A method for preparing a solid phase microextraction coating and use of the coating

Abstract

The application relates to a preparation method of a solid-phase microextraction coating, comprising the following steps: (1) dissolving a metal organic framework material MIL-101Cr as an adsorbent and a binder in a solvent to prepare a suspension; (2) uniformly mixing and ultrasonically treating the suspension, then inserting a stainless steel substrate into the suspension and slowly taking out the substrate, so that a coating is coated on the substrate, and the process is repeated for several times until the coating on the substrate reaches a required thickness. Compared with commonly used commercial solid-phase microextraction heads, the solid-phase microextraction fiber coating for sample pretreatment has better extraction effect than a two-in-one extraction head and is equivalent to a three-in-one extraction head, and the prepared solid-phase microextraction fiber coating has a long service life and can be repeatedly used for 160 times.

Description

Technical Field

[0001] This invention relates to the field of chemical analysis and detection technology, specifically to a method for preparing a solid-phase microextraction coating and a method for detecting volatile substances in polypropylene by combining the coating with gas chromatography-mass spectrometry. Background Technology

[0002] Polypropylene (PP) resin possesses excellent comprehensive properties and is lightweight and inexpensive, making it widely used in automotive interior parts. While existing PP resins can generally meet the performance requirements for automotive interior materials, the release of volatile organic compounds (VOCs) by PP resins and their products is still influenced by monomers, catalysts, polymerization processes, and degradation. This not only pollutes the environment but also produces odors that can harm health. Therefore, determining the types and contents of volatile substances in PP resins is of great significance.

[0003] There are various pretreatment methods for the extraction of volatile organic compounds (VOCs), such as purge-and-trap (dynamic headspace), static headspace, thermal desorption, and solid-phase microextraction (SPME). Combining these with gas chromatography-mass spectrometry (GC-MS) can achieve the separation and qualitative and quantitative analysis of VOC components. In recent years, SPME technology has been widely used for the extraction of VOCs from food, pharmaceuticals, air, soil, and water. Compared with traditional sample pretreatment methods, SPME has advantages such as no need for organic solvents, simplicity and convenience, rapid testing, and integration of sampling, extraction, concentration, and injection. The type of extraction head is the most important factor determining the effectiveness of SPME. Different extraction heads adsorbing the same sample will yield different quantities and concentrations of VOCs, mainly due to differences in parameters such as the coating material of different extraction heads. Currently, commonly used commercial solid-phase microextraction (SPE) heads include polymethylsiloxane (PDMS) extraction heads, polyacrylate (PA) extraction heads, polydimethylsiloxane and polydivinylbenzene (PDMS / DVB) extraction heads, and polydivinylbenzene / activated carbon / polydimethylsiloxane (DVB / CAR / PDMS) three-layer composite extraction heads. However, traditional fiber coatings still suffer from problems such as low absorption capacity, poor stability, short service life (generally about 40-100 times), and high price. Therefore, developing SPE heads with strong extraction capacity and easy preparation for the determination of volatile substances has become a new direction for development. Summary of the Invention

[0004] Based on the above, the main objective of this invention is to provide a method for preparing a solid-phase microextraction coating and a method for detecting volatile substances in polypropylene by combining the coating with gas chromatography-mass spectrometry, so as to solve the problem that the existing technology cannot completely extract and accurately quantify volatile substances in polypropylene resin.

[0005] To achieve the above objectives, the present invention provides a method for preparing a solid-phase microextraction coating, comprising the following steps:

[0006] (1) The metal-organic framework material MIL-101Cr was used as an adsorbent and dissolved in a solvent with a binder to form a suspension;

[0007] (2) Mix the suspension evenly and sonicate it. Then, insert the stainless steel substrate into the suspension and slowly remove it to coat the substrate. Repeat this process several times until the coating on the substrate reaches the required thickness.

[0008] Specifically, the MIL-101(Cr) involved in this invention is synthesized using chromium as the metal source and terephthalic acid as the ligand. It has a large specific surface area and high pore volume, good thermal stability, and does not undergo structural changes in air. Using it as a novel coating for solid-phase microextraction can effectively extract volatile compounds.

[0009] The method for preparing the solid-phase microextraction coating of the present invention preferably uses polysulfone as the binder. More preferably, in step (1), the weight ratio of the adsorbent MIL-101Cr to polysulfone is 9:1 to 5:5, and more preferably 7:3.

[0010] In the method for preparing the solid-phase microextraction coating of the present invention, preferably, the solvent is one or more of dichloromethane (DCM), tetrahydrofuran (THF), or N,N-dimethylformamide (DMF).

[0011] The method for preparing the solid-phase microextraction coating of the present invention preferably involves mixing the suspension evenly by shaking or stirring; more preferably, the shaking time is 3-7 minutes, and even more preferably 5 minutes; the ultrasonic treatment time is 10-30 minutes, and even more preferably 20 minutes.

[0012] The method for preparing the solid-phase microextraction coating of the present invention preferably has a coating thickness of 25-60 μm, more preferably 50 μm.

[0013] To achieve the above objectives, the present invention also provides a method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry, comprising the following steps:

[0014] S1. Solid-phase microextraction for extracting volatile substances.

[0015] Weigh a polypropylene resin sample into a headspace vial, tighten the seal, and balance it. Insert the prepared solid-phase microextraction coating into the headspace of the headspace vial for extraction. After removing it, immediately insert it into the gas chromatograph injection port for desorption.

[0016] S2. Gas chromatography-mass spectrometry was used to analyze and detect the extracted volatile substances;

[0017] S3. Perform qualitative analysis on the measured volatile substances, and then perform quantitative analysis on various volatile substances using the external standard method: prepare a series of standard solutions, establish standard curves for concentration and peak area, and calculate the content of each volatile substance.

[0018] The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to the present invention preferably has the following characteristics: the volume of the headspace vial is 10-30 mL, more preferably 15 mL, and the weight of the polypropylene resin sample is 1.5-3.5 g, more preferably 2.0 g.

[0019] The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to the present invention preferably has the following characteristics: the equilibration temperature is 50-80°C, more preferably 60°C; and the equilibration time is 10-30 min.

[0020] The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to the present invention preferably includes an extraction time of 10-40 min, more preferably 30 min, and an extraction temperature of 50-80°C.

[0021] The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to the present invention preferably includes a desorption time of 3 to 7 minutes, more preferably 5 minutes, and a desorption temperature of 230 to 250°C.

[0022] The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry (GC-MS) according to the present invention preferably includes the following GC-MS conditions:

[0023] The chromatographic column was a VF-WAXms capillary column with dimensions of 60m × 0.25μm × 0.25mm;

[0024] The carrier gas is pure helium; the flow rate is 0.9–1.1 mL / min, preferably 1.0 mL / min;

[0025] Procedure: Splitless injection; Inlet temperature: 230–250℃;

[0026] Temperature program: Initial column temperature 40-45℃, hold for 5-10 min; increase temperature by 5-10℃ / min to 80-150℃, hold for 5-10 min; then increase temperature by 5-10℃ / min to 210-230℃, hold for 5-10 min.

[0027] Mass spectrometry conditions: Ion source: EI ion source; Ion source temperature: 230℃; Transfer line temperature: 200℃; Electron impact energy: 70eV; Scan mode: Full scan; Mass scan range: 29~400m / z.

[0028] The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to the present invention preferably involves qualitative analysis of the polypropylene resin performed using a computer mass spectrometry workstation, the standard mass spectrometry library NIST11, the standard mass spectrometry library NIST11s, and matched fraction analysis.

[0029] Specifically, the method for preparing the solid-phase microextraction coating provided by this invention includes the following steps:

[0030] (1) Preparation of fiber coating for solid-phase microextraction

[0031] A suspension is prepared by dissolving a mixture of MIL-101(Cr) adsorbent and binder in a solvent. The suspension is then thoroughly agitated and sonicated. A stainless steel wire is immersed in the suspension and slowly removed, leaving a coating on its surface. The solvent is then allowed to evaporate. This coating process is repeated several times until the desired thickness is achieved.

[0032] (2) Solid-phase microextraction for the extraction of volatile substances

[0033] Solid-phase microextraction (SPE) was used to extract volatile substances from the sample: A certain amount of PP resin sample was weighed into a 15 mL headspace vial and sealed tightly. After equilibration at a certain temperature for a certain time, the SPE fiber coating was inserted into the headspace of the sample vial for extraction for a certain time. Then, it was immediately removed and inserted into the gas chromatograph injection port for desorption at 250 °C.

[0034] (3) Gas chromatography-mass spectrometry was used to analyze and detect the extracted volatile substances.

[0035] (4) Perform qualitative analysis on the measured volatile substances, and then perform quantitative analysis on various volatile substances by external standard method: prepare a series of standard solutions, establish standard curves of concentration and peak area, and calculate the content of each volatile substance.

[0036] The solid-phase microextraction fiber coating provided by this invention is made by coating a stainless steel wire with a metal-organic framework material MIL-101(Cr) and a binder. Volatile compounds in polypropylene are then extracted. After extraction, the fiber coating is subjected to headspace derivatization, and finally, the extracted volatile compounds are detected and analyzed by GC-MS. The beneficial effects of this invention are as follows:

[0037] (1) Sample pretreatment using solid phase microextraction fiber coating has a better extraction effect than commonly used commercial solid phase microextraction heads, and is comparable to three-in-one extraction heads. However, the solid phase microextraction fiber coating has a long service life and can be reused 160 times.

[0038] (2) The prepared solid-phase microextraction fiber-coated fiber was coupled with GC-MS, and the influencing factors were optimized. The external standard method was used to accurately quantify the volatile substances in polypropylene resin. The linear range of esters, alcohols, alkanes, and aldehydes was relatively wide, and R 2 All values ​​were above 0.99, indicating good linearity. The recoveries of each type of substance were between 80% and 110%, demonstrating high accuracy. The RSD was below 2%, indicating good reproducibility. The limits of detection (LODs) were relatively low: 0.3 μg / kg for aldehydes, 1.1 μg / kg for esters, 1.1 μg / kg for alcohols, and 0.6 μg / kg for alkanes. In summary, this method is highly sensitive, reproducible, accurate, and reliable, providing scientific support for tracing the sources of odor in polypropylene resin and researching measures to improve odor. Attached Figure Description

[0039] Figure 1 A schematic table showing the relationship between the number of times the fiber coating can be recycled and the recovery rate provided in Example 1.

[0040] Figure 2 The total ion chromatogram for analyzing volatile substances in polypropylene resin provided for Experimental Example 1.

[0041] Figure 3 The standard curve of n-octaldehyde, a volatile substance in polypropylene resin provided for Experimental Example 1.

[0042] Figure 4 The standard curve of undecane, a volatile substance in polypropylene resin, provided for Experimental Example 1.

[0043] Figure 5 The standard curve of linalool, a volatile substance in polypropylene resin provided for Experimental Example 1.

[0044] Figure 6 The standard curve of ethyl octanoate, a volatile substance in polypropylene resin provided in Experimental Example 1. Detailed Implementation

[0045] The following provides a detailed description of the embodiments of the present invention: These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and processes. However, the scope of protection of the present invention is not limited to the following embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions.

[0046] Example 1

[0047] Preparation and optimization of solid-phase microextraction fiber coatings

[0048] Extraction efficiency and repeatability are the two most important aspects of solid-phase microextraction fiber coatings in practical applications, and both are related to the ratio of MIL-101(Cr) to binder. The binder gives the MIL-101(Cr) solution adhesiveness, allowing it to adhere better to the stainless steel wire. However, excessive polysulfone can affect the extraction efficiency; therefore, the ratio of MIL-101(Cr) to polysulfone was investigated.

[0049] A mixture of MIL-101(Cr) powder and polysulfone in weight ratios of 9:1, 7:3, and 5:5 was dissolved in a mixture of DMC and DMF to prepare a suspension. The suspensions were agitated thoroughly for 7 minutes and then ultrasonically vibrated for 40 minutes. A stainless steel wire with a diameter of 130 μm and a length of 2 cm was then immersed in each of the three suspensions and slowly removed, forming a thin coating on the surface of the wire. The wire was then placed in an oven and dried at 40°C for 30 minutes to allow dichloromethane to evaporate. This coating process was repeated several times until the coating thickness on the three stainless steel wires was approximately 50 μm. Finally, the three fiber coatings were aged at 250°C for 40 minutes at the GC inlet.

[0050] The extraction efficiency of different fiber coatings was evaluated by using a standard of 1 mg / kg undecane and the extraction yield at 60℃ for 20 min. To investigate reproducibility, the extracted fiber coatings were thermally desorbed into a gas chromatograph at 250℃ for 5 min until the analyte peak was undetectable before being reused in the next extraction cycle. The extraction results are shown in Table 1.

[0051] Table 1. Effect of MIL-101 (Cr) ratio on extraction efficiency

[0052] weight ratio Extraction volume (mg / kg) 9:1 0.988 7:3 0.837 5:5 0.623

[0053] Table 1 shows that when the MIL-101(Cr) content on the stainless steel wire is 90%, 70%, and 50%, the extraction capacity gradually decreases, meaning that the extraction efficiency increases with the increase of the MIL-101(Cr) proportion. On the other hand, from... Figure 1It can be seen that a high proportion of MIL-101(Cr) and a low content of polysulfone lead to reduced adhesion, increased difficulty in coating preparation, and consequently, poorer coating stability. When the proportion of MIL-101(Cr) is 70%, the extraction efficiency of the analyte remains largely unchanged after 150 repeated uses of the fiber coating, demonstrating that the fiber coating exhibits excellent reproducibility and stability.

[0054] Example 2

[0055] Optimization of various influencing factors in solid-phase microextraction process

[0056] Since the extraction effect of solid-phase microextraction is affected by factors such as sample amount, extraction time, and extraction temperature, this embodiment uses a self-made solid-phase microextraction fiber coating to extract volatile substances from polypropylene resin. Based on the total number and total peak area of ​​volatile substances, the effects of different sample amounts, extraction adsorption times, and extraction temperatures on the extraction effect of volatile substances from polypropylene resin are compared, and optimized parameters are determined.

[0057] (1) Materials and reagents

[0058] Sample of polypropylene EP533N resin, Lanzhou Chemical Research Center, China National Petroleum Corporation.

[0059] (2) Instruments and equipment

[0060] MS-H380-Pro magnetic stirring apparatus, SCILOGEX, USA; 7890B-5977A gas chromatograph-mass spectrometer, VF-WAXms capillary column (60m×0.25μm×0.25mm), Agilent Technologies, USA; 15mL screw-top headspace vial, black open-hole cap, PTFE septum, CNW Technologies, Germany; AX 205 analytical balance, Mettler Toledo.

[0061] (3) Self-made solid-phase microextraction fiber coating: A mixture of MIL-101(Cr) powder and polysulfone at a weight ratio of 9:1 was dissolved in DCM to prepare a suspension. The suspension was shaken thoroughly for 6 min and ultrasonically vibrated for 30 min. Then, a stainless steel wire with a diameter of 130 μm and a length of 2 cm was immersed in the suspension and slowly removed from it, forming a thin coating on the surface of the stainless steel wire. The stainless steel wire was then placed in an oven and dried at 40 °C for 30 min to allow the dichloromethane to evaporate. The above coating process was repeated several times until the coating thickness was approximately 60 μm. Finally, the prepared fiber coating was aged at 250 °C for 40 min at the GC inlet.

[0062] (4) Detection and analysis of volatile substances, the specific steps are as follows:

[0063] (4-1) Solid-phase microextraction

[0064] Select the sample amount, extraction and adsorption time, and extraction temperature according to Table 2. Place the weighed sample in a 15 mL screw-top headspace vial and equilibrate for 20 min at a specific temperature using a magnetically heated stirrer. Then, insert the solid-phase microextraction (SPME) head (containing a self-made SPME fiber coating) into the headspace vial, positioning the head 1.0 cm above the sample, and allow it to extract and adsorb for a certain time. Immediately after extraction, insert the extraction head into the gas chromatograph inlet and desorb at 250 °C for 5 min. Finally, perform separation and detection using a gas chromatography-mass spectrometry (GC-MS) system.

[0065] (4-2) Gas chromatography-mass spectrometry for the detection and analysis of volatile substances in polypropylene resin

[0066] Chromatographic conditions: Injector temperature: 250℃; Carrier gas: High-purity helium with a purity ≥99.999%, flow rate 1.0 mL / min; Injection method: Splitless injection; Temperature program: Initial temperature 40℃, hold for 10 min; Increase temperature to 100℃ at 8℃ / min, hold for 5 min; Increase temperature to 220℃ at 8℃ / min, hold for 5 min.

[0067] Mass spectrometry conditions: Ionization method: Electron ionization (EI); Electron energy: 70 eV; Ion source temperature: 230℃; Transfer line temperature: 200℃; Scan mode: Full scan; Scan mass range m / z: 29~400 m / z; Quadrupole temperature: 150℃.

[0068] Compounds were searched using the NIST11 and NIST11s standard mass spectrometry libraries, and those with a matching degree greater than 80% were retained. The effect of the total number of peaks and total peak area of ​​volatile substances on the extraction effect of volatile substances by polypropylene resin was determined, as shown in Table 2.

[0069] Table 2. Effects of different factors on the extraction efficiency of volatile substances from polypropylene resin.

[0070]

[0071]

[0072] As shown in Table 2, the optimal conditions for solid-phase microextraction (SPE) to extract volatile substances from polypropylene resin are: sample amount 2g, extraction temperature 60℃, and extraction time 30min.

[0073] Experimental Example 1

[0074] Volatile substances in polypropylene were determined by using a self-made solid-phase microextraction fiber coating combined with GC-MS. The volatile substances in polypropylene resin were extracted according to the solid-phase microextraction conditions optimized in Example 2 and determined by gas chromatography-mass spectrometry.

[0075] (1) The materials are the same as in Example 2. Reagents: mixed standard of n-alkane (C10-C25), O2SI, USA; undecane, ethyl octanoate, linalool, and decanal external standard samples, Shanghai Anpu Reagent Co., Ltd.

[0076] (2) The instruments and equipment are the same as in Example 2.

[0077] (3) Self-made solid-phase microextraction fiber coating: A mixture of MIL-101(Cr) powder and polysulfone in a weight ratio of 7:3 was dissolved in DCM to prepare a suspension. The suspension was shaken thoroughly for 5 min and ultrasonically vibrated for 20 min. Then, a stainless steel wire with a diameter of 130 μm and a length of 2 cm was immersed in the suspension and slowly removed from it, forming a thin coating on the surface of the stainless steel wire. The stainless steel wire was then placed in an oven and dried at 40 °C for 30 min to allow the dichloromethane to evaporate. The above coating process was repeated several times until the coating thickness was approximately 50 μm. Finally, the prepared fiber coating was aged at 250 °C for 40 min at the GC inlet.

[0078] (4) Detection and analysis of volatile substances, the specific steps are as follows:

[0079] (4-1) Solid-phase microextraction

[0080] Weigh 2.0 g of sample into a 15 mL screw-top headspace vial and equilibrate for 20 min on a magnetically heated stirrer at 60 °C. Then, insert the solid-phase microextraction (SPME) head (containing a self-made SPME fiber coating) into the headspace vial, positioning the head 1.0 cm above the sample, and extract for 30 min. Immediately after extraction, insert the head into the gas chromatograph inlet and desorb at 250 °C for 5 min. Finally, proceed to a gas chromatography-mass spectrometry (GC-MS) system for separation and detection.

[0081] (4-2) Detection of volatile substances in polypropylene resin by gas chromatography-mass spectrometry

[0082] Chromatographic conditions: Injector temperature: 250℃; Carrier gas: High-purity helium with a purity ≥99.999%, flow rate 1.0 mL / min; Injection method: Splitless injection; Temperature program: Initial temperature 40℃, hold for 10 min; Increase temperature at 10℃ / min to 80℃, hold for 10 min; Increase temperature at 10℃ / min to 230℃, hold for 10 min.

[0083] Mass spectrometry conditions: Ionization method: Electron ionization (EI); Electron energy: 70 eV; Ion source temperature: 230℃; Transfer line temperature: 200℃; Scan mode: Full scan; Scan mass range m / z: 29~400 m / z; Quadrupole temperature: 150℃.

[0084] The total ionization spectroscopy of volatile substances in polypropylene resin is shown below. Figure 2 .

[0085] (4-3) Qualitative and quantitative analysis of volatile substances

[0086] Qualitative analysis: Compounds were searched using the NIST11 and NIST11s standard mass spectrometry libraries. Compounds with a match greater than 80% were retained. Unknown substances were identified by combining retention indices with literature reports. The retention index was calculated based on the retention time of the n-alkanes after a mixture of C10–C25 n-alkanes as a standard was injected under the same analytical conditions as the polypropylene resin sample. The total ion chromatogram of volatile substances in the polypropylene resin is shown below. Figure 2 As shown.

[0087] Quantitative analysis: Quantitative analysis was performed using the external standard method. Four standard samples—undecane, ethyl n-octanoate, n-octaldehyde, and linalool—were selected as external standards, and a series of standard solutions were prepared for each. Table 3 shows the concentrations of the series of standard solutions.

[0088] Table 3 Concentration of the prepared series of standard solutions

[0089]

[0090]

[0091] Standard solutions at different concentration levels were tested under optimal gas chromatography-mass spectrometry (GC-MS) conditions. Each level was injected three times, and the average of the three experiments was used to represent the results. A correlation coefficient (X) was established between concentration (X) and peak area (Y), calculated as 10⁻¹⁰. 7 The standard curve of ) is shown in Figures 2 to 5 .

[0092] The content of each volatile substance was calculated based on the standard curve. Information on volatile substances and their contents in polypropylene resin is shown in Table 4.

[0093] Table 4 Volatile substances of polypropylene resin

[0094]

[0095]

[0096]

[0097] In this experimental example, 66 volatile substances in polypropylene resin were identified using solid-phase microextraction-gas chromatography-mass spectrometry (SPI-MS), exceeding the number and variety reported in other literature, demonstrating the significant superiority of the sample pretreatment method and qualitative analysis techniques of this invention. Table 4 shows that the volatile compounds include alkanes, alkenes, alcohols, benzenes, esters, aldehydes, and other compounds. Alkanes were the most abundant, with 42 species, accounting for 63.6% of the total volatile substances; followed by alcohols, benzenes (13 species, 19.7%), benzenes (4 species, 6.1%), and alkenes (3 species, 4.5%). Among alkane compounds, the most abundant substance is eicosane, at 121.900 mg / kg, accounting for 20.2% of the total volatile substances; among alcohol compounds, the most abundant substance is 2-ethyl-2-methyltridecyl alcohol, at 2.153 mg / kg; and among benzene compounds, the most abundant substance is 2-benzylmethylimidazoline, at 3.855 mg / kg.

[0098] Comparative Example 1

[0099] Comparison of extraction efficiency with other commercially available fiber coatings

[0100] Considering that the fiber coating of solid-phase microextraction (SPE) is the most important factor affecting the extraction effect of volatile substances, this comparative example compares the extraction effect of the self-made SPE fiber coating with different commercially available extraction heads. The extraction effect is mainly determined by the number and peak area of ​​the total ion chromatogram of volatile substances in polypropylene resin.

[0101] (1) Materials and reagents, same as in Example 2.

[0102] (2) Instruments and equipment: 50 / 30μm DVB / CAR / PDMS, 75μm CAR / PDMS and 100μm PDMS solid phase microextraction heads (aged at 250℃ for 20 min before use), 57730-U type solid phase microextraction manual injection handle, Supelco, USA. Other instruments and equipment are the same as in Example 2.

[0103] (3) Self-made solid-phase microextraction fiber coating: A mixture of MIL-101(Cr) powder and polysulfone at a weight ratio of 8:2 was dissolved in THF to prepare a suspension. The suspension was shaken thoroughly for 5 min and ultrasonically vibrated for 20 min. Then, a stainless steel wire with a diameter of 130 μm and a length of 2 cm was immersed in the suspension and slowly removed from it, forming a thin coating on the surface of the stainless steel wire. The stainless steel wire was then placed in an oven and dried at 40 °C for 30 min to allow the dichloromethane to evaporate. The above coating process was repeated several times until the coating thickness was approximately 50 μm. Finally, the prepared fiber coating was aged at 250 °C for 40 min at the GC inlet.

[0104] (4) Detection and analysis of volatile substances, the specific steps are as follows:

[0105] (4-1) Solid-phase microextraction

[0106] Weigh 2.0 g of sample into a 15 mL screw-top headspace vial and equilibrate for 20 min at 60 °C using a magnetically heated stirrer. Then, insert a solid-phase microextraction (SPME) head (see Table 5 for head type) into the headspace vial, positioning the head 1.0 cm above the sample, and allow extraction and adsorption to proceed for 30 min. Immediately after extraction, insert the head into the gas chromatograph inlet and desorb at 250 °C for 5 min. Finally, perform separation and detection using a gas chromatography-mass spectrometry (GC-MS) system. Four different types of extraction heads were tested independently.

[0107] (4-2) Gas chromatography-mass spectrometry for the detection and analysis of volatile substances in polypropylene resin

[0108] Chromatographic conditions: Injector temperature: 250℃; Carrier gas: High-purity helium with a purity ≥99.999%, flow rate 1.0 mL / min; Injection method: Splitless injection; Temperature program: Initial temperature 40℃, hold for 10 min; Increase temperature at 10℃ / min to 80℃, hold for 10 min; Increase temperature at 10℃ / min to 230℃, hold for 10 min.

[0109] Mass spectrometry conditions: Ionization method: Electron ionization (EI); Electron energy: 70 eV; Ion source temperature: 230℃; Transfer line temperature: 200℃; Scan mode: Full scan; Scan mass range m / z: 29~400 m / z; Quadrupole temperature: 150℃.

[0110] (5) Comparison of extraction effects of different extraction heads

[0111] Compounds were searched using the NIST11 and NIST11s standard mass spectrometry libraries, and those with a matching degree greater than 80% were retained. The optimal extraction head was selected based on the total number of volatile substances and the total peak area. Table 5 shows the total number of volatile substances and the total peak area obtained using different types of extraction heads.

[0112] Table 5 shows the number and peak area of ​​volatile compounds obtained using different types of extraction heads.

[0113] Extraction head type Number of peaks Peak area Homemade solid-phase microextraction fiber coating 95 317257631 50 / 30μm DVB / CAR / PDMS 98 307587322 75μm CAR / PDMS 56 243956491 100μm PDMS 49 151233673

[0114] As shown in Table 5, the number and content of volatile substances adsorbed by different extraction heads are not the same. Among them, the self-made solid phase microextraction fiber coating and the 50 / 30μm DVB / CAR / PDMS extraction head have basically the same extraction effect in terms of the number of peaks and peak area, which is significantly better than the other two extraction heads. This indicates that the self-made solid phase microextraction fiber coating can comprehensively extract volatile compounds in polypropylene.

[0115] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the present invention.

Claims

1. A method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry, characterized in that, Includes the following steps: S1. Solid-phase microextraction for extracting volatile substances. Weigh the polypropylene resin sample into a headspace vial, tighten the seal, and balance it. Insert the solid phase microextraction coating into the headspace of the headspace vial for extraction. After removing it, immediately insert it into the gas chromatograph injection port for desorption. S2. Gas chromatography-mass spectrometry was used to analyze and detect the extracted volatile substances; S3. Perform qualitative analysis on the measured volatile substances, and then perform quantitative analysis on various volatile substances using the external standard method: prepare a series of standard solutions, establish a standard curve of concentration and peak area, and calculate the content of each volatile substance. The method for preparing the solid-phase microextraction coating includes the following steps: (1) The metal-organic framework material MIL-101Cr was used as an adsorbent and dissolved in a solvent with a binder to form a suspension; (2) Mix the suspension evenly and sonicate it. Then, insert the stainless steel substrate into the suspension and slowly remove it to coat the substrate. Repeat this process several times until the coating on the substrate reaches the required thickness. The adhesive is polysulfone, and in step (1), the weight ratio of adsorbent MIL-101Cr to polysulfone is 9 to 1:

1. The gas chromatography-mass spectrometry conditions are as follows: The chromatographic column was a VF-WAXms capillary column with dimensions of 60m × 0.25μm × 0.25mm; The carrier gas is pure helium; the flow rate is 0.9–1.1 mL / min. Procedure: Splitless injection; Inlet temperature: 230–250℃; Temperature program: Initial column temperature 40-45℃, hold for 5-10 min; increase temperature by 5-10℃ / min to 80-150℃, hold for 5-10 min; then increase temperature by 5-10℃ / min to 210-230℃, hold for 5-10 min. Mass spectrometry conditions: Ion source: EI ion source; Ion source temperature: 230℃; Transfer line temperature: 200℃; Electron impact energy: 70eV; Scan mode: Full scan; Mass scan range: 29~400m / z.

2. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, In step (1), the weight ratio of adsorbent MIL-101Cr to polysulfone is 7:

3.

3. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, The solvent is one or more of dichloromethane, tetrahydrofuran, or N,N-dimethylformamide.

4. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, The suspension is mixed evenly by shaking or stirring.

5. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 4, characterized in that, The shaking time is 3 to 7 minutes.

6. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 4, characterized in that, The shaking time is 5 minutes.

7. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, The ultrasonic treatment time is 10 to 30 minutes.

8. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, The ultrasonic treatment time is 20 minutes.

9. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, The thickness of the coating is 25–60 μm.

10. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, The coating has a thickness of 50 μm.

11. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, The headspace vial has a volume of 10-30 mL.

12. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, The headspace vial has a volume of 15 mL.

13. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, The weight of the polypropylene resin sample is 1.5 to 3.5 g.

14. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, The weight of the polypropylene resin sample was 2.0g.

15. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, The equilibrium temperature is 50–80°C.

16. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, The equilibrium temperature is 60°C.

17. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, The equilibration time is 10–30 minutes.

18. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, The extraction time is 10–40 min.

19. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, The extraction time was 30 minutes.

20. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, The extraction temperature is 50–80°C.

21. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, The desorption time is 3 to 7 minutes.

22. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, The desorption time is 5 minutes.

23. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, The desorption temperature is 230–250°C.

24. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, Under the specified gas chromatography-mass spectrometry conditions, the carrier gas flow rate is 1.0 mL / min.

25. The method for detecting volatile substances in polypropylene using gas chromatography-mass spectrometry according to claim 1, characterized in that, The qualitative analysis of the polypropylene resin was performed using a computer mass spectrometry workstation, the NIST11 standard mass spectrometry library, the NIST11s standard mass spectrometry library, and matched fraction analysis.

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