Two-Stage Ion Source for Simultaneous EI and CI GC-MS

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Solution Overview

Problem

Commercial GC-MS ion sources require time delays for switching between different ionization types due to vastly different pressure requirements for optimal electron ionization and chemical ionization, which is not feasible with current high vacuum pumps and affects analytical characteristics.

Innovation Solution

A two-stage ion source with a closed ion volume for chemical ionization and an open ion volume for electron ionization, allowing for simultaneous operation of both ionization types with separate filaments and a conical nozzle to maintain isothermal conditions and high sample density, enabling efficient ionization and chromatographic peak preservation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of time

If a single ion source is used for both electron ionization and chemical ionization, then ion source switching time is reduced, but optimal ionization conditions cannot be maintained due to vastly different pressure requirements

Engineering Contradiction:

Improveion source switching timeVSAvoidionization condition optimization

Core Design Contradiction:

Loss of timeVSReliability

Solution Approach 1:

The ion source is divided into two separate ionization volumes (first and second volumes) that can operate simultaneously at different pressures. The first volume operates at higher pressure for chemical ionization while the second volume operates at lower pressure for electron ionization, allowing both ionization types to function at optimal conditions without switching delays

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces a spatial dimension solution by creating two distinct ionization volumes at different pressure regimes within the same mass spectrometer. Instead of switching between single-volume configurations, the system uses parallel volumes connected to the mass analyzer, enabling simultaneous operation in the pressure dimension

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Quantity of substance

If high gas flow rate is used to increase ion volume pressure for chemical ionization, then chemical ionization efficiency improves, but electron ionization performance deteriorates due to insufficient vacuum pump speed

Engineering Contradiction:

Improvegas flow rateVSAvoidelectron ionization performance

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The vacuum system is segmented into two independent pumping paths, each serving a specific ionization volume. The first vacuum pump serves the first ionization volume for chemical ionization, while the second vacuum pump serves the second ionization volume for electron ionization, allowing each volume to maintain its optimal pressure independently

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A differential pumping system acts as an intermediary between the two ionization volumes and the mass analyzer. This intermediate pumping stage allows the first volume to operate at higher pressure while the second volume maintains lower pressure, mediating the pressure difference without compromising either ionization type

Inventive Principle:

Principle #24Intermediary (Mediator)

3Stress or pressure

If mechanically-resizable ion volume apertures are used to adjust pressure, then pressure adaptation for different ionization types is achieved, but temperature uniformity deteriorates due to difficulty in maintaining isothermal conditions

Engineering Contradiction:

Improveion volume pressureVSAvoidtemperature uniformity

Core Design Contradiction:

Stress or pressureVSTemperature

Solution Approach 1:

The ion source is segmented into two thermally independent ionization volumes, each with its own heating control. This segmentation allows each volume to be independently temperature-controlled, maintaining isothermal conditions in both volumes simultaneously without the mechanical aperture adjustments that cause thermal non-uniformity

Inventive Principle:

Principle #1Segmentation

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

Enables simultaneous collection of EI and CI type GC-MS spectra at optimal conditions, improving analytical performance by minimizing time delays and maintaining peak shapes, and increasing sensitivity and dynamic range.

Implementation Method 1

The first ionization volume may have a relatively high internal pressure, suited for chemical ionization (CI)

Methodology Applied

Scientific EffectChemical ionization:

Implementation Method 2

The second ionization volume may have a significantly lower pressure, close to the source chamber background pressure, typically found in open electron ionization (EI) sources

Methodology Applied

Scientific EffectElectron ionization:

Implementation Method 3

The open volume may be in fluid communication with, and downstream of, the closed volume, such that a gaseous sample may sequentially pass through the closed ion volume and into the open volume

Methodology Applied

Scientific EffectMolecular beam formation:

Data Source

PatentUS11328919B2Two-stage ion source comprising closed and open ion volumes

Publication Date: 2022.05.10 LECO CORP

AI summary

An ion source includes a base, a first chamber, a second chamber and an extractor. The first chamber is disposed downstream of the base and defines a first internal volume having a first pressure. The second chamber is disposed downstream of the first chamber and defines a second internal volume having a second pressure. The second pressure is less than the first pressure. The repeller electrode is disposed within the first chamber. The extractor is disposed downstream of the second chamber.