Ion Trap Waveform Amplitude Scaling for Isolation Efficiency
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Solution Overview
Problem
Existing ion trapping methods face inefficiencies in storing and manipulating ions due to limitations in ion isolation techniques, particularly in maintaining efficient ion isolation during variable accumulation times, leading to potential loss of precursor ions through ejection or fragmentation.
Innovation Solution
A method involving the application of a notched supplemental AC voltage waveform with a time-varying amplitude to RF ion trap electrodes, where the amplitude decays exponentially during accumulation, is used to selectively eject unwanted ions while optimizing the retention of precursor ions, thereby improving ion isolation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a constant amplitude supplemental AC voltage waveform is applied during ion accumulation, then unwanted ions are effectively ejected, but precursor ions may be lost through ejection or fragmentation during longer accumulation times
Solution Approach 1:
The waveform amplitude is made time-dependent, transitioning from a constant amplitude to a decaying amplitude profile. The amplitude decreases exponentially over time according to A(t) = A₀e^(-kt), where A₀ is the initial amplitude, k is the decay constant, and t is time. This dynamic adjustment allows effective ejection of unwanted ions during early accumulation while reducing precursor ion loss during later stages.
Solution Approach 2:
The amplitude parameter of the supplemental AC voltage waveform is changed over time during the accumulation process. By varying the amplitude from high initial values to lower final values, the system optimizes both unwanted ion rejection and precursor ion retention depending on the accumulation time duration.
2Quantity of substance
If ion accumulation time is extended to improve signal intensity, then more precursor ions are accumulated, but isolation efficiency deteriorates due to increased ejection and fragmentation
Solution Approach 1:
The system dynamically adjusts the waveform amplitude based on accumulation time requirements. For longer accumulation times, the decaying amplitude profile maintains isolation efficiency by reducing the amplitude after initial unwanted ion ejection, allowing extended accumulation without excessive precursor ion loss.
Solution Approach 2:
The high initial amplitude performs preliminary ejection of unwanted ions before the accumulation process fully begins. This preliminary action clears the trap of interfering ions, allowing subsequent longer accumulation times to proceed with reduced risk of contamination and improved overall isolation efficiency.
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 maintains good isolation efficiency for precursor ions while rejecting unwanted ions, even during longer accumulation times, reducing ion loss through ejection and fragmentation, and enhancing the signal-to-noise ratio in mass spectrometry.
Implementation Method 1
applying a notched supplemental AC voltage waveform to electrodes of the RF ion trap, the supplemental AC voltage waveform having component frequencies chosen to resonantly eject only ion species for which m/z ≠ (m/z) ISO
Implementation Method 2
wherein a time-varying amplitude, A(t), of the applied supplemental AC voltage waveform is caused to decay with time, t, during at least a portion of the accumulation time period
Data Source
Figure 1A~1B
Figure 1C~1D
Figure 2
AI summary
This disclosure describes a method of adjusting the amplitude of notched broadband waveforms for isolation, especially during injection to a multipole trapping device. Isolation during injection to a trapping device is known to be an effective way of accumulating a desired population of ions while rejecting unwanted species. The waveform amplitude required to eject unwanted species varies as a function of isolation time, but using automated gain control, the time required to accumulate a given population of ions may vary over several orders of magnitude. Thus, when the injection times are very long, precursor ions of interest are resonated for a long time and may be inadvertently ejected from the trap, using conventional methods. By setting the waveform amplitude lower for longer accumulation times, good isolation efficiency can be maintained for the precursor, while still rejecting unwanted ions.