Ion Trap Digital Waveform Isolation for Mass Spectrometry
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Solution Overview
Problem
Current ion selection methods in ion traps, particularly digital ion traps, require a significant amount of time for precursor isolation, which hampers the throughput of mass spectrometry analysis due to the need for prolonged frequency adjustments to ensure accurate removal of unnecessary ions, especially for ions with high mass-separating power.
Innovation Solution
The method employs a combination of techniques such as DAWI (Digital Asymmetric Waveform Isolation) and resonant excitation, using alternating voltages with shifting duty ratios and direct biases to efficiently remove ions by differentiating between low and high mass-to-charge ratios, allowing for simultaneous discharge of a wide range of ions with high separating power on the low-mass side and precise removal on the high-mass side using quadrupole excitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If resonant excitation discharge is performed using a single frequency synchronized with the rectangular voltage frequency to achieve high mass-separating power, then the mass-separating power is improved, but the time required for precursor isolation increases significantly
Solution Approach 1:
The ion selection process is divided into two distinct stages: rough isolation using frequency-swept resonant excitation to quickly remove ions outside the target mass range, and fine isolation using single-frequency resonant excitation to achieve high mass-separating power for the remaining ions. This segmentation allows each stage to optimize for its specific function, reducing total isolation time while maintaining high resolving power.
Solution Approach 2:
The rough isolation step is performed as a preliminary action before the fine isolation step. By预先 removing ions that are clearly outside the target mass range through frequency-swept excitation, the subsequent fine isolation step needs to process fewer ions, thereby reducing the overall time required while maintaining high mass-separating power for the final selection.
2Measurement precision
If the frequency of rectangular voltage is continuously decreased to sequentially discharge ions in ascending order of mass-to-charge ratio, then the mass separation is achieved, but the analysis throughput is reduced due to the prolonged discharge time
Solution Approach 1:
The ion discharge process is segmented into two phases: a rapid rough isolation phase using frequency-swept excitation that quickly removes the majority of unwanted ions, and a shorter fine isolation phase using single-frequency excitation. This segmentation dramatically reduces the total time required compared to traditional sequential frequency sweeping, thereby improving analysis throughput while maintaining ion selection accuracy.
Solution Approach 2:
The frequency-swept resonant excitation method allows the system to rapidly sweep through a wide frequency range to remove ions across the entire mass range outside the target window in a single operation, rather than sequentially adjusting frequencies for each ion. This 'rushing through' approach significantly reduces the time required for ion removal while maintaining accurate mass separation.
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 significantly reduces the time required for ion selection while maintaining high resolving power, thereby enhancing the throughput of mass spectrometry analysis by allowing for rapid and accurate isolation of target ions within the ion trap.
Implementation Method 1
an ion trap is used to capture and confine ions by an effect of a radio-frequency electric field
Implementation Method 2
a stability diagram, which is prepared based on the stability condition for the solution of a Mathieu equation
Implementation Method 3
another precursor isolation with a higher level of resolving power is performed using a resonant excitation discharge by dipole excitation
Implementation Method 4
the duty ratio of the rectangular voltage is varied to change the LMCO and HMCO and thereby achieve by the precursor isolation
Implementation Method 5
the quadrupole excitation, in which the excitation can be caused in two mutually orthogonal directions by selectively applying either voltages of opposite polarities or voltages of the same polarity to a pair of electrodes
Data Source
Figure 1~2
Figure 3~5(b)
Figure 6~8(b)
AI summary
Provided is an ion selection method capable of isolating and leaving a target ion in an ion trap within a short period of time and with high separating power. In a digital ion trap, after ions over a wide range of m/z near a target ion are selectively retained by rough isolation using an FNF signal or the like (S11), unnecessary ions on a low-mass side are removed with high separating power by changing the duty ratio of a rectangular voltage (S12). Furthermore, unnecessary ions on a high-mass side are removed with high separating power by resonant excitation discharge (S13).