Mass Spectrometer Inlet Electrode Voltage Control for Space Charge Reduction
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Solution Overview
Problem
In ICP-MS, the accumulation of unnecessary ions in the collision cell causes space charge effects, leading to unstable ion intensity and reduced detection sensitivity due to the off-axis optical system's inability to effectively remove Ar ions and the low transportation efficiency of target-element ions.
Innovation Solution
A mass spectrometer configuration with an inlet electrode and voltage generator applying a direct-current voltage with the same polarity as elimination-target ions during standby periods, and an attraction electrode with a skimmer to reduce the entry of unnecessary ions into the collision cell, combined with a radio-frequency electric field for ion ejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an off-axis optical system is used to remove reactive neutral particles, then the space charge effect is reduced, but the transportation efficiency of target-element ions decreases
Solution Approach 1:
The optical system is divided into separate functional sections: a first optical system for ion extraction and acceleration, and a second optical system for ion introduction into the collision cell. This segmentation allows each section to be optimized independently, maintaining high ion transportation efficiency while enabling effective removal of unwanted ions through the collision cell.
Solution Approach 2:
A collision cell filled with helium gas is introduced as an intermediary component between the ion source and the mass analyzer. The helium gas acts as a mediator that selectively removes reactive neutral particles and interference ions through collisions, reducing the space charge effect while allowing target ions to pass through with minimal loss.
2Stability of the object's composition
If the collision cell operates continuously during standby periods, then ion intensity stability improves, but accumulation of unnecessary ions increases
Solution Approach 1:
The collision cell operation is controlled periodically rather than continuously. During standby periods when no analysis is performed, the collision cell is deactivated or operated at reduced gas flow, preventing accumulation of unnecessary ions. During analysis periods, the collision cell is activated to ensure ion intensity stability, creating a periodic operation cycle that balances both requirements.
Solution Approach 2:
The operating parameters of the collision cell are dynamically adjusted based on the analysis state. The helium gas flow rate and collision cell voltage are modified in real-time: increased during analysis for stability, and decreased or halted during standby to prevent ion accumulation. This dynamic control allows the system to adapt to different operational requirements.
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 significantly reduces the space charge effect, stabilizes ion intensity, and enhances detection sensitivity by preventing the accumulation of unnecessary ions and reactive neutral particles in the collision cell, allowing for precise analysis.
Implementation Method 1
a voltage generator configured to apply a direct-current voltage to the inlet electrode; and a controller configured to control the voltage generator to apply, to the inlet electrode, a direct-current voltage with a polarity the same as a polarity of an elimination-target ion generated in the ion source
Implementation Method 2
The neutral particles are not trapped by a radio-frequency electric field formed by an ion guide in the collision cell, and thus are diffused
Implementation Method 3
an attraction electrode that is provided between the skimmer and the cell, and configured to promote attraction of the ion through the ion passing port of the skimmer, using an effect of an electric field
Implementation Method 4
During the analysis, helium (He) gas (or another inert gas) is introduced into the collision cell. Ions injected into the collision cell frequently come in contact with the He gas in the collision cell, and at every contact, the kinetic energy of each of the ions is reduced
Implementation Method 5
ions derived from the interference ions having altered mass-to-charge ratio are separated from the observation-target ions in a mass separator, such as a later-stage quadrupole mass filter
Data Source
AI summary
A mass spectrometer includes: an ion source; a collision cell into which a predetermined gas is introduced, for allowing an ion generated in the ion source to be in contact with the predetermined gas; and a quadruple mass filter for performing mass spectrometry on the ion ejected from the collision cell. The mass spectrometer further includes: an inlet electrode provided at an ion injection port through which the ion is incident in the collision cell; a voltage generator for applying a direct-current voltage to the inlet electrode; and a voltage controller and a controller for controlling the voltage generator to apply, to the inlet electrode, a direct-current voltage with a polarity same as a polarity of an unnecessary ion generated in the ion source, during at least a part of a standby period of time in which no analysis-target ion is analyzed.