Molecular identification method for organic sulfate in PM2.5 based on LC-MS / MS

Abstract

The invention discloses a molecular identification method for organic sulfate in PM2.5 based on LC-MS / MS. The molecular identification method is characterized by comprising the following steps: firstly, carrying out ultrasonic-assisted extraction on an atmospheric fine particulate matter sample by adopting ultrapure water, carrying out centrifugal separation, taking supernate, and filtering through a 0.45 mu m microporous filter membrane; then purifying the filtrate through a solid-phase extraction column, and purging and concentrating the collected eluent through nitrogen until the eluent is in a near-dry state to complete the enrichment of a target object; an LC-MS / MS combined electrospray ionization source (ESI) is adopted to perform mass spectrometric analysis on organic sulfate in atmospheric fine particulate matters in a negative ion mode, and structure confirmation of a target compound is realized. Compared with direct adoption of high-resolution mass spectrometry (FT-ICR MS), the method has the advantages that the sample pretreatment process is simplified, the analysis efficiency is remarkably improved, the powerful separation advantage and the high reliability advantage of LC-MS / MS are fully played, the organic sulfate in a complex matrix can be accurately identified, high-throughput and high-selectivity detection of the organic sulfate in the PM2.5 sample is achieved, and the method is suitable for large-scale popularization and application. The structure confirmation of the organic sulfate can be realized, and an analysis and confirmation integrated molecular identification method for the organic sulfate in the PM2.5 sample is provided.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of environmental analysis chemistry and atmospheric pollution monitoring technology, and particularly relates to a PM 2.5 Molecular identification method of organic sulfates in PM BACKGROUND

[0002] Organic components are important components of atmospheric PM 2.5 The study on the composition characteristics of organic components in PM 2.5 In the northern winter, it is found that the types and abundance of sulfur-containing compounds in water-soluble organic matter increase significantly in foggy weather, and secondary mass spectrometry analysis shows that these sulfur-containing compounds are organic sulfates. Organic sulfates are a class of ester compounds containing sulfate groups and their derivatives, which are important components of secondary organic pollutants, accounting for 5%-50% of the organic mass of particulate matter, and are often used as markers of secondary organic pollutants. Organic sulfates are mainly generated by various oxidation mechanisms and coupling of pollutants SO2 and VOCs.

[0003] In recent years, domestic and foreign studies on organic sulfates have found that the precursor composition of organic sulfates is very complex, reaching 10 4 -10 5 species, and the currently identified precursors are biogenic volatile organic compounds (such as isoprene and monoterpene) and anthropogenic volatile organic compounds (such as long-chain alkanes and naphthalene), but a large part (67%-79%) of the precursors have not been identified. Accurate and effective analysis methods are the cornerstone of in-depth exploration of the concentration, mixing state, formation and transformation mechanism of organic sulfates in atmospheric fine particulate matter, but the complex structure and numerous types of organic sulfates make it challenging in analysis and determination.

[0004] Therefore, how to effectively analyze and confirm the composition and structural information of atmospheric fine particulate organic sulfates is a problem to be solved. SUMMARY

[0005] The present application intends to identify the composition and structural information of atmospheric fine particulate organic sulfates from the molecular level based on LC-MS / MS high-resolution mass spectrometry technology, to provide a new method for high-precision molecular fingerprint analysis of environmental sources, formation mechanism and climate health effects.

[0006] The present application provides a method for extracting, enriching and molecular identification of organic sulfates in PM 2.5 , based on LC-MS / MS high-resolution mass spectrometry, comprising the following steps:

[0007] (1) ultrasonic-assisted extraction of atmospheric fine particulate matter samples with ultrapure water, centrifugal separation, and then taking the supernatant liquid filtered through a 0.45 μm microporous filter to obtain a filtrate;

[0008] (2) the filtrate is purified by a solid phase extraction column to effectively remove non-polar interferents, to obtain an extract; the extract is concentrated to a near-dry state by nitrogen blowing to enrich the target substance, to obtain an enriched solution;

[0009] (3) the enriched solution is reconstituted with a methanol / water mixed solution, and the reconstituted solution is analyzed and structurally confirmed by LC-MS / MS with an electrospray ionization source.

[0010] In some embodiments of the present application, the ultrasonic-assisted extraction in step (1) is performed at an ultrasonic frequency of 40±10 kHz, and / or for 40±20 min, and / or at a temperature of 4±2℃.

[0011] In step (1), ultrapure water is used as the extraction solvent, which has a high matching degree of polarity with organic sulfates, and combined with 40±10 kHz ultrasonic cavitation, can effectively destroy the surface structure of PM 2.5 particles, significantly improving the dissolution efficiency of organic sulfates by 30-50%; selecting an ultrasonic frequency of 40±10 kHz can ensure the extraction efficiency while avoiding molecular structure damage caused by excessive energy, achieving the best balance between extraction efficiency and molecular integrity; the entire extraction process is performed at a low temperature of 4±2℃, which can effectively inhibit the degradation of thermally unstable compounds; at the same time, the extraction time is strictly controlled within 40±2 min to significantly reduce the oxidative side reactions of the target substance, ensuring the accuracy of the analysis results.

[0012] In some embodiments of the present application, the solid phase extraction column in step (2) is an HLB solid phase extraction column and / or a PPL solid phase extraction column.

[0013] In some embodiments of the present application, the solid phase extraction column in step (2) needs to be activated by a polar organic solvent and ultrapure water in sequence before the purification operation, wherein the polar organic solvent is methanol and / or acetonitrile. The above activation treatment can remove impurities that may exist in the solid phase extraction column and activate the adsorption sites.

[0014] In some embodiments of the present application, the volume ratio of the polar organic solvent to ultrapure water in the activation treatment step is 1-2:1-2.

[0015] In some embodiments of the present application, the eluent used in the preliminary purification step in step (2) is methanol and / or acetonitrile.

[0016] In some embodiments of the present application, the methanol / water mixed solution in step (3) is prepared by mixing methanol and ultrapure water at a ratio of v / v = 1:1. The methanol / water mixed solution has the advantages of: ① the organic phase of methanol promotes the desorption of weakly polar compounds; ② the water phase maintains the solubility of polar substances. Moreover, the ratio of v / v = 1:1 can produce the best solvation effect and desolvation efficiency, so that the ESI ionization process reaches an optimal balance state.

[0017] In some embodiments of the present application, the concentration of the reconstituted solution in step (3) is 1-5 mg / mL.

[0018] In some embodiments of the present application, the mobile phase in LC analysis in step (3) is methanol mobile phase A containing 0.1% formic acid and water mobile phase B containing 0.1% formic acid.

[0019] In some embodiments of the present application, the elution gradient in step (3) is: the methanol mobile phase A is kept at 10% for 0-3 min, then increased to 100% for 3-23 min, kept for 3 min, and then returned to the initial ratio for 0.5 min and kept for 5 min.

[0020] In some embodiments of the present application, the analysis conditions of MS in step (3) are: electrospray ionization source, spray voltage of 2.6 kV, m / z range of 100 Da to 800-1000 Da, and full scan analysis in negative ion mode.

[0021] In some embodiments of the present application, the analysis and structure confirmation in step (3) include the following steps:

[0022] (a) Raw data preprocessing is performed using DataAnalysis 5.0, and the signal-to-noise ratio threshold S / N≥5 (relative intensity≥0.1%) is set;

[0023] (b) The mass error tolerance is limited to ±1 ppm (based on internal standard correction);

[0024] (c) The molecular formula screening condition is: the element composition range is 12C (0-100), 1H (0-200), 14N (0-2), 16O (0-50), and 32S (0-2);

[0025] (d) The stoichiometric relationship of O / (4S+3N)≥1 is set, and the molecular formula not meeting the characteristics of organic sulfuric acid ester is excluded. The structure confirmation method is:

[0026] (e) CID mode MS / MS secondary mass spectrum analysis is adopted, and the characteristic fragment ions (such as m / z 97 [HSO4] -) Verify the molecular structure, combine the retention time with the fragment rule to exclude false positive results.

[0027] Compared with the prior art, the advantages and positive effects of the present application are:

[0028] The present application innovatively constructs a whole-process analysis technical system of "precise extraction-directional enrichment-analysis + confirmation integration", effectively solves the key technical bottlenecks of low sensitivity, poor selectivity and molecular identification difficulty in the detection of organic sulfate in PM 2.5 This technical breakthrough not only fills the gap in the methodology of this field, but also shows excellent application performance in actual environmental monitoring, providing important technical means and theoretical support for in-depth exploration of the formation mechanism of atmospheric secondary organic aerosol, accurate assessment of fine particulate matter health risk and scientific formulation of regional pollution prevention and control strategy. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 Van graph of organic sulfates determined by FT-ICR MS in ESI negative ion mode based on the established extraction and enrichment method.

[0030] Figure 2 Mass spectrometry range of collision-induced precursor ions and product ions of S-containing compounds in PM 2.5 DETAILED DESCRIPTION

[0031] In order to enable the personnel in the technical field to better understand the technical solutions in the present application, the technical solutions of the present application will be described clearly and completely in combination with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by the personnel in the field without creative labor should belong to the scope of protection of the present application.

[0032] The extraction step of organic sulfates in PM 2.5 in the present embodiment includes:

[0033] (1) Place the collected PM 2.5 sample in a glass centrifuge tube, add 5 mL of ultrapure water, and after ultrasonic assisted extraction at a frequency of 40 kHz for 40 min and a temperature of 4 DEG C, centrifuge, remove insoluble substances through a 0.45 μm filter membrane, and obtain a filtrate;

[0034] (2) Adjust the pH of the filtrate to 2 with hydrochloric acid, and then sequentially pass through an HLB solid phase extraction column for preliminary purification to obtain an extraction solution 1; concentrate the extraction solution to near dryness by nitrogen blowing to complete the enrichment of the target substance, and obtain an enrichment solution 1.

[0035] ​The HLB solid phase extraction column is activated by 2.5 mL of methanol and 2.5 mL of ultrapure water in advance, and the eluent used for purification is 3 mL of methanol.

[0036] (3) The enrichment liquid is reconstituted with 1 mL of a methanol / water mixed solution with a volume ratio of 1:1, and the reconstituted solution is analyzed and structurally confirmed by LC-MS / MS combined with an electrospray ionization source.

[0037] In the LC analysis, the mobile phase is methanol mobile phase A containing 0.1% formic acid and water mobile phase B containing 0.1% formic acid; the elution gradient is: the methanol mobile phase A is kept at 10% for 0-3 min, then increased to 100% for 3-23 min, kept for 3 min, and then returned to the initial proportion for 0.5 min, kept for 5 min.

[0038] The analysis conditions of MS are: electrospray ionization source, spray voltage is 2.6 kV, m / z range is 100-1000 Da, and full scan analysis is carried out in negative ion mode.

[0039] The analysis and structural confirmation steps are:

[0040] The data processing software DataAnalysis5.0 is used to calculate the molecular formula of the mass spectrum peak with a signal-to-noise ratio of ≥5, the element composition range is set as: 12 C (1-100), 1 H (1-200), 16 O (0-50), 14 N (0-2), and 32 S (0-1), the molecular weight error is controlled within ±1 ppm, and the molecular formula satisfying the condition of O / (4S+3N)≥1 is screened. The analysis results show that more than 6000 sulfur-containing compounds are detected in PM 2.5 in an industrial city during the winter heating period, including CHOS1, CHOS2, CHON1S1, CHON1S2, CHON2S1 and CHON2S2 types ( Figure 1 ).

[0041] The characteristic neutral loss fragments (SO3 and / or SO4) of sulfur-containing compounds are confirmed by MS / MS secondary mass spectrum analysis, which confirms the organic sulfur acid ester structure characteristics of these compounds ( Figure 2 ).

[0042] A high-efficiency, simple and convenient PM 2.5The extraction and enrichment method of organosulfates significantly improves the recovery rate of target compounds by optimizing the extraction solvent system and operation process, and maximizes the integrity and diversity of organosulfates. On this basis, combined with the strong separation advantage and high reliability advantage of LC-MS / MS, and coupled with electrospray ionization (ESI) soft ionization source, the mild ionization of organosulfate molecules is realized in the negative ion mode. This combined technology can not only accurately identify the molecular composition of organosulfates in complex matrix, but also analyze and confirm its structural characteristics, providing important molecular level information and technical support for in-depth study of the source analysis, environmental behavior, and climate and health effects of organosulfates in atmospheric fine particulate matter.

[0043] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit it. Although the present application has been described in detail with reference to the above examples, those of ordinary skill in the art should understand that the specific embodiments of the present application can be modified or replaced by equivalents after reading the present application. However, these modifications or changes are still within the scope of the present application.

Claims

1. A PM based on LC-MS / MS 2.5 A molecular identification method for organic sulfate esters, characterized in that, The molecular identification method includes the following steps: (1) Ultrasonic-assisted extraction was performed on the atmospheric fine particulate matter sample using ultrapure water. After centrifugation, the supernatant was filtered through a 0.45 μm microporous membrane to obtain the filtrate. (2) The filtrate was preliminarily purified by passing it through a solid phase extraction column to effectively remove nonpolar interfering substances and obtain an extract; the extract was concentrated to near-dry state by nitrogen purging to complete the enrichment of the target substance and obtain an enriched solution. (3) The enriched solution was re-diluted with a methanol / water mixture, and the solution after re-diluted was analyzed and its structure confirmed by LC-MS / MS with an electrospray ionization source.

2. The PM according to claim 1 2.5 A molecular identification method for organic sulfate esters, characterized in that, The conditions for ultrasonic-assisted extraction in step (1) are: ultrasonic frequency 40±10 kHz; and / or extraction time 40±20 min; and / or temperature 4±2℃.

3. The PM according to claim 1 2.5 The molecular identification method for organic sulfate esters, wherein the solid phase extraction column in step (2) is an HLB solid phase extraction column and / or a PPL solid phase extraction column.

4. The PM according to claim 3 2.5 A molecular identification method for organic sulfate esters, characterized in that, Before the purification operation, the solid phase extraction column in step (2) needs to be activated by a polar organic solvent and ultrapure water in sequence. The polar organic solvent is methanol and / or acetonitrile.

5. The PM according to claim 1 2.5 A molecular identification method for organic sulfate esters, characterized in that, The eluent used in the preliminary purification step in step (2) is methanol and / or acetonitrile.

6. The PM according to claim 1 2.5 A molecular identification method for organic sulfate esters, characterized in that, The methanol / water mixed solution in step (3) is prepared by mixing methanol and ultrapure water in a ratio of v / v=1:

1.

7. The PM according to claim 1 2.5 A molecular identification method for organic sulfate esters, characterized in that, The concentration of the solution after re-adjustment in step (3) is 1-5 mg / mL.

8. The PM according to claim 1 2.5 A molecular identification method for organic sulfate esters, characterized in that, In step (3), the mobile phases used in the LC analysis are methanol mobile phase A containing 0.1% formic acid and aqueous mobile phase B containing 0.1% formic acid.

9. The PM according to claim 8 2.5 A molecular identification method for organic sulfate esters, characterized in that, In step (3), the elution gradient is as follows: the methanol mobile phase A is maintained at 10% for 0-3 min, then increased to 100% for 3-23 min, maintained for 3 min, and then returned to the initial ratio for 0.5 min, and maintained for 5 min.

10. The PM according to claim 1 2.5 A molecular identification method for organic sulfate esters, characterized in that... The analysis and structural verification in step (3) includes the following steps: (a) The mass spectrometry data were processed using the data processing software DataAnalysis 5.0, and mass spectrometry peaks with a signal-to-noise ratio (S / N) ≥ 5 were screened. (b) Set the allowable quality error range to ±1 ppm; (c) The range of elemental composition for the molecular formula is limited to: 12 C (0-100) 1 H(0-200), 14 N(0-2), 16 O (0-50) and 32 S(0-2); (d) Based on the structural characteristics of organic sulfate esters, the molecular formula screening condition is set as O / (4S+3N)≥1; (e) The structure of candidate organic sulfate ester molecules was confirmed by MS / MS secondary mass spectrometry analysis combined with characteristic fragment ions.

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