for vibrationally cooling the sample compounds prior to their ionization. Sample compounds are ionized by either illumination with vacuum ultra-violet photons produced by a continuously operated vacuum ultra-violet photon source or by electrons produced in a fly-through electron ionization ion source; and the ions are transferred to a mass analyzer mounted in a mass analyzer vacuum chamber to obtain mass spectra from vibrationally cold molecules. A quadrupole mass analyzer mounted may be used to obtain mass spectra with dominant molecular ions and fragment ion intensities below 3% of the molecular ion for hydrocarbons. Carrier gas flow rate may exceed 20 ml/min for vibrationally cooling the sample compounds prior to their ionization.