GC-MS Ion Source Control for Reducing Reagent Gas Adhesion
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Solution Overview
Problem
Conventional GC-MSs face issues with reagent-gas ion adhesion in the ionization chamber during chemical ionization, leading to reduced detection sensitivity and measurement reproducibility due to excessive reagent-gas ions, especially when operated for extended periods.
Innovation Solution
A GC-MS with an EI/CI combination ion source that controls the reagent-gas supply and thermion generation based on chromatogram analysis, limiting ionization by the chemical ionization method to specific time ranges where target compounds are present, thereby reducing reagent-gas ion adhesion and maintaining high sensitivity and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If chemical ionization method is continuously performed in GC-MS, then molecular weight information can be acquired, but reagent-gas ions adhere to the ionization chamber and reduce detection sensitivity and measurement reproducibility
Solution Approach 1:
The ion source performs chemical ionization only during specific time periods when target compounds are present in the ionization chamber, rather than continuously. The control unit switches between chemical ionization mode (when compounds are present) and electron ionization mode (when compounds are absent), thereby reducing reagent-gas ion adhesion while still acquiring molecular weight information when needed
Solution Approach 2:
The control unit determines whether to perform chemical ionization based on detection results from the ionization chamber. When the detection unit detects target compounds, the control unit switches to chemical ionization mode; when no compounds are detected, it switches to electron ionization mode. This feedback mechanism ensures chemical ionization is performed only when necessary, preventing excessive reagent-gas ion accumulation
2Power
If reagent gas is supplied continuously for chemical ionization, then ionization efficiency is maintained, but excessive reagent-gas ions are generated and adhere to chamber walls
Solution Approach 1:
The reagent gas supply is controlled to be active only during specific time periods when target compounds are present, rather than continuously. The control unit activates reagent gas supply during chemical ionization periods and deactivates it during electron ionization periods, thereby maintaining ionization efficiency when needed while preventing excessive reagent-gas ion generation and adhesion
Solution Approach 2:
The system performs chemical ionization with reagent gas supply only partially (during specific time windows when compounds are present) rather than excessively (continuously). This partial action approach maintains sufficient ionization efficiency for detecting target compounds while avoiding the harmful effects of excessive reagent-gas ion accumulation
3Measurement precision
If EI method is used for compound identification, then spectrum pattern matching can be performed, but some compounds cannot be identified with high certainty
Solution Approach 1:
The ion source combines both electron ionization (EI) and chemical ionization (CI) capabilities in a single device. The control unit switches between EI mode (for spectrum pattern matching and compound identification) and CI mode (for molecular weight determination and confirmation). By merging both ionization methods in one instrument, the system achieves both identification and confirmation capabilities, improving overall identification certainty
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 reduces reagent-gas ion adhesion, maintaining high detection sensitivity and reproducibility over time, and minimizes maintenance needs, improving the device's availability and reducing analysis costs.
Implementation Method 1
thermions generated from a filament are accelerated and made to come in contact with component molecules in the sample gas
Implementation Method 2
thermions generated from a filament are accelerated and made to come in contact with component molecules in the sample gas. This causes electrons to be expelled from the component molecules, whereby the molecules are ionized
Implementation Method 3
thermions are made to come in contact with the reagent gas to generate reagent-gas ions. Component molecules are introduced into the ambience of those reagent-gas ions to induce a chemical reaction and ionize the component molecules
Data Source
AI summary
A GC/MS measurement under an ionization by an electron ionization method is performed for a target sample (S1). Peaks are detected on a chromatogram based on obtained data, and a mass spectrum corresponding to each peak is compared with a compound database to identify a compound (S2-S4). A compound identified with a low degree of similarity is extracted as the measurement compound. For this compound, a measurement window including the retention time of a peak corresponding to the compound is set, and a control program for performing an ionization by a chemical ionization method only within the measurement window is created (S5-S8). According to this control program, a GC/MS measurement for the target sample is performed, with the device controlled so that a reagent gas is supplied into an ionization chamber and a filament for generating thermions is energized within the measurement window, whereas the supply of the reagent gas is discontinued and the filament is deenergized within time ranges other than the measurement window (S9). Since no reagent-gas ion is generated within the time ranges other than the measurement window, the adhesion of the ions to the inside of the ionization chamber and other locations will be reduced. Accordingly, a stable measurement can be performed for a long period of time.