A method for detecting and analyzing the spatial metabolome of carotenoids

Abstract

The present invention relates to a detection and analysis method of carotenoid spatial metabolome, and belongs to the field of agricultural chemical component analysis. This application takes sweet corn and pepper as an example, and utilizes desorption electrospray ionization mass spectrometry imaging technology (DESI-MSI), and the spray solvent used is acetonitrile: isopropanol: water: formic acid solution in a volume ratio of (40-60): (30-50): 10: 0.1. The method can intuitively observe the distribution characteristics of carotenoids in plants. By analyzing the response value of the imaging distribution map of the distribution of carotenoid metabolites, the spatial metabolome differences and tissue specificity that different carotenoid metabolites have are obtained, the difference between active metabolites in different tissues is analyzed, and a valuable reference basis is provided for extracting carotenoid metabolites in plants.

Description

Technical Field

[0001] The present invention belongs to the field of agricultural chemical component analysis, and in particular relates to a method for detecting and analyzing a carotenoid spatial metabolome. Background Art

[0002] Carotenoids are natural pigments widely found in plants, algae, and certain microorganisms. Currently, over 700 natural carotenoids are known, primarily divided into two categories: xanthophylls, which contain oxygen atoms in their molecules, and carotenes, which lack oxygen and contain only carbon and hydrogen. They not only give plants their vibrant colors but also possess numerous physiological functions, including antioxidant, immunomodulatory, and anti-cancer properties. Unfortunately, the human body cannot synthesize carotenoids on its own and must ingest them. In our daily diet, carotenoids are primarily obtained through the consumption of plant foods rich in these pigments, such as sweet corn and peppers. Peppers and sweet corn are both excellent sources of carotenoids, containing a wide variety of carotenoids, and their benefits to human health are self-evident. The spatial distribution of carotenoids in plant tissues significantly influences their biosynthesis, accumulation, and bioavailability. This information has important applications in food processing, nutritional research, and crop breeding.

[0003] Traditional carotenoid analysis methods, such as high-performance liquid chromatography (HPLC), can accurately determine the composition and content of carotenoids, but these methods usually require complex sample preparation steps and cannot provide information on the spatial distribution of carotenoids in plant tissues.

[0004] With the development of spatial metabolomics, a new analytical technology that can reveal the spatial distribution of biomolecules at the microscopic level has emerged. Desorption electrospray ionization-mass spectrometry imaging (DESI-MSI) technology can directly analyze compounds on the tissue surface while maintaining the in situ structure of biological tissues, thereby obtaining information on the spatial distribution of compounds. However, DESI-MSI technology faces some challenges when analyzing carotenoids. Because carotenoids belong to the tetraterpenoid class of compounds and have a long-chain conjugated polyene structure, this structure gives carotenoids their color but also results in their weak ionization ability. The electrons in the conjugated polyene chain are delocalized, which makes the overall electron cloud density distribution of the molecule more uniform, reducing the ability of the molecule to ionize at a specific location. In the existing technology, there is currently no literature reporting the application of mass spectrometry imaging technology (especially DESI-MSI technology) to the spatial analysis of carotenoids and reporting the results.

[0005] Therefore, it is crucial to explore the spray solvents that can respond to carotenoids during spatial metabolomics analysis. Summary of the Invention

[0006] The purpose of the present invention is to overcome at least one deficiency of the prior art and to provide a spray solvent for a carotenoid spatial metabolome analysis method and a method for detecting and analyzing the carotenoid spatial metabolome.

[0007] The technical solution adopted by the present invention is:

[0008] A spray solvent for a carotenoid spatial metabolome analysis method, wherein the spray solvent is a spray solvent used in an ionization source in desorption electrospray ionization-mass spectrometry imaging (DESI-MSI), and the spray solvent is an acetonitrile:isopropanol:water:formic acid solution with a volume ratio of (40-60):(30-50):10:0.1.

[0009] In some preferred embodiments, the spray solvent is an acetonitrile:isopropanol:water:formic acid solution with a volume ratio of (45-55):(35-45):10:0.1.

[0010] In some embodiments, the carotenoids include at least one of capsanthin, capsorubin, zeaxanthin, and lutein.

[0011] A method for detecting and analyzing the spatial metabolome of carotenoids, comprising the following steps:

[0012] The sample to be tested was placed on a glass slide and dried, and then subjected to spatial metabolomics analysis using a mass spectrometer equipped with a DESI ion source. The spray solvent used was as described above.

[0013] In some embodiments, the mass spectrometer includes a tandem quadrupole mass spectrometer or a high-resolution mass spectrometer.

[0014] In some embodiments, when the sample to be tested is a solution, 1-2 μl of the solution to be tested is placed on a glass slide.

[0015] In some embodiments, the sample to be tested is corn kernels or pepper fruits.

[0016] In some embodiments, when the sample to be tested is pepper fruit, the pepper fruit is pre-treated, and the pre-treatment method includes cutting the pepper into small segments of 0.8-1.2 cm; embedding the pepper with a gelatin solution with a mass percentage of 10-15%, and then freezing it at or below -80°C for a freezing time of not less than 12 hours; and cutting the frozen and embedded pepper segments into 15-25 μm slices.

[0017] In some embodiments, when the sample to be tested is corn kernels, the corn kernels are pre-treated, and the pre-treatment method includes embedding the corn kernels with a gelatin solution with a mass percentage of 10-15%, and then freezing them at or below -80°C for a freezing time of not less than 12 hours; and cutting the frozen and embedded corn kernels into 15-25um slices.

[0018] In some embodiments, when a high-resolution mass spectrometer is used for detection, the flow rate is set to 2-3 ul / min, the ion source temperature is 140-160° C., and the mass spectrometry data are collected in a positive ion scanning mode.

[0019] The beneficial effects of the present invention are:

[0020] This application uses the mass spectrometry imaging technique, Desorption Electrospray Ionization Mass Spectrometry Imaging (DESI-MSI), using sweet corn and peppers as examples. The spray solvent used is a solution of acetonitrile:isopropanol:water:formic acid in a volume ratio of (40-60):(30-50):10:0.1. This method allows for intuitive observation of the distribution characteristics of carotenoids in plants.

[0021] This application achieves spatial analysis of carotenoids by improving the spray solvent used in the ionization source of desorption electrospray ionization mass spectrometry imaging (DESI-MSI). This is the first reported spatial analysis technology for carotenoids, filling this gap and representing an innovation in carotenoid spatial analysis technology.

[0022] This application analyzes the response values ​​of the imaging distribution map of carotenoid metabolites to obtain the spatial metabolome differences and tissue specificity of different carotenoid metabolites, analyze the differences in active metabolites between different tissues, and provide a valuable reference for extracting carotenoid metabolites from plants. At the same time, it provides a new perspective for understanding the role and metabolic pathways of carotenoids in different plant tissues.

[0023] In the field of mass spectrometry imaging technology, especially DESI-MSI technology, although there have been many studies, they have not been applied to the spatial analysis of carotenoids and the results have not been reported. Therefore, the technical solution of this application is an important supplement in the field of carotenoid research.

[0024] This application not only achieves innovation in DESI-MSI technology, but also provides new analytical methods and perspectives in the field of carotenoid research, which is of great significance for promoting in-depth research on carotenoids. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Spatial distribution mass spectra of the three active compounds (capsaicin, zeaxanthin and lutein) in Examples 1-6 using different spray solvents.

[0026] Figure 2 Figure 2 is the spatial distribution mass spectrum of zeaxanthin and lutein in sweet corn samples.

[0027] Figure 3 This is the spatial distribution mass spectrum of capsanthin and capsorubin in sweet pepper fruit samples. DETAILED DESCRIPTION

[0028] The experimental methods in the following examples of the present invention, where specific conditions are not specified, are generally carried out under conventional conditions or conditions recommended by the manufacturers. The various commonly used chemical reagents used in the examples are all commercially available products.

[0029] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0030] The terms "comprise," "comprising," and "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, apparatus, product, or device comprising a series of steps is not limited to the listed steps or modules but may optionally include steps not listed, or other steps inherent to the process, method, product, or device.

[0031] Desorption electrospray ionization mass spectrometry imaging (DESI-MSI) technology is implemented in an open environment. It does not require complex pretreatment of the sample to be tested, and no matrix needs to be added. It is convenient to operate and avoids the displacement of the analyte molecules, ensuring the in situ and accuracy of the imaging analysis.

[0032] The entire process includes applying high voltage to the electrospray capillary nozzle, atomizing the spray solvent to form charged spray droplets, bombarding the sample surface for desorption and ionization, and then the charged droplets are desolvated and enter the mass spectrometer for detection. The sample platform moves for two-dimensional scanning, and the mass spectrometer records the signal intensity to obtain a spatial distribution map of the molecules and their content.

[0033] Therefore, the choice of spray solvent is crucial to the results of DESI-MSI.

[0034] A spray solvent for a carotenoid spatial metabolome analysis method, wherein the spray solvent is a spray solvent used in an ionization source in desorption electrospray ionization-mass spectrometry imaging (DESI-MSI), and the spray solvent is an acetonitrile:isopropanol:water:formic acid solution with a volume ratio of (40-60):(30-50):10:0.1.

[0035] In some embodiments, the spray solvent is an acetonitrile:isopropanol:water:formic acid solution with a volume ratio of (45-55):(35-45):10:0.1.

[0036] In some embodiments, the spray solvent is a solution of acetonitrile:isopropanol:water:formic acid in a volume ratio of 50:40:10:0.1.

[0037] In some embodiments, the carotenoids include capsanthin, capsorubin, zeaxanthin, and lutein.

[0038] The reason why substances such as capsanthin, capsorubin, zeaxanthin and lutein are not easily ionized is mainly related to their chemical structure and physicochemical properties:

[0039] (1) Carotenoids belong to the tetraterpenoid family of compounds and have a long-chain conjugated polyene structure. This structure gives carotenoids their color, but also results in their weak ionization ability. The electrons in the conjugated polyene chain are delocalized, which makes the overall electron cloud density of the molecule more uniform, reducing the ability of the molecule to ionize at a specific location.

[0040] (2) Carotenoids are a class of non-polar compounds. Their molecular structure contains multiple conjugated double bonds. These double bonds result in a lack of apparent charge distribution within the molecule, making it less susceptible to ionization. Carotenoids are chemically relatively stable and are less likely to undergo chemical reactions with other substances, including ionization reactions.

[0041] In summary, the stability of carotenoids such as capsanthin, capsanthin, zeaxanthin and lutein is determined by their molecular structure and electron configuration, so they face challenges in the ionization process and are therefore not easily ionized.

[0042] To overcome these challenges and improve carotenoid extraction efficiency and mass spectrometry signal response, this application proposes a method for carotenoid detection and analysis based on spatial metabolomics. By optimizing the spray solvent, this method enables analysis of the spatial distribution characteristics of carotenoid compounds in sweet corn and peppers. This approach provides a deeper understanding of the distribution patterns of carotenoids in plant tissues, providing a scientific basis for carotenoid extraction, application, and nutritional research.

[0043] A method for detecting and analyzing the spatial metabolome of carotenoids, comprising the following steps:

[0044] The sample to be tested is placed on a glass slide, dried, and then subjected to spatial metabolomics analysis using a mass spectrometer equipped with a DESI ion source. The spray solvent used in the ionization source of the mass spectrometer is as described in any of the above items.

[0045] In some embodiments, the mass spectrometer includes but is not limited to a tandem quadrupole mass spectrometer (such as Waters Xevo TQ Absolute), a high-resolution mass spectrometer (such as Waters' Xevo G2-XS QTof, Waters' Synapt XS).

[0046] In some embodiments, when the sample to be tested is a solution, 1-2 μl of the solution to be tested is placed on a glass slide.

[0047] For example, when the solution is a carotenoid standard solution, the concentration of the solution is adjusted to 0.8-1.2 mg / ml. The main purpose is to examine the ionization degree of the standard solution with the same concentration in different spray solvents.

[0048] For example, carotenoid standard solutions, including capsaicin, zeaxanthin, and lutein, are loaded onto the system first. The spray solvent parameters with the strongest response are compared and selected, and then the samples (sweet corn and peppers) are loaded onto the system to analyze the distribution characteristics of carotenoid metabolites in the samples.

[0049] In some embodiments, the sample to be tested is (sweet) corn kernels or pepper fruits.

[0050] In some embodiments, when the sample to be tested is pepper fruit, the pepper fruit is pre-treated, the pre-treatment method comprising cutting the pepper into 0.8-1.2 cm segments; embedding the pepper with a 10-15% by weight gelatin solution, and then freezing the frozen pepper segments at or below -80°C for at least 12 hours; and cutting the frozen-embedded pepper segments into 15-25 μm slices. The frozen-embedded 15-25 μm pepper slices are then quickly attached to a glass slide.

[0051] In some embodiments, when the sample to be tested is corn kernels, the corn kernels are pre-treated, and the pre-treatment method includes embedding the corn kernels with a gelatin solution with a mass percentage of 10-15%, and then freezing them at or below -80°C for a freezing time of not less than 12 hours; and cutting the frozen and embedded corn kernels into 15-25um slices.

[0052] In some embodiments, when a high-resolution mass spectrometer is used for detection, the flow rate is set to 2-3 ul / min, the ion source temperature is 140-160° C., and the mass spectrometry data are collected in a positive ion scanning mode.

[0053] In some of the embodiments, when a Synapt XS high-resolution mass spectrometer is used for detection, the flow rate is set to 2 ul / min, the ion source temperature is set to 150° C., and the mass spectrometry data are collected in a positive ion scan mode.

[0054] In some of the embodiments, HD Imaging v1.6 software, used in conjunction with a Synapt XS high-resolution mass spectrometer, was used to perform high-resolution imaging analysis on the collected mass spectrometry data.

[0055] The following describes the method in conjunction with specific embodiments.

[0056] The instruments and equipment involved in the examples are shown in Table 1.

[0057] Table 1. Instruments and equipment used in the examples

[0058]

[0059]

[0060] The reagents in the following examples are derived from commercially available products, for example:

[0061] Chlorophyll standard: Beijing Beina Chuanglian Biotechnology Research Institute; zeaxanthin standard: North Weiye Metrology Group Co., Ltd.; capsanthin standard: Shanghai MacLean Biochemical Technology Co., Ltd.; capsanthin standard: Cayman Chemical Company, Inc.; gelatin: Shanghai MacLean Biochemical Technology Co., Ltd.; acetonitrile, methanol, and isopropanol: Thermo Fisher Scientific.

[0062] Example 1

[0063] The analysis of three carotenoid standards (capsaicin, zeaxanthin, and lutein) includes the following steps:

[0064] S1. Prepare the standard solution: Dissolve capsuorubin, zeaxanthin, and lutein in a 1:1 volume ratio of isopropanol to acetonitrile to prepare a 1 mg / ml standard solution. Place 1-2 μl of the standard solution on a glass slide and allow to dry in the dark.

[0065] S2. Standard Spotting and Spray Solvent Treatment: Spot-coat 1-2 μL of the standard solution obtained in step S1 onto a glass slide. Subsequently, apply the three standards to the instrument using a spray solvent of a 50:40:10:0.1 (volume ratio) acetonitrile:isopropanol:water:formic acid solution at a flow rate of 2 μL / min to assess its effect on the standard signal.

[0066] The entire process includes applying high voltage to the electrospray capillary nozzle, atomizing the spray solvent to form charged spray droplets, bombarding the sample surface for desorption and ionization, and then the charged droplets are desolvated and enter the mass spectrometer for detection. The sample platform moves for two-dimensional scanning, and the mass spectrometer records the signal intensity to obtain a spatial distribution map of the molecules and their content.

[0067] S3. Mass spectrometry imaging data acquisition: Data were acquired using a Synapt XS HDMS 4k high-resolution mass spectrometer (Waters, USA) equipped with a DESI ion source. The flow rate was set at 2 μl / min, the ion source temperature was 150°C, and the gas pressure was 0.4 MPa. Full scan mode and positive ion mode were used for mass spectrometry data acquisition.

[0068] S4. Mass Spectrometry Imaging Data Analysis: High-resolution imaging analysis of the acquired mass spectrometry data was performed using HD Imaging v1.6 software (Waters, USA). The software automatically calculated and listed the exact molecular weights and total response values ​​of all detected compounds. By clicking the exact molecular weight of the ion of a compound to be detected, the software displays the total response value of that compound in the entire mass spectrometry image, enabling visualization of the compound's distribution.

[0069] Among them, qualitative: through mass-to-charge ratio and standard; quantitative: the color depth of the image, the color changes from blue to yellow and the response becomes gradually stronger; positioning: the color display position of the image.

[0070] By adjusting the spray solvent, the other steps were the same as in Example 1 to obtain Examples 2-6.

[0071] The spray solvent compositions of Examples 1-6 and the corresponding appendix of the results Figure 1 Part of Figure 1 and Table 2.

[0072] Table 2. Spray solvent composition and results of Examples 1-6

[0073]

[0074] Examples 1-6 are spray solvent selections for standard products, and the results are shown in Table 3. The images are normalized to obtain Figure 1 .

[0075] Table 3. Total response values ​​corresponding to standard mass spectrum peaks

[0076]

[0077] Comparative analysis of AC and DF revealed that the acetonitrile and isopropanol mixture exhibited a synergistic effect, while acetonitrile alone exhibited a weak response to the carotenoid standards. The intensity of the response was determined based on the color of the image, ultimately determining the spray solvent to be a solution of acetonitrile:isopropanol:water:formic acid in a volume ratio of (40-60):(30-50):10:0.1. The spray solvent ratio of acetonitrile:isopropanol:water:formic acid (50:40:10:0.1) was found to be the most effective.

[0078] Example 7

[0079] When the corn sample is sweet corn kernels, the detection and analysis method comprises the following steps:

[0080] S1. Preparation of Standard: Embed sweet corn kernels in a 10-15% gelatin solution by weight, then freeze at or below -80°C for at least 12 hours. Cut the freeze-embedded corn kernels into 15-25 μm slices. Quickly attach the freeze-embedded 15-25 μm corn kernel slices to a glass slide.

[0081] S2. Spray solvent treatment: The samples were loaded onto the instrument with a spray solvent of acetonitrile:isopropanol:water:formic acid solution in a volume ratio of 50:40:10:0.1 at a flow rate of 2 μl / min to evaluate its effect on the standard signal.

[0082] S3. Mass spectrometry imaging data acquisition: Data were acquired using a Synapt XS HDMS 4k high-resolution mass spectrometer (Waters, USA) equipped with a DESI ion source. The flow rate was set at 2 μl / min, the ion source temperature was 150°C, and the gas pressure was 0.4 MPa. Full scan mode and positive ion mode were used for mass spectrometry data acquisition.

[0083] S4. Mass Spectrometry Imaging Data Analysis: High-resolution imaging analysis of the acquired mass spectrometry data was performed using HD Imaging v1.6 software (Waters, USA). The software automatically calculated and listed the exact molecular weights and total response values ​​of all detected compounds. By clicking the exact molecular weight of the ion of a compound to be detected, the software displays the total response value of that compound in the entire mass spectrometry image, enabling visualization of the compound's distribution.

[0084] Among them, qualitative: through mass-to-charge ratio and standard; quantitative: the color depth of the image, the color changes from blue to yellow and the response becomes gradually stronger; positioning: the color display position of the image.

[0085] See the results Figure 2 .

[0086] Figure 2 is the spatial distribution map of zeaxanthin and lutein in sweet corn kernel samples, Figure 2 It can be seen that zeaxanthin and lutein metabolites are mainly distributed in the endosperm part of sweet corn.

[0087] Analyzing the distribution of zeaxanthin and lutein in sweet corn kernels can help agricultural scientists develop sweet corn varieties with higher levels of zeaxanthin and lutein through breeding techniques. Understanding the distribution of nutrients during food processing can help develop more effective processing methods, ensuring that the loss of these beneficial ingredients is minimized during processing. These data provide fundamental information for scientific research and help further explore the biosynthesis, accumulation, and degradation mechanisms of carotenoids in plants. Therefore, analyzing the distribution of zeaxanthin and lutein in sweet corn kernels using DESI mass spectrometry imaging technology not only helps to enhance the edible value of sweet corn, but also has important significance for agricultural scientific research and the development of the food industry.

[0088] Example 8

[0089] When the pepper sample is pepper fruit, the detection and analysis method comprises the following steps:

[0090] S1. Sample cryoembedding: Select fresh pepper fruit samples and cut them into approximately 1 cm long segments using a sharp blade. Embed the segments in a 13% gelatin solution by weight and freeze them in a -80°C freezer for at least 12 hours.

[0091] S2. Sample Sectioning and Drying: Remove the cryo-embedded samples and prepare 20-μm-thick sections using a Leica CM1950 cryostat. These sections are quickly mounted on glass slides and then dried in the dark for 2 hours.

[0092] S3. Spray solvent treatment: The samples were loaded onto the instrument with a spray solvent of acetonitrile:isopropanol:water:formic acid solution with a volume ratio of 50:40:10:0.1 at a flow rate of 2 μl / min to evaluate its effect on the standard signal.

[0093] S4. Mass spectrometry imaging data acquisition: Data were acquired using a Synapt XS HDMS 4k high-resolution mass spectrometer (Waters, USA) equipped with a DESI ion source. The flow rate was set at 2 μl / min, the ion source temperature was 150°C, and the gas pressure was 0.4 MPa. Full-scan mode was used for mass spectrometry data acquisition in positive ion mode.

[0094] S5. Mass Spectrometry Imaging Data Analysis: High-resolution imaging analysis of the acquired mass spectrometry data was performed using HD Imaging v1.6 software (Waters, USA). The software automatically calculated and listed the exact molecular weights and total response values ​​of all detected compounds. By clicking the exact molecular weight of the ion of a compound to be detected, the software displays the total response value of that compound in the entire mass spectrometry image, enabling visualization of the compound's distribution.

[0095] Among them, qualitative: through mass-to-charge ratio and standard; quantitative: the color depth of the image, the color changes from blue to yellow and the response becomes gradually stronger; positioning: the color display position of the image.

[0096] See the results Figure 3 .

[0097] Figure 3 is the spatial distribution map of capsanthin and capsorubin in pepper fruit samples, Figure 3 It can be seen that capsanthin and capsorubin metabolites are mainly distributed in the epidermis and placenta of pepper fruits, respectively.

[0098] Capsanthin and capsuorubin are important bioactive components in chili peppers, exhibiting diverse physiological functions, including antioxidant, anti-inflammatory, and anti-cancer properties. Understanding their distribution within chili pepper fruits facilitates investigation of their specific functions and mechanisms of action. Analyzing the distribution of capsuorubin and capsuorubin metabolites within chili pepper fruits can help breeders, through genetic engineering or traditional breeding methods, develop new varieties enriched in these beneficial components in specific parts. Understanding the distribution of capsuorubin and capsuorubin during chili pepper processing can aid in optimizing processing techniques. For example, when extracting these pigments, targeted treatment of the pepper epidermis and placenta can be used to improve extraction efficiency and pigment purity. In summary, the information provided by DESI mass spectrometry imaging technology has important guiding significance for scientific research, agricultural production, and food processing of chili peppers.

[0099] This application analyzes the response values ​​of the imaging distribution map of carotenoid metabolites to obtain the spatial metabolome differences and tissue specificity of different carotenoid metabolites, analyzes the differences in active metabolites between different tissues, and provides a valuable reference for the extraction of carotenoid metabolites in plants.

[0100] The above is a further detailed description of the present invention and should not be considered as a limitation on the specific implementation of the present invention. For those skilled in the art, simple deductions or substitutions that do not depart from the concept of the present invention are within the scope of protection of the present invention.

Claims

1. Application of a spray solvent in a method for spatial metabolomics analysis of carotenoids, characterized in that: The spray solvent is a spray solvent used in the ionization source of desorption electrospray ionization-mass spectrometry imaging, and the spray solvent is an acetonitrile:isopropanol:water:formic acid solution with a volume ratio of (40-60):(30-50):10:0.1; The carotenoids include at least one of capsanthin, capsorubin, zeaxanthin, and lutein; The analysis method comprises placing the sample to be tested on a glass slide, drying the sample, and then performing spatial metabolome analysis using a mass spectrometer equipped with a DESI ion source and the spray solvent.

2. The use according to claim 1, characterized in that The spray solvent is an acetonitrile:isopropanol:water:formic acid solution with a volume ratio of (45-55):(35-45):10:0.

1.

3. The use according to claim 1, characterized in that The mass spectrometer includes a tandem quadrupole mass spectrometer and a high-resolution mass spectrometer.

4. The use according to claim 3, characterized in that When the sample to be tested is a solution, take 1-2 μl of the solution to be tested and place it on a glass slide.

5. The use according to claim 3, characterized in that The samples to be tested are corn kernels or pepper fruits.

6. The use according to claim 5, characterized in that When the sample to be tested is a pepper fruit, the pepper fruit is pre-treated, and the pre-treatment method includes cutting the pepper into small segments of 0.8-1.2 cm; embedding the pepper with a gelatin solution with a mass percentage of 10-15%, and then freezing it at or below -80°C for a freezing time of not less than 12 hours; and cutting the frozen embedded pepper segments into 15-25 μm slices.

7. The use according to claim 5, characterized in that When the sample to be tested is corn kernels, the corn kernels are pretreated. The pretreatment method includes embedding the corn kernels with a gelatin solution with a mass percentage of 10-15%, and then freezing them at or below -80°C for a freezing time of not less than 12 hours; and cutting the frozen and embedded corn kernels into 15-25um slices.

8. The use according to claim 3, characterized in that When using a high-resolution mass spectrometer for detection, the flow rate is set to 2-3 ul / min, the ion source temperature is 140-160°C, and the mass spectrometry data are collected in positive ion scanning mode.

Images