Dual Electrostatic Lens Gating for Linear Ion Transmission
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Solution Overview
Problem
The linearity of ion signals in mass spectrometry is compromised due to ion mobility effects caused by gating mechanisms, particularly at lower duty cycles, leading to non-linear behavior and reduced performance in instruments like quadrupole traps and Time-of-Flight mass spectrometers.
Innovation Solution
A dual electrostatic lens gating apparatus is used, with one lens maintaining a fixed voltage to stabilize ions at high pressure regions and the other lens modulating voltage to control ion passage at lower pressure regions, minimizing ion mobility effects and ensuring linear ion transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single gating lens is used to control ion flow, then the device complexity is reduced, but the linearity of ion signal deteriorates due to ion mobility effects
Solution Approach 1:
The single gating lens is divided into two separate electrostatic lenses (first and second lenses) positioned at different locations. The first lens is placed in the high pressure region where ion mobility effects dominate and operates continuously, while the second lens is placed in the low pressure region and operates in pulsed mode. This segmentation allows each lens to address specific regions of the ion beam path, resolving the linearity issue without excessive complexity.
Solution Approach 2:
The first electrostatic lens acts as an intermediary element between the ion source and the second lens. It creates a stabilized ion beam in the high pressure region before the beam enters the low pressure region where the second lens performs the actual gating. This intermediary lens mitigates ion mobility effects that would otherwise directly impact the gating performance.
2Manufacturing precision
If the orifice diameter of the gating lens is reduced to improve resolution, then ion mobility effects are enhanced, but the axial velocity of ions decreases leading to greater non-linear behavior
Solution Approach 1:
The gating function is segmented between two lenses with different orifice characteristics. The first lens in the high pressure region has a larger effective aperture to maintain ion velocity, while the second lens in the low pressure region provides the precise gating function. This segmentation allows resolution to be maintained without sacrificing ion velocity.
Solution Approach 2:
Different regions of the ion beam path are given different optical qualities. The first lens region is optimized for maintaining ion velocity and reducing mobility effects, while the second lens region is optimized for precise gating control. Each lens has local properties tailored to its specific function in the overall system.
3Loss of time
If the duty cycle is reduced to improve ion trap fill time linearity, then the modulation frequency increases, but ion mobility effects cause greater deviation from linear behavior
Solution Approach 1:
The gating operation is segmented into two stages: continuous operation of the first lens that stabilizes the ion beam regardless of duty cycle, and pulsed operation of the second lens that provides the modulation function. This segmentation allows the system to achieve linear intensity counts even at low duty cycles by preventing ion mobility effects from interfering with the modulation process.
Solution Approach 2:
The first lens performs a preliminary stabilization of the ion beam before the second lens applies the modulation. By pre-conditioning the ion beam in the high pressure region where mobility effects are strongest, the system prepares the ions for subsequent pulsed gating without suffering from mobility-induced non-linearities.
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 improved linearity and increased ion trap fill efficiency, enhancing compound identification in triple-TOF instruments by reducing ion mobility-induced deviations and maintaining linear ion intensity modulation across varying frequencies.
Implementation Method 1
the first electrostatic lens is disposed adjacent to the region of higher pressure and operates in a continuous mode having a voltage that is fixed at a predetermined value so that ions are not caused by a modulation field to deviate to an unstable trajectory
Implementation Method 2
the second electrostatic lens is disposed adjacent to the region of lower pressure and is situated downstream from the first lens, the second electrostatic lens having a voltage that varies between at least two different voltages wherein, at a first voltage, the ions can traverse through the second lens and, at a second voltage, the ions are prevented from traversing through the second electrostatic lens
Implementation Method 3
The phenomenon of skimmer pulsing is mass dependent and has also exhibited surprisingly non-linear behavior in some cases. In particular, the linearity of an ion signal seen when pulsing a single gating lens over a wide duty cycle range is not very good at lower duty cycles. This affects fill time linearity on the quardupole trapping instruments and ITC (Total ion current) linearity on Time-of-Flight mass spectrometer instruments.
Data Source
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AI summary
A lens pulsing apparatus and method for transferring ions in a mass spectrometry system from an area of high pressure to an area of low pressure which includes a gating apparatus that contains multiple electrostatic lenses. Each of the lenses operates at different voltages. The first lens operates at a predetermined fixed voltage and the second lens operates between two different voltages.