Quadrupole Mass Analyzer RF Amplitude Modulation
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Solution Overview
Problem
Existing quadrupole mass spectrometers face limitations in achieving high mass resolution due to challenges in controlling the parallel relationship and inner field radius of elongated quadrupoles, which affects ion transmission efficiency and scanning speed, and require complex multi-phase and frequency-locked RF voltages for high-resolution analysis.
Innovation Solution
A quadrupole mass analyzer employing RF amplitude modulation and multiple AC excitation voltages with specific frequency ratios and amplitudes to optimize stability band formation, allowing for improved mass resolution without reducing ion transmission efficiency and simplifying the RF circuit requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the quadrupole length is increased to improve mass resolution, then the mass resolution is improved, but the ion transmission efficiency deteriorates and the scanning speed decreases
Solution Approach 1:
The patent applies RF amplitude modulation to the quadrupole voltage, changing the temporal parameter of the voltage application. By modulating the RF voltage amplitude at a specific frequency ratio (1:5 to 1:20), the system creates stability bands that improve mass resolution without requiring increased quadrupole length, thereby maintaining ion transmission efficiency and scanning speed.
2Measurement precision
If the quadrupole length is increased to improve mass resolution, then the mass resolution is improved, but the scanning speed deteriorates
Solution Approach 1:
The patent changes the voltage application parameter by introducing RF amplitude modulation at a frequency ratio of 1:5 to 1:20 relative to the main RF frequency. This modulation creates distinct stability bands in the Mathieu equation solution space, allowing for sharper mass filtering without increasing the number of RF periods required, thus maintaining fast scanning speed while achieving high mass resolution.
3Measurement precision
If complex multi-phase and frequency-locked RF voltages are used to achieve high mass resolution, then the mass resolution is improved, but the device complexity increases
Solution Approach 1:
The patent simplifies the voltage application scheme by using single-phase RF voltage with amplitude modulation rather than complex multi-phase frequency-locked voltages. The RF amplitude is modulated at a frequency 5 to 20 times lower than the main RF frequency, which can be easily generated using standard frequency division techniques, significantly reducing RF circuit complexity while achieving comparable or superior mass resolution.
4Measurement precision
If the RF voltage amplitude is increased to improve mass resolution, then the mass resolution is improved, but the ion loss increases
Solution Approach 1:
The patent applies periodic amplitude modulation to the RF voltage at a low frequency ratio (1:5 to 1:20). This periodic variation creates time-dependent stability bands that allow ions to be transmitted through the quadrupole during stable periods while filtering out unwanted mass-to-charge ratios during unstable periods. The modulation frequency is low enough that ions experience many RF cycles within each modulation period, ensuring sufficient filtering action while minimizing ion loss.
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
The solution achieves high mass resolution up to approximately 66,000 with enhanced ion transmission efficiency and faster scanning speeds, reducing the need for complex high-frequency AC signals and minimizing ion loss, while maintaining a stable quadrupole electric field.
Implementation Method 1
the quadrupole and the used power supply should make the electric field generated in the central region of the quadrupole as close as possible to the distribution of a pure quadrupole electric field
Implementation Method 2
Under the effect of the RF voltage, the ions oscillate periodically in respective direction of two pairs of poles
Implementation Method 3
When the ratio of the configured quadrupole RF voltage to the quadrupole DC voltage is appropriate, ions with specific mass-charge ratio Mz can stably pass through the quadrupole system, ions with mass-charge ratio smaller than this value tend to be lost on one pair of electrodes, and ions with mass-charge ratio greater than this value tend to be lost on the other pair of electrodes
Data Source
AI summary
A quadrupole mass analyzer according to the present invention optimizes a stability band formation mode of a quadrupole system, so as to facilitate passing of ions and blocking of excessive ions, thereby improving the mass resolution without reducing the ion transmission efficiency. The solution of the present invention avoids the superimposition of high-frequency AC signals needed in the ion two-direction resonance frequency control in the prior art, and can effectively reduce the risk of quadrupole working performance reduction caused by the non-linear distortion of an RF voltage caused by bandwidth limitation in a fast RF circuit. In addition, a scanning speed of an ion-controlled electric field required by the quadrupole mass spectrometry can also be controlled faster because of reduction of limit bandwidth of various needed AC excitation signals. It is advantageous to obtain high-speed quadrupole scanning mass spectrometry performance.