A method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions

Abstract

The present invention relates to a method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions, comprising: a first step: dissolving the petroleum fraction in chromatographically pure toluene or dichloromethane solvent to prepare a sample to be tested; a second step: analyzing the sample to be tested using liquid chromatography-electrospray ionization-high-resolution mass spectrometry in positive and negative ion modes, and extracting molecular information of N1 compounds in the positive ion mode; a third step: collecting secondary mass spectrometry information of the N1 compound in the sample to be tested using liquid chromatography-electrospray ionization-tandem mass spectrometry; a fourth step: obtaining a distribution pattern of nitrogen-containing daughter ions and carbon-hydrogen daughter ions from the secondary mass spectrum of the N1 compound; a fifth step: determining whether the N1 compound is an alkaline or neutral nitrogen compound based on the responses of the N1 compound in the positive and negative modes of electrospray ionization in step 2; and a sixth step: obtaining a parent nucleus structure of the N1 compound based on the distribution pattern of the nitrogen-containing daughter ions and carbon-hydrogen daughter ions; wherein the N1 compound is a compound having only one nitrogen atom in its molecular formula.

Description

Technical Field

[0001] The invention belongs to the technical field of analytical chemistry and petroleum omics analysis, and particularly relates to a method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions. Background Art

[0002] As oil products become heavier, the molecules and structural compositions of petroleum fractions become increasingly complex, posing a significant challenge to petroleum refining. Nitrogen-containing compounds in petroleum lead to problems such as catalyst poisoning and pipeline corrosion, seriously affecting the efficiency of petroleum refining. Therefore, it is very necessary to study the structural composition of nitrogen-containing compounds in petroleum, which is conducive to guiding and improving the petroleum refining process. High-resolution mass spectrometry, with its excellent mass resolution, can obtain the accurate molecular formula of petroleum fractions; tandem mass spectrometry further fragments the precursor ions to obtain daughter ions, providing structural information. High-resolution mass spectrometry combined with tandem mass spectrometry is an important means of characterizing compound structures.

[0003] High-resolution mass spectrometry combined with tandem mass spectrometry has been initially explored in the characterization of the chemical structure of heavy oils, such as in the study of island (polyaromatic nuclei) and island (monoaromatic nuclei) structures in heavy oils. Using a broadband secondary acquisition method, all precursor parent ions in the petroleum fraction are introduced into the collision cell for fragmentation. Monoaromatic nucleus compounds retain their equivalent double bond number (DBE) after collision-induced desorption (CID) fragmentation, while the carbon number decreases due to alkyl side chain cleavage. Polyaromatic nucleus compounds experience a significant decrease in both DBE and carbon number after CID fragmentation. Based on the DBE distribution and carbon number changes, the structure can be determined to be monoaromatic or polyaromatic. However, because the parent ions in broadband secondary acquisition are not isolated, all mass-to-charge ratios (m / z) enter the collision cell. Fragmentation of fragile compounds occurs preferentially, while stable compounds retain their original structure, resulting in limited structural information. In addition, the broadband secondary acquisition mode obtains complex secondary spectra, and it is impossible to extract secondary fragment ions of a single molecular formula, thus failing to obtain the specific parent nucleus structure of the compounds in the petroleum fraction, which has greater guiding significance for the processing and refining of petroleum. With the continuous development of mass spectrometry technology, the allowed parent ion isolation window has gradually narrowed. Some researchers have tried to use narrow-band secondary acquisition mode to use the most intense nitrogen-containing daughter ion fragments in the secondary spectrum and the DBE of the parent ion to infer a representative parent nucleus structure (Johann Le Ma^tre, et al., Faraday Discussion., 2019, 218, 417), but the accuracy of this method is poor. Currently, tandem mass spectrometry technology based on Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) cannot quickly obtain secondary information of compounds in batches. It mostly uses a single energy to obtain secondary fragments of compounds, and secondary information is not fully utilized. In addition, the composition of petroleum fractions is complex, and the separation capacity of the mass spectrometry quadrupole is limited. Tandem mass spectrometry often cannot obtain fragment information of compounds with a single molecular formula. However, existing similar technologies can only obtain the family composition information of petroleum fraction hydrocarbon molecules, but cannot obtain the parent core structure of their molecules (Chinese patents CN201911198914.2, CN201380064470.8). Summary of the Invention

[0004] In response to the shortcomings of existing petroleum structural characterization and analysis methods, the present invention establishes a structural characterization method for aromatic nitrogen heterocyclic compounds in petroleum fractions. The petroleum fractions are analyzed by liquid chromatography high-resolution electrospray ionization mass spectrometry. A narrow-band parent ion isolation window is used, and high-resolution tandem mass spectrometry in a wide-range, high-energy collision dissociation mode is utilized to collect secondary spectra of single parent ions in the petroleum fractions. The parent nucleus structure of the aromatic nitrogen heterocyclic compounds in the petroleum fractions is identified based on the daughter ion distribution pattern of the secondary spectrum.

[0005] To achieve the above object, the present invention provides a method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions, comprising the following steps:

[0006] Step 1: Dissolve the petroleum fraction directly in chromatographic grade toluene or dichloromethane solvent to fully dissolve and prepare the sample to be tested;

[0007] Step 2: Analyze the sample using liquid chromatography-electrospray ionization-high-resolution mass spectrometry in positive and negative ion modes, and extract the molecular information of compound N1 in positive ion mode from the data;

[0008] Step 3: Liquid chromatography-electrospray ionization-tandem mass spectrometry is used to collect secondary mass spectrometric information of N1 compound in the sample to be tested;

[0009] Step 4: Obtain the distribution pattern of nitrogen-containing daughter ions and carbon-hydrogen daughter ions from the secondary mass spectrum of compound N1;

[0010] Step 5: Determine whether the N1 compound is a basic or neutral nitrogen compound based on the positive and negative mode responses of the electrospray ionization in step 2;

[0011] Step 6: Obtain the parent nucleus structure of the N1 compound based on the distribution pattern of nitrogen-containing daughter ions and carbon-hydrogen daughter ions;

[0012] Wherein, the N1 compound is a compound containing only one nitrogen atom in its molecular formula.

[0013] The method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions described in the present invention, wherein the method for extracting molecular information of N1 compounds from the data in the second step is to calculate the molecular formula of the compound based on the accurate mass-to-charge ratio in the data, and extract the molecular formula containing only one nitrogen atom from all molecular formulas.

[0014] The method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions described in the present invention, wherein the method for collecting the secondary mass spectrum of the N1 compound in the sample to be tested in the third step is to include the quasi-molecular ions of the compound containing only one nitrogen atom screened out in the second step into the parent ion list, and adopt a narrow-band, wide-range, high-energy collision dissociation mode to target the collection of secondary mass spectrum information.

[0015] The method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions described in the present invention, wherein the narrow-band, wide-range, high-energy collisional dissociation mode refers to that when collecting the secondary mass spectrometry, the isolation window of the parent ion is ±0.2Da, the collision energy of the collisional dissociation is set to be in a step manner of 1 to 10eV, and the secondary mass spectrum is collected in the range of 10 to 100eV.

[0016] The method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions described in the present invention, wherein the method for obtaining the carbon-hydrogen daughter ion distribution pattern in the fourth step is to extract all collected secondary mass spectrometry raw data, calculate the elemental composition, equivalent double bond number and carbon number of each daughter ion based on the accurate mass-to-charge ratio, screen daughter ions whose elemental composition only contains carbon and hydrogen, and draw a scatter plot with the equivalent double bond number as the ordinate and the carbon number as the abscissa, which is the carbon-hydrogen daughter ion distribution pattern.

[0017] The method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions described in the present invention, wherein the method for obtaining the distribution pattern of nitrogen-containing daughter ions in the fourth step is to extract the secondary mass spectrum raw data at an energy between 5% and 30% of the relative intensity of the parent ion in the secondary mass spectrum, screen the daughter ions containing nitrogen atoms in the elemental composition, and draw a scatter plot with the equivalent double bond number of the nitrogen-containing daughter ions as the vertical coordinate and the carbon number as the horizontal coordinate, which is the distribution pattern of the nitrogen-containing daughter ions.

[0018] The method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions described in the present invention, wherein the method for distinguishing basic nitrogen compounds from neutral nitrogen compounds in the fifth step is: if the N1 compound responds only in the positive ion mode of the mass spectrometer, then the compound is a basic nitrogen compound; if the N1 compound responds in the negative ion mode, then the compound is a neutral nitrogen compound.

[0019] The method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions described in the present invention, wherein the method for obtaining the parent nucleus structure of the N1 compound in the sixth step is: first, judging whether the molecular structure contains a cycloalkane ring based on the carbon-hydrogen daughter ion distribution pattern; judging the parent nucleus carbon number of the neutral N1 compound without a cycloalkane ring based on the nitrogen-containing daughter ion distribution; judging the parent nucleus carbon number of the alkaline N1 compound without a cycloalkane ring structure based on the carbon-hydrogen daughter ion distribution pattern; judging the parent nucleus carbon number distribution range of the N1 compound containing a cycloalkane ring based on the carbon-hydrogen daughter ion distribution pattern.

[0020] The method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions described in the present invention, wherein the method for determining whether a molecular structure contains a cycloalkane ring is to determine whether a hydrocarbon daughter ion has a larger number of double bonds than the parent ion in the hydrocarbon daughter ion distribution pattern. If so, the compound does not contain a cycloalkane ring; if not, the compound contains a cycloalkane ring.

[0021] The method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions described in the present invention, wherein the method for determining the parent nucleus carbon number of the basic N1 compound that does not contain a cycloalkane ring is based on the carbon-hydrogen daughter ion distribution pattern, wherein the carbon number of the carbon-hydrogen daughter ion with the same equivalent double bond number as the parent ion and the lowest carbon number is the parent nucleus carbon number.

[0022] The method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions described in the present invention, wherein the method for determining the parent nucleus carbon number of neutral N1 compounds that do not contain cycloalkane rings is based on the corresponding nitrogen-containing daughter ion distribution pattern under sufficient fragmentation energy of the parent ion, wherein the carbon number of the nitrogen-containing daughter ion with the same equivalent double bond number as the parent ion and the lowest carbon number is the parent nucleus carbon number.

[0023] The method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions described in the present invention, wherein the method for determining the distribution range of the parent nucleus carbon number of N1 compounds containing cycloalkane rings is that, based on the distribution pattern of carbon-hydrogen daughter ions, the parent nucleus carbon number is not less than the lowest carbon number of carbon-hydrogen daughter ions under the equivalent double bond number of the parent ion.

[0024] Beneficial effects of the present invention:

[0025] The method of the present invention gives full play to the advantages of liquid chromatography and high-resolution mass spectrometry, and can be used for the efficient molecular characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions. The present invention discloses a new method for the structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions, including using liquid chromatography high-resolution electrospray mass spectrometry to analyze petroleum fractions, using a narrow-band parent ion isolation window, and utilizing a high-resolution tandem mass spectrometry in a wide-range, high-energy collision dissociation mode to collect secondary spectra of single parent ions in petroleum fractions; based on the secondary spectrum daughter ion distribution pattern, the parent nucleus structure identification of aromatic nitrogen heterocyclic compounds in petroleum fractions is achieved. Compared with existing methods, compound secondary information can be quickly collected in batches; liquid phase separation combined with a narrow parent ion isolation window makes it easier to obtain a secondary spectrum of a single molecular formula; through the daughter ion distribution pattern, the parent nucleus structure of the main aromatic nitrogen heterocyclic compounds in petroleum can be determined, providing a basis for structural characterization. The present invention fully utilizes the potential advantages of tandem mass spectrometry for compound structure analysis, and provides a method for the structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The carbon-hydrogen product ion distribution diagram of the neutral aromatic nitrogen heterocyclic N1 model compounds 3-hexylindole (A), 5-butyl-3-propylindole (B), 2-pentyl-3-butylindole (C), 2-pentyl-3,5-dibutylindole (D), 3,6-diethylcarbazole (E) and 6-propyl-3-ethylcarbazole (F).

[0027] The hollow points in the figure are carbon-hydrogen product ions with a higher DBE than the parent ion DBE, and the grid points are carbon-hydrogen product ions with the lowest carbon number that are the same as the parent ion DBE.

[0028] Figure 2The figure shows the distribution of nitrogen-containing daughter ions at the sufficient fragmentation energy of the parent ions of the neutral aromatic nitrogen heterocyclic N1 model compounds 3-hexylindole (A), 5-butyl-3-propylindole (B), 2-pentyl-3-butylindole (C), 2-pentyl-3,5-dibutylindole (D), 3,6-diethylcarbazole (E) and 6-propyl-3-ethylcarbazole (F).

[0029] Figure 3 The carbon-hydrogen product ion distribution diagram of the basic aromatic nitrogen heterocyclic N1 model compounds 2,6-dibutyl-3-propylquinoline (A), 2-butyl-3-propylquinoline (B), 2,4-diisobutylquinoline (C), 2-isobutylquinoline (D), 4-ethyl-2-propylpyridine (E) and 6-hexyl-2,4-diethylpyridine (F).

[0030] The hollow points in the figure are carbon-hydrogen product ions with a higher DBE than the parent ion DBE, and the grid points are carbon-hydrogen product ions with the lowest carbon number that are the same as the parent ion DBE.

[0031] Figure 4 The carbon-hydrogen product ion distribution diagrams of the aromatic nitrogen heterocyclic N1 (containing cycloalkane ring) model compounds 3-ethyl-2,3,4,9-tetrahydrocarbazole (A), 3-propyl-2,3,4,9-tetrahydrocarbazole (B), 3-tert-pentyl-2,3,4,9-tetrahydrocarbazole (C), 3,6-diethyl-2,3,4,9-tetrahydrocarbazole (D), 3-propyl-6-ethyl-2,3,4,9-tetrahydrocarbazole (E) and 3-tert-pentyl-6-ethyl-2,3,4,9-tetrahydrocarbazole (F).

[0032] Figure 5 The molecular formula of diesel is C 11 H 11 N(A), C 13 H 17 N(B) and C 16 H 21 Distribution diagram of carbon-hydrogen product ions of N(C) compounds.

[0033] The hollow points in the figure are carbon-hydrogen product ions with a higher DBE than the parent ion DBE, and the grid points are carbon-hydrogen product ions with the lowest carbon number that are the same as the parent ion DBE.

[0034] Figure 6 The molecular formula of diesel is C 11 H 11 N(A), C 13 H 17 N(B) and C 16 H 21 The predicted core structure of N(C) compounds.

[0035] Figure 7 The molecular formula of diesel is C11 H 11 Comparison of retention times of N compounds and standards.

[0036] Figure 8 The molecular formula of diesel is C 11 H 11 Comparison of secondary spectra of N and standard samples.

[0037] Figure 9 The molecular formula of diesel is C 13 H 17 Distribution diagram of nitrogen-containing product ions at the energy at which the parent ion of N compounds is fully fragmented.

[0038] Figure 10 The molecular formula of diesel is C 13 H 17 Comparison of retention times of N compounds and standards.

[0039] Figure 11 The molecular formula of diesel is C 13 H 17 Comparison of secondary spectra of N compound and standard.

[0040] Figure 12 The molecular formula of diesel is C 16 H 21 Comparison of retention times of N compounds and standards.

[0041] Figure 13 The molecular formula of diesel is C 16 H 21 Comparison of secondary spectra of N compound and standard.

[0042] Figure 14 The molecular formula of wax oil is C 24 H 35 Distribution diagram of carbon-hydrogen product ions of N compounds.

[0043] The hollow points in the figure are carbon-hydrogen product ions with a higher DBE than the parent ion DBE, and the grid points are carbon-hydrogen product ions with the lowest carbon number that are the same as the parent ion DBE.

[0044] Figure 15 The molecular formula of wax oil is C 24 H 35 The predicted core structure of compound N (method of the present invention).

[0045] Figure 16 This is the carbon-hydrogen product ion distribution diagram of model compound D1.

[0046] Figure 17 This is the predicted core structure of the model compound D1 (method of the present invention).

[0047] Figure 18Schematic diagram of the structure of model compound D1.

[0048] Figure 19 This is the mass spectrum of model compound D1 at 40 eV.

[0049] Figure 20 This is the nitrogen-containing daughter ion distribution diagram of model compound D1 at 40 eV.

[0050] Figure 21 This is the predicted core structure of the model compound D1 (existing method). DETAILED DESCRIPTION

[0051] The present invention is described in detail below by way of examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. Those skilled in the art may make some non-essential improvements and adjustments to the present invention based on the above disclosure.

[0052] The technical solution adopted in the present invention is as follows:

[0053] Step 1: Sample preparation: Weigh an appropriate amount of sample and dissolve it thoroughly in chromatographically pure toluene as a solvent to prepare the sample to be tested;

[0054] Step 2: Analyze the sample using liquid chromatography-electrospray ionization-high-resolution mass spectrometry full-scan mode, extract liquid chromatography-electrospray ionization-high-resolution mass spectrometry full-scan mode data, calculate the molecular formula of the compound based on the accurate mass-to-charge ratio (m / z) in the data, and extract the molecular information of N1 compounds from all molecular formulas. N1 compounds are compounds with only one nitrogen atom in their molecular formula;

[0055] Step 3: Liquid chromatography-high-resolution tandem mass spectrometry was used to collect the secondary mass spectrometry data of compound N1. The mass spectrometry conditions were as follows: the mass spectrometer was a Q Exactive HF mass spectrometer (Thermo Fisher Scientific, Rockford, IL, USA), and the full scan plus secondary mass spectrometry acquisition mode was adopted. The heated electrospray mode and positive ion mode were used, the spray voltage was 3.5 kV, the temperature of the ion transfer tube was 320 ° C, the flow rates of the sheath gas and auxiliary gas were 45 and 10, respectively, the heater temperature of the auxiliary gas was 350 ° C, and the S-lens was set to 50.0. In the primary mass spectrometry, the resolution of the FWHM at m / z 200 was 120,000. The automatic gain control target (AGC target) was set to 3×10 6 Ion capacity, maximum injection time (maximum IT) is set to 100ms. The N1 compound is targeted for the secondary acquisition list. During the secondary acquisition, the resolution is 30,000 and the automatic gain control target (AGCtarget) is set to 1×10 5The ion capacity, maximum injection time (maximum IT) was set to 50 ms, the isolation window was ±0.2 Da, the collision energy was 10–100 eV, and the interval was 5 eV;

[0056] Step 4: Read the collected secondary mass spectrometry data, calculate the molecular formula corresponding to the fragment ion of the compound based on the accurate m / z, and calculate the DBE of the compound based on the molecular formula. The method for the distribution pattern of carbon-hydrogen daughter ions is to extract all the collected secondary mass spectrometry raw data, calculate the elemental composition, equivalent double bond number and carbon number of each daughter ion based on the accurate mass-to-charge ratio; screen the daughter ions whose elemental composition only contains carbon and hydrogen, and make a scatter plot with the equivalent double bond number as the vertical coordinate and the carbon number as the horizontal coordinate, which is the carbon-hydrogen daughter ion distribution pattern. The method for the distribution pattern of nitrogen-containing daughter ions is to extract the secondary mass spectrometry raw data at a specified energy (the relative intensity of the parent ion in the secondary mass spectrometry is between 5% and 30%), screen the daughter ions containing nitrogen atoms in the elemental composition, and make a scatter plot with the equivalent double bond number of the nitrogen-containing daughter ions as the vertical coordinate and the carbon number as the horizontal coordinate, as the distribution pattern of nitrogen-containing daughter ions of this energy;

[0057] Step 5: Based on the response and retention time information of the N1 compound in the positive and negative ion modes, determine whether the compound is a neutral N1 compound or a basic N1 compound. If the compound responds only in the positive ion mode of the mass spectrometer, then the compound is a basic nitrogen compound. If the compound responds in the negative ion mode, then the compound is a neutral nitrogen compound.

[0058] Step 6: The method for determining the carbon number of the parent nucleus is as follows: First, determine whether the N1 compound contains a cycloalkane ring structure based on the carbon-hydrogen daughter ion distribution pattern. If there are carbon-hydrogen daughter ions with a larger number of double bonds than the parent ion in the carbon-hydrogen daughter ion distribution pattern, then the compound does not contain a cycloalkane ring; if not, then it contains a cycloalkane ring. Next, the method for determining the carbon number of the parent nucleus of the alkaline N1 compound without a cycloalkane ring is based on the carbon-hydrogen daughter ion distribution pattern, wherein the carbon number of the carbon-hydrogen daughter ion with the same equivalent double bond number as the parent ion and the lowest carbon number is the parent nucleus carbon number; the method for determining the carbon number of the parent nucleus of the neutral N1 compound without a cycloalkane ring is based on the nitrogen-containing daughter ion distribution pattern corresponding to the sufficient fragmentation energy of the parent ion (the energy between 5 and 30% of the relative intensity of the parent ion in the secondary mass spectrometry), wherein the carbon number of the nitrogen-containing daughter ion with the same equivalent double bond number as the parent ion and the lowest carbon number is the parent nucleus carbon number; the method for determining the range of the carbon number of the parent nucleus of the N1 compound containing a cycloalkane ring structure is based on the carbon-hydrogen daughter ion distribution pattern, wherein the carbon number of the parent nucleus is not less than the lowest carbon number of the carbon-hydrogen daughter ion under the equivalent double bond number of the parent ion.

[0059] Example 1 Structural Characterization of Neutral Aromatic Nitrogen Heterocyclic N1 Model Compounds Containing No Cycloalkane Rings

[0060] An appropriate amount of solution of a cycloalkane-free neutral aromatic nitrogen heterocyclic N1 model compound, including 3-hexylindole (A1), 5-butyl-3-propylindole (A2), 2-pentyl-3-butylindole (A3), 2-pentyl-3,5-dibutylindole (A4), 3,6-diethylcarbazole (A5) and 6-propyl-3-ethylcarbazole (A6), was placed in an injection vial for liquid chromatography-high-resolution mass spectrometry analysis. The structures of the model compounds are shown in Appendix 1.

[0061] Appendix 1. Summary of information on neutral aromatic nitrogen-hybridized N1 model compounds (without cycloalkane rings)

[0062]

[0063] Liquid chromatography conditions: A Waters ultra-high performance liquid chromatograph (ACQUITY Ultra Performance LC, UPLC, Waters, Milford, MA, USA) was used; the analytical column was an ACQUITY HSS T3 Column, 2.1 mm × 100 mm, 1.7 μm (Waters, Milford, MA, USA). The column temperature was 50°C, and the injection volume was 5 μL. In positive ion mode, the mobile phases (phase A) consisted of 0.1% (v / v) formic acid in water, and phase B consisted of acetonitrile containing 0.1% (v / v) formic acid. In negative ion mode, the mobile phases (phase A) consisted of pure water, and phase B consisted of pure acetonitrile. A linear gradient was used, with the mobile phase changing from 95% phase A to 100% phase B from 0 to 27 min, then switching to 95% phase A from 27 to 27.2 min, and maintaining 95% phase A for 30 min.

[0064] Mass spectrometry conditions: The mass spectrometer was a Q Exactive HF mass spectrometer (Thermo Fisher Scientific, Rockford, IL, USA). Heated electrospray mode was used, with a spray voltage of 3.5 kV, an ion transfer tube temperature of 320°C, sheath and auxiliary gas flow rates of 45 and 10 (in arbitrary units), respectively, an auxiliary gas heater temperature of 350°C, and an S-lens setting of 50.0. In the primary mass spectrometer, the full width half maximum resolution at m / z 200 was 240,000. The automatic gain control target (AGC target) was set to 3 × 10 6 Ion capacity, the maximum injection time (maximum IT) was set to 100ms.

[0065] Tandem mass spectrometry conditions: full scan plus secondary mass spectrometry acquisition mode was used, the resolution of the primary mass spectrum at m / z 200 was set to 120,000, and the automatic gain control target (AGC target) was set to 3×10 6 The ion capacity and maximum injection time (IT) were set to 100 ms. The secondary mass spectrometry acquisition was performed with the quasi-molecular ions of the model compound as the target secondary list, the resolution was 30,000, and the automatic gain control target (AGC target) was set to 1×10 5 The ion capacity and maximum injection time (maximum IT) were set to 50 ms, the isolation window was ±0.2 Da, the collision energy was 10–100 eV, and the interval was 5 eV.

[0066] Data processing: The acquired LC-HRMS data were processed using Xcalibur™ 2.2 (Thermo Fisher Scientific, Rockford, USA).

[0067] In positive ion mode, parent ions of A1 to A6 model compounds [M+H] + The m / z of the product ions were 202.15902, 216.17468, 244.20598, 300.26858, 224.14338 and 238.15903 respectively. All the secondary mass spectrometry raw data corresponding to the parent ions of the model compounds A1 to A6 at a collision energy of 10 to 100 eV were exported. The mass deviation was set to 10 ppm, and the elemental composition and DBE of the product ions were calculated based on the accurate m / z of the secondary mass spectrometry product ions. All the hydrocarbon product ions contained in the secondary mass spectrometry data obtained at 10 to 100 eV were extracted and a DBE-carbon number distribution scatter plot was made (see Figure 1 ); extract the nitrogen-containing daughter ions of A1 to A6 when the parent ion is fully fragmented (the relative intensity of the parent ion in the secondary mass spectrometry is between 5 and 30%), and make a DBE-carbon number distribution scatter plot (see Figure 2 ); A1 to A6 responded in both positive and negative ion modes.

[0068] The carbon-hydrogen daughter ion distribution pattern of the neutral aromatic nitrogen heterocyclic N1 model compound without cycloalkane ring: The carbon-hydrogen daughter ion distribution diagram of A1 to A6 ( Figure 1 ) It can be seen that the above neutral aromatic nitrogen heterocyclic N1 model compounds all have multiple carbon-hydrogen daughter ions larger than the parent ion DBE ( Figure 1 The hollow carbon hydride daughter ion is shown). Figure 1 In AD, there are carbon-hydrogen daughter ions with DBE greater than 6 (parent ion DBE = 5.5); Figure 1 EF all have carbon-hydrogen daughter ions with DBE greater than 9 (parent ion DBE=8.5).

[0069] Therefore, it can be seen from the above model compounds that the neutral aromatic nitrogen heterocycle N1 without a cycloalkane ring has a carbon-hydrogen product ion larger than the parent ion DBE.

[0070] Distribution of nitrogen-containing daughter ions of the model compound N1 containing neutral aromatic nitrogen heterocycles without cycloalkane rings: DBE-carbon number distribution of nitrogen-containing daughter ions from A1 to A6 at the energy level where the parent ion is fully fragmented (parent ion relative intensity is between 5% and 30%) ( Figure 2 ) It can be seen that the minimum carbon number of the nitrogen-containing daughter ions that are the same as the parent ion DBE is consistent with the parent nucleus carbon number of A1 to A6. Figure 2 AD shows that the minimum carbon number of the nitrogen-containing daughter ion with a DBE of 5.5 is 8 (DBE of the parent ions A1 to A4 = 5.5), which is consistent with the carbon number of the parent nucleus of indole compounds; Figure 2 From EF, it can be seen that the minimum carbon number of the nitrogen-containing daughter ion with a DBE of 8.5 is 12 (the parent ions of A5 and A6 have DBE=8.5), which is consistent with the carbon number of the parent nucleus (carbazole) of A5 and A6.

[0071] Therefore, from the above model compounds, it can be seen that according to the neutral aromatic nitrogen heterocyclic N1 compound without a cycloalkane ring, the distribution of nitrogen-containing daughter ions at the sufficient fragmentation energy of the parent ion can be obtained, and the parent nucleus carbon number is the lowest carbon number of the nitrogen-containing daughter ion that is the same as the parent ion DBE.

[0072] Example 2 Structural Characterization of Basic Aromatic Nitrogen Heterocyclic N1 Model Compounds Containing No Cycloalkane Ring

[0073] An appropriate amount of basic aromatic nitrogen heterocyclic N1 (without a cycloalkane ring) model compound solution, including: 2,6-dibutyl-3-propylquinoline (B1), 2-butyl-3-propylquinoline (B2), 2,4-diisobutylquinoline (B3), 2-isobutylquinoline (B4), 4-ethyl-2-propylpyridine (B5) and 6-hexyl-2,4-diethylpyridine (B6), was placed in an injection vial for liquid chromatography-high resolution mass spectrometry analysis. The structures of the model compounds are shown in Appendix 2.

[0074] Appendix 2. Summary of information on basic aromatic nitrogen-hybridized N1 model compounds (without cycloalkane ring)

[0075]

[0076]

[0077] The liquid chromatography, mass spectrometry and tandem mass spectrometry conditions were the same as those in Example 1.

[0078] Data processing: The acquired LC-HRMS data were processed using Xcalibur™ 2.2 (Thermo Fisher Scientific, Rockford, USA).

[0079] In positive ion mode, parent ions of model compounds B1 to B6 [M+H] + The m / z values ​​of the product ions were 284.23728, 228.17468, 242.19033, 186.12773, 150.12773, and 220.20598, respectively. All the secondary mass spectrometry raw data corresponding to the parent ions of the model compounds B1 to B6 at collision energies of 10 to 100 eV were exported. The mass deviation was set to 10 ppm, and the elemental composition and DBE of the product ions were calculated based on the accurate m / z values ​​of the secondary mass spectrometry product ions. All the hydrocarbon product ions obtained at 10 to 100 eV were extracted, and a DBE-carbon number distribution scatter plot was plotted (see Figure 3 ); B1 to B6 respond only in positive ion mode.

[0080] The carbon-hydrogen daughter ion distribution pattern of the basic aromatic nitrogen heterocyclic N1 model compound without cycloalkane ring: The carbon-hydrogen daughter ion distribution diagram from B1 to B6 ( Figure 3 ) It can be seen that the above basic aromatic nitrogen heterocyclic N1 model compounds all have multiple carbon-hydrogen daughter ions (hollow points in the figure) that are larger than the parent ion DBE. Figure 3 In AD, there are carbon-hydrogen daughter ions with DBE greater than 7 (parent ion DBE = 6.5); Figure 3 EF all have carbon-hydrogen daughter ions with DBE greater than 4 (parent ion DBE = 3.5).

[0081] Therefore, it can be seen from the above model compounds that, consistent with the rule obtained for the model compound of neutral aromatic nitrogen heterocycle N1 without cycloalkane ring, basic aromatic nitrogen heterocycle N1 without cycloalkane ring has carbon-hydrogen daughter ions larger than the parent ion DBE.

[0082] DBE-carbon number distribution diagram of carbon hydrogen daughter ions from B1 to B6 ( Figure 3 ) It can also be seen that the minimum carbon number of the hydrocarbon daughter ions that are the same as the parent ion DBE is consistent with the parent nucleus carbon number of B1 to B6 (grid point). Figure 3 AD shows that the minimum carbon number of the hydrocarbon daughter ion with DBE of 6.5 is 9 (DBE of parent ions B1 to B4 = 6.5), which is consistent with the carbon number of the parent nucleus of quinoline compounds. Figure 3 From EF, we can see that the minimum carbon number of a hydrocarbon daughter ion with a DBE of 3.5 is 5 (DBE = 3.5 for the parent ions of B5 and B6, and DBE = 4 for the odd-electron parent ion), which is consistent with the carbon number of the parent nucleus (pyridine) of B5 and B6.

[0083] Therefore, from the above model compounds, it can be seen that the presence of a cycloalkane ring in the structure of a basic aromatic nitrogen heterocycle N1 compound can be determined based on its carbon-hydrogen daughter ion distribution. Basic aromatic nitrogen heterocycle N1 compounds without cycloalkane rings have carbon-hydrogen daughter ions greater than the parent ion DBE. The carbon-hydrogen daughter ion distribution can also be used to determine the parent nucleus carbon number of basic aromatic nitrogen heterocycle N1 compounds without cycloalkane rings. The parent nucleus carbon number is the lowest carbon number of the carbon-hydrogen daughter ion that is identical to the parent ion DBE.

[0084] Example 3 Structural Characterization of Cycloalkane-Containing Aromatic Nitrogen Heterocyclic N1 Model Compounds

[0085] An appropriate amount of a solution of a cycloalkane-containing aromatic nitrogen heterocycle N1 model compound, including: 3-ethyl-2,3,4,9-tetrahydrocarbazole (C1), 3-propyl-2,3,4,9-tetrahydrocarbazole (C2), 3-tert-pentyl-2,3,4,9-tetrahydrocarbazole (C3), 3,6-diethyl-2,3,4,9-tetrahydrocarbazole (C4), 3-propyl-6-ethyl-2,3,4,9-tetrahydrocarbazole (C5) and 3-tert-pentyl-6-ethyl-2,3,4,9-tetrahydrocarbazole (C6), was placed in an injection vial for liquid chromatography-high resolution mass spectrometry analysis. The structures of the model compounds are shown in Appendix 3.

[0086] Appendix 3. Summary of information on neutral aromatic nitrogen-hybridized N1 (containing cycloalkane ring) model compounds

[0087]

[0088]

[0089] The liquid chromatography, mass spectrometry and tandem mass spectrometry conditions were the same as those in Example 1.

[0090] Data processing: The acquired LC-HRMS data were processed using Xcalibur™ 2.2 (Thermo Fisher Scientific, Rockford, USA).

[0091] In positive ion mode, parent ions of C1-C6 model compounds [M+H] + The m / z values ​​of the product ions were 200.14338, 214.15903, 242.19033, 228.17468, 242.19033, and 270.22163, respectively. All the secondary mass spectrometry raw data corresponding to the parent ions of the C1 to C6 model compounds at collision energies of 10 to 100 eV were exported. The mass deviation was set to 10 ppm, and the elemental composition and DBE of the product ions were calculated based on the accurate m / z values ​​of the secondary mass spectrometry product ions. All the hydrocarbon product ions obtained at 10 to 100 eV were extracted, and a DBE-carbon number distribution scatter plot was plotted (see Figure 4); C1 to C6 responded in both positive and negative ion modes.

[0092] The distribution pattern of carbon-hydrogen daughter ions of the N1 model compound containing cycloalkane ring aromatic nitrogen heterocycle: the distribution diagram of carbon-hydrogen daughter ions from C1 to C6 ( Figure 4 ) It can be seen that the above-mentioned neutral aromatic nitrogen heterocyclic N1 model compound containing a cycloalkane ring has almost no carbon-hydrogen daughter ions larger than the parent ion DBE, that is, Figure 4 In AF, there are no hydrocarbon product ions with a DBE greater than 7 (parent ion DBE = 6.5, odd-electron parent ion DBE = 7).

[0093] DBE-carbon number distribution diagram of C1~C6 hydrocarbon daughter ions ( Figure 4 ) It can be seen that the minimum carbon number of the hydrocarbon daughter ions with the same carbon number as the parent ion DBE is greater than the carbon number of the parent nucleus of C1 to C6. Figure 4 From AF, we can see that the minimum carbon number of a hydrocarbon daughter ion with a DBE of 6.5 is 9 (DBE of C1-C6 parent ions = 6.5), which is less than the carbon number of the parent nucleus of tetrahydrocarbazole, 12.

[0094] Therefore, the above model compounds show that the presence of a cycloalkane ring in the structure can be determined based on the carbon-hydrogen daughter ion distribution of aromatic nitrogen heterocyclic N1 compounds. Cycloalkane-containing aromatic nitrogen heterocyclic N1 compounds do not have carbon-hydrogen daughter ions greater than the parent ion DBE. The carbon-hydrogen daughter ion distribution provides a range of parent nucleus carbon numbers for compounds containing cycloalkane rings, with the parent nucleus carbon number exceeding the minimum carbon number of the carbon-hydrogen daughter ion corresponding to the parent ion DBE.

[0095] Example 4 Structural Characterization of Aromatic Nitrogen Heterocyclic N1 Compounds from Diesel Oil Fraction

[0096] Take an appropriate amount of diesel sample into a sampling vial, add chromatographic grade toluene first, vortex to fully dissolve it, and use it for liquid chromatography-high resolution mass spectrometry analysis.

[0097] The conditions for liquid chromatography, mass spectrometry and tandem mass spectrometry were the same as those in Example 1, wherein the tandem mass spectrometry acquisition was performed using the parent ions of all N1 compounds obtained by full scan as the targeted secondary list for tandem mass spectrometry acquisition.

[0098] Data processing: The acquired LC-HRMS data were processed using Xcalibur™ 2.2 (Thermo Fisher Scientific, Rockford, USA).

[0099] C in diesel 11 H 11 N, C 13 H 17 N and C 16 H 21Taking N as an example, the structural characterization of aromatic nitrogen heterocyclic N1 compounds in diesel fraction is explained.

[0100] Extract diesel with molecular formula C 11 H 11 N, C 13 H 17 N and C 16 H 21 The m / z of the compounds of N in positive ion mode were 158.09643, 188.1434 and 228.17468 respectively; the retention time was derived as 4.20min (C 11 H 11 N), 17.65min(C 13 H 17 N) and 20.46min(C 16 H 21 N), all secondary mass spectrometry data with collision energy of 10 to 100 eV. The mass deviation was set to 10 ppm, and the elemental composition and DBE were calculated based on the accurate m / z of the secondary mass spectrometry product ions. All the hydrocarbon product ions obtained by the above compounds at 10 to 100 eV were extracted and DBE-carbon number distribution scatter plots were made; the nitrogen-containing product ions of the compounds at the energy when the parent ion was fully fragmented (the relative intensity of the parent ion in the secondary mass spectrometry was between 5 and 30%) were extracted and DBE-carbon number distribution scatter plots were made. From diesel with molecular formula C 11 H 11 N, C 13 H 17 N and C 16 H 21 The mass spectrometric responses of N compounds in positive and negative ion modes show that C 11 H 11 N only emits peaks in positive ion mode and is a basic nitrogen compound. 13 H 17 N and C 16 H 21 The compounds containing N emit peaks in both positive and negative ion modes and are neutral nitrogen compounds.

[0101] Compound C 11 H 11 N, C 13 H 17 N and C 16 H 21 Distribution of hydrocarbon daughter ions of N: The molecular formula of diesel is C 11 H 11 The parent ion of N compound has a DBE of 6.5, and there are hydrocarbon daughter ions with a DBE greater than 7 ( Figure 5 A); molecular formula is C 13 H 17The parent ion DBE of the compound of N is 5.5, and there are hydrocarbon daughter ions with DBE greater than 6 ( Figure 5 B); molecular formula is C 16 H 21 The parent ion DBE of N is 6.5, and there is no hydrocarbon daughter ion with DBE greater than 7 ( Figure 5 C)

[0102] The above results show that the molecular formula of diesel is C 11 H 11 N compounds are basic N1 compounds that do not contain cycloalkane rings, C 13 H 17 N is a neutral N1 compound without a cycloalkane ring, C 16 H 21 N is a neutral N1 compound containing a cycloalkane ring. Based on the distribution patterns of the carbon-hydrogen daughter ions and nitrogen-containing daughter ions of the model compounds, the parent nucleus structures of the compounds of the above three molecular formulas in diesel are identified in turn.

[0103] Compound C 11 H 11 Identification of the parent nucleus structure of N: From C 11 H 11 The carbon-hydrogen daughter ion distribution diagram of N (5A) shows that the minimum carbon number of the carbon-hydrogen daughter ion with a DBE of 6.5 is 9 (C 11 H 11 The parent ion DBE of N is 6.5), so compound C 11 H 11 The number of carbon atoms in the parent nucleus of N is 9. The molecular formula of diesel is C 11 H 11 The compound N is a basic N1 compound with a parent nucleus carbon number of 9, a DBE of 7, and no cycloalkane ring. It is speculated to be a quinoline / isoquinoline compound with a structure such as Figure 6 As shown in A.

[0104] In order to verify the reliability of the inferred structure, the C 11 H 11 The extracted ion chromatogram of N compound was compared with that of ethylquinoline standard sample ( Figure 7 ), it was found that the retention time of the compound in the sample was close to that of the ethylquinoline standard. 11 H 11 The secondary spectrum of compound N and the secondary spectrum of ethylquinoline standard are as follows Figure 8 As shown in the figure, it can be seen that the secondary spectrum is similar to the secondary spectrum of ethylquinoline, which proves the feasibility of this method for inferring the parent nucleus structure of basic aromatic nitrogen heterocyclic N1 compounds without cycloalkane rings in petroleum fractions.

[0105] Compound C 13 H17 Identification of the parent nucleus structure of N: From C 13 H 17 DBE-carbon number distribution diagram of nitrogen-containing daughter ions at the energy of sufficient fragmentation of the parent ion (parent ion relative intensity between 5% and 30%) ( Figure 9 ) It can be seen that the minimum carbon number of the nitrogen-containing daughter ion with a DBE of 5.5 is 8 (C 13 H 17 The parent ion DBE of N is 5.5), so compound C 13 H 17 The number of carbon atoms in the parent nucleus of N is 8; the molecular formula of diesel is C 13 H 17 The compound of N is a neutral N1 compound with a parent nucleus carbon number of 8 and a DBE of 6, and does not contain a cycloalkane ring. Therefore, it can be inferred that its parent nucleus is indole. 13 H 17 N is an indole compound, and its structure is speculated to be Figure 6 As shown in B.

[0106] In order to verify the accuracy of the inferred structure, the C 13 H 17 The extracted ion chromatogram of N compound was compared with that of representative alkyl indole standard (2-methyl-3-isobutylindole) ( Figure 10 ), it was found that the retention time of the standard sample was similar to that of C 13 H 17 The retention time of N compounds is close. 13 H 17 The secondary spectrum of N and the secondary spectrum of the standard are as follows Figure 11 As shown in the figure, it can be seen that the secondary spectra of the two are similar, which proves the feasibility of this method for inferring the parent nucleus structure of neutral aromatic nitrogen heterocyclic N1 compounds without cycloalkane rings in oil samples.

[0107] Compound C 16 H 21 Identification of the parent nucleus structure of N: From C 16 H 21 The carbon-hydrogen daughter ion distribution diagram of N (5C) shows that the minimum carbon number of the carbon-hydrogen daughter ion with a DBE of 6.5 is 9 (C 16 H 11 The DBE of the N parent ion is 6.5), so compound C 16 H 21 The number of carbon atoms in the parent nucleus of N should be greater than 9. 16 H 21 The compound of N is a neutral N1 compound with a parent nucleus carbon number greater than 9, a DBE of 7, and a cycloalkane ring. It is speculated to be a tetrahydrocarbazole compound, and its structure is as follows Figure 6 As shown in C.

[0108] In order to verify the correctness of the inferred structure, the C 16 H 21 The extracted ion chromatogram of the N compound was compared with that of a typical alkyl-substituted tetrahydrocarbazole (3,6-diethyl-2,3,4,9-tetrahydrocarbazole) standard sample ( Figure 12 ), and found that the retention time of the two was close; further analysis of C 16 H 21 The secondary spectrum of compound N was compared with the secondary spectrum of 3,6-diethyl-2,3,4,9-tetrahydrocarbazole ( Figure 13 ), as can be seen from the figure, the secondary spectra of the two are similar. The standard sample results show that the method of the present invention is feasible for inferring the parent nucleus structure of aromatic nitrogen heterocyclic N1 compounds containing cycloalkane rings in petroleum fractions.

[0109] Example 5 Structural Characterization of Aromatic Nitrogen Heterocyclic N1 Compounds in Wax Oil Fractions

[0110] Weigh an appropriate amount of hydrodenitrogenated wax oil into a sampling vial, add chromatographic grade dichloromethane first, and vortex to fully dissolve it for liquid chromatography-high resolution mass spectrometry analysis.

[0111] Liquid chromatography conditions: A Waters ultra-high performance liquid chromatograph (ACQUITY Ultra Performance LC, UPLC, Waters, Milford, MA, USA) was used; an ACQUITY UPLC BEH phenyl column, 2.1 mm × 100 mm, 1.7 μm (Waters, Milford, MA, USA) was used as the analytical column, the column temperature was 50°C, and the injection volume was 5 μL. The mobile phases in the positive ion mode were phase A: 60% acetonitrile / water containing 0.1% by volume formic acid, and phase B: 90% isopropanol / acetonitrile containing 0.1% by volume formic acid. The mobile phases in the negative ion mode were phase A: 60% acetonitrile / water, and phase B: 90% isopropanol / acetonitrile. A linear gradient was used, with the mobile phase changing from 100% phase A to 100% phase B from 0 to 27 min, then switching to 100% phase A from 27 to 27.2 min, and maintaining 100% phase A for 30 min.

[0112] Mass spectrometry conditions and tandem mass spectrometry conditions: same as Example 4.

[0113] Data processing: The acquired LC-HRMS data were processed using Xcalibur™ 2.2 (Thermo Fisher Scientific, Rockford, USA).

[0114] In positive ion mode, the molecular formula of wax oil is C24 H 35 Taking the structural analysis of N as an example, its m / z is 338.28423; all secondary mass spectrometry data with a retention time of 1.40 min and a collision energy of 10-100 eV were derived. The mass deviation was set to 10 ppm, and the elemental composition and DBE were calculated based on the accurate m / z of the secondary mass spectrometry product ions. All hydrocarbon product ions were extracted and a DBE-carbon number distribution scatter plot was made ( Figure 14 ). This substance responds only in positive ion mode and is therefore a basic nitrogen compound.

[0115] C 24 H 35 Distribution of carbon-hydrogen daughter ions of N: C 24 H 35 The parent ion DBE of N is 7.5, from C 24 H 35 Distribution diagram of carbon-hydrogen daughter ions of N ( Figure 14 ) It can be seen that compound C 24 H 35 The presence of carbon-hydrogen daughter ions with DBE greater than 8 in N indicates that the molecular formula in the wax oil is C 24 H 35 The compound of N is a basic N1 compound without a cycloalkane ring. When DBE is 7.5, the minimum carbon number of the hydrocarbon daughter ion is 11, so compound C 24 H 35 The number of carbon atoms in the parent nucleus of N is 11, that is, the molecular formula of the wax oil is C 24 H 35 The compound of N is a basic N1 compound with a parent nucleus carbon number of 11, a DBE of 8, and no cycloalkane ring. It is speculated that its parent nucleus structure is as follows Figure 15 As shown, it is phenyl substituted pyridine.

[0116] The results of the above examples demonstrate that the present method analyzes petroleum fractions using high-resolution liquid chromatography-electrospray mass spectrometry. Using a narrow-band parent ion isolation window, high-resolution tandem mass spectrometry in a wide-range, high-energy collisional dissociation mode acquires secondary spectra of single parent ions in the petroleum fractions. The parent nucleus structure of nitrogen-containing compounds in the petroleum fractions is then identified based on the daughter ion distribution patterns of the secondary spectra. Compared to existing methods for structural elucidation of nitrogen-containing compounds in petroleum, this method allows for rapid batch acquisition of secondary information on compounds. The narrower isolation window makes it easier to obtain secondary spectra of single m / z values. The daughter ion distribution patterns allow for the determination of the parent nucleus structure of major aromatic heterocyclic nitrogen-containing compounds in petroleum, providing a basis for structural characterization. This present invention fully leverages the potential advantages of tandem mass spectrometry for compound structural elucidation, providing a method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions.

[0117] Example 6 Characterization of the Core Structure of the Model Compound 2-isobutyl-4-isopropylquinoline (D1)

[0118] Liquid chromatography conditions: A Waters ultra-high performance liquid chromatograph (ACQUITY Ultra Performance LC, UPLC, Waters, Milford, MA, USA) was used; the analytical column was an ACQUITY HSS T3 Column, 2.1 mm × 100 mm, 1.7 μm (Waters, Milford, MA, USA). The column temperature was 50°C, and the injection volume was 5 μL. In positive ion mode, the mobile phases (phase A) consisted of 0.1% (v / v) formic acid in water, and phase B consisted of acetonitrile containing 0.1% (v / v) formic acid. In negative ion mode, the mobile phases (phase A) consisted of pure water, and phase B consisted of pure acetonitrile. A linear gradient was used, with the mobile phase changing from 95% phase A to 100% phase B from 0 to 27 min, then switching to 95% phase A from 27 to 27.2 min, and maintaining 95% phase A for 30 min.

[0119] Mass spectrometry conditions: The mass spectrometer was a Q Exactive HF mass spectrometer (Thermo Fisher Scientific, Rockford, IL, USA). Heated electrospray mode was used, with a spray voltage of 3.5 kV, an ion transfer tube temperature of 320°C, sheath and auxiliary gas flow rates of 45 and 10 (in arbitrary units), respectively, an auxiliary gas heater temperature of 350°C, and an S-lens setting of 50.0. In the primary mass spectrometer, the full width half maximum resolution at m / z 200 was 240,000. The automatic gain control target (AGC target) was set to 3 × 10 6 Ion capacity, the maximum injection time (maximum IT) was set to 100ms.

[0120] Tandem mass spectrometry conditions: full scan plus secondary mass spectrometry acquisition mode was used, the resolution of the primary mass spectrum at m / z 200 was set to 120,000, and the automatic gain control target (AGC target) was set to 3×10 6 The ion capacity and maximum injection time (IT) were set to 100 ms. The secondary mass spectrometry acquisition was performed with the quasi-molecular ions of the model compound as the target secondary list, the resolution was 30,000, and the automatic gain control target (AGC target) was set to 1×10 5 The ion capacity and maximum injection time (maximum IT) were set to 50 ms, the isolation window was ±0.2 Da, the collision energy was 10–100 eV, and the interval was 5 eV.

[0121] Data processing: The collected data were processed using Xcalibur™ 2.2 (Thermo Fisher Scientific, Rockford, USA). The raw data of the secondary mass spectrum were exported, and the mass deviation was set to 10 ppm. The elemental composition and DBE were calculated based on the accurate m / z of the secondary mass spectrum product ions. All hydrocarbon product ions obtained in the range of 10 to 100 eV were extracted and a DBE-carbon number distribution scatter plot was plotted (see Figure 16 ); From the extracted ion chromatograms of compound D1 in positive and negative ion modes, it can be seen that the compound is a basic aromatic nitrogen heterocyclic model compound that only peaks in positive ion mode.

[0122] Judgment of the core structure of model compound D1: From the carbon-hydrogen daughter ion distribution diagram of compound D1 ( Figure 16 ) It can be seen that the compound has a carbon-hydrogen daughter ion with a DBE greater than 7, so it is speculated that the compound is a basic nitrogen compound without a cycloalkane ring. When DBE is 6.5 (the parent ion DBE of D1 is 6.5), the minimum carbon number of the carbon-hydrogen daughter ion of the compound is 9, so the parent nucleus carbon number of compound D1 is 9, and it is speculated that it is a quinoline / isoquinoline compound ( Figure 17 ), which is consistent with the parent nucleus of compound D1, indicating that the method of the present invention has good accuracy in judging the parent nucleus structure.

[0123] Comparative Examples

[0124] In the early stage of characterizing the chemical structure of heavy oil, high-resolution mass spectrometry combined with tandem mass spectrometry was mainly used through broadband secondary acquisition to infer the structures of heavy oil islands (multiple aromatic nuclei) and isolated islands (single aromatic nuclei). However, since the parent ions of the broadband secondary acquisition method are not isolated, the structural information obtained is limited, and the specific parent nucleus structure of the compounds in the petroleum fraction cannot be obtained. Recent representative work uses narrow-band secondary acquisition to use the nitrogen-containing daughter ion fragments with the highest intensity in the secondary spectrum and the DBE of the parent ion to infer the representative parent nucleus structure (Johann Le Ma^tre, et al., Faraday Discuss., 2019, 218, 417). To this end, taking the model compound 2-isobutyl-4-isopropylquinoline (D1) as an example, its structure is as follows Figure 18 As shown, the parent nucleus is quinoline, and its parent nucleus was inferred using literature methods. The experimental conditions and data processing methods for the model compound analysis are as follows:

[0125] Liquid chromatography conditions: A Waters ultra-high performance liquid chromatograph (ACQUITY Ultra Performance LC, UPLC, Waters, Milford, MA, USA) was used; the analytical column was an ACQUITY HSS T3 Column, 2.1 mm × 100 mm, 1.7 μm (Waters, Milford, MA, USA). The column temperature was 50°C, and the injection volume was 5 μL. In positive ion mode, the mobile phases (phase A) consisted of 0.1% (v / v) formic acid in water, and phase B consisted of acetonitrile containing 0.1% (v / v) formic acid. In negative ion mode, the mobile phases (phase A) consisted of pure water, and phase B consisted of pure acetonitrile. A linear gradient was used, with the mobile phase changing from 95% phase A to 100% phase B from 0 to 27 min, then switching to 95% phase A from 27 to 27.2 min, and maintaining 95% phase A for 30 min.

[0126] Mass spectrometry conditions: The mass spectrometer was a Q Exactive HF mass spectrometer (Thermo Fisher Scientific, Rockford, IL, USA). Heated electrospray mode was used, with a spray voltage of 3.5 kV, an ion transfer tube temperature of 320°C, sheath and auxiliary gas flow rates of 45 and 10 (in arbitrary units), respectively, an auxiliary gas heater temperature of 350°C, and an S-lens setting of 50.0. In the primary mass spectrometer, the full width half maximum resolution at m / z 200 was 240,000. The automatic gain control target (AGC target) was set to 3 × 10 6 Ion capacity, the maximum injection time (maximum IT) was set to 100ms.

[0127] Tandem mass spectrometry conditions: full scan plus secondary mass spectrometry acquisition mode was used, the resolution of the primary mass spectrum at m / z 200 was set to 120,000, and the automatic gain control target (AGC target) was set to 3×10 6 The ion capacity and maximum injection time (IT) were set to 100 ms. The secondary mass spectrometry acquisition was performed with the quasi-molecular ions of the model compound as the target secondary list, the resolution was 30,000, and the automatic gain control target (AGC target) was set to 1×10 5 The ion capacity, maximum injection time (maximum IT) were set to 50 ms, the isolation window was ±0.2 Da, and the collision energy was 40 eV.

[0128] Data processing: The collected data were processed using Xcalibur™ 2.2 (Thermo Fisher Scientific, Rockford, USA). Figure 19 The mass spectrum of compound D1 at 40 eV was obtained. The raw data of the secondary mass spectrum was exported, and the mass deviation was set to 10 ppm. The elemental composition and DBE were calculated based on the accurate m / z of the secondary mass spectrum product ions. The nitrogen-containing product ions of the compound were extracted at 40 eV and a DBE-carbon number distribution scatter plot was made (see Figure 20 ).

[0129] Judgment of the core structure of model compound D1: Figure 20 This is the DBE and carbon number distribution diagram of the nitrogen-containing daughter ion of model compound D1 at 40 eV. The DBE of the parent ion of compound D1 is 6.5. At 40 eV, the DBE of the compound does not change significantly, so it can be inferred that the compound has a mononuclear structure (island structure). Figure 19 The secondary mass spectrum of the model compound D1 at 40 eV is 170.09633 (the elemental composition is C 12 H 12 N + The relative intensity of the nitrogen-containing daughter ion is the largest. Based on the existing method, this daughter ion is considered to be the parent nucleus of the model compound D1. It is further speculated that C 12 H 12 N possible parent nucleus structures are Figure 21 The aromatic heterocycles shown have 12 carbon atoms. It is obvious that these structures do not conform to the parent core structure of compound D1 (quinoline with 9 carbon atoms).

[0130] Comparing the existing methods with the present invention clearly shows that the existing methods use the strongest nitrogen-containing daughter ion fragments in the secondary spectrum at a single energy level and the DBE of the parent ion to determine the representative parent nucleus structure, but this method has poor accuracy in parent nucleus structure inference. However, the present method fully utilizes the secondary fragment information of the compound at 10-100 eV, combined with the distribution of nitrogen-containing daughter ions and hydrocarbon daughter ions, to clearly determine the carbon number range of the parent nucleus of nitrogen-containing compounds, narrowing the range of parent nucleus structure prediction and improving the accuracy of structure prediction.

[0131] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims of the present invention.

Claims

1. A method for characterizing the structure of aromatic nitrogen heterocyclic compounds in petroleum fractions, characterized in that: The following steps are involved: Step 1: Dissolve the petroleum fraction directly in chromatographic grade toluene or dichloromethane solvent to fully dissolve and prepare the sample to be tested; Step 2: Analyze the sample using liquid chromatography-electrospray ionization-high-resolution mass spectrometry in positive and negative ion modes, and extract the molecular information of compound N1 in positive ion mode from the data; Step 3: Liquid chromatography-electrospray ionization-tandem mass spectrometry is used to collect secondary mass spectrometric information of N1 compound in the sample to be tested; Step 4: Obtain the distribution pattern of nitrogen-containing daughter ions and carbon-hydrogen daughter ions from the secondary mass spectrum of compound N1; Step 5: Determine whether the N1 compound is a basic or neutral nitrogen compound based on the positive and negative mode responses of the electrospray ionization in step 2; Step 6: Obtain the parent nucleus structure of the N1 compound based on the distribution pattern of nitrogen-containing daughter ions and carbon-hydrogen daughter ions; Wherein, the N1 compound is a compound containing only one nitrogen atom in its molecular formula; The method for collecting the secondary mass spectrum of the N1 compound in the sample to be tested in the third step is to include the quasi-molecular ion of the compound containing only one nitrogen atom screened in the second step into the parent ion list, and adopt narrow band, wide range, high energy collision dissociation mode to target and collect the secondary mass spectrum information; The narrowband, wide-range, high-energy collision dissociation mode refers to the acquisition of secondary mass spectra in which the parent ion isolation window is ±0.2 Da, the collision energy of the collision dissociation is set to be in a 1-10 eV step mode, and the secondary mass spectra are acquired in the range of 10-100 eV.

2. The method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions according to claim 1, characterized in that: The second step of extracting the molecular information of compound N1 from the data is to calculate the molecular formula of the compound based on the accurate mass-to-charge ratio in the data, and extract the molecular formula containing only one nitrogen atom from all molecular formulas.

3. The method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions according to claim 1, characterized in that: The method for obtaining the carbon-hydrogen daughter ion distribution pattern in the fourth step is to extract all the collected secondary mass spectrometry raw data, calculate the elemental composition, equivalent double bond number and carbon number of each daughter ion based on the accurate mass-to-charge ratio, screen the daughter ions whose elemental composition only contains carbon and hydrogen, and draw a scatter plot with the equivalent double bond number as the vertical coordinate and the carbon number as the horizontal coordinate, which is the carbon-hydrogen daughter ion distribution pattern.

4. The method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions according to claim 1, characterized in that: The method for obtaining the distribution pattern of nitrogen-containing daughter ions in the fourth step is to extract the secondary mass spectrum raw data at an energy between 5% and 30% of the relative intensity of the parent ion in the secondary mass spectrum, screen the daughter ions containing nitrogen atoms in the elemental composition, and draw a scatter plot with the equivalent double bond number of the nitrogen-containing daughter ions as the vertical coordinate and the carbon number as the horizontal coordinate, which is the distribution pattern of the nitrogen-containing daughter ions.

5. The method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions according to claim 1, characterized in that: The method for distinguishing basic nitrogen compounds from neutral nitrogen compounds in the fifth step is that if the N1 compound responds only in the positive ion mode of the mass spectrometer, the compound is a basic nitrogen compound; if the N1 compound responds in the negative ion mode, the compound is a neutral nitrogen compound.

6. The method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions according to claim 1, characterized in that: The method for obtaining the parent nucleus structure of the N1 compound in the sixth step is to first determine whether the molecular structure contains a cycloalkane ring based on the carbon-hydrogen daughter ion distribution pattern; determine the parent nucleus carbon number of the neutral N1 compound that does not contain a cycloalkane ring based on the nitrogen-containing daughter ion distribution pattern; determine the parent nucleus carbon number of the alkaline N1 compound that does not contain a cycloalkane ring structure based on the carbon-hydrogen daughter ion distribution pattern; and determine the distribution range of the parent nucleus carbon number of the N1 compound that contains a cycloalkane ring based on the carbon-hydrogen daughter ion distribution pattern.

7. The method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions according to claim 6, characterized in that: The method for determining whether a molecular structure contains a cycloalkane ring is to determine whether there is a carbon-hydrogen daughter ion with a larger number of double bonds than the parent ion in the carbon-hydrogen daughter ion distribution pattern. If so, the compound does not contain a cycloalkane ring; if not, the compound contains a cycloalkane ring.

8. The method for structural characterization of aromatic nitrogen heterocyclic compounds in petroleum fractions according to claim 6, characterized in that: The method for determining the carbon number of the parent nucleus of the alkaline N1 compound without a cycloalkane ring is, based on the carbon-hydrogen daughter ion distribution pattern, wherein the carbon number of the carbon-hydrogen daughter ion with the same equivalent double bond number as the parent ion and the lowest carbon number is the carbon number of the parent nucleus; the method for determining the carbon number of the parent nucleus of the neutral N1 compound without a cycloalkane ring is, based on the nitrogen-containing daughter ion distribution pattern corresponding to the sufficient fragmentation energy of the parent ion, wherein the carbon number of the nitrogen-containing daughter ion with the same equivalent double bond number as the parent ion and the lowest carbon number is the carbon number of the parent nucleus; the method for determining the distribution range of the carbon number of the parent nucleus of the N1 compound containing a cycloalkane ring is, based on the carbon-hydrogen daughter ion distribution pattern, the carbon number of the parent nucleus is not less than the lowest carbon number of the carbon-hydrogen daughter ion under the equivalent double bond number of the parent ion.

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