A detection method for determining volatile substances in polypropylene

Abstract

The present invention discloses a detection method for determining volatile substances in polypropylene, comprising: (1) Preparation of a solid-phase microextraction fiber coating: i. Dissolve a mixture of MIL-101(Cr) adsorbent and binder in a solvent to form a suspension, and shake and ultrasonically treat the suspension; ii. Immerse the carrier in the suspension and then take it out from the suspension, leaving a layer of coating on the surface of the carrier, and then let the solvent volatilize; iii. Repeat step ii to form a solid-phase microextraction fiber coating on the carrier; Place the polypropylene resin sample in a headspace vial, seal and equilibrate, then insert the solid-phase microextraction fiber coating into the headspace of the headspace vial for extraction, and immediately insert it into the gas chromatography injection port for desorption after taking it out; (3) Use comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry to analyze and detect the extracted volatile substances; (4) Qualitatively and quantitatively analyze the measured volatile substances.

Description

Technical Field

[0001] The invention relates to the technical field of analytical chemistry, and in particular to a detection method for determining volatile substances in polypropylene. Background Art

[0002] Polypropylene (PP) resin has been widely used due to its good comprehensive performance, especially in the automotive and home appliance fields. A considerable part of the automotive interior plastic parts (such as dashboards, door panels) in relatively closed spaces and the home appliance plastic parts (such as washing machine inner drums, bases) used in family rooms are prepared by modifying PP resin. In the preparation process of PP modified materials, in order to achieve the required performance of the products, it is often necessary to add some mineral fillers, coupling agents, lubricants, stabilizers and other auxiliary materials. These materials may bring some obvious abnormal odors; in addition, the incomplete elimination of small molecules that are not fully polymerized during the synthesis process will also have some obvious odors. With the continuous improvement of people's quality of life, green, environmental protection, health and safety have become people's higher pursuit of household products. Therefore, determining the types and contents of volatile substances in PP resins can provide technical support for reducing the odor of PP resins. At present, the detection of volatile substances in polypropylene resin mainly relies on one-dimensional gas chromatography and gas chromatography-mass spectrometry technology for analysis. The pretreatment methods include purge and trap (dynamic headspace), static headspace, thermal analysis and solid phase microextraction (SPME), etc. Among them, SPME has gradually been widely used due to its advantages of no need for organic solvents, simplicity and convenience, fast testing, and integration of sampling, extraction, concentration and injection. However, due to the complexity of volatile substances in PP resin and the large number of interferences, the use of one-dimensional chromatography is subject to certain limitations; in addition, the commercial extraction heads commonly used in SPME have problems such as short service life, poor thermal and chemical stability, and easy breakage. Therefore, it is necessary to study more efficient, more economical, higher resolution, and more qualitatively reliable technologies for detecting volatile substances in PP.

[0003] "Study on the Release Behavior of Volatile Organic Compounds in Polypropylene" (Synthetic Resins and Plastics, Issue 1, 2010, Pages 60-63) disclosed: The types and relative contents of VOCs in polypropylene were studied by automatic purge and trap-gas chromatography-mass spectrometry, and more than 50 types of VOCs in polypropylene resins were found, including alkanes, alkenes and ketones. Although purge and trap can extract more volatile compounds, this pretreatment technology is prone to foaming, which overloads the instrument; in addition, the blowing of water vapor is not conducive to the next step of adsorption, and water also has a quenching effect on flame detectors. Due to problems such as insufficient separation, small peak capacity, and serious interference from impurities, the volatile substances measured by one-dimensional gas chromatography and gas chromatography-mass spectrometry technology are not comprehensive.

[0004] "Analysis and Research on Odor of Automotive Polypropylene Composites" (Engineering Plastics Application, Vol. 7, 2010, pp. 51-53) discloses that: The dynamic headspace-gas chromatography-mass spectrometry (HS-GC-MS) technique was used to analyze the odor of automotive polypropylene composites, and 19 volatile compounds such as alkanes, alkenes, ketones, aldehydes, and esters were detected. However, the extraction of volatile substances by this method is incomplete. Due to problems such as insufficient resolution, small peak capacity, and severe impurity interference in one-dimensional gas chromatography and GC-MS techniques, the determined volatile substances are not comprehensive and not quantified.

[0005] "Determination of Volatile Components in Polymer Materials by Headspace-GC-MS" (Shandong Chemical Industry, Vol. 11, 2013, pp. 78-80) discloses that: The headspace-gas chromatography-mass spectrometry (HS-GC-MS) technique was used to determine the volatile components in polypropylene-based composites and rubbers. Five volatile components such as n-butanol, 2-chloroethanol, 2-ethylhexanol, o-toluidine, and phenol were detected in the polypropylene-based composites, and the relative contents of the volatile components were obtained by quantitative analysis using the peak area normalization method. However, the extraction of volatile substances by this method is incomplete. Due to problems such as insufficient resolution, small peak capacity, and severe impurity interference in one-dimensional gas chromatography and GC-MS techniques, the determined volatile substances are not comprehensive. The normalization method can only be semi-quantitative, requiring all components used in the sample to elute completely and assuming that the response factors of all components are equal, but in reality, they are not equal, resulting in a large deviation in quantification.

[0006] "Thermal Desorption-Gas Chromatography-Mass Spectrometry Analysis of Volatile Organic Compounds in Polypropylene under Light Aging" (Chinese Journal of Analysis Laboratory, Vol. 11, 2014, pp. 1338-1341) discloses that: Tenax adsorption tubes were used to collect the volatile organic compounds generated during the light aging process of a certain polypropylene material, and the types of VOCs were analyzed by thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) technique. A total of 29 VOCs such as alkanes, alkenes, ketones, and aldehydes were qualitatively identified. However, the extraction of volatile substances by this method is incomplete. Due to problems such as insufficient resolution, small peak capacity, and severe impurity interference in one-dimensional gas chromatography and GC-MS techniques, the determined volatile substances are not comprehensive and not quantified.

[0007] "Analysis of Volatile Gases Generated by Polypropylene by Solid Phase Microextraction - Chromatography - Mass Spectrometry" (Plastics, Vol. 1, 2010, pp. 129 - 131) discloses that: 5 g of polypropylene pellets are placed in a 20 - mL special sampling bottle for solid - phase microextraction. An 80 - μm PDMS extraction head is used. After extraction at 80 °C for 20 min, it is desorbed at the gas chromatography injection port at 250 °C for 5 min, and finally gas chromatography - mass spectrometry determination is carried out. This method qualitatively studies the volatile gases generated by polypropylene after extrusion through a twin - screw extruder, and a total of 28 volatile components including alkanes, aldehyde - ketone - acid esters, alcohol - ethers, and olefins are identified; and the relative content of each component in the volatile compounds is determined by the peak area normalization method. However, the extraction of volatile substances by this method is incomplete. Due to problems such as insufficient resolution, small peak capacity, and serious impurity interference in one - dimensional gas chromatography and gas chromatography - mass spectrometry techniques, the volatile substances determined are not comprehensive enough. The normalization method can only be semi - quantitative, requiring that all components used in the sample must peak, and defaulting that the response factors of all components are equal, but in fact they are not equal, so there is a large deviation in quantification.

[0008] "Preparation of a New Solid - Phase Microextraction Coating Material and Its Application in the Detection and Analysis of Volatile Components in Rosemary" (Journal of Instrumental Analysis, Vol. 10, 2017, pp. 1185 - 1190) discloses that: A new solid - phase microextraction coating containing fully substituted hydroxy - pentacyclic cucurbituril is prepared by the sol - gel technique for extracting volatile components in rosemary. However, the extraction of volatile substances by this method is incomplete, and at the same time, the volatile components determined are not accurately quantified.

[0009] "Preparation of a Multi - Layered Porous Activated Carbon Membrane Coated Solid - Phase Microextraction Head and Detection of VOCs Gases" (Journal of Wuyi University, Vol. 6, 2018, pp. 44 - 47) discloses that: Using a stainless - steel wire as a carrier, a PAN porous membrane is coated on the surface of the stainless - steel wire by the steam - assisted method, and then a multi - layered porous activated carbon membrane coated solid - phase microextraction head is obtained through soaking in acetic acid and potassium permanganate, pre - oxidation, low - temperature carbonization, and high - temperature carbonization. The detection limit of benzene for this extraction head is 4.432×10 -3 g / L. This method uses a benzene standard mixed gas and does not measure other types of volatile compounds. Summary of the Invention

[0010] The object of the present invention is to provide a detection method for volatile substances in polypropylene to solve the problems in the prior art that commercial solid - phase microextraction heads have poor stability, short service life, high price, and one - dimensional chromatography has certain limitations in comprehensively and accurately detecting the composition and content of volatile substances in polypropylene resin.

[0011] To achieve the above object, the present invention provides a detection method for volatile substances in polypropylene, including the following steps:

[0012] (1) Preparation of solid-phase microextraction fiber coating

[0013] i. Preparation of suspension: Dissolve the mixture of MIL-101(Cr) adsorbent and binder in a solvent to form a suspension, and shake and ultrasonically treat the suspension.

[0014] ii. Immerse the carrier in the suspension and then take it out, leaving a layer of coating on the surface of the carrier, and then let the solvent evaporate.

[0015] iii. Repeat step ii to form a solid-phase microextraction fiber coating on the carrier.

[0016] (2) Extraction of volatile substances from the sample

[0017] Place the polypropylene resin sample in a headspace vial, seal and equilibrate, then insert the solid-phase microextraction fiber coating into the headspace of the headspace vial for extraction, and immediately insert it into the gas chromatography injection port for desorption after taking it out.

[0018] (3) Use comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry to analyze and detect the extracted volatile substances;

[0019] (4) Qualitative and quantitative analysis of the measured volatile substances.

[0020] For the detection method of measuring volatile substances in polypropylene according to the present invention, in step i, the binder is polysulfone, and the weight ratio of MIL-101(Cr) to polysulfone is 9:1 to 5:5; the solvent is one or more of dichloromethane, N,N-dimethylformamide, and tetrahydrofuran.

[0021] For the detection method of measuring volatile substances in polypropylene according to the present invention, in step i, the shaking time of the suspension is 3 to 7 min; the ultrasonic time is 10 to 30 min.

[0022] For the detection method of measuring volatile substances in polypropylene according to the present invention, in step ii, the carrier is a fiber filament or a metal wire.

[0023] For the detection method of measuring volatile substances in polypropylene according to the present invention, repeat step ii until the coating thickness is about 25 to 60 μm.

[0024] For the detection method of measuring volatile substances in polypropylene according to the present invention, the weighing amount of the polypropylene resin sample is 1.5 to 3.5 g.

[0025] For the detection method of measuring volatile substances in polypropylene according to the present invention, in step (2), the equilibration temperature is 40 to 100 °C; the equilibration time is 10 to 30 min.

[0026] The detection method for determining volatile substances in polypropylene according to the present invention, wherein in the step (2), the extraction time is 10 to 40 min; the desorption time is 1 to 8 min, and the desorption temperature is 230 to 250 °C.

[0027] The detection method for determining volatile substances in polypropylene according to the present invention, wherein in the step (3), the analysis conditions of the comprehensive two-dimensional gas chromatograph are as follows:

[0028] The chromatographic column adopts a GC×GC column system. The first-dimensional column is DB-WAX (30 m × 0.25 mm × 0.25 μm); the second-dimensional column is DB-17MS (1.195 m × 0.25 mm × 0.15 μm);

[0029] The carrier gas is high-purity helium, and the flow rate is 0.9 to 1.1 mL / min;

[0030] The inlet temperature is 230 to 250 °C, and splitless injection is used;

[0031] The temperature programming of the column oven is as follows: the initial temperature is 40 to 45 °C, held for 8 to 12 min, and then raised to 230 to 250 °C at a rate of 1 to 3 °C per minute;

[0032] The modulation period is 4 to 12 s. Preferably, the modulation period is 6 s.

[0033] The detection method for determining volatile substances in polypropylene according to the present invention, wherein in the step (3), the analysis conditions of the time-of-flight mass spectrometry are as follows: the ion source is EI, 70 eV; the ion source temperature is 200 to 220 °C; the transfer line temperature is 230 to 250 °C; the full scan mode is adopted, the mass scan range is 40 to 500 amu; the scan rate is 100 to 120 spectra / s, and the detector voltage is 1500 to 1750 V.

[0034] The detection method for determining volatile substances in polypropylene according to the present invention, wherein in the step (4), external standard method is used for quantitative analysis of various volatile substances: a series of standard solutions are prepared, a standard curve of concentration and peak area is established, and the content of each volatile substance is calculated.

[0035] The detection method for determining volatile substances in polypropylene according to the present invention, wherein in the step (4), the Canvas comprehensive two-dimensional chromatographic data processing software is adopted, and the mass spectrometry data is automatically subjected to peak detection and merging by the Canvas data processing software; the detection threshold is set as all peaks with a signal-to-noise ratio greater than 3, and the mass spectrometry library is NIST 14; component peaks with both forward and reverse matching degrees greater than 700 and a peak area percentage content greater than or equal to 0.02% are selected to establish a compound peak list.

[0036] Advantages of the present invention:

[0037] MIL-101(Cr) has a large specific surface area and high pore volume, and good thermal stability, and its structure does not change in air. Using it as a novel coating for solid-phase microextraction (SPME) can effectively extract volatile compounds. The present invention uses a solid-phase microextraction fiber coating based on the metal-organic framework material MIL-101(Cr) for sample pretreatment, which has a long service life and can be reused 140 times.

[0038] The comprehensive two-dimensional gas chromatography-time of flight mass spectrometry (GC×GC-TOF MS) technology adopted by the present invention is suitable for the separation and analysis of multi-components, with accurate and reliable results, high sensitivity, and can detect more than 100 volatile substances in PP resin at one time, exceeding the volatile substances detected by other analytical methods in PP resin. Traditional one-dimensional gas chromatography can only use one chromatographic column, which is either polar or non-polar, while comprehensive two-dimensional gas chromatography uses a GC×GC dual-column system. When the components to be detected in the sample pass through the one-dimensional polar chromatographic column, they are first separated according to the molecular polarity, and then passed through the two-dimensional non-polar chromatographic column to be separated according to the molecular size. Similarly, the components to be detected can also be first separated according to the molecular size and then according to the molecular polarity, so as to realize the orthogonal separation of the components to be detected. The high acquisition frequency of time of flight mass spectrometry can enhance the detection of the effluent signal of comprehensive two-dimensional gas chromatography, and has an absolute advantage for analyzing volatile substances in PP resin. Therefore, the technology developed by the present invention can provide scientific support for tracing the odor source in polypropylene resin and studying measures to improve the odor. Brief Description of the Drawings

[0039] Figure 1 : Comprehensive two-dimensional gas chromatography-time of flight mass spectrometry contour map of analyzing volatile substances in PP resin sample 1 provided in Example 2.

[0040] Figure 2 : Comprehensive two-dimensional gas chromatography 3D view of analyzing volatile substances in PP resin sample 1 provided in Example 2.

[0041] Figure 3 : Comprehensive two-dimensional gas chromatography-time of flight mass spectrometry contour map of analyzing volatile substances in PP resin sample 2 provided in Example 3.

[0042] Figure 4 : Comprehensive two-dimensional gas chromatography 3D view of analyzing volatile substances in PP resin sample 2 provided in Example 3. Detailed Description of the Invention

[0043] The present invention will be specifically described below through examples. It is necessary to point out here that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the protection scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention according to the above content of the present invention.

[0044] Example 1

[0045] Preparation and optimization of solid-phase microextraction fiber coating:

[0046] Polysulfone makes the MIL-101(Cr) solution adhesive, enabling MIL-101(Cr) to adhere better to the carrier. However, excessive polysulfone will affect the extraction effect. Therefore, the ratio of MIL-101(Cr) to polysulfone was investigated.

[0047] Mixtures with weight ratios of MIL-101(Cr) powder to polysulfone of 9:1, 7:3, and 5:5 were dissolved in dichloromethane to form suspensions. The above suspensions were shaken vigorously for 7 min and ultrasonically vibrated for 30 min. Then, a carrier with a diameter of 130 μm and a length of 2 cm was immersed in the suspension and slowly taken out. A thin coating was formed on the surface of the carrier. Subsequently, the carrier was placed in an oven and dried at 40 °C for 30 min to volatilize dichloromethane. 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 in the GC injection port for 40 min.

[0048] A standard sample of 1 mg / kg undecane was used for testing, and the extraction efficiency of different prepared fiber coatings was evaluated by the extraction amount at 60 °C for 20 min. As can be seen from Table 1, when the content of MIL-101(Cr) on the carrier is 90%, 70%, and 50% respectively, the extraction ability gradually decreases, that is, the extraction efficiency increases with the increase in the proportion of MIL-101(Cr). On the other hand, it was found during the preparation process that a high proportion of MIL-101(Cr) and a low content of polysulfone would lead to a decrease in adhesion, increase the difficulty of coating preparation, and thus result in poor coating stability.

[0049] Weight ratio Extraction amount / (mg / kg) 9:1 0.983 7:3 0.844 5:5 0.601

[0050] Example 2

[0051] Detection of volatile substances in PP resin sample 1:

[0052] Preparation of solid-phase microextraction coating: A mixture of MIL-101(Cr) powder and polysulfone with a weight ratio of 8:2 was dissolved in dichloromethane to form a suspension. The above suspension was shaken vigorously for 5 min and ultrasonically vibrated for 20 min. Then, a carrier with a diameter of 130 μm and a length of 2 cm was immersed in the suspension and slowly taken out from the suspension to form a thin coating on the surface of the carrier. Subsequently, the carrier was placed in an oven and dried at 40 °C for 30 min to volatilize dichloromethane. The above coating process was repeated several times until the coating thickness was about 50 μm. Finally, the prepared fiber coating was aged at 250 °C in the GC injection port for 40 min.

[0053] Solid-phase microextraction for extracting volatile substances: Weighed 2.0 g of the sample and placed it in a 15 mL screw-top headspace vial, and equilibrated it on a magnetic heating stirrer at 60 °C for 20 min. Then, the prepared solid-phase microextraction fiber coating was inserted into the headspace vial, and the extraction head was placed 1.0 cm above the sample for extraction and adsorption for 30 min. Immediately after extraction, the extraction head was inserted into the injection port of the gas chromatograph and desorbed at 250 °C for 5 min. Finally, it entered the comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry system for separation and detection.

[0054] Comprehensive two-dimensional gas chromatography conditions: Column 1 was DB-WAX (30 m × 0.25 mm × 0.25 μm); Column 2 was DB-17MS (1.195 m × 0.25 mm × 0.15 μm). The carrier gas was high-purity helium with a flow rate of 1 mL / min; the injection port temperature was 250 °C, and splitless injection was used; the temperature programming of the column oven was: the initial temperature was 40 °C, held for 10 min, and increased to 230 °C at a rate of 3 °C per minute for a total of 74.33 min; the modulation period was 6 s.

[0055] Mass spectrometry conditions: The ion source was EI, 70 eV; the ion source temperature was 220 °C; the transfer line temperature was 230 °C; the full scan mode was used, and the mass scan range was 40 - 500 amu; the scan rate was 100 spectra / s. The detector voltage was 1750 V.

[0056] Qualitative analysis: The above detection data were analyzed using Canvas comprehensive two-dimensional chromatography data processing software. Compounds with a detection threshold greater than the signal-to-noise ratio of 3 were selected for retrieval. The mass spectrometry data were automatically subjected to peak detection and merging by the Canvas data processing software and matched with the NIST 14 mass spectrometry library; component peaks with both forward and reverse matching degrees greater than 700 and a peak area percentage greater than or equal to 0.02% were selected to establish a compound peak list. The comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry profile of the volatile substances in PP resin sample 1 is shown as Figure 1 shown; the comprehensive two-dimensional gas chromatography 3D view of the volatile substances in PP resin sample 1 is shown as Figure 2 shown.

[0057] Quantitative analysis: External standard method was used for quantitative analysis. Four standard samples of undecane, ethyl octanoate, octanal, and linalool were selected as external standards, and a series of standard solutions were prepared respectively. The standard solutions at different concentration levels were tested under the optimal test conditions, and each level was injected three times repeatedly. The measurement results were represented by the average value of the three tests, and the standard curve of concentration (X) and peak area (Y, ×10 7 ) was established. According to the standard curve, the content of each volatile substance was calculated. The information and content of volatile substances in PP resin sample 1 are shown in Table 1.

[0058] Table 1 Volatile substances in PP resin sample 1

[0059]

[0060]

[0061]

[0062] In this example, a total of 114 volatile substances in PP resin sample 1 were identified by solid-phase microextraction-comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry. The quantity and variety are more than those reported in other literatures, indicating that the analysis and detection method has significant advantages. As known from Table 1 above, the detection results of PP resin sample 1 were screened by mass spectrometry information and standard spectral library matching, and the compounds with higher matching degrees were selected as target compounds (both positive and negative matching degrees are greater than 700), mainly including alkanes, esters, alcohols, aldehydes, ethers, ketones, benzene rings and other substances. Alkanes are the main volatile compounds in resin sample 1, and a total of 51 kinds were measured. In addition to alkane compounds, relatively more kinds of esters, alcohols, and aldehydes were detected, with 10 kinds, 8 kinds, and 10 kinds measured respectively; relatively fewer kinds of ethers, ketones, benzene rings, acids, and olefins were detected. And as can be seen from Table 1, the alkane content in PP resin sample is the highest, which is 420.86 mg / kg, accounting for 88.07% of the total compound content; in addition to alkane compounds, the contents of alcohols, aldehydes, and ethers are the next, which are 10.10 mg / kg, 8.37 mg / kg, and 8.42 mg / kg respectively, accounting for 2.11%, 1.75%, and 1.76% of the total compound amount respectively. The content of aromatic hydrocarbons and aromatic compounds is the smallest, which is 1.229 mg / kg, only accounting for 0.20% of the total compound amount.

[0063] Example 3

[0064] Detection of volatile substances in PP resin sample 2:

[0065] Preparation of solid-phase microextraction coating: A mixture of MIL-101(Cr) powder and polysulfone with a weight ratio of 6:4 was dissolved in dichloromethane to form a suspension. The above suspension was shaken vigorously for 3 min and ultrasonically vibrated for 10 min. Then a carrier with a diameter of 130 μm and a length of 2 cm was immersed in the suspension and slowly taken out from the suspension to form a thin coating on the surface of the carrier. Subsequently, the carrier was placed in an oven and dried at 40 °C for 30 min to volatilize dichloromethane. The above coating process was repeated several times until the coating thickness was about 30 μm. Finally, the prepared fiber coating was aged at 250 °C in the GC injection port for 40 min.

[0066] Solid-phase microextraction for extracting volatile substances: Weigh 1.5 g of the sample and place it in a 15 mL screw-top headspace vial, and equilibrate it on a magnetic heating stirrer at 60 °C for 30 min. Then insert the prepared solid-phase microextraction fiber coating into the headspace vial, and keep the extraction head 1.0 cm above the sample for extraction and adsorption for 40 min. Immediately after extraction, insert the extraction head into the injection port of the gas chromatograph and desorb it at 250 °C for 4 min. Finally, it enters the comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry system for separation and detection.

[0067] Comprehensive two-dimensional gas chromatography conditions: Column 1 is DB-WAX (30 m × 0.25 mm × 0.25 μm); Column 2 is DB-17MS (1.195 m × 0.25 mm × 0.15 μm). The carrier gas is high-purity helium with a flow rate of 1 mL / min; the injection port temperature is 240 °C, and splitless injection is used; the temperature programming of the column oven is: initial temperature 45 °C, hold for 8 min, increase to 250 °C at a rate of 3 °C per minute, for a total of 76.33 min; the modulation period is 6 s.

[0068] Mass spectrometry conditions: The ion source is EI, 70 eV; the ion source temperature is 220 °C; the transfer line temperature is 230 °C; the full scan mode is adopted, the mass scan range is 40 - 500 amu; the scan rate is 100 spectra / s. The detector voltage is 1750 V.

[0069] Qualitative analysis: The above detection data was analyzed using Canvas comprehensive two-dimensional chromatography data processing software. Compounds with a detection threshold greater than the signal-to-noise ratio of 3 were selected for retrieval. The mass spectrometry data was automatically subjected to peak detection and merging by the Canvas data processing software, and was matched with the NIST 14 mass spectrometry library; components with a forward and reverse matching degree greater than 700 and a peak area percentage greater than or equal to 0.02% were selected to establish a compound peak list. The comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry profile of volatile substances in PP resin sample 2 is shown as Figure 3 shown; the comprehensive two-dimensional gas chromatography 3D view of the comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry of volatile substances in PP resin sample 2 is shown as Figure 4 shown.

[0070] Quantitative analysis: External standard method was used for quantitative analysis. Four standard samples, undecane, ethyl octanoate, octanal, and linalool, were selected as external standards, and a series of standard solutions were prepared respectively. The standard solutions at different concentration levels were tested under the optimal test conditions, and each level was injected three times repetitively. The measurement results were represented by the average value of the three tests, and the standard curve of concentration (X) and peak area (Y, ×10 7 ) was established. According to the standard curve, the content of each volatile substance was calculated. The information and content of volatile substances in PP resin sample 2 are shown in Table 2.

[0071] Table 2 Volatile substances in PP resin sample 2

[0072]

[0073]

[0074]

[0075]

[0076] In this example, a total of 109 volatile substances in PP resin sample 2 were identified by solid-phase microextraction-comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry. The quantity and variety are both more than those reported in other literatures, indicating that the analysis and detection method has significant advantages. As known from Table 2 above, the detection results of PP resin sample 2 were matched with the mass spectrometry information and the standard spectral library, and the compounds with higher matching degrees were selected as target compounds (both positive and negative matching degrees are greater than 700), mainly including alkanes, esters, alcohols, aldehydes, ethers, ketones, benzene rings and other substances. Among them, 58 alkanes were measured in total; except for alkane compounds, relatively more types of alcohol, aldehyde, and ketone compounds were detected, with 8, 10, and 10 types detected respectively, while relatively fewer types of ether, benzene ring, acid, and olefin compounds were detected. Among them, the ether and olefin compounds were the least, with only 2 types detected. And it can be seen from Table 2 that the alkane content in PP resin sample is the highest, which is 422.75 mg / kg, accounting for 87.68% of the total amount of compounds. Except for alkane compounds, the contents of alcohol, aldehyde, and acid compounds are the next, which are 17.12 mg / kg, 11.67 mg / kg, and 15.33 mg / kg respectively, accounting for 3.39%, 2.31%, and 3.04% of the total amount of compounds respectively. The contents of the remaining several compounds are less, all less than 5.0 mg / kg, and the content of olefin compounds is the smallest, only 2.49 mg / kg, accounting for 0.49% of the total amount of compounds.

[0077] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention. However, these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A detection method for determining volatile substances in polypropylene, characterized in that, It includes the following steps: (1) Preparation of the solid-phase microextraction fiber coating i. Preparation of the suspension: Dissolve the mixture of MIL-101-Cr adsorbent and binder in a solvent to form a suspension, and shake and ultrasonically treat the suspension; ii. Immerse the carrier in the suspension and then take it out of the suspension, leaving a layer of coating on the surface of the carrier, and then let the solvent volatilize; iii. Repeat step ii to form a solid-phase microextraction fiber coating on the carrier; (2) Extraction of volatile substances from the sample Place the polypropylene resin sample in a headspace vial, seal and equilibrate it, and then insert the solid-phase microextraction fiber coating into the headspace of the headspace vial for extraction. Immediately after taking it out, insert it into the gas chromatography injection port for desorption; (3) Analyze and detect the extracted volatile substances using comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry; (4) Qualitatively and quantitatively analyze the measured volatile substances; The binder is polysulfone, and the weight ratio of MIL-101-Cr to polysulfone is 9:1 to 5:5; the solvent is one or more of dichloromethane, N,N-dimethylformamide, and tetrahydrofuran; In step (3), the analysis conditions of the comprehensive two-dimensional gas chromatograph are as follows: The chromatographic column uses a GC×GC column system. The first-dimensional column is DB-WAX, 30m×0.25mm×0.25μm; the second-dimensional column is DB-17MS, 1.195m×0.25mm×0.15μm; The carrier gas is high-purity helium, and the flow rate is 0.9~1.1mL / min; The injection port temperature is 230~250°C, and splitless injection is used; The temperature programming of the column oven is as follows: the initial temperature is 40~45°C, hold for 8~12min, and rise to 230~250°C at a rate of 1~3°C per minute; The modulation period is 4~12s; In step (3), the analysis conditions of the time-of-flight mass spectrometry are as follows: the ion source is EI, 70eV; the ion source temperature is 200~220°C; the transfer line temperature is 230~250°C; the full scan mode is adopted, the mass scan range is 40~500 amu; the scan rate is 100~120 spectra / s, and the detector voltage is 1500~1750V.

2. The detection method for determining volatile substances in polypropylene according to claim 1, wherein, In step i, the shaking time of the suspension is 3~7min; the ultrasonic time is 10~30min.

3. The detection method for measuring volatile substances in polypropylene according to claim 1, characterized in that, In step ii, the carrier is a fiber filament or a metal wire.

4. The detection method for determining volatile substances in polypropylene according to claim 1, characterized in that Repeat step ii until the coating thickness is 25~60μm.

5. The detection method for measuring volatile substances in polypropylene according to claim 1, characterized in that, The weighing amount of the polypropylene resin sample is 1.5~3.5g.

6. The detection method for determining volatile substances in polypropylene according to claim 1, wherein In step (2), the equilibration temperature is 40~100°C; the equilibration time is 10~30min.

7. The detection method for determining volatile substances in polypropylene according to claim 1, characterized in that, In step (2), the extraction time is 10~40min; the desorption time is 1~8min, and the desorption temperature is 230~250°C.

8. The detection method for determining volatile substances in polypropylene according to claim 1, characterized in that, In step (3), the modulation period is 6s.

9. The detection method for determining volatile substances in polypropylene according to claim 1, characterized in that, In step (4), various volatile substances are quantitatively analyzed by 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.

10. The detection method for determining volatile substances in polypropylene according to claim 1, wherein In step (4), the Canvas two-dimensional chromatographic data processing software is used. The mass spectrometry data is automatically subjected to peak detection and merging by the Canvas data processing software. The detection threshold is set for all peaks with a signal-to-noise ratio greater than 3, and the mass spectrometry library is NIST 14. Component peaks with both forward and reverse matching degrees greater than 700 and peak area percentage contents greater than or equal to 0.02% are selected to establish a compound peak list.

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