A method for molecular formula matching of fourier transform ion cyclotron resonance mass spectrometry

Abstract

This application belongs to the field of environmental analytical chemistry and environmental geochemistry, and specifically discloses a molecular formula matching method for Fourier transform ion cyclotron resonance mass spectrometry, including: calculating all possible candidate molecular formulas based on the mass spectrometric information of dissolved organic matter samples determined by FT-ICR MS; identifying double-charged molecular formulas based on the double-charge recognition rule; and based on... 18 O-marking validation rules, filtering out initially valid entries containing... 18 O candidate molecular formula; based on 13 C / 12 C 34 S / 32 S and 15 N / 14 The isotopic patterns of N were used to eliminate false positive molecular formulas; the optimal molecular formula for each mass spectral peak was determined from the remaining candidate molecular formulas, and the optimal formula was determined based on the double charge recognition rule and... 18 O-labeling verification rules, for double-charged molecular formulas and those containing O-labeling in the optimal molecular formula. 18 The molecular formula of O was re-verified. This application enables the verification of molecules containing O. 18 The high accuracy of matching between O-labeled molecules and double-charged molecules improves the accuracy of molecular formula matching.

Description

Technical Field

[0001] This application belongs to the field of environmental analytical chemistry and environmental geochemistry, and more specifically, relates to a molecular formula matching method for Fourier transform ion cyclotron resonance mass spectrometry. Background Technology

[0002] Dissolved organic matter (DOM) is a highly complex organic mixture widely found in various natural and engineered environments, including freshwater, oceans, water treatment systems, soil, and sediments. DOM has diverse sources and strong structural heterogeneity; its chemical composition is easily influenced by various chemical reactions, redox reactions, microbial processes, and other biogeochemical processes, thereby altering its environmental and ecological functions. In recent years, ozone and ultraviolet disinfection processes in water treatment, photochemical processes in the surface of natural water bodies, and the alternating wet and dry conditions in paddy fields and the interaction between surface water and groundwater, have been studied using hydroxyl radicals (H₂O₃). • Redox reactions mediated by DOM have been shown to have a significant impact on the chemical composition of DOM. Given the complex composition of DOM and the diverse transformation pathways, it is difficult to trace its specific reaction pathways using only traditional methods, and revealing its transformation mechanisms faces a huge challenge.

[0003] In recent years, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), as an ultra-high resolution instrument, has become a powerful tool for exploring detailed information such as the molecular composition of DOM (morphotropic ions). It can detect thousands of molecular formulas, thus providing a more comprehensive and accurate understanding of DOM molecules. Numerous studies have used FT-ICR MS to characterize DOM in environmental media such as oceans, lakes, and soils. In routine FT-ICR MS analyses, researchers mainly use high-precision mass-to-charge ratios (MTBF) to characterize DOM. m / z The deduction of tens of thousands of molecular formulas in DOM (morphotropic terephthalic acid) enables the exploration of its biogeochemical behavior, primarily based on molecular formula matching using common elemental combinations (such as C, H, O, N, S, P, etc.) found in natural DOM samples. Furthermore, FT-ICR MS combined with the pairwise mass distance method has been applied to reveal the molecular transformation patterns and mechanisms of DOM in various reaction processes. However, some problems remain despite the relatively comprehensive research status. For example, if the reaction products and unreacted molecules in the reaction system have the same molecular composition, then relying solely on changes in molecular composition is insufficient to determine the source and fate of key molecules in the reaction, thus limiting in-depth analysis of the reaction mechanism. Against this backdrop, stable isotopes... 18 O-labeling technology is widely used to trace the origin, introduction, and retention or rearrangement of oxygen atoms in molecules, playing an irreplaceable role in research on hydroxyl radical oxidation, photochemistry, and advanced oxidation processes. 18The O-label can distinguish the source of oxygen atoms in a reaction, thus providing direct evidence for reaction pathway analysis. However, traditional algorithms often fail to accurately distinguish the source of oxygen atoms. 16 O and 18 O has poor fine quality, and in complex DOM systems, there are often multiple [various characteristics]. 18 Isotope peaks with similar O masses lead to errors in molecular formula matching, biases in isotope peak identification, and uncertainties in reaction pathway deduction. Therefore, a method specifically designed for... 18 The molecular formula matching algorithm for O-labeled DOMs can achieve [the following] based on ultra-high resolution data from FT-ICR MS. 18 Accurate identification and molecular formula allocation of O-labeled isotope peaks.

[0004] Furthermore, in DOM molecular composition analysis based on FT-ICR MS, ions typically exist as single-charged molecules, thus existing molecular formula matching algorithms are primarily developed for single-charged ions. However, some large DOM molecules with high polarity or numerous functional groups may form double-charged ions during actual electrospray ionization, and their mass spectrometric peaks may overlap with those of other single-charged molecules or isotopes, leading to misclassification of the molecular formula. Currently, FT-ICR MS molecular formula matching algorithms typically employ strategies of ignoring or simply filtering double-charged ions. While this approach simplifies the computation to some extent, it easily leads to information loss and systematic bias in DOM samples containing significant double-charged signals. Therefore, introducing the identification of double-charged molecular formulas into the FT-ICR MS mass spectrometry analysis algorithm for DOM is of great significance for improving the accuracy of molecular formula matching.

[0005] Therefore, how to achieve [the desired outcome] in ultra-high resolution mass spectrometry data of complex soluble organic matter systems? 18 Achieving high-accuracy matching between O-labeled molecular formulas and double-charged molecular formulas is a problem that urgently needs to be solved. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this application is to provide a molecular formula matching method for Fourier transform ion cyclotron resonance mass spectrometry, which can achieve molecular formula matching in ultra-high resolution mass spectrometry data of complex soluble organic matter systems. 18 The high accuracy of matching between O-labeled molecules and double-charged molecules effectively improves the accuracy of molecular formula matching.

[0007] To achieve the above objectives, firstly, this application provides a molecular formula matching method for Fourier transform ion cyclotron resonance mass spectrometry, applied to... 18 O isotope labeling of soluble organic matter systems includes the following steps: S10: Obtain and calculate all possible candidate molecular formulas in the mass spectrum of the soluble organic matter sample based on the mass spectrometry information of the Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). S20, Based on the preset double charge identification rules, identify and verify double charge molecular formulas from the candidate molecular formulas; S30, based on preset 18 O-marking validation rules, for those containing 18 The candidate molecular formulas of O were verified, and preliminary effective ones were screened out. 18 O candidate molecular formula; S40, based on 13 C / 12 C 34 S / 32 S and 15 N / 14 The isotopic patterns of N, for the preliminary effective content 18 The candidate molecular formulas were tested to eliminate false positive molecular formulas. S50, determine the optimal molecular formula for each mass spectral peak from the remaining candidate molecular formulas, and based on the stated double charge identification rule and the stated... 18 O-labeling verification rules, for double-charged molecular formulas and those containing O-labeling in the optimal molecular formula. 18 The molecular formula of O was verified again.

[0008] As a further preferred embodiment, in step S20, the preset dual-charge identification rule includes: Double charge rule 1: For a mass spectrum peak, if both single-charged and double-charged candidate molecular formulas exist simultaneously, the double-charged molecular formula is deemed invalid. Rule 2 for double charge: If the elemental composition of an identified double charge candidate molecular formula does not belong to the CHO- or CHON1- type, its validity must be verified by the existence of a single charge candidate molecular formula with the same neutral chemical formula.

[0009] As a further preferred embodiment, in step S30, the preset... 18 O-mark validation rules include: 18 Rule 1: For any of the following conditions, ... 18 Candidate molecular formula: Signal-to-noise ratio less than 150; 18 The mass spectrum must contain at least 4 O atoms, at least 3 nitrogen atoms, or a sum of 0 sulfur and phosphorus atoms, and must show at least one atom with a different number of atoms. 18 A series of molecular formulas with the same number of O atoms but the same neutral chemical formula.

[0010] As a further preferred option, in step S50, determining the optimal molecular formula includes: For multiple candidate molecular formulas corresponding to a single mass spectral peak, the preferred selection is... 18 A single-charge molecular formula with ≤1 O atom, ≤1 sum of nitrogen and sulfur atom, and 0 phosphorus atom; If among the plurality of candidate molecular formulas there is a... 18 For the molecular formula of O, the preferred choice is a molecular formula where the sum of the number of nitrogen atoms and sulfur atoms is ≤1 and the number of phosphorus atoms is 0. After the initial selection, the final optimal molecular formula is determined based on the principle of minimizing the number of non-oxygen heteroatoms and the mass error.

[0011] As a further preferred embodiment, the method further includes: S60, for the optimal molecular formula, its isotopic formula is based on... 37 Cl / 35 Cl、 81 Br / 79 Br、 13 C / 12 C 34 S / 32 S, 33 S / 32 S, 18 O / 16 O and 15 N / 14 The natural isotopic pattern of N is labeled on the peaks in the calculated FT-ICR MS spectrum.

[0012] As a further preferred embodiment, the method further includes an isotope verification step, specifically: For the single isotopic molecular formula in the optimal molecular formula, generate the corresponding 18 List of O and Cl- isotropes; A mass error threshold is set based on the number and mass error of adjacent molecular formulas with the same nominal mass. Based on multiple preset judgment conditions, it is determined whether to replace the matched monoisotope molecular formula with an allotrope; the judgment conditions involve the absolute mass errors Error1 and Error2 between the matched molecular formula and its allotrope, the number of isotope molecules IFN0 and IFN1, and the mass error threshold Error0.

[0013] As a further preferred embodiment, the isotope verification step further includes: For containing 18 The molecular formula of O1, its natural 18 The abundance of the O isotope peak is obtained by multiplying its corresponding monoisotope peak abundance by . 16 O / 18 The natural abundance of O was determined to be 2.06%; The containing 18 The measured abundance of the O1-labeled molecular formula is [value missing]. 18 The difference between the measured abundance of an O1-labeled molecule and its natural abundance, where the difference is greater than 0.

[0014] Secondly, this application provides a molecular formula matching system for Fourier transform ion cyclotron resonance mass spectrometry, used to implement the steps of the method as described in any one of the above statements, including: The data acquisition module is used to acquire mass spectrometry information of dissolved organic matter samples determined by FT-ICR MS; A candidate molecular formula calculation module is used to calculate all possible candidate molecular formulas based on the mass spectrometry information. The dual-charge processing module is used to identify and verify dual-charge molecular formulas in candidate molecular formulas based on preset dual-charge recognition rules. 18 The O verification module is used for verification based on preset parameters. 18 O-mark validation rules validate including 18 Candidate molecular formulas for O were identified, and false positive molecular formulas were eliminated based on isotope patterns. The result adjudication output module is used to determine the optimal molecular formula for each mass spectral peak from the processed candidate molecular formulas and output the final verification result.

[0015] Thirdly, this application provides an electronic device including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the method as described in any one of the above.

[0016] Fourthly, this application provides a computer-readable storage medium having computer instructions stored thereon, which, when executed by a processor, implement the steps of the method as described in any one of the above statements.

[0017] This application has the following advantages: by integrating the double-charge molecular formula recognition rule with... 18 By employing the O-labeled molecular formula verification rule, supplemented by isotope mode testing and a multi-round verification mechanism, this method can synergistically address double-charged ion interference and [other issues] when processing ultra-high resolution mass spectrometry data of complex soluble organic matter systems. 18 The problem of O-mark recognition, thus enabling the identification of O-marks. 18 The high accuracy of matching between O-labeled molecules and double-charged molecules effectively improves the accuracy of molecular formula matching, facilitating a comprehensive understanding of the transformation mechanism of dissolved organic matter in environmental geochemistry, free radical oxidation, and water treatment process research. Attached Figure Description

[0018] Figure 1This is a flowchart of the molecular formula matching method for Fourier transform ion cyclotron resonance mass spectrometry provided in this application; Figure 2 These are effect diagrams provided in the embodiments of this application; wherein, (A) is a Van Krevelen image of the sample after 12 h of UV irradiation; (B) is the concentration of [unspecified substance] in the sample after the reaction. 18 O-labeled molecules and natural 16 (C) is the O / C and H / C distribution diagram of the O molecule; (D) is the Van Krevelen diagram of the elemental composition of the sample after the reaction; (D) is the Van Krevelen diagram of single-charged and double-charged molecules in the sample after the reaction. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0020] This application proposes a method for applying... 18 A molecular formula matching analysis algorithm for ultra-high resolution mass spectrometry data processing of O isotope-labeled soluble organic matter systems. This method is based on FT-ICR MS for molecular composition analysis of DOM, combined with a molecular formula recognition rule with dual charge properties and... 18 The molecular formula matching algorithm based on O-labeled molecular formula verification rules can quickly and accurately identify molecular formulas from thousands to tens of thousands of ion peaks. 18 O-labeled DOM and accurate identification of double-charged molecules in the spectrum are beneficial for tracking the reaction pathways and component changes of DOM in many reaction systems. It is suitable for studying the transformation mechanism of DOM in environmental media and for the refined identification and analysis of pollutants.

[0021] Specifically, the application provides for... 18 The molecular formula matching method for Fourier transform ion cyclotron resonance mass spectrometry of O isotope-labeled soluble organic matter systems, including steps S10 to S50, is detailed below: Step S10: Obtain and calculate all possible candidate molecular formulas in the mass spectrum of the soluble organic matter sample based on the mass spectrometry information of the Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS).

[0022] This step calculates all possible elemental compositions based on the raw mass spectrometry data, providing a comprehensive candidate set for subsequent molecular formula matching, ensuring coverage of all possible molecular formulas, and laying a data foundation for accurate matching.

[0023] Step S20: Based on the preset double charge recognition rules, identify and verify double charge molecular formulas from candidate molecular formulas.

[0024] This step, by applying the dual-charge recognition rule, can effectively distinguish between single-charged and dual-charged ions, avoiding misjudgment of molecular formulas due to the presence of dual-charged ions, thereby improving the accurate identification of dual-charged molecules and reducing information loss and systematic bias.

[0025] Step S30, based on preset 18 O-marking validation rules, for those containing 18 The candidate molecular formulas of O were verified, and preliminary effective ones were screened out. 18 O candidate molecular formula.

[0026] This step is successful. 18 O-mark verification rules for containing 18 Preliminary screening using O molecular formulas can eliminate false-positive molecular formulas that clearly do not conform to the labeling rules, providing a foundation for subsequent fine-grained validation and improving the accuracy of the results. 18 Reliability of O-mark recognition.

[0027] Step S40, based on 13 C / 12 C 34 S / 32 S and 15 N / 14 The isotopic patterns of N are initially effective for containing 18 The candidate molecular formulas were tested, and false positive molecular formulas were eliminated.

[0028] This step utilizes natural isotope abundance patterns for verification, which can further eliminate false positive molecular formulas whose isotope distributions do not match the natural abundance, thus enhancing the accuracy and reliability of the results. 18 The accuracy of O-labeled molecular formula recognition.

[0029] Step S50: Determine the optimal molecular formula for each mass spectral peak from the remaining candidate molecular formulas, and base the determination on the double charge recognition rule and... 18 O-labeling verification rules, for double-charged molecular formulas and those containing O-labeling in the optimal molecular formula. 18 The molecular formula of O was verified again.

[0030] This step determines the optimal molecular formula by considering factors such as overall quality error and elemental composition, and then verifies it again to ensure that the final matched molecular formula is in a double-charge state and 18 The O-marking was accurate, improving the confidence and consistency of the overall matching results.

[0031] The molecular formula matching method for Fourier transform ion cyclotron resonance mass spectrometry provided in this application has the following advantages: by integrating the double-charge molecular formula recognition rule with... 18By employing the O-labeled molecular formula verification rule, supplemented by isotope mode testing and a multi-round verification mechanism, this method can synergistically address double-charged ion interference and [other issues] when processing ultra-high resolution mass spectrometry data of complex soluble organic matter systems. 18 The problem of O-mark recognition, thus enabling the identification of O-marks. 18 The high accuracy of matching between O-labeled molecules and double-charged molecules effectively improves the accuracy of molecular formula matching, facilitating a comprehensive understanding of the transformation mechanism of dissolved organic matter in environmental geochemistry, free radical oxidation, and water treatment process research.

[0032] The following is a specific implementation example of this application: Specific example: DOM solution in 18 Molecular composition analysis of O-labeled air after irradiation with ultraviolet light.

[0033] (1) Sample preparation and experimental procedures: Weigh 10 mg of natural humic acid (SRFA, purchased from the International Humic Acid Association) solid standard powder and dissolve it in 1000 mL of ultrapure water. Pour the solution into a brown glass bottle. o Store under C conditions. Prepare a DOM solution of appropriate concentration and expose it to C. 18 Molecular changes were analyzed after irradiation with an O-labeled atmospheric low-pressure ultraviolet lamp for 12 hours. Before each experiment, the ultraviolet low-pressure mercury lamp must be turned on for at least 30 minutes to ensure a stable output of ultraviolet photon flux.

[0034] (2) Solid-phase extraction treatment: Before entering the FT-ICR MS test, the sample must undergo solid-phase extraction (SPE) to enrich the DOM in the concentrated water sample. In this example, an HLB column (500 mg 6 mL, Waters, USA) was selected for SPE. The main steps are as follows: Before SPE, the water sample and ultrapure water were acidified with hydrochloric acid (pH≈2). 1) The HLB column was activated sequentially with 120 mL of methanol (LC-MS grade) and 25 mL of ultrapure water (pH≈2); 2) The water sample (pH≈2) was flowed through the HLB column under gravity to enrich the DOM in the water sample; 3) After enrichment by the HLB column, the water sample was desalted and rinsed sequentially with 20 mL of ultrapure water (pH≈2) and 50 mL of ultrapure water; 4) The water in the HLB column packing was thoroughly dried with high-purity N2 (≥99.999%); 5) The DOM enriched in the HLB column was recovered by eluting with 5 mL of methanol, and the eluent was collected in 10 mL glass vials. o Store in a dark place.

[0035] (3) FT-ICR MS test: Ultra-high resolution mass spectrometry was obtained using an FT-ICR MS (SolariX 2XR, Bruker, Germany) from China University of Geosciences (Wuhan) equipped with a 7 T superconducting magnet, an electrospray ionization source (ESI), and a dynamic harmonic fourth-order (2ω) detector. 18 Characterization of O-labeled DOM molecules and double-charged molecules. All tests were performed in negative charge mode (ESI(-)) of the electrospray ionization source. The instrument was externally calibrated with 10 mg / L sodium formate solution, with a mass error of less than 0.5 ppm. The eluent was prepared using methanol / water (… v / v After being diluted to a suitable concentration (1:1), the sample was filtered through a 0.22 μm organic phase filter membrane and injected into the ESI unit via a syringe pump at a flow rate of 120 μL / h. The mass acquisition range was set to m / z 110–1050 Da, the ion accumulation time range to 0.1–0.5 s, the ion flight time to 0.8 s, and the data size for each broadband mass acquisition was 4 M, with an average of 400 mass spectra acquired per sample. Before each measurement of the next sample, a methanol-water mixture (Methanol-Water) was used. v / v Rinse the syringe and tubing three times (1:1) to minimize cross-contamination between samples.

[0036] (4) Data processing: First, the mass spectrometry data acquired by FT-ICR MS were internally calibrated using the instrument's accompanying software, Bruker Data Analysis 5.0, and the internally calibrated mass spectrometry information (including mass-to-charge ratio) was saved. m / z Intensity, resolution, and signal-to-noise ratio (SNR) S / N (etc.) and named it masslist. Then, using MATLAB... ® The software (The MathWorks, Inc., USA) combines the FTMSDeu algorithm for molecular formula matching. The FTMSDeu algorithm proposed and applied in this embodiment has been further improved and upgraded, adding recognition... 18 The function of O-labeling and double-charged molecular formula, applicable to 18 FT-ICR MS mass spectrometry analysis of DOM samples marked with O. The execution flow of the FTMSDeu algorithm in this embodiment is as follows: Figure 1 As shown, the upgraded features are highlighted in red in the flowchart.

[0037] Detailed calculation steps: Set appropriate calculation parameters and import the masslist file containing mass spectrometry information into MATLAB. ®The software calculates all possible molecular formulas in the FT-ICR MS spectrum. Under pre-set calculation conditions, all calculated possible molecular formulas are checked according to "Double Charge Rule 1" and "Double Charge Rule 2" to determine which are double-charged. According to "Double Charge Rule 1": for a specific peak with both double-charged and single-charged results, the double-charged molecular formula is deemed invalid because the single-charged peak dominates in the DOM FT-ICR MS spectrum. Furthermore, according to "Double Charge Rule 2": given the elemental composition of DOM, all other types of double-charged molecular formulas, except for CHO- and CHON1- type double-charged molecular formulas, must be verified by the presence of a single-charged precursor with the same neutral chemical formula. Subsequently, for those meeting at least one condition ( S / N <150、 18 (O≥4, N≥3, S+P>0) containing 18 The molecular formula of O, according to " 18 Check according to "Rule 1" to ensure that each FT-ICR MS spectrum contains 18 The molecular formula of O must have a "different" one. 18 A series of chemical formulas with the same number of oxygen atoms and the same neutral chemical formula. Furthermore, if applicable, utilize... 13 C / 12 C 34 S / 32 S and 15 N / 14 The isotopic pattern of N is used to further eliminate false positives. Next, according to "Rule 3 of Double Charge," the optimal molecular formula for a specific peak with both double and single charges is determined: for a specific peak, a single-charge molecular formula with 18O≤1, N+S≤1, and P=0 is preferred. If multiple results contain... 18 For the molecular formula of O, a formula with N+S≤1 and P=0 is selected. All selected molecular formulas are further determined by minimizing the number of non-oxygen heteroatoms and minimizing mass error. Since many precursors of doubly charged molecular formulas have been eliminated during the determination of the optimal molecular formula, all doubly charged molecular formulas need to be verified again according to "Doubly Charge Rule 2" to improve the accuracy of molecular formula matching. For the determined optimal molecular formula, its isotopic formula is based on... 37 Cl / 35 Cl、 81 Br / 79 Br、 13 C / 12 C 34 S / 32 S, 33 S / 32 S, 18 O / 16 O and15 N / 14 The peaks in the calculated FT-ICR MS spectrum are labeled with the natural isotope pattern of N. All 18 The molecular formula containing 18 O is verified again according to the " 18 O-Rule 1" to ensure the matching accuracy of the double-charged molecular formula. According to the "Double-Charge Rule 4": the double-charged molecular formula containing 13 C / 12 C isotope pattern is further verified.

[0038] Since 18 the mass difference between 18 O and Cl is only at the sub-mDa level, which is a typical isobar, so the molecular formula is supplemented and tested according to the " 18 O-Rule 2", that is, the low mass error criterion for isobars. First, the algorithm generates a corresponding list of isobaric molecular formulas for all matching monoisotopic molecular formulas based on typical 18 O- and Cl-isobars. For a certain matching monoisotopic molecular formula, its mass error threshold is mainly confirmed in the following way: if the number of adjacent molecular formulas with the same nominal mass ≤ 4, then take the average of the absolute mass errors of these adjacent molecular formulas; otherwise, arrange the absolute mass errors of these adjacent molecular formulas in descending order, and take the quantile value after arrangement as the mass error threshold. Isobars are determined according to the following conditions: (1) Condition 1: abs(Error1 - Error2) < max(Error1, Error2) × 1.414 and IFN0 ≥ IFN1 (abs is the abbreviation of absolute mass error, Error1 and Error2 refer to the absolute mass errors of the matching molecular formula and the isobar respectively, IFN0 and IFN1 refer to the number of isotope molecules of the matching molecular formula and the isobar respectively); (2) Condition 2: the number of adjacent molecular formulas with the same nominal mass (NNF) ≥ 4; (3) Condition 3: Error1 ≤ Error0; (4) Condition 4: Error2 ≥ Error0; (5) Condition 5: Error2 > Error0 and Error2 < Error0; (6) Condition 6: Error1 > Error2. If both Condition 1 and Condition 2 are false and Condition 5 is true, the matching monoisotopic molecular formula will be replaced by the isobar, and this isobar will be further saved in the isobaric molecular formula list (IIFL). If Condition 1 is false, Condition 2 is true, and both Condition 3 and Condition 4 are false, the matching monoisotopic molecular formula will also be replaced by the isobar saved in IIFL. Otherwise, the isobar will be rejected. Subsequently, another already-matched monoisotopic value is used to perform the above calculations to verify at the sub-mDa level the 18Chemical formulas of O- and Cl- related allotropes. For the allotropes C1Cl1 and O1P1 (mass difference of 0.177 mDa), Cl1-type allotropes with mass errors smaller than that of the P1-type molecule were labeled as potentially Cl1-containing molecules and removed from the list of matched molecular formulas in the detected FT-ICR MS spectra. For a given O- and Cl--containing allotropes... 18 The molecular formula of O1, its natural 18 The abundance of O isotopes is calculated by multiplying the abundance of their corresponding monoisotope peaks by 1 / 2. 16 O / 18 The natural abundance of O was determined by (2.06%), while 18 The abundance of O1-labeled molecular formulas is then expressed as the abundance of that formula. 18 The difference between the measured abundance of the O1-labeled molecular formula and its natural abundance (>0).

[0039] Subsequently, the upgraded FTMSDeu algorithm in this embodiment will perform the functions of the original algorithm, including addition molecular formula analysis (only applicable to FT-ICR MS data detected in positive ion electrospray ionization mode), determination of the optimal molecular formula of F-related allotropes at the sub-mDa mass difference level, isotope peak matching of all confirmed allotropes, low-intensity peak verification based on isotope series and dynamic homologue series, molecular parameter summarization, and output of calculation results. Finally, the algorithm will automatically extract the FT-ICR MS mass spectrometry information of the next sample and perform the above data analysis process.

[0040] The key points of this embodiment are: (1) setting up multi-level double-charge molecular formula recognition rules, and realizing reliable recognition of double-charge molecular formulas based on the presence characteristics of double-charged and single-charged ions in DOM mass spectrometry; (2) proposing 18 The rules for verifying molecular formulas with O-labeling, combined with S / N、 The labeling was achieved through multiple rounds of verification using elemental composition, natural isotopes, and allotropes. 18 Accurate identification of O isotope peaks; (3) The functional upgrade and optimal parameter setting of the FTMSDeu algorithm ensured the accuracy of the FT-ICR MS spectrum. 18 High-precision matching and result output of O-labeled and double-charged molecular formulas.

[0041] The effect after implementing this embodiment is as follows: like Figure 2 As shown in (A) and (B), a total of 9867 oxygen-containing DOM molecules were detected in the samples after 12 h of UV irradiation. Among them, 2760 oxygen-containing DOM molecules were identified using the upgraded FTMSDeu algorithm in this embodiment. 18 O-labeled molecules and 7107 natural species 16 O molecules. With natural... 16Compared to O molecules, those containing 18 O-labeled molecules generally have higher O / C and H / C values. 16 The O / C and H / C distributions of the O molecule are more widespread. For example... Figure 2 As shown in (C), from the perspective of elemental composition, the reaction contains 18 O-labeled molecules are mainly CHON and CHO molecules, followed by CHOS molecules, with small amounts of CHONS and CHOSP molecules. In terms of substance categories, the reaction produces molecules containing... 18 O-labeled molecules contain a large amount of lignin and tannins, which is similar to the results reported in previous studies, namely, that the O / C value of the compound is positively correlated with the degradation of DOM under ultraviolet irradiation. • The formation of [something] triggers chemical transformations such as substitution or addition, thereby promoting [something]. 18 O was introduced into the DOM. In summary, 18 The labeling of O stable isotopes has facilitated a deeper understanding of DOM transformations, and our results indicate that the upgraded FTMSDeu algorithm can identify them more accurately. 18 The O isotope peak significantly improves the accuracy of molecular formula matching, facilitating a comprehensive understanding of the transformation of DOM molecules during various redox reactions.

[0042] In addition, such as Figure 2 As shown in Figure (D), a total of 9793 single-charged molecules and 74 double-charged molecules (accounting for only 0.75%) were detected in the sample after 12 h of UV irradiation. The significant reduction in the number of double-charged ions after UV treatment reflects the HO • The upgraded FTMSDeu algorithm in this embodiment adopts the newly added "double charge rules 1-4" and "...". 18 Rule 1-2” realizes the double-charge molecular formula and in complex DOM samples 18 Our findings highlight the applicability and reliability of the algorithm for processing FT-ICR MS ultra-high resolution mass spectrometry data in complex environmental samples through the collaborative recognition of O stable isotope-labeled DOM molecular formulas. This is of great significance for exploring the behavior of DOM in various reaction systems.

[0043] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A molecular formula matching method for Fourier transform ion cyclotron resonance mass spectrometry, applied to... 18 An O isotope-labeled soluble organic matter system, characterized in that... Includes the following steps: S10: Obtain and calculate all possible candidate molecular formulas in the mass spectrum of the soluble organic matter sample based on the mass spectrometry information of the Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). S20, Based on the preset double charge identification rules, identify and verify double charge molecular formulas from the candidate molecular formulas; S30, based on preset 18 O-marking validation rules, for those containing 18 The candidate molecular formulas of O were verified, and preliminary effective ones were screened out. 18 O candidate molecular formula; S40, based on 13 C / 12 C 34 S / 32 S and 15 N / 14 The isotopic patterns of N, for the preliminary effective content 18 The candidate molecular formulas were tested to eliminate false positive molecular formulas. S50, determine the optimal molecular formula for each mass spectral peak from the remaining candidate molecular formulas, and based on the stated double charge identification rule and the stated... 18 O-labeling verification rules, for double-charged molecular formulas and those containing O-labeling in the optimal molecular formula. 18 The molecular formula of O was verified again.

2. The molecular formula matching method for Fourier transform ion cyclotron resonance mass spectrometry as described in claim 1, characterized in that, In step S20, the preset dual-charge identification rule includes: Double charge rule 1: For a mass spectrum peak, if both single-charged and double-charged candidate molecular formulas exist simultaneously, the double-charged molecular formula is deemed invalid. Rule 2 for double charge: If the elemental composition of an identified double charge candidate molecular formula does not belong to the CHO- or CHON1- type, its validity must be verified by the existence of a single charge candidate molecular formula with the same neutral chemical formula.

3. The molecular formula matching method for Fourier transform ion cyclotron resonance mass spectrometry as described in claim 1, characterized in that, In step S30, the preset 18 O-mark validation rules include: 18 Rule 1: For any of the following conditions, ... 18 Candidate molecular formula: Signal-to-noise ratio less than 150; 18 The mass spectrum must contain at least 4 O atoms, at least 3 nitrogen atoms, or a sum of 0 sulfur and phosphorus atoms, and must show at least one atom with a different number of atoms. 18 A series of molecular formulas with the same number of O atoms but the same neutral chemical formula.

4. The molecular formula matching method for Fourier transform ion cyclotron resonance mass spectrometry as described in claim 1, characterized in that, In step S50, determining the optimal molecular formula includes: For multiple candidate molecular formulas corresponding to a single mass spectral peak, the preferred selection is... 18 A single-charge molecular formula with ≤1 O atom, ≤1 sum of nitrogen and sulfur atom, and 0 phosphorus atom; If among the plurality of candidate molecular formulas there is a... 18 For the molecular formula of O, the preferred choice is a molecular formula where the sum of the number of nitrogen atoms and sulfur atoms is ≤1 and the number of phosphorus atoms is 0. After the initial selection, the final optimal molecular formula is determined based on the principle of minimizing the number of non-oxygen heteroatoms and the mass error.

5. The molecular formula matching method for Fourier transform ion cyclotron resonance mass spectrometry as described in claim 1, characterized in that, The method further includes: S60, for the optimal molecular formula, its isotopic formula is based on... 37 Cl / 35 Cl、 81 Br / 79 Br、 13 C / 12 C 34 S / 32 S, 33 S / 32 S, 18 O / 16 O and 15 N / 14 The natural isotopic pattern of N is labeled on the peaks in the calculated FT-ICR MS spectrum.

6. The molecular formula matching method for Fourier transform ion cyclotron resonance mass spectrometry as described in claim 1, characterized in that, The method further includes an isotope verification step, specifically: For the single isotopic molecular formula in the optimal molecular formula, generate the corresponding 18 List of O and Cl- isotropes; A mass error threshold is set based on the number and mass error of adjacent molecular formulas with the same nominal mass. Based on multiple preset judgment conditions, it is determined whether to replace the matched monoisotope molecular formula with an allotrope; the judgment conditions involve the absolute mass errors Error1 and Error2 between the matched molecular formula and its allotrope, the number of isotope molecules IFN0 and IFN1, and the mass error threshold Error0.

7. The molecular formula matching method for Fourier transform ion cyclotron resonance mass spectrometry as described in claim 6, characterized in that, The isotope verification step further includes: For containing 18 The molecular formula of O1, its natural 18 The abundance of the O isotope peak is obtained by multiplying its corresponding monoisotope peak abundance by . 16 O / 18 The natural abundance of O was determined to be 2.06%; The containing 18 The measured abundance of the O1-labeled molecular formula is [value missing]. 18 The difference between the measured abundance of an O1-labeled molecule and its natural abundance, where the difference is greater than 0.

8. A molecular formula matching system for Fourier transform ion cyclotron resonance mass spectrometry, characterized in that, The steps for implementing the method as described in any one of claims 1 to 7 include: The data acquisition module is used to acquire mass spectrometry information of dissolved organic matter samples determined by FT-ICR MS; A candidate molecular formula calculation module is used to calculate all possible candidate molecular formulas based on the mass spectrometry information. The dual-charge processing module is used to identify and verify dual-charge molecular formulas in candidate molecular formulas based on preset dual-charge recognition rules. 18 The O verification module is used for verification based on preset parameters. 18 O-mark validation rules verify including 18 Candidate molecular formulas for O were identified, and false positive molecular formulas were eliminated based on isotope patterns. The result adjudication output module is used to determine the optimal molecular formula for each mass spectral peak from the processed candidate molecular formulas and output the final verification result.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps of the method as described in any one of claims 1 to 7.

10. A computer-readable storage medium storing computer instructions thereon, characterized in that, When executed by a processor, the computer instructions implement the steps of the method as described in any one of claims 1 to 7.

Images