Ion Trap Inverse Mathieu q Scan for Mass Range
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Solution Overview
Problem
Existing ion trap mass spectrometers face limitations in mass range extension and resolution due to the nonlinear relationship between mass-to-charge ratio and rf frequency, requiring complex calibration procedures and instrumental modifications.
Innovation Solution
The implementation of an inverse Mathieu q scan method, where the frequency of a supplementary AC signal is scanned nonlinearly with time, allowing for a linear relationship between mass-to-charge ratio and time, enabling mass range extension without instrumental modifications and maintaining resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If linear frequency sweeping is used to scan ions out of the ion trap, then the mass range can be extended, but the mass calibration becomes nonlinear and requires complex calibration procedures
Solution Approach 1:
The patent inverts the conventional approach by applying a nonlinear frequency sweep to the supplementary AC signal instead of a linear sweep. This inverse Mathieu q scan uses the relationship q = 8zeV0-p/(mΩ2r02) to create a nonlinear frequency-time profile that compensates for the natural nonlinearities in ion secular frequency, resulting in a linear mass-to-charge versus time relationship during the ejection scan
Solution Approach 2:
The patent changes the frequency parameter of the supplementary AC signal in a nonlinear manner over time, specifically designing the frequency sweep to follow an inverse Mathieu q trajectory. This parameter change approach transforms the conventional linear frequency sweep into a nonlinear sweep that maintains linear mass calibration across the extended mass range
2Measurement precision
If resonance ejection with linear frequency sweep is used, then resolution and sensitivity are improved, but position-dependent ion frequency shifts occur due to higher-order field contributions
Solution Approach 1:
The patent applies an inverse Mathieu q scan that nonlinearly sweeps the supplementary AC frequency to counteract the position-dependent frequency shifts caused by higher-order field contributions. By inverting the conventional linear sweep approach and using a nonlinear frequency-time profile, the method compensates for the instability in ion secular frequencies across different trap positions
3Quantity of substance
If the main trapping rf frequency is scanned to analyze high mass ions, then the mass range is increased, but the relationship between m/z and rf frequency becomes nonlinear and calibration is difficult
Solution Approach 1:
Instead of scanning the main trapping rf frequency, the patent inverts the approach by keeping the rf frequency constant and scanning the supplementary AC frequency in a nonlinear inverse Mathieu q manner. This inversion simplifies calibration because the linear mass-to-charge versus time relationship is achieved through the AC frequency sweep rather than rf frequency scanning
Solution Approach 2:
The patent applies the supplementary AC signal locally to specific trapping electrodes to induce resonance ejection, rather than modifying the global rf trapping field. This localized approach allows for precise control of the ejection process and simplifies the calibration requirements while maintaining the ability to analyze high mass ions
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 increases the mass range and power savings while simplifying the mass spectrometer's operation, allowing for linear mass calibration and maintaining high resolution, making it suitable for miniature and portable instruments.
Implementation Method 1
When this frequency, generally set near qu=0.88, matches the secular frequency of an ion in the trap, the ion will be excited or ejected from the trap depending on waveform amplitude and time of application.
Implementation Method 2
Ion traps are generally operated without DC potentials (au=U=0) so that all ions occupy the q axis of the Mathieu stability diagram.
Data Source
AI summary
The invention generally relates to ion traps that operate by applying an inverse Mathieu q scan. In certain embodiments, the invention provides systems that include a mass spectrometer having an ion trap and a central processing unit (CPU). The CPU includes storage coupled to the CPU for storing instructions that when executed by the CPU cause the system to apply an inverse Mathieu q scan to the ion trap.