A method for analyzing multiple new psychoactive substances in food by gas chromatography-mass spectrometry

Abstract

The present invention provides a method for analyzing multiple new psychoactive substances in foods by gas chromatography-mass spectrometry, which mainly solves the problems of extracting new psychoactive substances from foods and removing the influencing factors such as proteins, fats, and inorganic minerals in foods. By adopting a unique pretreatment method in combination with gas chromatography / mass spectrometry and other means for detection, accurate detection and analysis of more than 20 cannabinoids and cathinones can be achieved.

Description

Technical Field

[0001] The present invention belongs to the fields of food safety and chemical analysis, and provides a detection method for detecting multiple novel psychoactive substances of cannabinoids and cathinones in foods such as meat, milk, and honey. Background Art

[0002] New Psychoactive Substances (NPS) are new types of drugs following traditional drugs, having similar or stronger effects of excitement, hallucination, anesthesia, etc. as controlled drugs, and mostly disguised with novel packages and names such as candies, beverages, and snacks, with extremely strong concealment. The public generally has insufficient understanding of them, and they are more harmful than traditional drugs. Cannabinoids and cathinone compounds both belong to new psychoactive substances, and strict control measures have been implemented.

[0003] In addition to being used in psychotropic drugs, the roots, stems, etc. of cannabis and khat are also used in feed, and enter the meat and milk of farmed animals through feed conversion, or bring psychoactive substances into honey or other plants through bee collection and pollen transmission. With the continuous warming of current trade globalization, food raw materials show the characteristics of diversification and cross-region. Especially in recent years, the development of cross-border e-commerce trade in China has enabled these foods that may contain cannabinoid or cathinone substances to enter the tables of ordinary people through processing, repackaging, or cross-border circulation, bringing non-negligible harm.

[0004] Most of the current detection methods for new psychoactive substances are aimed at biological samples such as blood, urine, and hair (such as CN113109491A, CN 104833743A, CN 113804746A, CN 115060562A, Khalid A, Alsenedi, Calum Morrison. Determination and long-term stability of twenty-nine cathinones and amphetamine-type stimulants (ATS) in urine using gas chromatography–mass spectrometry[J]. Journal of Chromatography B. 2018, 91-102., etc.), or focus on the suspected drugs themselves (such as CN 107345946A, CN 106324149A, CN 115144489A, Elisabeth Pendl, Udo Pauritsch, Manfred Kollroser, et al. Determination of cathinone and cathine in Khat plant material by LC–MS / MS: Fresh vs. dried leaves[J]. Forensic Science International. 2021, 319:110658., etc.). The purpose is to detect drug users or identify suspected drugs, and none of them involve the detection methods and pretreatment research on the illegal addition and residues of new psychoactive substances in food. The food matrix is more complex than biological samples, and due to biological metabolism, synthesis and processing, etc., the content of cannabinoids and cathinones in food is lower. Therefore, more accurate and targeted extraction, purification and analysis methods are needed. When using the detection methods for drugs and biological samples in the current literature to detect food samples, it is easily affected by fat, protein, pigment, inorganic mineral elements and secondary metabolites in food, far from reaching the sufficient detection limit, and the matrix effect of the detection results is obvious, which is extremely likely to cause interference and deviation in the results. Therefore, it is very important to establish an efficient and accurate analysis method for food matrices, especially for foods such as dairy products, honey, and meat that are easily contaminated and affected, to ensure food safety and carry out anti-drug work. Summary of the Invention

[0005] The present invention provides an efficient detection method for multiple cannabinoids and cathinone-based new psychoactive substances in foods, mainly solving the problems of extracting new psychoactive substances from foods and removing factors affecting detection such as proteins, fats, and inorganic minerals in foods. Detection is carried out by combining methods such as gas chromatography / mass spectrometry, and accurate detection and analysis of more than 20 cannabinoid and cathinone-based compounds can be achieved.

[0006] The main research contents of the present invention include: 1. The extraction method was studied. In addition to using ultrasonic extraction, it was also found that the pH value of the extraction solution has a great influence on the results. Especially for some new psychoactive substances, they need to be effectively extracted within a specific pH range (5.0 - 6.0). However, this pH range will cause more matrix residues in some special food samples (such as yogurt, milk powder, deacidified beef, etc.), thus affecting the stability of the results. Therefore, the extraction operation needs to be carried out by first adjusting the alkalinity and then adjusting the acidity, and controlling the pH value range during extraction is the key to the effectiveness of the detection results. 2. A purification material of nano-ferroferric oxide loaded with N-propylethylenediamine (PSA@Fe3O4) was used, and combined with the combination of C18, graphitized carbon black (GCB), and anhydrous sodium sulfate, matrix dispersion extraction was used to carry out the purification operation. This scheme can effectively remove sugars, fats, proteins, inorganic minerals, metal ions, and pigment substances in food samples such as meat, dairy products, and honey, and can also utilize the characteristics of magnetic nanomaterials being easy to separate and having good binding degree, which has a better effect than using purification materials separately. 3. The research on instrumental analysis methods was carried out. It is necessary to simultaneously detect more than 20 cannabinoid and cathinone compounds, and the methodological indicators such as detection precision and accuracy also need to reach the level of identifying trace-level psychoactive substances, which are not involved in relevant literatures or patents. The present invention compared various analytical methods, including Raman spectroscopy, Fourier transform infrared spectroscopy, liquid chromatography, gas chromatography, liquid chromatography-mass spectrometry, gas chromatography-mass spectrometry, etc. The results showed that only gas chromatography-mass spectrometry can meet the detection requirements of multiple items, and the spectral library data can be used to carry out rapid identification and analysis of the target substances, with fast, accurate, and precise effects.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for gas chromatography-mass spectrometry analysis of multiple new psychoactive substances in foods, comprising the following steps:

[0009] (1) Preparation of PSA@Fe3O4: Mix nano-Fe3O4 with a particle size of 10 - 50 nm and PSA (ethylenediamine-N-propylsilane) in a weight ratio of 7:3 - 5, then add anhydrous ethanol 5 times the weight of the solid. After vortexing and mixing evenly, ultrasonicate for 1 h at a power of 1000 - 2000 W. Take it out and let it stand at room temperature for more than 2 h, then centrifuge at 3000 - 5000 r / min for 1 - 3 min. Remove the supernatant. Place the product in a vacuum dryer and vacuum dry at 80 °C for 4 h. Then take out the centrifuge tube, crush the obtained material and pass it through a 150 μm sieve to prepare the magnetic nano-adsorbent material PSA@Fe3O4;

[0010] (2) Extraction: Weigh the food sample, add methanol according to a solid-liquid ratio of 1:5 - 10 g / ml, vortex and mix evenly for 1 min, let it stand for 1 min, add an appropriate amount of 200 g / L sodium hydroxide solution to make the pH value of the extract between 8.0 - 9.0, vortex and mix evenly for 3 min, let it stand for 1 min, then add an appropriate amount of 1 mol / L hydrochloric acid to adjust the pH value of the solution between 5.0 - 6.0. Ultrasonicate at 50 °C for 15 min, centrifuge at 8000 - 10000 r / min for 3 - 5 min, take the supernatant for purification. (3) Purification: Take the above-obtained extract in a centrifuge tube, add PSA@Fe3O4 with a liquid-solid ratio of 1:0.05 - 0.5 mL / g, GCB filler with a liquid-solid ratio of 1:0.02 - 0.1 mL / g, C18 filler with a liquid-solid ratio of 1:0.02 - 0.15 mL / g, and anhydrous sodium sulfate with a liquid-solid ratio of 1:0.1 - 0.4 mL / g. Then add an appropriate amount of 200 g / L sodium hydroxide solution to adjust the pH value of the system between 8.0 - 9.0, vortex and mix evenly for 2 min. Use a magnet to adsorb the solid matter to the bottom and side walls of the centrifuge tube or centrifuge at 4000 r / min for 3 min. Take 1 mL of the upper organic phase solution and pass it through a 0.22 μm filter membrane for testing;

[0011] (4) Analysis: The test solution is analyzed by gas chromatography-tandem mass spectrometry.

[0012] Furthermore, the gas chromatography conditions are as follows: Chromatographic column: DB-17MS capillary column, 30 m × 0.25 mm × 0.25 μm; Injection port temperature: 250 °C; Injection volume: 1.0 μL; Injection mode: splitless injection; Carrier gas: high-purity helium; Flow rate: constant flow rate of 1.5 mL / min; Temperature programming: Initial temperature 70 °C, hold for 2 min, increase to 180 °C at a rate of 10 °C / min, then increase to 300 °C at a rate of 15 °C / min, hold for 1 min; Solvent delay time: 7.5 min. Furthermore, the mass spectrometry conditions are as follows: Electron impact ionization; Ionization energy: 70 eV; Ion source temperature: 310 °C; Transfer line temperature: 290 °C; Solvent delay time: 7.5 min; Detection mode: selected ion monitoring. Furthermore, the foods to be detected include meat, dairy products and honey.

[0013] The advantages of the present invention are as follows:

[0014] First, there is no research and literature on new psychoactive substances such as cannabis and cathinones in meat, dairy products, and honey. Second, most of the methods in the literature are for biological samples (blood, urine, hair, etc.) or suspected drugs, and cannot solve the problem of residues and illegal addition of new psychoactive substances in the above food matrices. Third, when using methods for biological samples to conduct food matrix detection, there will be greater impacts, especially in extraction and purification. Fourth, the influence range of pH value during extraction was optimized and discovered. Fifth, a purification material was invented, which can effectively target new psychoactive substances in food. Sixth, by integrating purification methods such as adjusting pH value and optimizing purification materials, combined with gas chromatography-mass spectrometry analysis, more than 20 kinds of cannabis and cathinone substances can be detected simultaneously. Description of the Drawings

[0015] Figure 1 It is the selected ion source chromatogram of cannabis and cathinone substances. In the figure, 1. Benzocaine; 2. MDMC; 3. 4-MMC; 4. MDEC; 5. Sanedrine; 6. α-PVP; 7. Butylone; 8. MPBP; 9. Pentylone; 10. 4-MeO-α-PVP; 11. Methoxymethamphetamine hydrochloride; 12. CBD; 13. PV-4; 14. MDPBP; 15. Δ9-THC; 16. Naphthyrone hydrochloride; 17. CBN; 18. CP-47497; 19. ADB-PINACA; 20. RCS-4; 21. AB-CHMINACA; 22. AM2201; 23. JWH-210;

[0016] Figure 2 It is the total ion current chromatogram of a beef sample spiked at the limit of quantitation;

[0017] Figure 3 It is the total ion current chromatogram of a milk sample spiked at the limit of quantitation;

[0018] Figure 4 It is the total ion current chromatogram of a honey sample spiked at the limit of quantitation. Detailed Embodiments

[0019] To make the above features and advantages of the present invention more obvious and understandable, specific embodiments are given below for detailed description. Unless otherwise specified, the methods of the present invention are all conventional methods in the art.

[0020] 1 Experimental Part

[0021] 1.1 Experimental Instruments

[0022] Agilent 7890A / 5975C gas chromatography - mass spectrometry; electronic balance; centrifuge; nitrogen evaporator.

[0023] 1.2 Reagents and materials

[0024] Methanol, sodium hydroxide, hydrochloric acid, anhydrous sodium sulfate, iron oxide (Fe3O4) particles: 50 nm; ethylenediamine - N - propylsilane (PSA); graphitized carbon black (GCB), C18 packing material.

[0025] 1.3 Preparation method of ethylenediamine - N - propylsilane magnetic nano - adsorbent material (PSA@Fe3O4) supported on nano - iron oxide

[0026] Mix nano - Fe3O4 with a particle size of 10 - 50 nm and ethylenediamine - N - propylsilane (PSA) in a weight ratio of 7:4, then add anhydrous ethanol 5 times the weight of the solid, vortex and mix evenly, ultrasonicate at a power of 1500 W for 1 h, take it out and let it stand at room temperature for 2 h, then centrifuge at 4000 r / min for 2 min, remove the supernatant, place the product in a vacuum dryer and dry it under vacuum at 80 °C for 4 h, take out the centrifuge tube, crush the obtained product and pass it through a 150 μm sieve to obtain the prepared magnetic nano - adsorbent material PSA@Fe3O4.

[0027] 1.4 Extraction

[0028] Weigh 2 g of samples of meat (take beef as an example), dairy products (take milk as an example), and honey (take linden honey as an example) respectively, add 10 mL of methanol, vortex and mix evenly for 1 min, let it stand for 1 min, add an appropriate amount of 200 g / L sodium hydroxide solution to make the pH value of the extraction solution between 8.0 - 9.0, vortex and mix evenly for 3 min, let it stand for 1 min, then add an appropriate amount of 1 mol / L hydrochloric acid to adjust the pH value of the solution between 5.0 - 6.0, ultrasonicate at 50 °C for 15 min, centrifuge at 9000 r / min for 4 min, take the supernatant for purification.

[0029] 1.5 Purification

[0030] Take 10 mL of the above - obtained extraction solution, add 0.5 g of PSA@Fe3O4, 0.2 g of GCB packing material, 0.2 g of C18 packing material, 2 g of anhydrous sodium sulfate, and then add 20 μL of 200 g / L sodium hydroxide solution (to make the adjusted pH value between 8.0 - 9.0), vortex and mix evenly for 2 min, use a magnet to adsorb the solid to the bottom and side walls of the centrifuge tube or centrifuge at 4000 r / min for 3 min.

[0031] Take 1 mL of the above organic phase solution and pass it through a 0.22 μm filter membrane for testing.

[0032] 1.6 Quantitative analysis

[0033] (1) Pretreat the samples such as extraction and purification according to the above steps.

[0034] (2) Select beef, milk, and honey samples without the target substances. After pretreatment according to steps 1.3 - 1.5, obtain blank matrix solutions. Use them to prepare mixed standard solutions of cannabis and cathinone at concentrations of 25.00 μg / L, 50.00 μg / L, 100.00 μg / L, 200.00 μg / L, and 400.00 μg / L. Detect them under the selected chromatographic conditions and mass spectrometry parameters. Establish a linear standard curve with the peak area of the quantitative ion of the target compound as the ordinate and the concentration as the abscissa.

[0035] (3) Analyze the test solutions of cannabis and cathinone compounds in the samples obtained in step (1) by gas chromatography - tandem mass spectrometry. Determine the types of target substances according to the retention time and qualitative and quantitative ions respectively. Substitute their peak areas into the corresponding cannabis and cathinone mixed standard curves respectively to obtain the contents of various target substances in the test solution.

[0036] 1.7 Gas Chromatography Conditions

[0037] Chromatographic column: DB - 17MS capillary column (30 m × 0.25 mm × 0.25 μm); injection port temperature 250 °C; injection volume 1.0 μL; injection mode: splitless injection; carrier gas: high - purity helium (99.999%); flow rate: constant flow rate of 1.5 mL / min; temperature programming: initial 70 °C, hold for 2 min, increase to 180 °C at 10 °C / min, then increase to 300 °C at 15 °C / min, hold for 1 min. Solvent delay time: 7.5 min.

[0038] 1.8 Mass Spectrometry Conditions

[0039] Electron ionization (EI source); ionization energy: 70 eV; ion source temperature: 310 °C; transfer line temperature: 290 °C; solvent delay time: 7.5 min; detection mode: selected ion monitoring (SIM), see Table 1 for details.

[0040] Table 1 Retention times and monitored ion information of 23 cannabis and cathinone compounds

[0041]

[0042]

[0043] 2 Result Analysis

[0044] 2.1 Optimization of Extraction Method

[0045] This study found that different cannabinoids and cathinone compounds have different pH requirements during extraction. Some compounds are not sensitive to pH, while others require a narrow range for optimal extraction. The pH values of different food matrices also vary. Even for the same type of food, they can be affected by factors such as source, origin, and processing techniques (such as whether meat is aged or milk is fermented). Therefore, in common extraction methods, the pH value of the extraction solution needs to be adjusted to the range of 5.0 - 6.0 to achieve the best extraction effect.

[0046] Through a large number of experiments, it was also found that if the pH value is directly adjusted to the acidic range of 5.0 - 6.0, the matrix effect of the test results is more obvious, especially for samples rich in pigments and fats. Therefore, the present invention adopts a method of first adjusting the extraction solution to weak alkalinity (pH 8.0 - 9.0) to remove matrix interference and then to weak acidity (pH 5.0 - 6.0). The results show that this method can not only effectively remove interferences such as pigments, but also has a better matching degree with the purification materials used in this research, thus improving the purification effect.

[0047] 2.2 Comparison of purification methods

[0048] In view of the characteristics of food samples, the present invention uses a purification combination of N-propylethylenediamine loaded on nano-ferroferric oxide (PSA@Fe3O4) + graphitized carbon black (GCB) + C18, which can conveniently and quickly remove organic acids, pigments, and metal ions in food. Moreover, by preparing PSA magnetic nano-adsorption materials loaded with ferroferric oxide, the binding efficiency with biological substances is high, and separation and purification can be achieved under the action of an external magnetic field. In addition, the proportion and combination of the purification materials used have been accurately calculated for various foods, which can meet the purification requirements of meat, dairy products, and honey, and the effect is significantly better than other purification combinations.

[0049] In literature reports and traditional detections, solid-phase extraction cartridges and QuEChERS purification methods are mostly used. Compared with the purification method described in the present invention, solid-phase extraction purification mostly has purification cartridges with only single materials and is cumbersome to operate. When multiple materials such as PSA, C18, and GCB are required for purification, the solid-phase extraction method needs to pass through the columns for purification one by one, and different extraction solvents or additional drying steps are also required, greatly increasing the time and operation costs. The QuEChERS method only directly adds powders of several purification materials to the sample, unable to take into account the requirements of different materials for solvents, acids and bases, and adsorption effects, and has great limitations in use. While this method uses nano-ferroferric oxide as the core and is wrapped with PSA to form a core-shell layer with a tight structure, solving the problem of poor material stability of PSA materials under acidic and alkaline conditions.

[0050] 2.2 Matrix effect

[0051] This method investigated the matrix effect for various matrices. The slope of the standard curve prepared with methanol (SlopeA) was compared with the slope of the standard curve of the same concentration prepared with blank matrix (SlopeB). According to the calculation formula of matrix effect (ME) = (Slope B - SlopeA) / SlopeA × 100%, the results are shown in Table 2.

[0052] Table 2 Matrix effect of different foods

[0053]

[0054] According to the judgment criteria of matrix effect, when |ME| < 20%, it is a weak matrix effect; when 20% < |ME| < 50%, it is a medium-strength matrix effect; when |ME| > 50%, it is a strong matrix effect. It can be seen from Table 2 that most of the matrices have a medium matrix effect. To further reduce the influence of the matrix effect, this method uses the matrix curve quantification method to further correct the influence of the matrix effect, thereby improving the stability of the method. From the results of the recovery rate and precision of the spiking test, the results after correction with the matrix curve have good stability and meet the required recovery rate and precision indicators.

[0055] 2.3 Linear range and regression equation of the method

[0056] Twenty-three standard products of cannabis and cathinone were prepared into a mixed standard working curve with mass concentrations of 25.0 μg / L, 50.0 μg / L, 100.0 μg / L, 200.0 μg / L, and 400.0 μg / L using the blank matrix solutions of beef, milk, and honey. After determination by the instrument, the linear equations and correlation coefficients of each component were calculated, and the results are shown in Table 3.

[0057] Table 3 Table of linear equations and correlation coefficients of 23 cannabis and cathinone compounds

[0058]

[0059]

[0060] 2.4 Method detection limit and quantification limit

[0061] 23 kinds of cannabis and cathinone standard solutions with concentrations of 1 - 100 μg / L were added to samples of various negative matrices respectively, and were determined according to the optimized pretreatment method and instrument conditions. The detection limit (LOD) and quantification limit (LOQ) of the method were defined by the responses when the signal-to-noise ratio of the quantitative ions was 3 and 10. According to the signal-to-noise ratio results, the LOD of various matrices was between 5 - 8 μg / kg, and the LOQ was about 25 μg / kg. The LOQ of some matrix samples could be lower, but considering the convenience of operation and use, the LOQ based on the least sensitive compound was unified. Therefore, the LOQ of cannabis and cathinone in various matrices of this method was determined to be 25 μg / kg. The total ion chromatograms of various matrices spiked at the quantification limit are shown in Figures 2 to 4 .

[0062] 2.5 Recovery and precision

[0063] According to the methods described in 1.3 - 1.8, beef, milk, and honey samples without the analytes were selected for the addition recovery test. The spiking amount was 25 μg / kg, and each level was repeated 6 times. The average recovery rate and relative standard deviation (RSD) were calculated, and the results are shown in Table 4.

[0064] Table 4 Recovery and precision table (n = 6) %

[0065]

[0066]

[0067] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A method for analyzing multiple new psychoactive substances in food by gas chromatography-mass spectrometry, characterized in that It includes the following steps: (1) Preparation of PSA@Fe3O4: Mix nano-Fe3O4 with a particle size of 10 - 50 nm and N-(3-aminopropyl)trimethoxysilane (PSA) in a weight ratio of 7:3 - 5, then add anhydrous ethanol 5 times the weight of the solid. After vortex mixing evenly, ultrasonicate for 1 h at a power of 1000 - 2000 W. Take it out and let it stand at room temperature for more than 2 h, then centrifuge at 3000 - 5000 r / min for 1 - 3 min, remove the supernatant. Place the product in a vacuum dryer and vacuum dry at 80 °C for 4 h. Take out the centrifuge tube, crush the obtained material and pass it through a 150 μm sieve to prepare the magnetic nano-adsorbent material PSA@Fe3O4; (2) Extraction: Weigh the food sample, add methanol according to a solid-liquid ratio of 1:5 - 10 g / ml, vortex mix for 1 min, let it stand for 1 min, add an appropriate amount of 200 g / L sodium hydroxide solution to make the pH value of the extraction solution between 8.0 - 9.0, vortex mix for 3 min, let it stand for 1 min, then add an appropriate amount of 1 mol / L hydrochloric acid to adjust the pH value of the solution between 5.0 - 6.0, ultrasonicate at 50 °C for 15 min, centrifuge at 8000 - 10000 r / min for 3 - 5 min, take the supernatant for purification; (3) Purification: Take the above-obtained extraction solution in a centrifuge tube, add PSA@Fe3O4 with a liquid-solid ratio of 1:0.05 - 0.5 mL / g, GCB filler with a liquid-solid ratio of 1:0.02 - 0.1 mL / g, C18 filler with a liquid-solid ratio of 1:0.02 - 0.15 mL / g, and anhydrous sodium sulfate with a liquid-solid ratio of 1:0.1 - 0.4 mL / g. Then add an appropriate amount of 200 g / L sodium hydroxide solution to adjust the pH value of the system between 8.0 - 9.0, vortex mix for 2 min, use a magnet to adsorb the solid matter to the bottom and side walls of the centrifuge tube or centrifuge at 4000 r / min for 3 min, take 1 mL of the upper organic phase solution and pass it through a 0.22 μm filter membrane for testing; (4) Analysis: The test solution is analyzed by gas chromatography-tandem mass spectrometry; The foods to be detected are meat, dairy products, and honey; The said new psychoactive substances include: ephedrine hydrochloride, 4-methylmethcathinone, methoxymethamphetamine hydrochloride, benzocaine, α-pyrrolidinopentiophenone, 2-methylamino-1-(3,4-methylenedioxyphenyl)-1-propanone, 4-methyl-α-pyrrolidinobutiophenone, ethylone hydrochloride, 2-methylamino-1-(3,4-methylenedioxyphenyl)butan-1-one, pyrovalerone, pentylone, 4'-methyl-α-pyrrolidinophexanone, 3',4'-methylenedioxy-α-pyrrolidinobutiophenone, cannabidiol, naphyrone hydrochloride, Δ9-tetrahydrocannabinol, cannabinol, cis-5-(1,1-dimethylheptyl)-2-[(1 R ,3 S )-3-hydroxycyclohexyl]phenol, N -(1-carbamoyl-2,2-dimethylpropyl)-1-pentylindazole-3-carboxamide, pentyl-3-(4-methoxybenzoyl)indole, N -(1-carbamoyl-2-methylpropyl)-1-(cyclohexylmethyl)indazole-3-carboxamide, 1-(5-fluoropentyl)-3-(1-naphthoyl)-1 H -indole, pentyl-3-(4-ethyl-1-naphthoyl)indole, a total of 23 kinds; Gas chromatography conditions: Chromatographic column: DB-17MS capillary column 30 m × 0.25 mm × 0.25 µm; Temperature programming: Initial temperature 70 °C, hold for 2 min, increase to 180 °C at a rate of 10 °C / min, then increase to 300 °C at a rate of 15 °C / min, hold for 1 min.

2. The method according to claim 1, characterized in that, Gas chromatography conditions: Injection port temperature 250 °C; Injection volume 1.0 μL; Injection mode: Splitless injection; Carrier gas: High-purity helium; Flow rate: Constant flow rate 1.5 mL / min; Solvent delay time: 7.5 min.

3. The method according to claim 1, characterized in that, Mass spectrometry conditions: Electron impact ionization; Ionization energy: 70 eV; Ion source temperature: 310 °C; Transfer line temperature: 290 °C; Solvent delay time: 7.5 min; Detection mode: Selected ion monitoring.

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