Nonlinear Chirp Excitation for ICR Mass Spectrometers
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Solution Overview
Problem
Current ion cyclotron resonance mass spectrometers face challenges in achieving high mass resolution and efficient measurement times due to the generation of 'beats' in ion image current transients, particularly when analyzing mixtures of ions with similar mass differences, which requires lengthy measurement times and high stability in magnetic and electrical parameters.
Innovation Solution
The use of nonlinear chirps with non-linear frequency functions and compensating amplitude changes to excite ions in ICR measuring cells, preventing the generation of beats by ensuring ions do not converge at the same point in time, thus maintaining orbital separation and enhancing measurement efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If linear chirps are used to excite ions, then all ions are excited uniformly to cyclotron trajectories, but beats are generated when ions with similar mass differences converge at the same point in time
Solution Approach 1:
The patent applies a nonlinear frequency function (specifically a quadratic function) to the chirp excitation signal, changing the temporal distribution of frequency components. This parameter change ensures that ions with different mass-to-charge ratios are excited at different rates, preventing their simultaneous convergence and eliminating beat formation while maintaining mass spectral resolution
Solution Approach 2:
The patent introduces dynamic adjustment of the excitation frequency over time through a nonlinear (quadratic) frequency function. This dynamic approach allows the excitation frequency to vary non-uniformly during the chirp pulse, creating differential excitation patterns that prevent synchronized ion convergence and eliminate beats
2Measurement precision
If extensive summation of transients is performed to achieve high mass resolution, then measurement accuracy improves, but measurement time increases significantly
Solution Approach 1:
The patent extracts and eliminates the harmful beat component from the ion signal through nonlinear frequency modulation. By removing the beat formation mechanism, the patent achieves high mass resolution without requiring extensive transient summation, thereby significantly reducing measurement time while maintaining analytical accuracy
3Measurement precision
If high stability in magnetic and electrical parameters is maintained to reduce beats, then measurement accuracy improves, but device complexity and operational constraints increase
Solution Approach 1:
The patent converts the potential harm of parameter variations into a benefit by using nonlinear frequency modulation. Instead of requiring extremely stable magnetic and electrical parameters, the nonlinear chirp technique actively exploits parameter variations to create differential excitation patterns that prevent beat formation, thereby reducing operational constraints and simplifying system requirements
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 or eliminates beat formation, allowing for shorter measurement times and improved mass spectral resolution without the need for extensive summation of transients, even in complex ion mixtures, thereby enhancing analytical efficiency and accuracy.
Implementation Method 1
the charge-related masses m/z of the ions are determined by measuring their orbital frequencies in a homogeneous magnetic field with high field strength. The orbital motion is essentially a cyclotron motion
Implementation Method 2
The ions are excited by absorbing energy in a dipolar alternating electric field between the two excitation electrodes. The frequency of the field must resonantly coincide with the cyclotron frequency of an ion species
Implementation Method 3
The two other electrodes, the 'measuring electrodes ', serve to measure the orbiting of the ion clouds by image currents induced in the measuring electrodes as the ion clouds fly past
Implementation Method 4
The Fourier analysis transforms the sequence of the original ion image current values of the transient from the 'time domain' into a sequence of frequency values in a 'frequency domain'
Data Source
AI summary
In an ion cyclotron resonance mass spectrometer ions are excited into cyclotron orbits by an alternating current excitation signal having a nonlinear function of the excitation frequency vs. time in a “chirp.” Such an excitation signal produces transients which have no pronounced beats, even if mixtures of many ion species, all having the same mass differences, are present. The dynamic measuring range for the image currents can thus be better utilized. In particular, sum spectra of specified quality can be generated from a significantly smaller number of individual transients, and thus in a significantly shorter measuring time.