Composite Mass Spectrum Generation via Centroid Histogramming
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Solution Overview
Problem
Mass spectrometers employing image current detection face limitations in resolving power, particularly for analyzing large proteins, due to signal decay and peak broadening, which restricts the mass range of resolvable proteins and requires lengthy detection times, making it challenging to accurately identify and quantify heavier proteins and their modifications.
Innovation Solution
A method that acquires a plurality of mass spectra with high signal-to-noise ratios, determines centroids, and constructs a composite mass spectrum using a histogram with narrower data groups, significantly improving resolving power by reducing peak width and enhancing mass precision and accuracy, allowing for better differentiation of ions and their isotopes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If detection time is increased to improve resolving power, then resolving power is improved, but signal decay and ion loss occur which limit maximum achievable resolution
Solution Approach 1:
The patent segments the detection process into multiple shorter transient acquisitions instead of using a single long detection period. By acquiring multiple transients of shorter duration and combining them through histogramming of centroid frequencies, the method achieves high resolving power equivalent to or exceeding that of a single long transient while avoiding signal decay issues.
Solution Approach 2:
The patent performs preliminary frequency analysis on each individual transient to determine centroid frequencies before combining results. This preliminary action allows each short transient to be optimally processed independently, and the centroid frequencies are then accumulated in a histogram to build the final high-resolution spectrum without requiring the ions to maintain coherence throughout an extended detection period.
2Measurement precision
If detection time is extended to achieve higher resolving power, then mass precision is improved, but ion loss by collisions and metastable fragmentation increase
Solution Approach 1:
The detection process is divided into multiple short transient acquisitions rather than one long acquisition. This segmentation reduces the time ions are exposed to collision and fragmentation risks in the detector, thereby reducing ion loss while still achieving high mass precision through the combination of multiple measurements.
Solution Approach 2:
The patent maintains continuous useful action by repeatedly acquiring new transients and accumulating their centroid frequencies in a histogram. This continuous accumulation process builds up the high-resolution mass spectrum over time without requiring any single ion to persist throughout the entire measurement period, thus reducing ion loss from collisions and fragmentation.
3Measurement precision
If multiple transients are acquired and combined through histogramming, then resolving power increases 3-6 times, but computational effort increases
Solution Approach 1:
The patent extracts only the essential information (centroid frequency and intensity) from each transient rather than processing the entire time-domain signal. By taking out only the peak centroid parameters and using these to populate a histogram, the method achieves high resolving power with significantly reduced computational complexity compared to processing complete transients through full Fourier transformation and combination.
Solution Approach 2:
The patent creates a simplified representation (copy) of each transient by extracting its centroid frequency and intensity. Instead of working with the complete, complex time-domain signal, the method uses these simplified centroid parameters to build the final histogram spectrum, reducing computational requirements while preserving the essential spectral information.
4Measurement precision
If the number of ions in the spectrometer is reduced to achieve mostly single-ion peaks, then mass accuracy improves, but signal intensity decreases
Solution Approach 1:
The patent compensates for the reduced signal intensity from single-ion peaks by continuously acquiring multiple transients and accumulating their centroid frequencies in a histogram. This continuous accumulation process builds up sufficient signal intensity in the final spectrum while maintaining the mass accuracy benefits of low ion population during each individual measurement.
Solution Approach 2:
The patent performs preliminary identification of single-ion peaks in survey spectra acquired at higher ion populations. This preliminary action allows the method to identify which mass regions contain suitable single-ion peaks, which are then targeted for high-precision measurement at lower ion populations, optimizing both signal intensity and mass accuracy.
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 enhances the resolving power of mass spectrometers by 3-6 times or more, enabling the accurate identification and quantification of heavier proteins and their modifications, even at higher signal-to-noise ratios and longer detection times, while maintaining low computational effort.
Implementation Method 1
The oscillatory motion may be of various forms including, for example, circular oscillatory motion in the case of FT-ICR and axial oscillatory motion whilst orbiting about a central electrode in the case of certain harmonic potential-FTMS such as an OrbitrapTM MS. The oscillatory image charge in turn induces an oscillatory image current in circuitry connected to the detection electrodes
Implementation Method 2
Fourier transformation of the transient yields the oscillation frequencies associated with the particular detected oscillating ions and from the frequencies the m/z values of the ions can be determined
Data Source
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Figure 3A~3B
AI summary
A method of generating a mass spectrum, e.g. for Fourier transform mass spectrometry, having improved resolving power, comprising: acquiring a plurality of mass spectra from a mass spectrometer using image current detection wherein most of the peaks are due to the detection of individual ions; determining the centroids of at least some of the peaks which are due to the individual ions and which have a sufficient signal-to-noise (S/N) ratio so that the variation of the centroid of each such peak from the plurality of mass spectra is significantly lower than the full-width at half-maximum, dM, of the peak in the m/z domain; and generating a histogram of the centroids determined from the plurality of acquired mass spectra thereby forming a composite mass spectrum wherein the composite mass spectrum comprises peaks and the full-width at half-maximum, dMC, of these peaks in the m/z domain is significantly narrower than the peak width, dM, of the corresponding peaks in the plurality of acquired mass spectra.