Method for determining ion abundance

Abstract

A method of determining an initial abundance of one or more of a plurality of ions in an ion sample is provided. The ion sample is analyzed by a Fourier transform mass spectrometer, and the plurality of ions decay over time during the analysis. The method includes obtaining a mass spectrum of an ion sample. The mass spectrum includes a plurality of peaks indicative of an abundance of each of the plurality of ions in the ion sample over an analysis duration. The method further includes calculating an initial amplitude of the transient signal for a first ion of the plurality of ions using a fitting of an inverse Fourier transform (FT) to the first peak of the plurality of peaks.

Description

Technical Field

[0001] This disclosure relates to the field of Fourier transform mass spectrometry. Specifically, this disclosure relates to a method for improving the accuracy of calculating ion abundance in ion samples. Background Technology

[0002] Historically, accurate isotope ratio measurements have been achieved by ionizing low-molecular-weight gases produced from the combustion of analytes, followed by mass spectrometry analysis. Sector-magnetic field (SMP) mass spectrometers are the preferred platform due to their high stability, simplicity, dynamic range, and ion counts per second. The accuracy and precision of isotope ratio measurements are further enhanced by calibration using one or more reference compounds. However, SMP mass spectrometers have very limited mass resolution, narrowing the mass range to small gas molecules such as H2, CH4, CO2, O2, N2, and SO2. Isotope analysis of more complex molecules using SMP mass spectrometry requires them to be pre-converted / combusted into smaller, analyzable compounds, resulting in a large amount of isotopic information. Compound-specific isotope analysis (CSIA) further requires compound separation (e.g., by liquid chromatography or gas chromatography).

[0003] Ion cyclotron resonance (ICR) and orbital trapping systems (e.g., Orbitrap (RTM)) both fall under the category of Fourier transform mass spectrometry (FTMS). Both ICR and orbital trapping systems can provide the required mass accuracy and resolution to resolve whole-molecule analyte ions with different heavy isotopic substitutions. Different molecules that differ only in their isotopic composition or the intramolecular position of the isotopes can be called isotopic molecules. In beam-type instruments, ions directly bombard the detector, and the resulting electron current (reported as intensity) is a direct measure of its count. On the other hand, in Fourier transform mass spectrometry (FTMS), the signal can be induced at detection by oscillating ions, which are trapped, digitized, and stored as transients by an electric field (orbital trapping) or a combination of electric and magnetic fields (FT ICRMS). Its spectrum is calculated via Fourier transform (with some additional post-processing) and converted to the m / z domain via calibration.

[0004] Different space charge effects and the characteristics of ion motion adversely affect the coherence of oscillating ion packets, leading to distortion of observed peak intensities. This distortion increases non-linearly with decreasing ion abundance (reduced signal-to-noise ratio), resulting in distorted peak amplitudes, especially for low-abundance ion signals. Similarly, scattering of ions on background gas molecules leads to observed resolution loss and distortion of the original peaks. Both attenuation mechanisms compromise the fidelity of the reported signal intensity for ions. This can result in inaccuracies and low precision in any quantitative FTMS analysis, particularly for low-abundance ions and long transient lengths (high resolution). Ultimately, absolute quantification of compounds in mixtures, as well as any ratios of two peaks (including isotope ratio analysis) and targeted quantification using internal standards, can be compromised by doping.

[0005] Known methods (Hilkert, A.; JK; Mrozzkowski, SJ; Fort, KL; Aizikov, K.; Wang, XT; Kopf, SH; Neubauer, C. Exploring the Potential of Electrospray-Orbitrap for Stable Isotope Analysis Using Nitrate as a Model. Analytical Chemistry (Anal. Chem. 2021, 93(26), 9139–9148) explains signal intensity instabilities by introducing compounds with known isotopic distributions into the FTMS analyzer as a reference during experiments. However, reference materials are not available for every compound, and this approach significantly complicates experimental setup, leading to substantial additional costs and a significant increase in required analysis time, thus negatively impacting throughput. Summary of the Invention

[0006] In view of this background and according to the first aspect, a method is provided for determining the initial abundance of one or more ions among a plurality of ions in an ion sample analyzed by a Fourier transform mass spectrometer. Specifically, this disclosure uses fitting of the inverse Fourier transform (FT) of the ion peaks within the mass spectrum to calculate the initial amplitude of the decay transient signal of the ion isotopes. The initial amplitude of the decay transient signal, i.e., the amplitude before signal decay, is determined by extrapolating the ion abundance to the time at the start of the analysis.

[0007] Specifically, in a first aspect, a method is provided for determining the initial abundance of one or more ions among a plurality of ions in an ion sample analyzed by a Fourier transform mass spectrometer, the plurality of ions decaying over time during analysis, the method comprising:

[0008] Obtain a mass spectrum of an ion sample, wherein the mass spectrum comprises multiple peaks indicating the abundance of each of a plurality of ions in the ion sample during the analysis duration T; and

[0009] The initial amplitude of the transient signal of the first ion among multiple ions is calculated by fitting the inverse Fourier transform (FT) of the first peak among multiple ions, where the first peak corresponds to the first ion, to extrapolate the abundance of the first ion to the time at the start of the analysis duration.

[0010] This disclosure recognizes that transient decay in FTMS can be defined by two factors. First, the number of oscillating ions may decrease due to collisions with background gas molecules (hereinafter referred to as collisional decay). Second, if trapped in a non-ideal isochronous ion trap, ions with the same m / z can oscillate at different frequencies. This can cause the phase difference between ions to increase over time (hereinafter referred to as phase shift). Therefore, when all phases are aligned, the total partial contribution to the signal peak is a smaller amplitude than at the start of the transient. This first aspect provides advantages in improving the accuracy, precision, repeatability, and overall quality of measurements of the ratio of one or more ions (such as isotopes, isotopic bodies, or isotopic molecules).

[0011] Additionally or alternatively, calculating the initial amplitude of the transient signal of the first ion may include using a collision attenuation parameter and a phase-shift attenuation parameter of the first peak corresponding to the first ion among multiple peaks, thereby extrapolating the abundance of the first ion indicated by the mass spectrometer to the time at the start of the analysis duration. This provides the advantage that the initial amplitude can be accurately determined using both the collision attenuation parameter and the phase-shift attenuation parameter. By using both the collision attenuation parameter and the phase-shift attenuation parameter, the initial amplitude can be calculated for ions with both high and low abundance. Furthermore, since the attenuation is divided into collision attenuation and phase-shift attenuation, the collision attenuation can be used to determine the collision cross-section (CCS) of the ion.

[0012] Optionally, the method may further include determining the collision attenuation parameter and / or phase shift attenuation parameter of the first peak.

[0013] Optionally, determining the collision attenuation parameter and / or phase shift attenuation parameter of the first peak includes: centering the first peak at zero frequency; applying the inverse Fourier transform; and fitting the function to the magnitude of the inverse Fourier transform. Optionally, the method may include fitting the function to the logarithm or natural logarithm of the inverse Fourier transform. Optionally, the function may be a linear regression.

[0014] Optionally, determining the collision attenuation parameter and / or phase shift attenuation parameter may include using the polynomial – αt 2-βt-c is the logarithm of the magnitude fitted to the inverse FT. Further, alternatively, the initial amplitude I0 of the transient signal can be calculated based on the parameter c, where I0 = I(0) = e c Therefore, the initial intensity of the transient signal can be directly calculated by fitting an inverse Fourier transform to compute the parameter c. Thus, in some examples, it is not necessary to calculate the phase shift rate and collision decay rate.

[0015] Optionally, calculating the initial amplitude of the transient signal may also include calculating a correction factor for the abundance, wherein the correction factor is calculated using collision attenuation parameters and phase shift attenuation parameters.

[0016] Alternatively, the correction factor can be calculated using the following equation: Where α is the phase-shift attenuation parameter and β is the collision attenuation parameter.

[0017] Optionally, the phase-shift attenuation parameter can be pre-calibrated. For example, the phase-shift attenuation rate can be predetermined and selected from predetermined values ​​of the phase-shift attenuation rate for each SNR value. This can have the advantage that the phase-shift attenuation rate does not need to be calculated for each peak in the mass spectrum, but can be predetermined, which improves computational speed and reduces data processing requirements.

[0018] Optionally, the collision decay rate can be pre-calibrated.

[0019] Optionally, the pre-calibration of the phase attenuation parameter may include: calculating multiple phase attenuation parameters for multiple signal-to-noise ratio (SNR) values; and fitting a curve to multiple phase attenuation parameters so that the phase attenuation parameter can be determined for additional SNR values.

[0020] Optionally, the second ion among the multiple ions has the same collision cross-section as the first ion, such that the collision decay parameter of the second ion is equal to the collision decay parameter of the first ion.

[0021] Optionally, the collision decay parameters of the first ion can be used to calculate the correction factor and / or initial amplitude for the second ion.

[0022] Alternatively, the phase-shift attenuation parameter or correction factor can be calculated without calculating the collision attenuation parameter.

[0023] Optionally, two or more of the multiple ions may differ in their isotopic composition. For example, an ion can be an isotope or an isotopic molecule. Therefore, the novel technique described herein can be used for the analysis of isotope, isotopic body, or isotopic molecule ratios.

[0024] Optionally, before calculating the initial amplitude, the method may further include determining a collision decay parameter for a second peak in the mass spectrum, wherein the second peak has an abundance above a threshold abundance; and wherein the collision decay parameter of the first peak is equal to the collision decay parameter of the second peak. This can have the advantage that it eliminates the need to calculate the collision decay parameter for each peak, thus reducing the required processing.

[0025] Optionally, before calculating the initial amplitude, the method may further include calculating the phase-shifting attenuation parameter of the first peak by using the logarithm of the inverse Fourier transform of the first peak and the collision attenuation parameter of the first peak.

[0026] Optionally, calculating the initial amplitude of the transient signal may also include calculating a correction factor for abundance, where the correction factor is calculated using collision decay and phase-shift decay parameters. This can have the advantage of correcting for abundance by taking into account the collision decay and phase-shift decay parameters. Therefore, the abundance of ions can be corrected, and the initial amplitude can be found. Abundance is relative to the calculated SNR value, as ions with higher abundance exhibit a higher SNR due to their stronger signal. The correction factor can be used to improve the accuracy, precision, repeatability, and overall quality of quantitative or semi-quantitative analysis of one or more ions and / or isotopic molecules in an ion sample.

[0027] It should be understood that in the examples described herein, SNR can be replaced by another mass spectrometry parameter used as a measure of abundance, while still using the novel techniques described herein.

[0028] Optionally, the method includes calculating multiple phase-shift attenuation parameters for multiple signal-to-noise ratio (SNR) values ​​and fitting a curve to the multiple phase-shift attenuation parameters, such that the phase-shift attenuation parameters can be determined for additional SNR values. This can have the advantage that it is not necessary to explicitly calculate the phase-shift attenuation rate for each SNR value and each peak in the mass spectrum.

[0029] On the other hand, a computer program is provided for determining the initial abundance of one or more ions among a plurality of ions in an ion sample analyzed by a Fourier transform mass spectrometer, the computer program including instructions that, when executed by a computer, cause the method to be performed according to any of the methods described herein.

[0030] On the other hand, a Fourier transform mass spectrometer is provided, which is configured to perform any of the methods described herein.

[0031] Alternatively, the Fourier transform mass spectrometer is an orbital trap mass spectrometer. Attached Figure Description

[0032] The following discussion of at least one embodiment is with reference to the accompanying drawings, which are not intended to be drawn to scale. The drawings are included to provide illustration and further understanding of the aspects and embodiments, and are incorporated in and constitute a part of this specification, but are not intended to be a definition of limitation of the invention. In the drawings, each identical or substantially identical component illustrated in the various figures is represented by similar numerals. For clarity, not every component will be labeled in every figure.

[0033] Figure 1 A graph showing the relationship between resolution and SNR is presented.

[0034] Figure 2 A flowchart of a method according to one implementation scheme is shown;

[0035] Figure 3 A flowchart of a method according to one implementation scheme is shown;

[0036] Figure 4A , Figure 4B and Figure 4C The three stages of the method for determining the attenuation parameter are shown;

[0037] Figure 5 A graph of the transient signal is shown;

[0038] Figure 6 The graph shows the phase shift attenuation parameter (α) versus SNR;

[0039] Figure 7A The theoretical mass spectrum is shown, and Figure 7B An experimental mass spectrometry result determined according to one implementation scheme is shown;

[0040] Figure 8 A schematic diagram of the Orbitrap mass spectrometer is shown; and

[0041] Figure 9 A flowchart of a method according to one implementation scheme is shown. Detailed Implementation

[0042] This disclosure will now describe specific implementation methods. The implementation methods described herein are not intended to be limiting, but are for illustrative purposes.

[0043] The methods described herein relate to ions in an ion sample. In some examples, the ions are substances that differ only in their isotopic composition (i.e., the ions are isotopic molecules). In such examples, the analysis aims to perform a ratio analysis of the strengths of these isotopic molecules (isotope ratio analysis). In other words, to determine an isotope ratio measurement, complex molecules carrying different isotopes in their chemical structure can be analyzed. This method can be performed by analyzing isotopic isotopes, isotopic molecules, or isotopic bodies. Therefore, the technical aspects described herein can be used for any other quantitative analysis of ions, isotopic isotopes, or isotopic bodies or ions in a sample.

[0044] In the examples described herein, the initial abundances of two or more isotopic molecules or isotopes can be calculated. Such initial abundances can be used to determine the isotopic ratios within an ionic sample.

[0045] However, in other examples, the initial abundance of ions (i.e., the initial abundance of ions in any given peak) can be calculated. In other words, the initial amplitude of one or more individual ion peaks can be calculated. In some examples, one or more ion peaks can be analyzed where the ions are not isotopes or isotopic molecules, or where the ratio of peaks is not of interest. Three non-limiting examples of uses for such methods are now described.

[0046] In the first example, the method described herein can be used for quantitative analysis, such as for the absolute or relative quantification of one or more ions in an ion sample. For example, this quantification can use internal or external standards or calibrators. The internal standard can be isotopically labeled and added to a known concentration. The ratio of the compound in the sample to the added standard can be used to quantify the compound in the sample.

[0047] In the second example, the method described herein can be used for non-targeted semi-quantitative analysis of a variety of compounds. This can be performed in metabolomics, lipidomics, or other studies. In these applications, peak ratios are not calculated. Instead, the method described herein can be performed on individual peaks within a mass spectrum. In other words, the method may include performing the inverse FT and fitting procedure as described herein for each individual peak of interest in the mass spectrum and determining the decay rate or initial amplitude for each peak.

[0048] In the third example, the method described herein can be used for soft labeling experiments. One or more compounds rich in one or more heavy isotopes are introduced into a system (cell culture, bacteria, animal, human), and then a non-targeted screening of a set of compounds is performed to quantify the peaks of isotopic labeling in these compounds to see how much of the initial compound has been incorporated into the organism. Transient decay in FTMS can be defined by two factors. First, the number of oscillating ions may be reduced due to collisions between ions and background gas molecules. Second, if trapped in a non-ideal isochronous ion trap, ions with the same m / z can oscillate at slightly different frequencies. As the phase difference between ions increases over time, the partial contribution to the signal can sum up to a smaller amplitude than at the start of the transient when all phases are aligned.

[0049] Based on theoretical and experimental examinations of signal attenuation in FTMS (and especially Orbitrap (RTM) mass spectrometry), it has been recognized that ions undergo many space charge-related effects. One of these effects is the so-called "self-bundling," which is the effective synchronization of all ions with the same m / z due to Coulomb interactions between them. In other words, the "natural" broadening of the ion pack is suppressed in high ion packs due to the combined effects of space charge and electric field nonlinearity.

[0050] It has been recognized that, due to self-bundling, there may be no phase-shifting mechanism for signal attenuation. Therefore, when the number of ions in a peak exceeds a certain self-bundling threshold, the signal may not attenuate due to phase shift attenuation.

[0051] While it may be difficult to determine the actual number of ions in the packet, the number may be proportional to the SNR of the peak for a given transient duration and decay constant, where the coefficient of the proportion depends only on the thermal noise of the detector's preamplifier and its frequency dependence. The relationship between SNR and ion number is described, for example, in Section 2.1 of Eiler et al. (Analysis of molecular isotopic structures at high precision and accuracy by Orbitrap (RTM) mass spectrometry) (International Journal of Mass Spectrometry, Vol. 422, 2017, pp. 126-142, ISSN 1387-3806), which is incorporated herein by reference. The relationship described by Eiler et al. for determining ion number can be used in the embodiments of this disclosure when the signal intensity or SNR is described as being used.

[0052] Signal attenuation can be estimated from mass spectrometry using the observed peak width. Resolution can indicate or be proportional to the temporal signal loss, and SNR can be equivalent to or proportional to the size of the ion population in the cloud. Therefore, in the following description of a novel concept, SNR can be used to refer to the population of ions in an ion sample, i.e., its abundance.

[0053] Figure 1 This demonstrates that for ion packs with ion clusters larger than a threshold (referred to herein as the self-bundling threshold), the decay rate can be determined entirely by collisional decay. The threshold is determined by... Figure 1 The dashed line marked 101 is shown. The self-bundling threshold can be at an SNR value of approximately 80. It should be understood that the same concepts described herein apply to examples where isotopic molecular populations are determined.

[0054] Ions may decay due to collisional decay. This collisional decay arises from collisions between ions and background gas molecules and remains constant for a given ionic substance under consistent pressure conditions. In other words, for a given ionic substance (i.e., all isotopic states of a compound), collisional decay can be approximately constant and can be precisely calculated. Therefore, the collisional decay rate determined for one isotopic molecule in an ionic sample (also referred to herein as the collisional decay parameter) is equal to the collisional decay rate for another isotopic molecule in the same ionic sample. Collision-induced decay provides information about the ion collision cross section (CCS), as ions with a higher CCS are expected to collide with the background gas more frequently, and therefore the image signal provided by such ions is expected to decay more quickly. Collisional decay also provides information about the pressure within the analyzer.

[0055] like Figure 1As shown, for ions with abundances below the self-coalescing threshold (i.e., ion peaks with amplitudes below the self-coalescing threshold), attenuation comprises components of phase-shifting attenuation and collisional attenuation. It has been recognized that the collisional attenuation rate (β) and the phase-shifting attenuation rate (α) can be separate. Phase-shifting attenuation arises due to non-ideals in the mass spectrometer (i.e., defects in the mass spectrometer) and does not provide useful information about CCS. The rate of phase-shifting attenuation is different for most ions, and it may be different for most isotopes (and isotopic molecules). Most molecules have multiple non-monoisotopic (non-M0) peaks, where each peak may correspond to one or more isotopes of the molecule. Due to the different relative abundances of heavy isotopes, different isotopic molecules exist at different abundances in an FTMS analyzer. Therefore, each isotopic molecule has its own individual phase-shifting rate. Thus, in some of the methods described herein, the phase-shifting attenuation rate is determined for each peak. In a mass spectrum containing multiple peaks, the peaks may be associated with isotopes of the same molecule, or they may be associated with different ions (i.e., ions of different molecules). In other words, the peaks may not be related to isotopes.

[0056] It should be understood that the following description will relate to ions, where one or more ion peaks may be considered individually. However, the same concept applies to examples where multiple isotopic peaks are analyzed to calculate the isotopic ratio within an ion sample. As will be described, it has been recognized that a phase-shifting attenuation parameter can be calculated and used in combination with a collisional attenuation parameter to provide improved accuracy in the measurement of ion (or isotopic molecule) abundance within an ion sample. Using the attenuation parameter, the abundance of an ion can be found before it decays due to collisional attenuation and / or phase-shifting attenuation.

[0057] As described in this paper, the intensity of the induced current (which indicates the abundance of ions) decreases over time because ions are broken up or pushed into unstable orbits upon collision with gas molecules, where they decay rapidly. The cloud also loses its coherence due to the phase shift.

[0058] The intensity as a function of time can be represented as shown in Equation 1, where the intensity decreases with time.

[0059] I(t) = e -γ(t) (1) where t is the transient time and γ is the decay rate. In particular, γ is the sum of the collision (β) decay rate and the phase shift (α) decay rate, where γ increases with time t. Equation 1 can be rewritten based on collision phase shift decay, as shown in Equation 2:

[0060] I(t) = e c-α(t)-β(t) (2)

[0061] Random collision decay follows a Poisson distribution, resulting in a linear term -βt. The phase-shifting component α(t) is typically nonlinear. In the case that the ion pack is initially strictly phase-determined (all ions begin to oscillate in one phase), the function α(t) is expected to have a zero slope at t = 0, and its least-complexity model is a quadratic function αt. 2 Thus, we obtain equation 3:

[0062]

[0063] The coefficient c gives the intensity at t=0 as I0=I(0)=e c Its value is proportional to the number of ions in the peak.

[0064] The intensity of the observed peak can be suppressed in the frequency domain, or equivalently in the m / z domain. The overall decrease in peak intensity observed during a transient period of duration T can be determined by Equation 4. This can be referred to as the correction factor. The correction factor allows for the determination of the corrected SNR, where, as described herein, the SNR is related to abundance. Equation 4 can be used to calculate the correction factor, and time T is the length of the transient, i.e., the length of the analysis. For example, for a 480,000 resolution measurement, this could be 1.024 seconds. Here, "erf" is determined by… Defined error function.

[0065]

[0066] Therefore, as will be described, using the method described herein, the original intensity value (i.e., at time point T = 0) can be determined if the values ​​of α and β are known.

[0067] Therefore, if the collision attenuation parameter β and the phase shift attenuation parameter α are known, Equation 4 can be used to determine the initial intensity.

[0068] The initial abundance can be calculated by dividing the decay abundance (i.e., the abundance at time T) by the correction factor calculated according to Equation 4.

[0069] Figure 2 A method 200 according to an example is shown. This method determines the initial abundance of one or more ions among a plurality of ions in an ion sample. The ion sample is analyzed by Fourier transform mass spectrometry. As described herein, the abundance of multiple ions (i.e., ion abundance) decays over time during analysis due to collisional decay and phase-shift decay. Therefore, an analysis measured at time T cannot accurately provide the initial abundance of ions in the ion sample (i.e., the abundance of each type of ion).

[0070] In step 210, a mass spectrum of the ion sample is obtained. The mass spectrum provides the relationship between the intensity (i.e., abundance) of ions within the analyzed ion sample and their mass-to-charge ratio (m / z). The intensity is indicated over the analysis time T. As described herein, the intensity shown on the mass spectrum can vary over time because ions decay due to collisional decay and / or phase-shift decay. Each peak on the mass spectrum is associated with an ion, meaning each peak on the mass spectrum is associated with a molecule having the same m / z ratio. For example, when the ion sample contains isotopic molecules or isotopes, the mass spectrum may include more than one peak.

[0071] In step 220, the initial amplitude (i.e., initial signal amplitude) of the transient signal of the first ion is calculated. The transient signal represents the intensity or abundance of an ion over time at a specific mass-to-charge ratio. Therefore, the initial amplitude of the transient signal of the first ion provides quantitative information about the first ion (i.e., about the ion of interest). The initial amplitude provides information about the abundance or intensity of the first ion at an initial time (i.e., before the ion has decayed). Thus, the initial amplitude of the transient signal for each ion provides the abundance of the corresponding ion in the ion sample before the ion sample undergoes mass analysis. In Example Method 200, the initial amplitude of the transient signal of the first ion is calculated using a fit to the inverse Fourier transform of the first peak among a plurality of peaks. The first peak corresponds to the first ion. The abundance of the first ion is extrapolated to the time at the start of the analysis duration (i.e., to the start of the analysis) using the fit to the inverse Fourier transform. In other words, the abundance is extrapolated to the time at the start of the analysis duration.

[0072] In examples where the mass spectrometer includes two or more peaks, the method may include calculating the initial amplitude of each ion peak individually.

[0073] In relation to Figure 9 In another example described, multiple peaks can be analyzed, where each peak corresponds to one or more isotopes or isotopic molecules.

[0074] about Figure 3 Another example method 300 for determining the initial abundance of ions is described.

[0075] Step 310 includes obtaining a mass spectrum of the ion sample. This step can be the same as step 210, such that step 310 has the same characteristics as step 210.

[0076] Step 311 involves determining the collision attenuation parameter and / or phase-shift attenuation parameter. This document describes methods for determining the collision attenuation parameter and / or phase-shift attenuation parameter, and any such method may be used herein. For example, as shown in step 312, the first peak (i.e., the peak being analyzed) is centered at zero frequency, and an inverse Fourier transform (FT) is applied to this peak. A suitable function is then fitted to the magnitude of the inverse FT. By fitting the function to the magnitude of the inverse FT, the collision attenuation parameter and / or phase-shift attenuation parameter can be determined. In some examples, the function may be fitted to the logarithm or natural logarithm of the inverse FT to determine the collision attenuation parameter and / or phase-shift attenuation parameter. This document describes the method in more detail.

[0077] In some examples, such as in calculating the abundance of one or more isotopic molecules, the collisional decay parameter and phase-shift decay parameter of the first peak among multiple peaks can be used alternatively or additionally to calculate the initial amplitude (which corresponds to...). Figure 3 (The method described in [reference needed]). In this example, the first peak corresponds to the first isotopic molecule. Using these attenuation parameters, the abundance of the first isotopic molecule can be extrapolated to the time at the start of the analysis duration. It has been recognized that abundance or intensity decays over time during analysis due to collisional attenuation and / or phase-shift attenuation. Therefore, the initial attenuation can be calculated using the collisional attenuation parameter and the phase-shift attenuation parameter of the first isotopic peak, where the phase-shift attenuation parameter can be zero. The collisional attenuation parameter can be substantially the same for each isotopic molecule, and the phase-shift attenuation parameter can be different for each isotopic molecule.

[0078] Therefore, in such examples, it has been recognized that, by using the methods described herein, both the phase-shifting decay parameter and the collisional decay parameter can be used to determine the initial abundance of isotopic molecules in an ionic sample. Thus, the initial abundance of isotopic molecules with abundances above or below the self-bundling threshold can be determined, as described in more detail herein.

[0079] Example method 900 further describes an example of calculating the initial abundance of isotopic molecules. Method 900 may include any of the features described with respect to method 200, or may be combined with any features of method 200 or 300. It should be understood that, in this example, the mass spectrum includes multiple peaks, wherein two or more of the multiple peaks correspond to isotopic molecules, i.e., the peaks are isotopic peaks.

[0080] Step 910 includes obtaining a mass spectrum of the ion sample. This step can be the same as step 210, such that step 910 has the same characteristics as step 210. In this example, the mass spectrum includes multiple peaks that indicate the abundance of each of the multiple isotopic molecules in the ion sample during the analysis duration T.

[0081] Step 911 is an optional step that includes determining the collisional decay parameter of the second peak. The second peak corresponds to a second isotope molecule within the ion sample that is identical to the first isotope molecule. In this example, the second isotope molecule has an abundance above a threshold abundance. In other words, the SNR of the second isotope molecule is greater than the threshold described herein. The threshold abundance is determined by the threshold at which isotope molecules self-bundle due to the Coulomb effect. Therefore, the threshold abundance can also be referred to as the self-bundling threshold. Isotope molecules with a threshold above the self-bundling threshold do not decay due to phase shift. Therefore, it has been recognized that by considering second isotope molecules with an abundance above the threshold abundance, it can be determined (or approximated) that the decay of the second isotope molecule during mass analysis is solely due to collisional decay.

[0082] The collisional decay parameter of the first peak is equal to or substantially equal to the collisional decay parameter of the second peak. It has been recognized that the collisional decay parameter is approximately the same for all isotopic states of the compound. Therefore, it is recognized that the collisional decay parameter already determined for the second peak can also be used as the collisional decay parameter for the first isotopic molecule, which may have an abundance above or below a threshold.

[0083] Step 920 may follow either step 910 or step 911. At step 920, the initial amplitude of the transient signal of the first isotope molecule can be calculated using the collision decay parameter and phase-shift decay parameter of the first peak corresponding to the first isotope molecule among multiple peaks, thereby extrapolating the abundance of the first isotope molecule indicated by the mass spectrometer to the time at the start of the analysis duration. The parameters determined in step 911 or by any method described herein can be used to calculate the initial amplitude of the transient signal.

[0084] Therefore, by using about Figure 9 The described method 900 can calculate the initial abundance of a first isotope molecule. This method provides an efficient way to calculate such abundance because it has been recognized that phase-shift decay and collision decay can be separated, and that collision decay can be the same for isotope molecules of the same compound. It should be understood that the method used to determine the initial abundance of each isotope molecule in a sample can alternatively be the method described with respect to step 220, i.e., the inverse Fourier transform.

[0085] As discussed above, the phase-shift attenuation parameter is denoted as α in this paper, and the collision attenuation parameter is denoted as β in this paper. Using the collision attenuation parameter and / or the phase-shift attenuation parameter, the intensity can be projected (i.e. extrapolated) to its original value at time point t=0.

[0086] If the phase-shift attenuation parameter and the collision attenuation parameter are known, the initial amplitude can be calculated by determining a correction factor based on the collision attenuation parameter and the phase-shift attenuation parameter. As described herein, Equation 4 can be used to calculate the correction factor, where time T is the length of the transient, i.e., the length of the analysis. Therefore, if the collision attenuation parameter β and the phase-shift attenuation parameter α are known, the initial intensity can be determined, for example, by using Equation 4.

[0087] The corrected SNR (relative to the corrected abundance) can be calculated according to Equation 5, where the decayed SNR, i.e. the SNR at time T, is divided by the correction factor (calculated according to Equation 4).

[0088]

[0089] Simultaneously calculate the attenuation parameter

[0090] Example methods for determining phase-shift attenuation parameters and collision attenuation parameters will now be described. However, it should be understood that other methods for determining any one or both of these parameters may be used without departing from the methods described herein. These methods may be used in any of the methods 200, 300, and / or 900 described herein.

[0091] Figure 4A , Figure 4B and Figure 4C An example method for determining the collision attenuation parameter β and the phase shift attenuation parameter α is shown. Three figures are used. Figure 4A , Figure 4B and Figure 4C The method is illustrated in the figures. For the method described in these figures, raw transient data is required to enable the determination of parameters using the described method.

[0092] First of all, Figure 4A The image shows the mass spectrum of the ion. The peak of interest, 402 (i.e., the spectral peak), is separated from the other peaks in the mass spectrum. This peak can be isolated from the other peaks in the mass spectrum by using a smoothing function. Figure 4A The application of a smoothing function is illustrated, where the inner line corresponds to the original mass spectrum and the outer line corresponds to a smoothing function, such as a window function. However, it should be understood that another suitable method can be used to isolate peaks from other peaks.

[0093] After the selected peak has been isolated, it is centered at zero frequency and an inverse Fourier transform is applied. Figure 4B The time plotted relative to the transient is shown. Figure 4A The inverse Fourier transform is the logarithm of the reciprocal of the amplitude of the Fourier transform signal of the peak shown. As described in this paper, the inverse Fourier transform can be used to determine the initial abundance of ions or isotopic molecules.

[0094] Linear regression can be fitted to the inverse Fourier transform. In one example, to determine α and β, Equation 3 can be fitted to the result of the inverse Fourier transform (FT). This equation can be fitted to the interior of a curve that is artifact-free, such as... Figure 4C As shown. This equation can be fitted in the linear range, where the range is within... Figure 4C It is shown between the two vertical lines.

[0095] As Figure 4C The method shown is an alternative to fitting Equation 3 to the curve, which allows the polynomial –αt to be replaced. 2 -βt-c is the logarithm of the result of fitting to the inverse FT. Figure 4C (Not shown in the image).

[0096] The coefficient c gives the intensity at t=0 as I0=I(0)=e c The coefficient c is proportional to the number of ions in the peak. Therefore, by fitting a suitable polynomial, the coefficients c, and α and β, can be determined. Thus, α and β (and optionally c) can be determined simultaneously using the method described above. However, due to noise and end-space artifacts in the inverse FT, simultaneously evaluating both parameters α and β from the observed signal (whether transient or mass spectrometric) is not always reliable. Therefore, it is advantageous to provide a method that does not evaluate the parameters simultaneously.

[0097] Calculate attenuation parameters independently

[0098] In another example, where two or more isotopic peaks are present in the mass spectrum, the collisional decay rate can be determined by analyzing isotopic molecules with abundances above an abundance threshold. In one example, the abundance threshold is approximately 80 SNR. The abundance threshold is an abundance above which no phase-shifting decay due to self-bundling occurs, as described herein. The threshold can be a predetermined value. Thus, by analyzing isotopic molecules above the threshold, it is determined that the isotopic molecules decay solely due to collisional decay. The collisional decay parameter can be calculated using linear regression. In particular, collisional decay follows a first-order exponential decay, and therefore, when there is no phase-shifting decay, collisional decay can be calculated using linear regression of the logarithm of the amplitude of the inverse Fourier transform. In particular, the collisional decay parameter can be determined using Equation 3 as described herein.

[0099] It has been recognized that for isotopic molecules obtained under similar conditions (e.g., similar gas pressures, accelerating voltages, etc.), the collision cross-sections are essentially the same. Therefore, the collision decay parameters of isotopic molecules are essentially the same, meaning we can estimate that isotopic molecules have the same collision decay rate. Thus, for isotopic molecules with abundances above a threshold, the isotopic molecules decay at essentially the same rate because there is no phase-shift decay.

[0100] After calculating the collision attenuation parameters separately, you can use the parameters related to... Figure 4A , Figure 4B , Figure 4C The same method described is used to determine the phase-shift attenuation parameter α. For example, Equation 3 can be fitted to the inverse Fourier transform, or a second-order polynomial can be fitted to the magnitude of the inverse Fourier transform (or the logarithm of the magnitude of the inverse Fourier transform). For example, polynomial –αt 2 -βt-c can be used to determine the phase-shift attenuation parameter α. By calculating the collisional attenuation parameter before determining the phase-shift attenuation parameter, and by using any of the methods described herein, making the parameter β known, a fitting procedure can be used to determine only the phase-shift attenuation parameter α. Therefore, the phase-shift attenuation parameter can be determined independently of the collisional attenuation parameter. Once the collisional attenuation parameter and the phase-shift attenuation parameter are determined, the initial abundance can be calculated. This provides an improved method for determining the attenuation parameter and thus the initial abundance of the isotopic molecule. By using a high-abundance peak to determine β, the calculation of β will be more accurate than using a low-abundance peak, because the high-abundance peak will be less affected by noise and has no phase-shift attenuation. Using this more accurate β value to calculate α will result in a more accurate calculation of α. Therefore, this method provides a more accurate and precise calculation of the attenuation parameter.

[0101] Figure 5 The spectrum of a single peak is shown. The intensity versus frequency is plotted in this graph. The frequency can be converted to a mass-to-charge (m / z) ratio (not shown here) to provide a mass spectrum. This graph shows the Orbitrap (RTM) transient signal of a cloud of monoisotopic MRFA ions (methionine, arginine, phenylalanine, alanine ions) with a charge z = 1, simulated using assumed phase-shift decay rates and collision decay rates of α = 0.495 and β = 0.3, respectively. This graph shows the transient signal 503 including decay, i.e., the signal has decreased due to ion decay over time. Therefore, the ion abundance decreases over time and does not show the initial ion abundance in the ion sample. This graph also shows the transient signal 504 without any decay, i.e., the signal shows the initial amplitude of the transient signal as described herein. Therefore, the transient signal without any decay shows the initial ion abundance in the sample. Figure 5 Also shown is the “recovered” transient signal 505 according to the invention, i.e., Figure 5The attenuated signal has been extrapolated to determine the initial intensity using collisional attenuation and phase-shifting attenuation parameters. As shown, the non-attenuated signal 504 has a higher intensity than the attenuated signal 503. For example, the non-attenuated signal has a maximum intensity of approximately 2e6, while the attenuated signal has a maximum intensity of approximately 1.5e6. The recovered signal is shown by data point 505, and it is shown that the recovered signal has an intensity that recovers to approximately the intensity of the unattenuated signal. Thus, it is shown that the ion abundance in an ion sample, i.e., before any attenuation occurs, can be determined using the techniques described herein. The same applies to the determination of the abundance of isotopic molecules. It should be understood that some spoilers may exist due to simulation noise, which may cause the recovered signal to not have the exact same intensity as the unattenuated signal. However, as shown, this method provides an accurate extrapolation of the signal to illustrate the attenuation found in Fourier transform mass spectrometry.

[0102] Precalibration parameters

[0103] In the example described in this article, the value of the phase shift attenuation parameter can be precalibrated. Figure 6 The plots show the phase shift attenuation parameter along the y-axis and the SNR along the x-axis. It has been recognized that for packets with the same ion number, the phase shift rate is reproducible, where the ion cluster is associated with the SNR. Therefore, for ion or isotopic molecules with the same SNR, the phase shift rate is reproducible. Figure 6 As shown, the data can be organized for the calculated phase shift attenuation rate under different SNR values. In other words, the phase shift attenuation rate is determined for multiple SNR values, where the multiple SNR values ​​are different, making it possible to determine the phase shift attenuation rate for a series of SNR values. One of the methods described in this paper (e.g., regarding...) can be used. Figure 4A , Figure 4B , Figure 4C The described method is used to determine the phase-shifting attenuation rate. A smoothing function can be fitted using multiple calculated phase-shifting attenuation rates, and an equation fitting this function can be determined. Therefore, an equation providing the relationship between the SNR and the phase-shifting attenuation rate can be determined. Thus, the phase-shifting attenuation rate can be determined for isotopic molecules with additional SNR values, i.e., isotopic molecules having SNR values ​​for which the phase-shifting attenuation rate has not yet been explicitly calculated.

[0104] Equation 6 provides an example of a smoothing function, which in Figure 6 The line in the middle is shown as a dashed line. Equation 6 provides the relationship between the phase shift attenuation parameter and the SNR value.

[0105] A(SNR)=Ae -b*SNR (6)

[0106] As shown in Equation 6, the phase-shifting attenuation parameter can be provided by an exponential function. Parameters A and b can be determined by fitting Equation 6 to a smoothing function. Once parameters A and b have been calculated using the fitted curve, the relationship between the phase-shifting attenuation parameter and the SNR can be determined. Therefore, using the fitted curve and / or Equation 6, the phase-shifting attenuation rate can be accurately determined for isotopic molecules (or ions) at any SNR value.

[0107] As stated above regarding Equation 4, once the collision decay parameter and phase shift decay parameter have been calculated, this method can calculate the corrected SNR value (i.e., initial abundance) for each isotopic molecule. As described in this article, Equation 7 can be used to calculate the corrected initial amplitude:

[0108]

[0109] Equation 4 is used to calculate the correction factor. Readers can refer to publicly available information describing Equation 4, whose features can be combined with the example methods described here.

[0110] The collision decay rate can be pre-calibrated (i.e., predetermined). The collision decay rate can be pre-calibrated in addition to or isolated from the pre-calibrated phase-shift decay parameter. The collision decay rate β can be pre-calibrated by analyzing the compound, molecule, or ion of interest at a higher signal-to-noise ratio (SNR). Figure 6 As shown, at SNRs above approximately 80, the phase-shifting decay rate α is approximately 0. Therefore, as mentioned above, when the approximate phase-shifting decay rate is 0, β can be determined using Equation 3. Thus, the collision decay rate can be pre-calibrated, allowing the collision decay rate to be pre-determined for ions with the same collision cross-section. Multiple data points can be acquired for the same SNR value to improve the accuracy of the determined collision decay parameters; however, it is not necessary to acquire data at different SNR values. Furthermore, as described herein, the collision decay rate is approximately the same for all isotopic states of the compound. Therefore, by determining the collision decay parameters using linear progression and using the pre-calibrated phase-shifting decay parameters, two decay parameters for the isotopic peaks can be determined, and thus the initial abundance (i.e., intensity) of each isotopic molecule in the ion sample can be determined using Equation 4 with the undamaged decay intensity.

[0111] In some examples, as an alternative to determining the values ​​of α and β for different SNR values ​​and fitting a curve with the results, the values ​​of β and α can be directly estimated. Instead of determining specific SNR values, the resolution can be plotted relative to the SNR, such as... Figure 1 As shown. Figure 1As shown, above the SNR value, isotope molecules decay only due to collisional decay. Therefore, the values ​​of α and β can be estimated from the resolution versus decay curve without needing to determine α and β individually for multiple SNR values. It should be understood that this only provides estimates, but does not require the use of inverse Fourier transform and transients, and therefore may require less processing.

[0112] Figure 7A The theoretical mass spectrum is shown, and Figure 7B The mass spectra obtained experimentally are shown. In the experiment, in order to obtain... Figure 7B The mass spectra shown are from an experimental MRFA (z=1) mass spectrum acquired on a research-grade Orbitrap Exploris (RTM) system. The resolution was set to 480 kJ@m / z=200; the injection time was gradually increased to ensure different ion clusters were present in the peaks. The collision decay rate β = 0.3 s was calculated for the self-bundling material. -1 (where the self-bundling threshold is 20), the coefficients for Equation 6 are obtained by least squares fitting: A = 2.58 and b = 0.11.

[0113] Figure 7A The theoretical MRFA mass spectrum is shown, where the theoretical ratio of isotopes (or isotopic molecules) M1 / M0 = 25.52%. Isotope peaks M0, M1, M2, and M3 are shown in... Figure 7A middle.

[0114] Experimental mass spectrometry ( Figure 7B The study showed significant suppression of the M1 peak at M1 / M0 = 18.54%, where peaks M1 and M0 were at... Figure 7B The difference could be due to the abundance of the M0 peak being sufficient to enforce space charge-dependent self-bundling. The single isotope peak (M0) has an SNR of 26.55, which is above the self-bundling threshold (SNR > 20), therefore the isotopes of the M0 peak do not decay due to phase shift, and thus the phase shift rate α... M0 =0. However, the abundance of the M1 peak is much smaller, and phase-shifting decay occurs. According to Equation 3, the SNR of the M1 isotope is 4.92, resulting in a phase-shifting rate α. M1 =1.50s -2 By correcting for time signal loss using the values ​​of parameters α and β in Equation 4, the isotope ratio M1 / M0 is increased. 经校正的 = 26.02%. Therefore, the isotopic ratio M1 / M0 obtained experimentally using the method described herein is... 经校正的 It is a good approximation of the theoretical value for a given mass spectrometry noise level.

[0115] Figure 8An example mass spectrometer that can be operated according to the implementation scheme described herein is shown. The mass spectrometer may be based on reference US2023282471A1. Figure 2 The mass spectrometer described in this patent is incorporated herein by reference.

[0116] In the example mass spectrometer, the instrument's ion source 810 is an electrospray ionization (ESI) ion source. The instrument includes a vacuum interface comprising a transfer tube 821, an ion funnel 822, a quadrupole pre-filter ion guide 823, and a "bent flat bar" ion guide 824. The bent flat bar ion guide 824 can be a design described in U.S. Patent No. 9,536,722, the entire contents of which are incorporated herein by reference.

[0117] The instrument also includes a mass filter in the form of a quadrupole mass filter 826, an ion trap 830a in the form of a curved linear ion trap (“C-Trap”), and a collision cell 830b in the form of an ion routed multipolar collision cell (“IRM”). Ions from the ion source 810 can be accumulated in the C-Trap 830a and / or the collision cell 830b by opening and closing a gated electrode located in a charge detector assembly 827, which is arranged between the C-Trap 830a and the mass filter 826.

[0118] The instrumentation also includes the 840a mass analyzer in the form of an orbital ion trap mass analyzer. For example... Figure 8 As shown, the orbital trap 840a includes an inner electrode 841 extending along the orbital trap axis and a pair of separate outer electrodes 842, 843. The pair of outer electrodes surrounds the inner electrode 841 and defines a trapping volume therebetween, in which ions are trapped and oscillated by orbital motion around the inner electrode 841, applying a trapping voltage to the inner electrode while oscillating back and forth along the trap axis. The pair of outer electrodes 842, 843 serve as detection electrodes to detect the mirror current induced by the oscillation of ions in the trapping volume, thereby providing a detection signal.

[0119] External electrodes 842 and 843 are typically used as a differential detection electrode pair and coupled to a differential amplifier (in...). Figure 8 The differential amplifier (not shown in the diagram) then forms part of a digital data acquisition system to receive the detected signal. Fourier transform can be used to process the detected signal to obtain a mass spectrum of the ion within the trap.

[0120] Once accumulated in ion trap 830a and / or collision cell 830b, ions can be ejected into mass analyzer 840a. For this purpose, ions can be ejected from trap 830a in a direction orthogonal to the axis of the trap (orthogonal ejection), for example, by applying one or more suitable DC voltages to ion trap 830a. Ions can be injected into mass analyzer 840a via one or more lenses and deflection electrodes. Mass analyzer 840a is arranged downstream of ion trap 830a and configured to receive ions from ion trap 830a (via one or more lenses and deflection electrodes).

[0121] A collision or reaction cell 830b is arranged downstream of the ion trap 830a. Ions collected in the ion trap 830a can be orthogonally injected into the mass analyzer 40a without entering the collision or reaction cell 830b, or the ions can be axially transmitted into the collision or reaction cell 830b for processing, and then the processed ions are returned to the ion trap 830a for subsequent orthogonal injection into the mass analyzer 840a. Processing may include, for example, fragmenting the ions by collision with a collision gas and / or reagent in the collision cell 830b, or further cooling the ions by collision with a lower-energy gas that does indeed fragment the ions.

[0122] A typical Fourier transform mass spectrometry experiment involves ionizing the ion sample, selecting the substance of interest (i.e., ions), optionally fragmenting the ions, and introducing the fragmented ions into the analyzer. Ions trapped within the mass analyzer can oscillate at a frequency that can depend on the ion's mass-to-charge ratio and can be detected using mirror current detection. Ions can perform essentially harmonic oscillations along an axis in an electrostatic field while simultaneously orbiting internal electrodes. As the ions oscillate within the detector, they induce mirror currents on the detection plate. Figure 8 In the example mass spectrometer, the external electrodes 842 and 843 serve as detection electrodes to detect the mirror current induced by the oscillations of ions in the trap volume, thereby providing a detection signal. External electrodes 842 and 843 are typically used as a differential detection electrode pair and coupled to a differential amplifier (in... Figure 8 The differential amplifier (not shown in the diagram) then forms part of a digital data acquisition system to receive the detected signal at its corresponding input terminal. The detected signal is amplified, digitized, and stored as a transient signal. The transient signal is then converted into a mass spectrum using a Fourier transform.

[0123] Alternative methods or devices may be used in conjunction with the techniques described herein to determine the initial abundance of ions in an ion sample. For example, novel techniques may be used in orbital trap mass spectrometry and FT-ICR as described herein without departing from the scope of the invention.

[0124] All aspects and / or features disclosed in this specification may be combined in any combination, except for mutually exclusive combinations of at least some of such features and / or steps. Specifically, preferred features of this disclosure apply to all aspects and embodiments of this disclosure and may be used in any combination. Similarly, features described in non-essential combinations may be used individually (not in combination).

[0125] It should be understood that there are implicit "approximate" terms preceding the temperature, concentration, time, pressure, flow rate, cross-sectional area, voltage, current, etc., discussed in this teaching, resulting in slight and non-substantial deviations within the scope of this teaching. Furthermore, values ​​referred to as "equal" may actually differ by less than a threshold amount. For example, the threshold amount could be 5%. The threshold can also be greater than 5% (e.g., 10%, 20%, or 50%) or less than 5% (e.g., 2% or 1%).

[0126] As used herein, including in the claims, unless the context otherwise indicates, the singular form of a term herein shall be construed to include the plural form, and vice versa. For example, unless the context otherwise indicates, the singular form included herein in the claims, such as “an” (e.g., an electrode difference), means “one or more” (e.g., one or more electrodes).

[0127] In the specification and claims of this disclosure, the words “comprising,” “including,” “having,” and “containing,” as well as variations thereof, such as “comprising” and “including” or similar words, mean “including but not limited to,” and are not intended to (and do not) exclude other components. Furthermore, the use of “or” is inclusive, such that the phrase “A or B” is true when “A” is true, “B” is true, or both “A” and “B” are true.

[0128] The use of any and all examples or exemplary language (“for example,” “such as,” “e.g.,” and similar language) provided herein is intended only to better illustrate this disclosure and, unless otherwise required, does not indicate a limitation on the scope of this disclosure. No language in this specification should be construed as indicating any unrequired element necessary for the practice of this disclosure.

[0129] The terms "first" and "second" may be reversed without changing the scope of the invention. That is, an element referred to as a "first" element may be referred to as a "second" element, and an element referred to as a "second" element may be regarded as a "first" element.

[0130] Unless otherwise stated or required by context, any steps described in this specification may be performed in any order or simultaneously. Furthermore, the fact that a step is described as being performed after another step does not preclude intermediate steps being performed.

[0131] It should also be understood that, unless otherwise implied or expressly understood or stated, any possible candidates or alternatives listed for any given component or embodiment described herein may generally be used alone or in combination with each other. It should be understood that any list of such candidates or alternatives is merely illustrative and not restrictive, unless otherwise implied or expressly understood or stated.

[0132] In the detailed description of the various embodiments, numerous specific details are set forth for illustrative purposes to provide a thorough understanding of the disclosed embodiments. However, those skilled in the art will understand that these various embodiments may be practiced with or without these specific details. Furthermore, those skilled in the art will readily understand that the particular order in which the methods are presented and performed is exemplary, and that the order is contemplated to be changeable while remaining within the scope of the various embodiments disclosed herein.

[0133] Unless otherwise stated, all technical and scientific terms used herein have the meanings commonly understood by one of ordinary skill in the art to which the various embodiments described herein pertain.

Claims

1. A method for determining the initial abundance of one or more ions among a plurality of ions in an ion sample analyzed by a Fourier transform mass spectrometer, said plurality of ions decaying over time during the analysis, said method comprising: Obtain a mass spectrum of the ion sample, wherein the mass spectrum includes multiple peaks, the multiple peaks indicating the abundance of each of the multiple ions in the ion sample during the analysis duration T; as well as The initial amplitude of the transient signal of the first ion among the plurality of ions is calculated by fitting the inverse Fourier transform (FT) of the first peak among the plurality of peaks, wherein the first peak corresponds to the first ion, to extrapolate the abundance of the first ion to the time at which the analysis duration begins.

2. The method according to claim 1, wherein the method further comprises: Determine the collision attenuation parameter and / or phase shift attenuation parameter of the first peak.

3. The method according to claim 2, wherein determining the collision attenuation parameter and / or the phase shift attenuation parameter of the first peak comprises: Center the first peak at zero frequency; Apply the inverse FT; as well as The function is fitted to the magnitude of the inverse FT.

4. The method according to claim 3, wherein the function is linear regression.

5. The method of claim 2, wherein the determination of the collision attenuation parameter and / or the phase shift attenuation parameter comprises applying the polynomial –αt 2 -βt-c is the logarithm of the magnitude fitted to the inverse FT.

6. The method of claim 5, wherein the initial amplitude I0 of the transient signal of the first ion is calculated based on parameter c, wherein I0 = I(0) = e c .

7. The method of claim 1, wherein calculating the initial amplitude of the transient signal further comprises calculating a correction factor for the abundance, wherein the correction factor is calculated using a collision attenuation parameter and a phase shift attenuation parameter.

8. The method of claim 7, wherein the correction factor is calculated using the following equation: Where α is the phase-shift attenuation parameter and β is the collision attenuation parameter.

9. The method of claim 1, wherein the phase shift attenuation parameter is pre-calibrated.

10. The method of claim 9, wherein the pre-calibration comprises: Calculate multiple phase attenuation parameters for multiple signal-to-noise ratio (SNR) values; The curve is fitted to the plurality of phase attenuation parameters, making it possible to determine the phase attenuation parameters for the additional SNR value.

11. The method according to any of the preceding claims, wherein the second ion of the plurality of ions has the same collision cross-section as the first ion, such that the collision decay parameter of the second ion is equal to the collision decay parameter of the first ion.

12. The method of claim 11, wherein the collision decay parameter of the first ion is used to calculate the correction factor and / or initial amplitude of the second ion.

13. The method according to any of the preceding claims, wherein the phase-shift attenuation parameter or correction factor is calculated without calculating the collision attenuation parameter.

14. The method according to any of the preceding claims, wherein two or more of the plurality of ions are different in their isotopic composition.

15. A Fourier transform mass spectrometer configured to perform the method according to any one of claims 1 to 14.

16. The Fourier transform mass spectrometer according to claim 15, wherein the Fourier transform mass spectrometer is an orbital trap mass spectrometer.

17. A computer program for determining the initial abundance of one or more ions among a plurality of ions in an ion sample analyzed by a Fourier transform mass spectrometer, the computer program comprising instructions that, when executed by a computer, cause the method according to any one of claims 1 to 14 to be performed.

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