Proton transfer reaction time-of-flight mass spectrometer calibration method based on mass-to-charge ratio

Abstract

The invention provides a mass-to-charge ratio-based proton transfer reaction time-of-flight mass spectrometer calibration method, and the method comprises the steps: S1, obtaining a function relation between the sensitivity of each standard gas group and the charge ratio of a corresponding protonation product, each standard gas group independently comprises organic matter gases belonging to the same category but different specific categories; s2, respectively substituting the mass-to-charge ratios of the protonated products of different gas components in the gas to be detected into the function relationship of the respective corresponding standard gas group, and calculating to obtain the respective sensitivity of the different gas components in the gas to be detected; and S3, calculating the concentration of the gas component in the gas to be detected according to the respective peak response intensity and sensitivity of different gas components in the gas to be detected. According to the method, the reaction rate constant between the volatile organic compound and the hydrated hydrogen ions does not need to be obtained in advance, and the quantitative analysis efficiency of the proton transfer reaction time-of-flight mass spectrometer in a complex environmental sample is remarkably improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of quantitative calibration of volatile organic compounds by mass spectrometry analysis technology, and relates to a proton transfer reaction time-of-flight mass spectrometer calibration method based on mass-to-charge ratio. BACKGROUND

[0002] Volatile organic compounds (VOCs) widely exist in the atmosphere, which not only affect atmospheric chemical processes, but also pose potential threats to human health and ecological environment. Accurate determination of the concentration of VOCs in the atmospheric environment is a key prerequisite for studying their atmospheric chemical behavior, evaluating their toxic effects and exposure risks, and scientifically preventing and controlling them. In traditional VOCs analysis methods, gas chromatography technology is widely used, but it usually requires sample enrichment and pretreatment, has low time resolution, and is difficult to achieve rapid real-time monitoring. In contrast, proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS) can realize real-time online monitoring of VOCs without pretreatment, and has advantages such as high sensitivity, high time resolution, fast response, wide mass range, and soft ionization without destroying the molecular structure, and has been widely used in environmental monitoring, clinical analysis, food chemistry and many other fields.

[0003] When using PTR-ToF-MS to quantify VOCs, the mass spectrometric signal intensity of its protonated product is usually combined with the sensitivity of the corresponding VOCs to calculate its actual concentration. Although calibration of target VOCs can obtain the most accurate sensitivity data, the composition of actual atmospheric samples is complex, PTR-ToF-MS can simultaneously detect hundreds of ion signals with different mass-to-charge ratios, and many VOCs lack reliable gas standard, which is the main bottleneck for quantitative analysis of multi-component VOCs; in addition, if each VOC is calibrated, the workload is huge and the actual operation will be extremely time-consuming.

[0004] In theory, if the reaction rate constant of VOCs and hydronium ion (H3O + ) and the product ion branching ratio are known, PTR-ToF-MS can realize the absolute quantification of VOCs without calibration. However, this method depends on detailed instrument parameters and the reaction rate constant of each VOC and H3O + . The existing alternative method is to construct a linear relationship based on the sensitivity and reaction rate constant of a few known standard gases, combined with the transmission efficiency (related to mass-to-charge ratio) to estimate the sensitivity of the VOCs to be measured, but this method still needs to obtain the reaction rate constant of all VOCs. Since the reaction rate constant depends on the specific molecular structure information, it is difficult to obtain, which restricts the rapid calibration and practical application of PTR-ToF-MS. SUMMARY

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a proton transfer reaction time-of-flight mass spectrometry calibration method based on mass-to-charge ratio. This calibration method estimates the sensitivity of VOCs protonation products based on their mass-to-charge ratio, without requiring prior acquisition of VOCs and H3O. + The reaction rate constant between the two is used to achieve rapid calibration of PTR-ToF-MS, which helps to obtain the concentration of VOCs to be measured more easily and efficiently, and is especially suitable for rapid quantitative analysis of multi-component VOCs in actual atmospheric environmental samples.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] This invention provides a calibration method for a proton transfer reaction time-of-flight mass spectrometer based on mass-to-charge ratio, the calibration method comprising:

[0008] S1. Obtain the functional relationship between the sensitivity of each standard gas group and the charge ratio of its corresponding protonation product, wherein each standard gas group independently includes organic gases belonging to the same category but of different types.

[0009] S2. Substitute the mass-to-charge ratio of the protonation products of different gas components in the gas to be tested into the functional relationship of their respective standard gas groups to calculate the sensitivity of each gas component in the gas to be tested.

[0010] S3. Calculate the concentration of the gas component in the gas to be tested based on the peak response intensity and sensitivity of each gas component in the gas to be tested.

[0011] It should be noted that the organic gases in the standard gas group can be obtained by mixing standard gases, multiple single standard gases, or a combination of mixing standard gases and single standard gases, as long as they can cover the corresponding organic species.

[0012] In this invention, the above method is simple to operate and does not require the acquisition of any VOCs and H3O. + The reaction rate constant (k) can be obtained by calibrating a standard gas group under the same instrument parameters. Based on the characteristics of each organic gas in the standard gas group, it can be classified and numerically fitted to construct a functional relationship between the VOCs sensitivity (S) and its corresponding protonation product mass charge ratio (m / z). Based on this relationship, the sensitivity (S) of the VOCs to be measured can be estimated, which effectively expands the calibration range of VOCs and significantly improves the instrument calibration efficiency.

[0013] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and outstanding advantages of the present invention can be better achieved and realized through the following preferred technical solutions.

[0014] Preferably, step S1, which involves obtaining the functional relationship between the sensitivity of each standard gas group and the corresponding protonation product mass-charge ratio, specifically includes:

[0015] S11. Under constant instrument parameters, multiple sets of standard gases are successively introduced into the proton transfer reaction time-of-flight mass spectrometer, and the mass-to-charge ratio of different organic gases in each set of standard gases and their corresponding peak response intensities at different preset concentrations are tested.

[0016] S12. Using the preset concentration of each organic gas as the independent variable and the peak response intensity of each organic gas at different preset concentrations as the dependent variable, fit multiple sets of data to obtain the sensitivity of each organic gas.

[0017] S13. Using the mass-to-charge ratio of the protonation products of different organic gases in each standard gas group as the independent variable and the sensitivity as the dependent variable, fit multiple sets of data to obtain the functional relationship between the sensitivity of each standard gas group and the mass-to-charge ratio of its corresponding protonation product.

[0018] Preferably, the constant instrument parameters in step S11 include constant drift tube operating voltage, constant drift tube pressure, constant drift tube temperature, and a constant ratio of electric field strength to neutral gas number concentration, and H2O is used as the reaction ion source during the test.

[0019] Preferably, the classification rules for the same category in step S1 include: classification based on the elemental composition and / or molecular structure of organic gases.

[0020] Preferably, the molecular structure includes unsaturated bonds and / or functional groups.

[0021] It is understandable that when classifying organic gases in a standard gas, classification is prioritized based on their elemental composition; however, if an organic gas has significant structural characteristics and classification by molecular structure can significantly improve the fitting effect of organic sensitivity on the mass charge ratio of its corresponding protonation product, then classification by molecular structure is prioritized.

[0022] Preferably, the method for testing the mass-to-charge ratio of protonation products of different gas components in the gas to be tested in step S2 and the peak response intensity of different gas components in the gas to be tested in step S3 includes: under the constant instrument parameters described in step S11, the gas to be tested is introduced into the proton transfer reaction time-of-flight mass spectrometer, and the mass-to-charge ratio and peak response intensity of protonation products of different gas components in the gas to be tested are obtained.

[0023] Preferably, the method for calculating the sensitivity in step S2 specifically includes:

[0024] Analyze the elemental composition and / or molecular structure of different gas components in the gas to be tested, and determine the category to which the different gas components in the gas to be tested belong according to the same classification rules as the standard gas group;

[0025] The mass-to-charge ratios of the protonation products of different gas components in the gas to be tested are substituted into the functional relationships of the standard gas group of the same category to calculate the corresponding sensitivities.

[0026] Understandably, after PTR-ToF-MS testing, the mass-to-charge ratio and elemental composition of the protonation products of different gas components in the test gas can be obtained. Combined with the source of the test gas, the possible molecular structures of different gas components in the test gas can be inferred, thereby determining their category.

[0027] Preferably, the raw data of each standard gas group and the raw data of the sample to be tested obtained by the proton transfer reaction time-of-flight mass spectrometer adopt a unified data processing flow.

[0028] Preferably, the data processing flow includes mass axis correction, baseline correction, peak width and peak shape determination, and high-resolution mass spectrometry peak fitting, ultimately converting the original signal into a data format of a single ion signal.

[0029] Understandably, to ensure the accuracy of the results, it is necessary to ensure that the instrument parameters of the proton transfer reaction time-of-flight mass spectrometer remain consistent when testing the standard gas and the sample to be tested, and that the data processing procedures are also consistent.

[0030] Preferably, the gas to be tested includes volatile organic compounds in the atmosphere.

[0031] The mass-to-charge ratio range described in this invention includes not only the values ​​listed above, but also any values ​​within the range that are not listed. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific values ​​included in the range.

[0032] Compared with the prior art, the present invention has the following outstanding advantages:

[0033] The calibration method provided by this invention estimates the sensitivity of VOCs based on the mass-to-charge ratio of their protonation products, without requiring prior acquisition of VOCs and H3O. + The reaction rate constant between the two significantly improves the efficiency and practical application capability of PTR-ToF-MS in quantitative analysis of samples in complex environments. Attached Figure Description

[0034] Figure 1A schematic diagram of the PTR-ToF-MS calibration method based on the mass-to-charge ratio of VOCs protonation products provided in this embodiment of the invention.

[0035] Figure 2 This is a graph showing the calculated sensitivity (S) of each organic component in each standard gas group calibrated by PTR-ToF-MS in this embodiment of the invention.

[0036] Figure 3 This is a fitting graph showing the functional relationship between the sensitivity (S) of each standard gas group and its corresponding protonation product mass charge ratio (m / z) in the embodiments of the present invention.

[0037] Figure 4 This is a schematic diagram of the traditional calibration method of PTR-ToF-MS based on the reaction rate constant, provided as a comparative example of the present invention.

[0038] Figure 5 A comparison chart showing the results of estimating the sensitivity (S) of the VOCs to be measured using two calibration methods provided for embodiments and comparative examples of the present invention. Detailed Implementation

[0039] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0041] Example

[0042] This embodiment provides a method for quantitative testing of VOCs based on their mass-to-charge ratio, such as... Figure 1 As shown, the specific process is as follows:

[0043] (1) Under constant instrument parameters (including drift tube working voltage, drift tube pressure, drift tube temperature, electric field strength to neutral gas number concentration ratio, and H2O as the reaction ion source during the test), multiple standard gas groups were introduced into the PTR-ToF-MS one after another, and the mass-to-charge ratio of different organic gas protonation products in each standard gas group and their corresponding peak response intensity at different preset concentrations were tested.

[0044] The specific types of organic gases calibrated include 23 VOCs, such as unsaturated straight-chain hydrocarbons, aromatic hydrocarbons, oxygen-containing organic compounds, and heteroatom-containing organic compounds. The classification criteria for the standard gas groups are the elemental composition and molecular structure of each organic component. Specific grouping information is as follows:

[0045] The first standard gas group consists of 7 cyclic hydrocarbons; the second standard gas group consists of 9 non-hydrocarbon VOCs containing elements such as O, N, S, and Cl; and the third standard gas group consists of 7 unsaturated straight-chain hydrocarbons. The specific organic gas types in each group and their corresponding sensitivity calculations are as follows: Figure 2 As shown;

[0046] Using dry zero air as the dilution gas, the concentrations of each VOC were sequentially diluted to the range of 0–40 ppbv. Stability tests were performed at each preset concentration point (test time not less than 20 minutes, with test time not less than 30 minutes for low concentration points such as 0, 5, and 10 ppbv), and the mass-to-charge ratio (m / z) of the corresponding protonated products of each VOC and their peak response intensity under equilibrium conditions were obtained in PTR-ToF-MS.

[0047] (2) Using the preset concentration of each organic gas as the independent variable and the peak response intensity of each organic gas at different preset concentrations as the dependent variable, fit multiple sets of data to obtain the measured sensitivity (S) of each organic gas under the current instrument conditions. meas The fitting results are as follows: Figure 2 As shown.

[0048] (3) Using the m / z of the protonation products of different organic gases in each standard gas group as the independent variable, S meas Using the standard gas as the dependent variable, multiple sets of data were fitted to obtain the functional relationship between the sensitivity of each standard gas group and the corresponding protonation product mass charge ratio, such as... Figure 3 As shown.

[0049] (4) Under the same instrument parameters as in step (1), the VOCs to be tested (including acrylonitrile, acetone, phenol, chlorobenzene, benzene, toluene, styrene, etc.) are introduced into the PTR-ToF-MS, and the mass-to-charge ratio and peak response intensity of the protonation products of different gas components in the gas to be tested are obtained.

[0050] (5) According to the same classification criteria as in step (1), determine the category to which different gaseous components in the VOCs to be tested belong, and substitute the mass-to-charge ratio of the protonation products of different gaseous components in the VOCs to be tested into the functional relationship of the standard gas group of the same category to calculate the corresponding estimated sensitivity (S). cal ).

[0051] (6) Estimate the sensitivity (S) based on the peak response intensity of each gas component in the gas to be measured. cal The concentration of the gas component can be calculated.

[0052] Comparative Example

[0053] This comparative example provides a method for quantitative testing of VOCs based on the traditional reaction rate constant, such as... Figure 4 As shown, the specific process is as follows:

[0054] (1) The same 23 VOCs as in the examples were used as calibration objects. The polarizability (α) and permanent dipole moment (μ) of the VOC species were used as the calibration targets. D ), query 23 types of calibrated VOCs and H3O + The reaction rate constant (k) is used in the literature, combined with the transport efficiency (related to m / z) to influence the measured sensitivity (S) of VOCs. meas The corrected sensitivity (S) is obtained by performing calibration. 校正 ), and analyze S 校正 The correlation coefficient α between k and the data was obtained after data fitting. During this process, VOCs that significantly deviated from the fitting trend or lacked reaction rate constant (k) data, as well as methanol (CH5O4), which has a proton affinity close to that of water, were removed. + );

[0055] (2) Test the VOCs to be tested (including acrylonitrile, acetone, phenol, chlorobenzene, benzene, toluene, styrene, etc.) and obtain the reaction rate constant k' of each component in the VOCs to be tested. Based on the correlation coefficient a obtained in step (1), estimate the S of each component in the VOCs to be tested. 校正 ', and its estimated sensitivity (S) is calculated based on the transmission efficiency. cal ');

[0056] (3) Based on the peak response intensity and S of different gas components in the gas to be tested cal The concentration of the gas component can be calculated.

[0057] Accuracy verification

[0058] The estimated sensitivity (S) of the VOCs components to be measured obtained from the examples and comparative examples. cal S cal ') and the measured sensitivity (S) obtained from standard gas testing meas A comparison was performed, and the results can be found in [link to comparison]. Figure 5 This verifies the feasibility and accuracy of the mass-to-charge ratio calibration method proposed in this invention. It is understood that... Figure 5 The vertical coordinate S calEstimated sensitivity (S) of the VOCs components to be measured obtained from the examples and comparative examples cal or S cal ').

[0059] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for calibrating a proton transfer reaction time-of-flight mass spectrometer based on mass-to-charge ratio, characterized in that, The calibration method includes: S1. Obtain the functional relationship between the sensitivity of each standard gas group and the charge ratio of its corresponding protonation product, wherein each standard gas group independently includes organic gases belonging to the same category but of different types. S2. Substitute the mass-to-charge ratio of the protonation products of different gas components in the gas to be tested into the functional relationship of their respective standard gas groups to calculate the sensitivity of each gas component in the gas to be tested. S3. Calculate the concentration of the gas component in the gas to be tested based on the peak response intensity and sensitivity of each gas component in the gas to be tested.

2. The calibration method according to claim 1, characterized in that, Step S1, which involves obtaining the functional relationship between the sensitivity of each standard gas group and the corresponding protonation product mass charge ratio, specifically includes: S11. Under constant instrument parameters, multiple sets of standard gases are successively introduced into the proton transfer reaction time-of-flight mass spectrometer, and the mass-to-charge ratio of different organic gas protonation products in each set of standard gases and their corresponding peak response intensities at different preset concentrations are tested. S12. Using the preset concentration of each organic gas as the independent variable and the peak response intensity of each organic gas at different preset concentrations as the dependent variable, fit multiple sets of data to obtain the sensitivity of each organic gas. S13. Using the mass-to-charge ratio of the protonation products of different organic gases in each standard gas group as the independent variable and the sensitivity as the dependent variable, fit multiple sets of data to obtain the functional relationship between the sensitivity of each standard gas group and the mass-to-charge ratio of its corresponding protonation product.

3. The calibration method according to claim 2, characterized in that, The constant instrument parameters mentioned in step S11 include constant drift tube operating voltage, constant drift tube pressure, constant drift tube temperature, and a constant ratio of electric field strength to neutral gas number concentration, and H2O is used as the reaction ion source during the test.

4. The calibration method according to claim 2 or 3, characterized in that, The classification rules for the same category mentioned in step S1 include: classification based on the elemental composition and / or molecular structure of organic gases.

5. The calibration method according to claim 4, characterized in that, The molecular structure includes unsaturated bonds and / or functional groups.

6. The calibration method according to any one of claims 2-5, characterized in that, The test methods for determining the mass-to-charge ratio of protonation products of different gas components in the test gas in step S2 and the peak response intensity of different gas components in the test gas in step S3 include: Under the constant instrument parameters described in step S11, the gas to be tested is introduced into the proton transfer reaction time-of-flight mass spectrometer, and the mass-to-charge ratio and peak response intensity of the protonation products of different gas components in the gas to be tested are obtained.

7. The calibration method according to any one of claims 4-6, characterized in that, The method for calculating sensitivity in step S2 specifically includes: Analyze the elemental composition and / or molecular structure of different gas components in the gas to be tested, and determine the category to which the different gas components in the gas to be tested belong according to the same classification rules as the standard gas group; The mass-to-charge ratios of the protonation products of different gas components in the gas to be tested are substituted into the functional relationships of the standard gas group of the same category to calculate the corresponding sensitivities.

8. The calibration method according to any one of claims 1-7, characterized in that, The raw data of each standard gas group and the raw data of the sample to be tested obtained by the proton transfer reaction time-of-flight mass spectrometer are processed using a unified data processing workflow.

9. The calibration method according to claim 8, characterized in that, The data processing flow includes mass axis correction, baseline correction, peak width and peak shape determination, and high-resolution mass spectrometry peak fitting, ultimately converting the original signal into a data format of a single ion signal.

10. The calibration method according to any one of claims 1-9, characterized in that, The gas to be tested includes volatile organic compounds in the atmosphere.

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