RF Ion Trap Overload Removal via Asymmetric DC Field
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Solution Overview
Problem
RF quadrupole ion traps face challenges in efficiently isolating ions of a predefined narrow range of charge-related masses due to overloading, space charge effects, and the difficulty in removing heavy ions, which can disturb analytical results and reduce mass resolution.
Innovation Solution
An asymmetric electric DC field is applied to ion trap electrodes to remove heavy ions without resonance excitation, using a combination of DC and RF voltage ramps to shift mass limits and efficiently eliminate undesired ions within a short time frame, ensuring desired ions remain intact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If resonant excitation is used to eliminate undesired ions, then ion isolation effectiveness is improved, but heavy ions cannot be removed efficiently and the process time increases
Solution Approach 1:
The patent applies a preliminary asymmetric DC field before resonant excitation to rapidly remove heavy ions. This preliminary action reduces the ion load and eliminates heavy ions that would otherwise be difficult to remove, making the subsequent resonant excitation more effective and faster.
Solution Approach 2:
The asymmetric DC field acts as an intermediary mechanism between the ion trap and the resonant excitation process. It prepares the ion population by removing heavy ions first, creating optimal conditions for the subsequent resonant excitation to efficiently isolate desired ions.
2Quantity of substance
If ion trap is overloaded with ions, then signal intensity is improved, but space charge effects destroy mass resolution and prevent effective isolation
Solution Approach 1:
The patent segments the ion removal process into two distinct phases: first removing heavy ions using asymmetric DC fields, then removing lighter undesired ions using resonant excitation. This segmentation allows the system to handle overloaded ion populations while maintaining mass resolution by addressing different ion mass ranges with appropriate methods.
Solution Approach 2:
The asymmetric DC field is applied as a preliminary step to remove heavy ions before the main isolation process. This preliminary removal reduces space charge effects that would otherwise degrade mass resolution, enabling subsequent resonant excitation to work effectively even when the trap initially contains large numbers of ions.
3Speed
If DC voltage is applied to remove heavy ions, then heavy ion elimination speed is improved, but desired ions may be affected if voltage is too high
Solution Approach 1:
The patent applies a asymmetric DC field that creates a non-uniform electric field distribution within the ion trap. This local quality difference ensures that heavy ions experience sufficient force for rapid removal while lighter desired ions within the isolation window are affected minimally, allowing fast heavy ion elimination without compromising desired ion integrity.
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 method effectively removes over 90% of undesired ions in under 5 milliseconds, reducing overload and allowing for successful subsequent ion isolation and analysis with improved mass resolution and signal quality.
Implementation Method 1
The electric force field pushes the ions from the center towards one of the trap electrodes
Implementation Method 2
forming inside quadrupolar pseudopotential wells in two or three dimensions, in which the ions can oscillate as in a real potential well
Implementation Method 3
The damping process decreases the oscillation amplitudes exponentially with a time constant of about one millisecond
Data Source
AI summary
In an RF quadrupole ion trap having electrodes to which RF voltages are applied, ions having m/z ratios outside of a predefined narrow range of charge-related masses m/z are removed from the trap by applying a DC voltage pulse to at least one of the trap electrodes to remove from the trap the ions with high values of charge-related masses. The DC voltage pulse is preferably applied in combination with a variation of the RF voltage amplitudes to simultaneously remove from the trap ions of low charge-related masses. The DC and RF voltage amplitudes are changed in such a manner that any excitation of ions having charge-related masses within the predefined range by frequency mixtures is avoided.