Method for pre-judging high polymer material interference fire scene gasoline inspection and identification degree

Abstract

The invention relates to a method for comprehensively pre-judging and evaluating the interference degree of a high polymer material on fire scene gasoline inspection and identification, mainly relates to a method for pre-judging and evaluating the interference of the high polymer material on fire scene gasoline inspection and identification based on a chemical structure and a pyrolysis mechanism, and belongs to the field of fire scene residue material evidence technical identification. The method comprises the following steps: 1, analyzing chemical structure characteristics, and determining whether the chemical structure characteristics comprise a-C = C-structure; 2, analyzing the element composition of the double-bond-containing high polymer material, and determining whether the material contains heteroatoms or not; 3, analyzing the pyrolysis mechanism of the high polymer material, and analyzing whether a large number of-C = C-double bond structures can be generated in the pyrolysis process; 4, preparing free combustion residues of the high polymer material, and analyzing the residue components of the free combustion residues through GC-MS (Gas Chromatography-Mass Spectrometer); 5, preparing the mixed combustion residues of the macromolecules and the gasoline, and analyzing the components of the residues through GC-MS (Gas Chromatography-Mass Spectrometer); step 6, analyzing thermal behaviors and pyrolysis products of the material through TG-IR-GC / MS, wherein the thermal behaviors and the pyrolysis products mainly comprise pyrolysis process stages, pyrolysis products corresponding to each stage and weight loss; and step 7, analyzing the interference of each pyrolysis stage from two aspects of qualitative analysis (types of pyrolysis products) and quantitative analysis (contents of the pyrolysis products).

Description

Technical Field

[0001] The invention relates to a method for predicting the interference degree of polymer materials on the inspection and identification of gasoline at a fire scene, in particular to predicting the interference degree of polymer materials on the inspection and identification of gasoline at a fire scene based on chemical structure and pyrolysis mechanism, and belongs to the technical field of physical evidence identification technology. Background Art

[0002] The inspection and identification of accelerants plays a vital role in determining the nature of fires. The analysis of combustion residues relies on laboratory instruments, especially gas chromatography-mass spectrometry (GC-MS). This method intuitively compares the chromatogram profiles of the extracted sample and the accelerant standard, matches the mass spectrometry results to detect the target compound, and determines whether there is an accelerant and the type of accelerant in the sample. However, the fire scene is complicated, which can easily interfere with the inspection and identification of accelerant evidence. During the occurrence and development of the fire, the high temperature and thermal environment of the fire scene will act on the combustion residues of the accelerants that have been formed, causing the characteristic components of the accelerants to volatilize and pyrolyze to varying degrees, thereby affecting their detection; at the same time, a large number of petrochemical products at the fire scene have similar or even identical characteristic components in their combustion / pyrolysis products to common accelerants, which greatly interferes with the judgment of whether there is an accelerant at the scene. Even wrong "false positive" and "false negative" identification results are obtained, thus affecting the fairness of justice. In the United States, there have been cases of unjust, false and wrong cases caused by "false positive" residue inspection and identification analysis. Therefore, it is necessary to propose a method based on chemical structure and pyrolysis mechanism to predict the interference of polymer materials on the inspection and identification of gasoline at fire scenes. This method can predict whether the results are likely to be false before instrumental analysis of the extracted combustion residues, and remind inspectors to eliminate the influence of polymer material matrix interference during the identification process.

[0003] At present, the research on the interference of polymer matrix in the identification of gasoline in the fire scene mostly selects the research object based on the principle of "common in the fire scene" rather than the specific chemical structure or typical functional group. Based on this, the previous research can be classified as a scattered "trial and error" research. Although some research has been carried out on common polymer materials in the fire scene, there is no in-depth research on the essential source of interference, the chemical composition, molecular structure, pyrolysis mechanism of the interferents, and how the mixed combustion factors with gasoline affect the interference. There are even large differences in the judgment conclusions of different studies on the interference degree of the same polymer material, or even completely opposite situations. More importantly, there is no scientific method to predict the interference of polymer materials. Therefore, it is necessary to propose a method that can predict the interference of polymer materials and analyze and compare the interference degree. The chemical structure and pyrolysis process of polymer materials in the fire scene are discussed to infer the interference degree of gasoline identification when they are in the thermal environment of different pyrolysis stages. Summary of the invention

[0004] The present invention proposes a method for predicting the interference of polymer materials on the inspection and identification of gasoline at a fire scene based on chemical structure and pyrolysis mechanism.

[0005] A method for predicting the interference of polymer materials on the inspection and identification of gasoline at a fire scene based on chemical structure and pyrolysis mechanism, characterized in that it comprises the following steps:

[0006] Step 1: Analyze the chemical structure characteristics to determine whether it contains a -C=C- structure;

[0007] Step 2: Analyze the elemental composition of the polymer material containing double bonds to determine whether it contains heteroatoms;

[0008] Step 3: Analyze the pyrolysis mechanism of polymer materials and analyze whether the pyrolysis process can generate a large number of -C=C- double bond structures;

[0009] Step 4: preparing a free combustion residue of the polymer material, and analyzing the residue components by GC-MS;

[0010] Step 5: preparing a mixed combustion residue of the polymer and gasoline, and analyzing the components of the residue by GC-MS;

[0011] Step 6: Analyze the thermal behavior and pyrolysis products of the material by TG-IR-GC / MS, mainly including the pyrolysis process stages, the pyrolysis products corresponding to each stage, and the weight loss;

[0012] Step 7: Analyze the interference of each pyrolysis stage from both qualitative (type of pyrolysis products) and quantitative (content of pyrolysis products) aspects.

[0013] Furthermore, in the step one, it is further determined whether C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene and indane, methylindane and other components can be detected in the combustion residue of the polymer material.

[0014] Furthermore, in the step 2, it is further determined whether the polymer material containing heteroatoms has false negative interference.

[0015] Furthermore, in the step three, it is determined whether C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene and indane, methylindane and other components can be detected in the combustion residue, then the interference of false positives and false negatives will still be strong.

[0016] Furthermore, the polymer material having false negative interference is a heteroatom rubber represented by chloroprene rubber.

[0017] Further, in the step 4, according to the national standard GB18264 and ASTM1618, C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene and indane, methylindane and other components are detected, and the three peaks of the relative peak area C2 meet the "trident" profile characteristics, that is, according to the retention From small to large time, the relative peak area of ​​the second peak is the largest, the relative peak area of ​​the third peak is slightly larger than or close to the first peak, and the relative peak area ratios of the three peaks are approximately 1:1.5~2:1~1.5, respectively. C3 meets the "castle-shaped" distribution of the six characteristic peaks, and the relative peak area ratios are approximately 1:5~6:1~2:1~2:10~12:3~4, respectively, which is basically the same as the situation of gasoline. It is believed that its false positive interference is very strong both from a qualitative and quantitative perspective.

[0018] Furthermore, in the step five, according to the national standards GB18264 and ASTM1618, C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene and indane, methylindane and other components are detected, but the relative peak areas C2, C3 and C4 are greatly different from those of gasoline combustion residues, then it is considered that the false negative interference is significant.

[0019] Furthermore, the instruments used in steps 4 and 5 include: METTLER TOLEDO TGA2 thermogravimetric analyzer, BRUKER TENSOR II infrared spectrometer, Agilent 7890B-5977B gas chromatograph-mass spectrometer, Fourier transform infrared spectrometer, and HP-5MS chromatographic column.

[0020] Further, the analysis conditions of the instrumental analysis method used in step 6 are: TG-IR-GC / MS analysis conditions: TG analysis conditions: air atmosphere, heating rate 20°C / min, analysis temperature range 60-800°C. IR analysis conditions: wave number range 4000-400cm-1, scan number 32, scan mode continuous scan. GC-MS analysis conditions: injection port temperature: 260°C, injection volume 1μL. Helium was used as carrier gas, with a flow rate of 1 mL / min and a split ratio of 5:1. The temperature program was as follows: the initial temperature was 50°C (maintained for 2 minutes), rising to 150°C at a rate of 10°C / min (maintained for 2 minutes), further rising to 186°C at 6°C / min (maintained for 3 minutes), and finally rising to 260°C at 4°C / min (maintained for 20 minutes). The ion source temperature was set at 230°C, the GC-MS interface temperature was 280°C, and the quadrupole temperature was 150°C. The electron impact ion source (EI) was used, and the electron energy was 70 eV. The scanning mode was full scan, with a mass range of 50 to 500 aum. The FTIR analysis conditions were as follows: the wave number range was 1200 to 600 cm-1, the number of scans was 64, and the scanning mode was continuous scan.

[0021] The present invention proposes a method for predicting the interference of polymer materials with fire scene gasoline inspection and identification based on chemical structure and pyrolysis mechanism, which has the following beneficial effects:

[0022] Based on the chemical structure and pyrolysis mechanism of polymer materials in the fire scene background, the present invention proposes a method that can predict the matrix interference and its interference degree before using instruments to analyze the combustion residues. Then, the interference of the fire scene matrix on gasoline inspection and identification can be eliminated while effectively predicting and analyzing the interference of the polymer material matrix. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the analysis and inference of the chemical structure and pyrolysis mechanism of butadiene rubber;

[0024] Figure 2 It is the detection of characteristic components in the combustion residue of butadiene rubber;

[0025] Figure 3 The thermogravimetric analysis results of butadiene rubber include thermogravimetric curve and differential thermogravimetric curve;

[0026] Figure 4 It is the analytical inference of the chemical structure and pyrolysis mechanism of chloroprene rubber;

[0027] Figure 5 It is the detection of characteristic components in the combustion residue of chloroprene rubber;

[0028] Figure 6 It is the analysis and inference of the chemical structure and pyrolysis mechanism of styrene-butadiene rubber;

[0029] Figure 7 The chromatograms of gasoline combustion residues and the detection of characteristic components include total ion current chromatogram (a), extracted ion current chromatogram of alkylbenzenes (b), extracted ion current chromatogram of polycyclic aromatic hydrocarbons (c), and extracted ion current chromatogram of indanes (d);

[0030] Figure 8 The total ion current chromatogram of the pyrolysis products of styrene-butadiene rubber at each stage with different styrene contents;

[0031] Fig. 9 The extracted ion chromatograms of alkylbenzenes of pyrolysis products of styrene-butadiene rubber at different stages with different styrene contents;

[0032] Fig.10 The extracted ion chromatograms of polycyclic aromatic hydrocarbons of pyrolysis products of styrene-butadiene rubber at different stages with different styrene contents;

[0033] Fig.11 The indan-type extracted ion chromatograms of the pyrolysis products of styrene-butadiene rubber at different stages with different styrene contents;

[0034] Fig.12 The thermogravimetric analysis results of styrene-butadiene rubber with different styrene contents, where Figure (a) is the thermogravimetric curve and Figure (b) is the differential thermogravimetric curve;

[0035] Fig.13 The three-dimensional infrared spectra of styrene-butadiene rubber with different styrene contents during pyrolysis;

[0036] Fig.14 is the Fourier transform infrared spectra of styrene-butadiene rubber with different styrene contents;

[0037] Fig.15 It is the analysis and inference of the chemical structure and pyrolysis mechanism of polyvinyl chloride (PVC) plastics;

[0038] Fig.16 It is the detection of characteristic components in the combustion residue of polyvinyl chloride (PVC);

[0039] Fig.17 The thermogravimetric analysis results of polyvinyl chloride (PVC), including thermogravimetric curve and differential thermogravimetric curve. DETAILED DESCRIPTION

[0040] The following is combined with Figure 1-17 The present invention is further described in detail with specific implementations to facilitate a clear understanding of the present invention, but they do not constitute a limitation on the present invention.

[0041] The present invention relates to a method for comprehensively predicting and evaluating the degree of interference of polymer materials in gasoline inspection and identification at a fire scene, which is mainly based on the method of predicting and evaluating the interference of polymer materials in gasoline inspection and identification at a fire scene based on chemical structure and pyrolysis mechanism, and belongs to the field of technical identification of physical evidence of fire scene residues.

[0042] The method comprises the following steps: (1) analyzing whether the molecular structure of the material contains a double bond structure. The double bond structure is easy to form a ring during the pyrolysis / combustion process, and its interference with gasoline inspection and identification is significantly greater than that of other polymer materials without a double bond structure. C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene and indane, methylindane and other components can be basically detected in the combustion residue. These components are all stable characteristic components that are essential for determining the presence of gasoline. Therefore, qualitatively speaking, this situation has a more significant impact on gasoline inspection and identification.

[0043] (2) Analyze the elemental composition of the polymer material containing double bonds to determine whether it contains heteroatoms. If it contains heteroatoms, its combustion residue generally contains heteroatoms, which makes it easier to identify the presence of the polymer material. Therefore, the false positive interference caused by it in gasoline inspection and identification is relatively small, but it can still cause certain false negative interference. Taking heteroatom rubber as an example, in addition to the target compounds that interfere with gasoline identification, the thermal decomposition products of chloroprene rubber can also detect octadecane chloride, benzyl chloride, chloroxylene, ethylbenzyl chloride and chloronaphthalene. Heteroatom substitutes such as heptadecanitrile, benzylamine, m-methylbenzonitrile and naphthylamine can be detected in nitrile rubber. These heteroatom-containing components can be used as a basis for eliminating matrix interference.

[0044] (3) If the molecule itself does not contain double bonds or unsaturated bonds, but according to the pyrolysis mechanism of the material, if a double bond structure is generated through elimination mechanism or other mechanisms during the pyrolysis process, its combustion residue can still basically detect C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene and indane, methylindane and other components, then the false positive and false negative interference will still be strong.

[0045] (4) The free combustion residue of the prepared material was analyzed by GC-MS. According to the national standard GB18264 and ASTM1618, C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene, indane, methylindane and other components were detected. At the same time, the three peaks of the relative peak area of ​​C2 met the "trident" standard. The profile characteristics, that is, in order of retention time from small to large, the second peak has the largest relative peak area, the third peak has a slightly larger relative peak area than or close to the first peak, and the relative peak area ratios of the three peaks are approximately 1:1.5~2:1~1.5, respectively. C3 meets the "castle-shaped" distribution of the six characteristic peaks, and the relative peak area ratios are approximately 1:5~6:1~2:1~2:10~12:3~4, respectively, which is basically the same as the situation of gasoline. It is believed that its false positive interference is very strong both from a qualitative and quantitative perspective.

[0046] (5) Prepare the residues from the mixed combustion of the material and gasoline, and analyze the residue components by GC-MS. According to the national standards GB18264 and ASTM1618, C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene and indane, methylindane and other components were detected. However, the relative peak areas of C2, C3 and C4 were significantly different from those of gasoline combustion residues, and it was considered that the false negative interference was significant.

[0047] (6) The interference of polymer materials is significantly correlated with their combustion / pyrolysis stages. Based on the analysis of the interference of free combustion products, the thermal behavior and pyrolysis products of the material were further analyzed by TG-IR-GC / MS, mainly including the pyrolysis process stages, the pyrolysis products corresponding to each stage, and the weight loss. Taking SBR1505 with a styrene content of 9.5wt as an example, there are three stages of pyrolysis, with weight losses of 29.74%, 48.55%, and 20.38%, respectively. The content of the target characteristic components in the pyrolysis products of the first stage is relatively low, and a C2 benzene (ethylbenzene) and a C3 Benzene (3-ethyltoluene), naphthalene, 2-methylnaphthalene, 1-methylnaphthalene, indene, indane, 4-methylindane and 1-methylindane. Three C2 benzenes (ethylbenzene, o-(m-)xylene, p-xylene), six C3 benzenes (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, 2-methylnaphthalene, 1-methylnaphthalene, indene, indane, 4-methylindane and 1-methylindane were detected in the pyrolysis products of the second and third stages, and their relative contents were much higher than those in the first stage. Therefore, based on the comprehensive weight loss and pyrolysis products, the second stage of SBR 1205 pyrolysis has the most significant interference with gasoline identification. Taking PVC as an example, its pyrolysis process is divided into three stages. The weight loss in the first pyrolysis stage is the most obvious, with a weight loss of 70.64%. The weight losses in the following two stages are relatively small, at 10.63% and 18.73%, respectively. More target components were detected in the pyrolysis products of the first and second stages, including three C2 benzenes (ethylbenzene, o-(m-)xylene, and p-xylene), six C3 benzenes (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, 1-methylnaphthalene, indene, indane, 3-methylindane, and 5-methylindane. The number and relative abundance of target components in the pyrolysis products of the last stage are significantly reduced. Therefore, based on the comprehensive weight loss and pyrolysis products, the first two stages of PVC pyrolysis have the most significant interference with gasoline identification.

[0048] (7) The interference of each pyrolysis stage was analyzed from both qualitative (type of pyrolysis products) and quantitative (content of pyrolysis products) aspects, where interference includes both false positive and false negative aspects.

[0049] (8) The interference of copolymeric polymer materials is strongly related to their chemical composition. For example, the interference of styrene butadiene rubber is closely related to the relative content of butadiene and styrene. Styrene butadiene rubber with a styrene content of 8-18wt% has significant interference. For example, the styrene content of SBR 1505 and SBR 1205 is 9.5% and 18% respectively. Compared with HS 60 and HS 80 with higher styrene content, they have higher butadiene content and more cis-1,4-butadiene units in their structures. These units undergo Diels-Alder reaction to form aromatization precursors, thus causing more significant interference in gasoline identification. For example, polyvinyl chloride (PVC) contains a large number of -C=C- double bond structures in its vinyl chloride monomer, which has the conditions to form aromatic hydrocarbons. After thermal decomposition, the -C-Cl- bond breaks first, and the side group is eliminated and HCl is removed to form a large amount of conjugated olefins and a small amount of aromatic hydrocarbons. As the temperature continues to rise, the -CC- bond breaks to form a polyene structure. In addition to generating aliphatic hydrocarbon compounds, a part of the polyene structure also forms aromatic hydrocarbons through molecular rearrangement, cyclization, and polymerization. Therefore, it can also significantly interfere with gasoline identification.

[0050] (9) Analyze the degree of interference of matrix materials in fire residue analysis based on chemical structure and pyrolysis mechanism. The present invention is a method that can predict whether the results are "false positive" and / or interfering before instrumental analysis of combustion residues. It can effectively predict the interference of polymer matrix and eliminate the interference of fire matrix on gasoline inspection and identification.

[0051] Example 1

[0052] like Figure 1As shown in the figure, when cis-1,4-butadiene rubber is used as a polymer material, its chemical structure characteristics are first analyzed: it is polymerized from butadiene monomers, contains a large number of -C=C- double bond structures, has the conditions to form aromatic hydrocarbons and does not contain heteroatoms; secondly, its pyrolysis mechanism is inferred: there may be three reaction pathways for butadiene monomers as pyrolysis proceeds: one is the bond breaking reaction, due to the breaking of carbon-carbon single bonds or carbon-hydrogen bonds, small molecular acetylene and free radicals such as vinyl and butadienyl will be generated; the second is the activation reaction, as the pyrolysis continues, the activated molecules in a high vibrational state are converted into stable compounds or continue to react, on the one hand, forming stable compounds propylene or generating free radicals such as butadienyl, on the other hand, on the basis of the formed 1-butene-3-yne, further hydrogen abstraction reaction with free radicals occurs to generate isopropenyl acetylene; the third is the hydrogen abstraction reaction, smaller free radicals, such as hydrogen atoms, methyl and ethyl radicals, capture hydrogen atoms on carbons at different positions on butadiene to generate isoprene, etc. The intermediate products of the above process undergo secondary random cleavage and other reaction processes to further generate more complex products. The intermediate propenyl acetylene undergoes hydrogen abstraction reaction with methyl to generate isopropenyl acetylene, and three molecules of propyne undergo addition polymerization to generate benzene. In the reaction of butadiene and ethylene or acetylene, the cycloaddition reaction of the diene system with olefins or alkynes is the Diels-Alder reaction, i.e. diene synthesis. Two molecules of butadiene undergo cycloaddition to generate 4-vinylcyclohexene, and butadiene and ethylene or acetylene diene addition generate cyclohexene and 1,3-cyclohexadiene. In addition, 4-vinylcyclohexene will further undergo aromatization to generate styrene, and the styrene monomer will further undergo bond breaking reaction to form stable toluene. The intermediate substance toluene generated will undergo free radical substitution to generate aromatic hydrocarbon components such as C2 benzene. The degree of conversion of the styrene intermediate may vary depending on the reaction conditions, but generally, the conditions for the formation of aromatic hydrocarbons are met.

[0053] like Figure 2 As shown in the figure, C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene, indane, methylindane and other components were detected in the combustion residues obtained by the combustion of butadiene rubber alone (a) and after loading gasoline ((a1) 0.05mL (a2) 0.1mL). The relative abundance of the characteristic peaks of the C2 benzene component did not change significantly, and always maintained a "trident" shape of "the first peak has the lowest relative abundance, and the second peak has the highest relative abundance", which is similar to the common characteristic peaks of the C2 benzene component in gasoline, and the overall chromatogram profile is highly similar to gasoline.

[0054] like Figure 3As shown in the figure, the pyrolysis process of cis-1,4-butadiene rubber is divided into three stages, roughly in the temperature range of 350℃ to 436℃, 436℃ to 470℃ and 470℃ to 580℃. The weight loss rate of the first pyrolysis stage is 14.10%, the second pyrolysis stage shows the most obvious weight loss, with a weight loss of 71.99%, and the weight loss rate of the third pyrolysis stage is 13.91%. Combined with the detection of characteristic components, it can be considered that the interference degree of cis-1,4-butadiene rubber on gasoline identification is very significant, especially in the second pyrolysis stage, the corresponding thermal environment temperature reaches 436℃ to 470℃.

[0055] The specific identification method includes the following steps:

[0056] Step 1: Analyze the chemical structure of butadiene rubber, which is polymerized from butadiene monomers. It does not contain a benzene ring structure, but contains a large number of -C=C- double bond structures, which have the conditions to form aromatic hydrocarbons;

[0057] Step 2: Analyze the elemental composition of butadiene rubber. It does not contain heteroatoms and interference cannot be eliminated based on this.

[0058] Step 3: Analyze the pyrolysis mechanism of butadiene rubber. There is a possibility that the -C=C- double bond undergoes addition polymerization to form an aromatic hydrocarbon structure, which may produce a large amount of aromatic hydrocarbons, including alkylbenzene compounds, condensed aromatic hydrocarbon compounds and indane compounds, which will interfere with gasoline identification.

[0059] Step 4: preparing the free combustion residue of butadiene rubber, analyzing the residue components by GC-MS, and detecting C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene and indane, methylindane and other components;

[0060] Step 5: preparing the mixed combustion residue of butadiene rubber and gasoline, and analyzing the residue components by GC-MS; similarly, C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene, indane, methylindane and other components were detected;

[0061] Step 6: Analyze the thermal behavior and pyrolysis products of butadiene rubber by TG-IR-GC / MS, mainly including the pyrolysis process stages, the pyrolysis products corresponding to each stage and the weight loss. The pyrolysis process of butadiene rubber is divided into three stages, roughly in the temperature range of 350°C to 436°C, 436°C to 470°C and 470°C to 580°C. The weight loss rate of the first pyrolysis stage is 14.10%, the second pyrolysis stage shows the most obvious weight loss, with a weight loss of 71.99%, and the weight loss rate of the third pyrolysis stage is 13.91%. The characteristic components that interfere with gasoline identification can exist relatively stably during its pyrolysis process;

[0062] Step 7: The interference of each pyrolysis stage was analyzed from both qualitative (type of pyrolysis products) and quantitative (content of pyrolysis products) aspects. The second pyrolysis stage of butadiene rubber showed the most obvious weight loss, and the characteristic components in the pyrolysis products that were the same as those of gasoline could also be stably detected. Therefore, it is believed that the degree of interference of butadiene rubber on gasoline identification is very significant.

[0063] The analysis shows that according to the results of chemical structure and pyrolysis mechanism analysis, when butadiene rubber is used as a background matrix at a fire scene, it has the conditions to generate a large amount of aromatic hydrocarbons when it undergoes pyrolysis and combustion in a hot environment, which can easily cause false positive results in the instrumental analysis of combustion residues. It can also affect the relative abundance ratio of the corresponding characteristic components in gasoline, thereby presenting false negative results. It is very easy to cause false results in the instrumental analysis of combustion residues, and greatly interfere with the identification of gasoline at the fire scene.

[0064] Example 2

[0065] like Figure 4 As shown in the figure, when chloroprene rubber is used as a polymer material, its chemical structure characteristics are first analyzed: it is formed by the polymerization of chloroprene monomers, contains -C=C-, has the conditions to form aromatic hydrocarbons, and contains heteroatoms Cl. Secondly, its pyrolysis mechanism is inferred: chloroprene monomers undergo pyrolysis, and free chloride ions are formed after dechlorination, which are easily substituted with alkanes, benzene and their homologues. Part of the polyene structure containing double bonds formed during the pyrolysis process is converted into aliphatic hydrocarbon compounds, and the other part forms aromatic hydrocarbons through molecular rearrangement, cyclization and polymerization.

[0066] like Figure 5 As shown, C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene and indane, methylindane and other components were detected in the combustion residues of chloroprene rubber, which are the same as the characteristic components of alkylbenzenes in the inspection and identification of fire accelerants, and are easy to cause "false positive" interference in its inspection and identification. However, at the same time, alkylbenzene components containing heteroatom substitution can be detected, which can serve as a basis for the existence of such rubber.

[0067] The specific identification method includes the following steps:

[0068] Step 1: Analyze the chemical structure of chloroprene rubber, which is polymerized from chloroprene monomers. It does not contain a benzene ring structure, but contains a -C=C- double bond structure, which has the conditions to form aromatic hydrocarbons;

[0069] Step 2: Analyze the elemental composition of chloroprene rubber to determine whether it contains heteroatom Cl;

[0070] Step 3: Infer the pyrolysis mechanism of chloroprene rubber and analyze the possibility that the -C=C- double bond undergoes addition polymerization to form aromatic hydrocarbons during its pyrolysis process. When used as a background matrix at a fire scene, aromatic hydrocarbons may be produced, including alkylbenzene compounds, condensed ring aromatic compounds and indane compounds, which may interfere with gasoline identification.

[0071] Step 4: Prepare the free combustion residue of chloroprene rubber, and analyze the residue composition by GC-MS. C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene) and C4 benzene components can be detected in the chloroprene rubber residue, which are the same as the characteristic components of alkylbenzenes in the inspection and identification of fire accelerants, and are easy to cause "false positive" interference in the inspection and identification. However, at the same time, alkylbenzene components containing heteroatom substitution can be detected, which can eliminate interference and serve as a basis for the existence of such rubber.

[0072] The analysis shows that according to the results of chemical structure and pyrolysis mechanism analysis, when chloroprene rubber is used as a background matrix in a fire scene, it has the conditions to generate aromatic hydrocarbons when it undergoes pyrolysis and combustion in a hot environment. The chloroalkylbenzenes detected based on the GC-MS results can be used to exclude false positive results.

[0073] Example 3

[0074] like Figure 6 It is shown that when styrene-butadiene rubber is used as a polymer material, its chemical structure characteristics are first analyzed: SBR is mainly composed of styrene and butadiene monomers, among which butadiene monomers have three structures, including 1,2-unit, cis-1,4-unit and trans-1,4-unit. Secondly, its pyrolysis mechanism is inferred: during the pyrolysis process, the cis and trans structures of butadiene may be converted to each other under heating conditions. All three butadiene structures exist in SBR 1505 and SBR 1205, among which the trans-1,4-unit (967cm -1 ) has the highest relative content, followed by the cis-1,4-unit (730 cm -1 ), followed by 1,2-unit (911cm -1). Compared with the other four samples, SBR 1505 and SBR 1205 involve more abundant butadiene in their chemical compositions, as well as more cis-1,4-units. These units form aromatization precursors through the Diels-Alder reaction, thus causing more significant interference in gasoline identification.

[0075] Figure 7 The chromatogram of gasoline combustion residues and the detection of characteristic components are used for comparison of subsequent pyrolysis product gas chromatography / mass spectrometry analysis results.

[0076] Figure 8 Figure 5 is the total ion current chromatogram of the pyrolysis products of styrene-butadiene rubber at each stage with different styrene contents. It shows that in the pyrolysis products of styrene-butadiene rubber samples with lower styrene contents (SBr 1505, SBr 1205 and SBr 1502), the relative abundance of the target characteristic compounds increases first and then decreases with increasing temperature, reaching a peak at about 450°C. However, for the pyrolysis products of styrene-butadiene rubber samples with higher styrene contents (SBr 303, HS60 and HS80), a larger relative abundance of the target compounds was observed in the first pyrolysis stage.

[0077] Fig. 9 The results show that the relative abundance of alkylbenzene compounds in the pyrolysis products of styrene-butadiene rubber samples increases first and then decreases as the pyrolysis process progresses. More interfering compounds can be produced in the second pyrolysis stage of SBr 1505, SBr 1205, and SBr 1502 and in the first pyrolysis stage of SBr 303, HS60, and HS 80, which significantly interfere with gasoline identification.

[0078] Fig.10 The results show that during the pyrolysis of styrene butadiene rubber samples, the relative abundance of polycyclic aromatic hydrocarbons increases first and then decreases. At 450 °C, naphthalene, methylnaphthalene and dimethylnaphthalene are detected in the pyrolysis products of SBr 1505, SBr 1502 and SBr 303, while only naphthalene and methylnaphthalene are detected in SBr 1205, HS 60 and HS 80.

[0079] Fig.11 It shows that the formation of indane components during the pyrolysis of styrene butadiene rubber presents a trend of first increasing and then decreasing. Indene, indene, methylindene and dimethylindene were detected in the pyrolysis products of SBr 1505, SBr 1205, SBr 1502 and SBr 303 at 450°C, while only indene was detected in the pyrolysis residues of HS 60 and HS 80.

[0080] Fig.12The thermogravimetric analysis results of styrene-butadiene rubber with different styrene contents show that when heated in an air atmosphere, the three styrene-butadiene rubber samples with low styrene contents (SBr 1505, SBr 1205 and SBr 1502) show three obvious weight loss stages, and the main weight loss and the highest weight loss rate are shown in the second pyrolysis stage, among which SBr1205 and SBr 1502 have a weight loss of more than 80% in this stage; while the other three styrene-butadiene rubber samples with high styrene contents (SBr 303, HS60 and HS80) only show two obvious weight loss stages during the pyrolysis process, and the most significant weight loss is shown in the first pyrolysis stage, and the weight loss exceeds 86%.

[0081] Fig.13 The products formed during the pyrolysis process were further identified based on the three-dimensional infrared spectra of different styrene-butadiene rubber samples. The infrared spectra of all six samples showed two significant absorption peaks, located at 600-800 cm -1 and 2300-2400cm -1 , corresponding to substituted benzene functional groups, also proves that a large amount of aromatic compounds are generated in the main weight loss stage of each sample.

[0082] Fig.14The results show that there are three main sources of aromatic compounds produced during the pyrolysis of SBR: first, the side chain addition reaction of styrene forms monosubstituted alkylbenzenes related to the styrene content in the molecule; second, the Diels-Alder reaction of the diene structure and its subsequent aromatization reaction lead to the formation of polysubstituted alkylbenzenes and alkylnaphthalenes; third, the further pyrolysis of 4-vinylcyclohexene produces butadiene, linear olefins and cyclic olefins, which then continue to undergo Diels-Alder reaction and aromatization reaction to finally form aromatic compounds. Obviously, the latter two pathways involve butadiene in SBR. From this point of view, butadiene plays a more important role than styrene in forming pyrolysis products that interfere with gasoline identification. The specific gravity of butadiene and styrene monomers in different types of styrene-butadiene rubber is different, and the position and content of the cyclic structure and -C=C- structure contained in the intermediates formed by pyrolysis, as well as the difficulty of the formation of the intermediates, are also different. Therefore, the degree of interference caused by different types of styrene-butadiene rubber to the identification of gasoline at the fire scene will be different. Combined with the pyrolysis mechanism of styrene-butadiene rubber, it is inferred that the pyrolysis process of different types of styrene-butadiene rubber is different, but the reaction sequence and mechanism of the characteristic compounds that can interfere with gasoline identification during the pyrolysis process are basically the same. In the early stage of pyrolysis of styrene-butadiene rubber, long-chain breakage and dehydrogenation and depolymerization and recombination of styrene and butadiene monomers mainly occur. As the pyrolysis proceeds, the styrene monomer is pyrolyzed, the alkyl side chain of the benzene ring is broken, and the β-bond of the olefin is broken by the pyrolysis of butadiene, which can generate a large number of functional groups such as -C=C-, =CH, and -CH-, which can combine with free radicals to further undergo a series of complex reactions such as alkylation, cyclization, and aromatization, and meet the conditions for the formation of aromatic hydrocarbons.

[0083] The specific identification method includes the following steps:

[0084] Step 1: Analyze the chemical structure of styrene-butadiene rubber, which is polymerized from styrene and butadiene monomers. It contains structures such as benzene rings and dienes containing -C=C- double bonds, and has the conditions to form aromatic hydrocarbons.

[0085] Step 2: Analyze the elemental composition of styrene-butadiene rubber to determine that it does not contain heteroatoms;

[0086] Step 3: Analyze the pyrolysis mechanism of styrene butadiene rubber and analyze whether its pyrolysis process can generate a large number of -C=C- double bond structures. It is inferred that when styrene butadiene rubber is used as a background matrix in the fire scene, it may produce aromatic hydrocarbons, including alkylbenzene compounds, condensed aromatic hydrocarbon compounds and indane compounds, which will interfere with the identification of gasoline.

[0087] Step 4: prepare the free combustion residue of styrene-butadiene rubber, analyze the residue components by GC-MS, and detect C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene and indane, methylindane and other components;

[0088] Step 5: preparing a mixed combustion residue of styrene-butadiene rubber and gasoline, analyzing the residue components by GC-MS, and detecting C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene and indane, methylindane and other components;

[0089] Step 6: Analyze the thermal behavior and pyrolysis products of styrene-butadiene rubber by TG-IR-GC / MS, mainly including the pyrolysis process stages, the corresponding pyrolysis products and weight loss of each stage. SBR shows more significant weight loss in the early stage of pyrolysis, and the types and quantities of the corresponding pyrolysis products are closer to those of gasoline.

[0090] Step 7: Analyze the interference of each pyrolysis stage from both qualitative (type of pyrolysis products) and quantitative (content of pyrolysis products) aspects. In the early stage of pyrolysis, styrene-butadiene rubber shows obvious weight loss, and the abundance of characteristic components in the pyrolysis products that are the same as gasoline is also greater. Therefore, it is believed that styrene-butadiene rubber has a very significant interference degree on gasoline identification, especially in the early stage of pyrolysis.

[0091] The analysis shows that, based on the results of chemical structure and pyrolysis mechanism analysis, when styrene-butadiene rubber is used as a background matrix at a fire scene, pyrolysis and combustion in a hot environment can generate a large amount of aromatic hydrocarbons, which can easily cause false positive results in instrumental analysis of combustion residues, and can also affect the relative abundance ratio of corresponding characteristic components in gasoline, thereby presenting false negative results, which significantly interferes with the identification of gasoline at the fire scene.

[0092] Example 4

[0093] like Fig.15As shown in the figure, when polyvinyl chloride (PVC) is used as a polymer material, its chemical structure characteristics are first analyzed: the PVC molecule itself does not have a double bond, but its typical side group breakage pyrolysis mechanism leads to the formation of double bonds in the molecule during the heating process, which is a functional group that further interferes with the identification of flammable liquid residues; secondly, its pyrolysis mechanism is inferred: PVC undergoes pyrolysis, first of all, the dechlorination stage, which is mainly the breakage of the -C-Cl- bond. After the side group eliminates HCl, a large amount of conjugated olefins and a small amount of aromatic hydrocarbons are formed. As the temperature continues to rise, the -CC- bond breaks to generate a polyene structure. In addition to generating aliphatic hydrocarbon compounds, a part of the polyene structure forms aromatic hydrocarbons through molecular rearrangement, cyclization, and polymerization.

[0094] like Fig.16 As shown in the figure, C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene and indane, methylindane and other components were detected in the PVC combustion residues. These components are the same as the characteristic components of alkylbenzenes in the inspection and identification of fire accelerants, and may easily cause "false positive" interference in the inspection and identification.

[0095] like Fig.17 As shown in the figure, PVC undergoes three different pyrolysis stages, roughly in the temperature ranges of 200°C to 400°C, 400°C to 500°C, and 500°C to 613°C. The first pyrolysis stage starts at 200°C and ends at 400°C, showing the most obvious weight loss in this temperature range, with a weight loss of 70.64%. The subsequent two stages occur at 400°C to 500°C and 500°C to 613°C, with relatively small weight loss rates of 10.63% and 18.73%, respectively.

[0096] The specific identification method includes the following steps:

[0097] Step 1: Analyze the chemical structure of PVC. It is made by polymerizing chloroprene monomers and does not have double bonds itself. However, its typical side group cleavage pyrolysis mechanism can cause the molecule to form double bonds during heating, which has the conditions to form aromatic hydrocarbons.

[0098] Step 2: Analyze the elemental composition of PVC to determine whether it contains heteroatom Cl;

[0099] Step 3: Infer the pyrolysis mechanism of PVC, analyze the possibility of the existence of -C=C- double bond addition polymerization to form aromatic hydrocarbons in its pyrolysis process, infer the reaction pathways that may produce aromatic hydrocarbons in its pyrolysis process, and infer that PVC may produce aromatic hydrocarbons when used as a background matrix at a fire scene, including alkylbenzene compounds, condensed ring aromatic hydrocarbons and indane compounds, which may interfere with gasoline identification.

[0100] Step 4: Prepare the free combustion residue of PVC, analyze the residue components by GC-MS, and detect C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene and indane, methylindane and other components;

[0101] Step 5: preparing the mixed combustion residue of PVC and gasoline, analyzing the residue components by GC-MS, and detecting C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene and indane, methylindane and other components;

[0102] Step 6: Analyze the thermal behavior and pyrolysis products of PVC by TG-IR-GC / MS, mainly including the pyrolysis process stages, the pyrolysis products corresponding to each stage and the weight loss. The most obvious weight loss is shown in the first pyrolysis stage, with a weight loss of 70.64%. C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene and indane, methylindane and other components are detected in the pyrolysis products of all stages;

[0103] Step 7: Analyze the interference of each pyrolysis stage from both qualitative (type of pyrolysis products) and quantitative (content of pyrolysis products) aspects. The PVC residues in the first and second pyrolysis stages interfere more significantly with gasoline identification, while the PVC residues with a high degree of pyrolysis interfere less with gasoline identification.

[0104] The analysis shows that, based on the results of chemical structure and pyrolysis mechanism analysis, when PVC is used as a background matrix at a fire scene, it has the conditions to generate aromatic hydrocarbons when it undergoes pyrolysis and combustion in a hot environment. In particular, if the extracted on-site combustion residues contain PVC products in the late pyrolysis stage, it is easy to cause false positive results in the instrumental analysis of the combustion residues, and it can also affect the relative abundance ratio of the corresponding characteristic components in gasoline, thereby presenting a false negative result, which significantly interferes with the identification of gasoline at the fire scene.

[0105] The above is only a preferred embodiment of the present invention, and does not impose any formal limitation on the structure of the present invention. The layout type and the number of uses of the present invention are not limited to this example, and can be optimized and selected according to the actual project. Any modification, equivalent change and decoration of the above embodiment based on the technical principle of the present invention that does not deviate from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for predicting the interference of polymer materials with the inspection and identification of gasoline at a fire scene based on chemical structure and pyrolysis mechanism, characterized in that: The steps include: Step 1: Analyze the chemical structure characteristics to determine whether it contains a -C=C- structure; Step 2: Analyze the elemental composition of the polymer material containing double bonds to determine whether it contains heteroatoms; Step 3: Analyze the pyrolysis mechanism of polymer materials and analyze whether the pyrolysis process can generate a large number of -C=C- double bond structures; Step 4: preparing a free combustion residue of the polymer material, and analyzing the residue components by GC-MS; Step 5: preparing a mixed combustion residue of the polymer and gasoline, and analyzing the components of the residue by GC-MS; Step 6: Analyze the thermal behavior and pyrolysis products of the material by TG-IR-GC / MS, mainly including the pyrolysis process stages, the pyrolysis products corresponding to each stage, and the weight loss; Step 7: Analyze the interference of each pyrolysis stage from both qualitative (type of pyrolysis products) and quantitative (content of pyrolysis products) aspects.

2. The method for predicting the interference of polymer materials with gasoline inspection and identification at a fire scene according to claim 1, characterized in that: In the step 1, it is further determined whether C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene and indane, methylindane and other components can be detected in the combustion residue of the polymer material.

3. The method for predicting the interference of polymer materials with the inspection and identification of gasoline at a fire scene according to claim 1, characterized in that: In the step 2, it is further determined whether the polymer material containing heteroatoms has false negative interference.

4. The method for predicting the interference of polymer materials with gasoline inspection and identification at a fire scene according to claim 1, characterized in that: In the step 3, it is determined whether C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene and indane, methylindane and other components can be detected in the combustion residue, then the interference of false positive and false negative will still be strong.

5. The method for predicting the interference of polymer materials with gasoline inspection and identification at a fire scene according to claim 1, characterized in that: The polymer materials with false negative interference are heteroatom rubbers represented by chloroprene rubber.

6. The method for predicting the interference of polymer materials with gasoline inspection and identification at a fire scene according to claim 1, characterized in that: In the step 4, according to the national standard GB18264 and ASTM1618, C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene and indane, methylindane and other components are detected, and the three peaks of the relative peak area C2 meet the "trident" profile characteristics, that is, according to the retention time From small to large, the second peak has the largest relative peak area, and the third peak has a slightly larger relative peak area than or close to the first peak. The relative peak area ratios of the three peaks are approximately 1:1.5~2:1~1.5, respectively. C3 meets the "castle-shaped" distribution of the six characteristic peaks, and the relative peak area ratios are approximately 1:5~6:1~2:1~2:10~12:3~4, respectively, which is basically the same as the situation of gasoline. It is believed that its false positive interference is very strong both from a qualitative and quantitative perspective.

7. The method for predicting the interference of polymer materials with the inspection and identification of gasoline at a fire scene according to claim 1, characterized in that: In the step 5, according to national standards GB18264 and ASTM1618, C2 benzene (ethylbenzene, o-(m-)xylene, p-xylene), C3 benzene (propylbenzene, 3-ethyltoluene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene), naphthalene, methylnaphthalene, indene and indane, methylindane and other components are detected, but the relative peak areas C2, C3 and C4 are greatly different from those of gasoline combustion residues, and it is considered that the false negative interference is significant.

8. The method for predicting the interference of polymer materials with the inspection and identification of gasoline at a fire scene according to claim 1, characterized in that: In the step six, the analysis conditions of the instrumental analysis method are: TG-IR-GC / MS analysis conditions: TG analysis conditions: air atmosphere, heating rate 20°C / min, analysis temperature range 60-800°C; IR analysis conditions: wave number range 4000-400cm-1, scan number 32, scanning mode continuous scanning; GC-MS analysis conditions: injection port temperature: 260°C, injection volume 1 μL. Helium was used as the carrier gas with a flow rate of 1 mL / min and a split ratio of 5:

1. The temperature was programmed to rise to 50 °C (maintained for 2 min), then to 150 °C (maintained for 2 min) at a rate of 10 °C / min, then to 186 °C (maintained for 3 min) at a rate of 6 °C / min, and finally to 260 °C (maintained for 20 min) at a rate of 4 °C / min. The ion source temperature was set to 230 °C, the GC-MS interface temperature to 280 °C, and the quadrupole temperature to 150 °C. The electron impact ion source (EI) was used with an electron energy of 70 eV. The scanning mode was full scan with a mass range of 50 to 500 aum. The FTIR analysis conditions were as follows: the wavenumber range was 1200 to 600 cm-1, the number of scans was 64, and the scanning mode was continuous scan.

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