The invention relates to a method for reducing p, papos in a pesticide analysis process. Method for determining degradation rate of-DDT and isodiels

Abstract

The invention discloses a method for reducing the degradation rate of p, p '-DDT and isodielin in the pesticide analysis process, and relates to the technical field of chromatographic analysis, and the method comprises the following steps: S1, introducing gas containing unpaired electrons into a sample inlet of a pesticide analysis instrument, and maintaining for 10-60 seconds, and S2, feeding a pesticide detection sample into the sample inlet of the analysis instrument, and carrying out sample analysis. According to the method provided by the invention, the degradation rate of p, p '-DDT and isodielin can be maintained below 15% and even below 10% in the organochlorine pesticide analysis process, so that the analysis stability is ensured, and the analysis accuracy is greatly improved. Meanwhile, the control on the degradation rates of p, p '-DDT and the isodielin can be realized at the same time only by adopting a small amount of nitric oxide gas as a degradation inhibitor, the cost is low, the operation is simple, the maintenance frequency of a chromatographic system is greatly reduced, and the analysis cost and time are effectively saved.

Description

Technical Field

[0001] The invention relates to the technical field of chromatographic analysis, and in particular to a method for reducing the degradation rates of p,p'-DDT and endrin in the pesticide analysis process. Background Art

[0002] At present, during the gas chromatography or gas chromatography / mass spectrometry analysis of organochlorine pesticides, p,p'-DDT and endrin are very easy to degrade during the analysis process, resulting in sample analysis failure. The reason for the degradation of p,p'-DDT and endrin is that when the injection port and the chromatographic system contain many impurities after a long period of analysis, these impurities produce many active sites. At a higher gasification chamber temperature (such as: 220℃~280℃), these active sites produce a large number of highly active substances similar to hydrogen free radicals in the silanized chromatographic system. These substances have catalyst-like properties, causing p,p'-DDT to degrade into p,p'-DDD and p,p'-DDE, and endrin to degrade into endrin aldehyde and endrin ketone.

[0003] According to the provisions of "HJ 921-2017 Determination of Organochlorine Pesticides in Soil and Sediment by Gas Chromatography", the degradation rate of p,p'-DDT (%) = peak area (p,p'-DDE + p,p'-DDD) / peak area (p,p'-DDE + p,p'-DDD + p,p'-DDT), the degradation rate of endrin (%) = peak area (endrin aldehyde + endrin ketone) / peak area (endrin aldehyde + endrin ketone + endrin). When the degradation rate of p,p'-DDT or endrin is ≥15%, or the sum of the degradation rates of the two is ≥30%, it means that the degradation rate exceeds the standard requirement range. Only when the degradation rates of p,p'-DDT and endrin are kept within 15%, the obtained analysis results are true and valid. Therefore, effective measures must be taken to ensure that the degradation rates of p,p'-DDT and endrin in each analysis are always kept within 15%.

[0004] This degradation reaction is essentially a free radical type reduction reaction. On the quaternary carbon atom with three chlorine atoms substituted in p,p'-DDT, the strong electron-withdrawing induction effect of the chlorine atom makes the quaternary carbon atom bonded to the chlorine atom highly active. Under the combined action of high temperature and active sites, these active sites produce highly active substances similar to hydrogen free radicals. These free radicals either undergo halogenated hydrocarbon reduction reactions to replace the chlorine free radicals on the quaternary carbon atom connected to the three chlorine atoms to generate p,p'-DDD, or undergo elimination reactions to generate p,p'-DDE. Endrin is a relatively complex ring structure. When attacked by hydrogen free radical active substances, it forms endrin aldehyde after ring opening, and hydrogen free radicals replace chlorine free radicals to form endrin ketone.

[0005] At present, the traditional methods for controlling the excessive degradation rate of p,p'-DDT and endrin in the analysis of organochlorine pesticides are mainly cleaning and maintenance of the chromatographic system, such as cleaning the chromatographic injection port with organic reagents, silanization or inertization of the gas path, replacing a new split plate or inert liner, cutting off the front 5~10cm of the chromatographic column, re-aging the chromatographic column, replacing a new chromatographic column and other maintenance methods. The purpose of these traditional methods is to reduce the active sites introduced or generated in the chromatographic system, and to reduce the generation of hydrogen free radicals by reducing the number of active sites, so as to stabilize the degradation rate at a lower level and ensure the smooth progress of the experiment. However, the problem with traditional methods is that consumables are expensive, costly, maintenance is frequent, and efficiency is low. Because the injection process of chromatography is a process of contaminating the chromatography system, the impurities in the sample (such as macromolecular substances, humus, protein, pigment, etc.) will inevitably produce active sites at high temperature and cause degradation. The continuous injection process is a process of continuously increasing the active sites of the system. The degradation rate of p,p'-DDT and endrin will inevitably increase with the number of injections and the degree of contamination of the chromatography system by the sample. In order to ensure that the degradation rate of p,p'-DDT and endrin is always kept within 15%, the chromatography system needs to be continuously cleaned and maintained. Too high a maintenance frequency of the chromatography system is not only time-consuming and labor-intensive, but also has low sample analysis efficiency, and high consumables and labor costs, and it is difficult to guarantee the accuracy of the analysis.

[0006] The invention patent with patent number CN201911169168.4 adopts the method of adding organic compounds with strong electronegative halogen groups as degradation inhibitors during sample injection to maintain the degradation rate of p,p'-DDT below 15%. Compared with the above-mentioned traditional methods, this invention ensures the stability of the analysis, improves the accuracy of the analysis, greatly reduces the maintenance frequency of the chromatographic system, effectively saves the consumables and labor costs of the analysis, and shortens the analysis time. However, since the outer electrons of the chlorine atoms in the molecules of halogen organic compounds (such as CCl4) are 8-electron stable structures, their ability to react with highly active substances such as hydrogen radicals is limited. Therefore, this invention only has an inhibitory effect on the degradation of p,p'-DDT, and has no inhibitory effect on the degradation of endrin. In addition, the liquid organic compounds with strong electronegative halogen groups need to be completely vaporized at the chromatographic injection port before they can be used. It reacts with highly active substances similar to hydrogen radicals produced at active sites in the system, thereby inhibiting the reaction of p,p'-DDT with highly active substances similar to hydrogen radicals, thereby reducing the degradation rate of p,p'-DDT. This is a competitive reaction process between halogen compounds and p,p'-DDT for highly active substances similar to hydrogen radicals. Therefore, when the sample has more impurities or there are a large number of active sites in the system, a large number of highly active substances similar to hydrogen radicals are produced, or the gasification process of the liquid halogen organic compound becomes slower or incomplete, the effect of the liquid halogen organic compound in inhibiting degradation is reduced. Summary of the invention

[0007] The object of the present invention is to overcome the deficiencies of the prior art and provide a method for reducing the degradation rates of p,p'-DDT and endrin in the pesticide analysis process.

[0008] The objective of the present invention is achieved through the following technical solutions: A method for reducing the degradation rate of p,p'-DDT and endrin in a pesticide analysis process comprises the following steps: S1. Pass the gas containing unpaired electrons into the inlet of the pesticide analyzer and keep it for 10s-60s; S2. The pesticide test sample is sent to the sample inlet of the analysis instrument for sample analysis.

[0009] Specifically, the gas containing unpaired electrons is nitric oxide.

[0010] The pesticide analysis instrument is a gas chromatograph / mass spectrometer or a gas chromatograph.

[0011] When the gas containing unpaired electrons is used for pesticide analysis, the linear relationship of the standard curves of organochlorine pesticides, organophosphorus pesticides and pyrethroids can be improved, and the matrix effect in the analysis system can be reduced.

[0012] The beneficial effects of the present invention are: The present invention utilizes the competitive reaction between nitric oxide gas and highly active substances similar to hydrogen free radicals generated by active sites accumulated in the chromatographic system, thereby reducing the degradation rate of p,p'-DDT and endrin. At the same time, since nitric oxide can significantly eliminate free radicals generated in the chromatographic system, nitric oxide can also improve the linear relationship of the standard curve of certain compounds with high activity, easy decomposition, and poor chromatographic performance and improve the chromatographic matrix effect of these substances. And since nitric oxide itself is a gas, it does not need to be gasified during injection, and the introduction of nitric oxide gas in advance to consume active substances further ensures that the degradation rate of p,p'-DDT and endrin is reduced.

[0013] The present invention makes up for the problem that the invention patent with patent number CN201911169168.4 cannot solve the degradation problem of endrin during the chromatographic analysis of organochlorine pesticides. The use of gaseous nitric oxide avoids the problem that the degradation inhibition effect of liquid halogen organic compounds on p,p'-DDT is weakened when the gasification is unfavorable or incomplete.

[0014] The method provided by the present invention can maintain the degradation rates of p,p'-DDT and endrin below 15% during the analysis of organochlorine pesticides, and can even maintain them below 10% (still quite far from the red line), thereby ensuring the stability of the analysis and greatly improving the accuracy of the analysis. At the same time, the present invention can simultaneously control the degradation rates of p,p'-DDT and endrin by only using a small amount of nitric oxide gas as a degradation inhibitor, with low cost and simple operation, greatly reducing the maintenance frequency of the chromatographic system, and effectively saving analysis cost and time. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The chromatogram is the degradation rate of p,p'-DDT when no nitric oxide is introduced in Example 1; Figure 2 The chromatogram of p,p'-DDT degradation rate when nitric oxide is introduced in Example 1; Figure 3 This is a chromatogram of the degradation rate of endrin when no nitric oxide is introduced in Example 1; Figure 4 The chromatogram of degradation rate of endrin when nitric oxide is introduced in Example 1; In the figure, 1- p,p'-DDT, 2- p,p'-DDD, 3- p,p'-DDE, 4-endrin, 5-endrin aldehyde, 6-endrin ketone. DETAILED DESCRIPTION

[0016] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0017] According to the provisions of "HJ 921-2017 Determination of Organochlorine Pesticides in Soil and Sediment by Gas Chromatography", the degradation rate of p,p'-DDT (%) = peak area (p,p'-DDE + p,p'-DDD) / peak area (p,p'-DDE + p,p'-DDD + p,p'-DDT), the degradation rate of endrin (%) = peak area (endrin aldehyde + endrin ketone) / peak area (endrin aldehyde + endrin ketone + endrin). When the degradation rate of p,p'-DDT or endrin is ≥15%, or the sum of the degradation rates of the two is ≥30%, it means that the degradation rate exceeds the standard requirement range. Only when the degradation rates of p,p'-DDT and endrin are kept within 15%, the obtained analysis results are true and valid. Therefore, effective measures must be taken to ensure that the degradation rates of p,p'-DDT and endrin in each analysis are always kept within 15%. The present invention provides a treatment method for reducing the degradation of p,p'-DDT and endrin, ensuring that the degradation rates of p,p'-DDT and endrin are kept within 15% during the analysis process, thereby obtaining a true analysis result.

[0018] The main technical means adopted by the present invention is to introduce nitric oxide into the gas chromatography injection port through the gas chromatography carrier gas flow path and maintain it for a period of time before the detection sample is injected, and then the sample of organochlorine pesticide to be tested is sampled into the chromatography system through a liquid injector for analysis. The nitric oxide maintained in the injection port can inhibit the degradation of p,p'-DDT and endrin.

[0019] Example 1 Experiment on the reduction of p,p'-DDT and endrin degradation rate by nitric oxide when p,p'-DDT and endrin were mixed with other organochlorine pesticide components. Standard solutions (concentration of 10μg / mL) of 7 organochlorine pesticide mixtures (α666, hexachlorobenzene, β666, pentachloronitrobenzene, γ666, δ666, heptachlor) containing P,P'-DDT and endrin and 7 organochlorine pesticide mixtures without P,P'-DDT and endrin and their degradation products p,p'-DDD, P,P'-DDE, endrin aldehyde and endrin ketone were prepared respectively. During the test, nitric oxide gas was first introduced into the injection port of the gas chromatograph / mass spectrometer for 30s; then the pesticide test sample was sent into the injection port of the gas chromatograph / mass spectrometer for sample analysis.

[0020] The gas chromatography-mass spectrometry analysis conditions were as follows: Inlet temperature: 280°C, split, split ratio: 5:1; Standard solution injection volume: 1 μL Nitric oxide infusion time: 30S Column flow rate: 1.0mL / min Program temperature rise: 120℃ for 2 min, 10℃ / min to 180℃, hold for 2 min, 20℃ / min to 260℃, hold for 6 min, 30℃ / min to 320℃, hold for 3 min Gas-gas interface temperature: 280℃ Mass spectrometry scanning mode: SCAN, scanning range: 45~500 mass numbers Mass Spectrometry Tuning: Automatic Tuning Example 2 Calibration curves of 34 organochlorine pesticides were prepared. The 34 organochlorine pesticides were 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, 1,3,5-trichlorobenzene, 1,2,3,4-tetrachlorobenzene, 1,2,4,5-tetrachlorobenzene, 1,2,3,5-tetrachlorobenzene, pentachlorobenzene, tetrachloro-m-xylene, α666, hexachlorobenzene, β666, pentachloronitrobenzene, γ666, δ666, heptachlor, aldrin, dicofol, heptachlor epoxide, exo-epoxide heptachlor, O,p'-DDE, γ-chlordane, α-chlordane, sulfur Endrin Ⅰ, p,p'-DDE, o,p'-DDD, dieldrin, endrin, p,p'-DDD, endosulfan Ⅱ, o,p'-DDT, endrin aldehyde, p,p'-DDT, thiosulfate, methoxychlor, endrin ketone, decachlorobiphenyl, the concentration points of the calibration curve are 20μg / L, 50μg / L, 100μg / L, 200μg / L, 500μg / L, 1000μg / L, 2000μg / L, and the internal standard is phenanthrene-d10, with a concentration of 200μg / L. During the detection, nitric oxide gas is first introduced into the gas chromatography / mass spectrometer injection port and maintained for 40s; then the pesticide test sample is sent into the gas chromatography / mass spectrometer injection port for sample analysis.

[0021] The gas chromatography-mass spectrometry analysis conditions were as follows: Inlet temperature: 280°C, split, split ratio: 5:1; Nitric oxide infusion time: 40S Column flow rate: 1.0mL / min Program temperature rise: 120℃ for 2 min, 10℃ / min to 180℃, hold for 2 min, 20℃ / min to 260℃, hold for 6 min, 30℃ / min to 320℃, hold for 3 min Gas-gas interface temperature: 280℃ Mass spectrometry scanning mode: SIM, scanning mass numbers are 180, 216, 250, 244, 181, 284, 237, 188, 100, 263, 139, 353, 246, 373, 241, 246, 79, 67, 272, 227, 498, etc. Mass Spectrometry Tuning: Automatic Tuning Example 3 Calibration curves of 47 organophosphorus pesticides and pyrethroids were prepared. The 47 organophosphorus pesticides and pyrethroids were dichlorvos, mefenphos, chlorpyrifos, pyrethroid 1, chlorpyrifos, chlorpyrifos, pyrethroid 2, dimethoate, diazinon, chlorpyrifos, chlorpyrifos, methyl parathion, chlorpyrifos, chlorpyrifos sulfone, fenthion, parathion, triadimefon, pyrethroid, chlorpyrifos, chlorpyrifos sulfone, fenthion, parathion, triadimefon, pyrethroid, fipronil, trans-allethrin, chlorpyrifos ... , tetramethrin 1, bifenthrin, tetramethrin 2, fenthion, bromofen, pyrethrin, bromofenphos, cis-cyhalothrin, pyraclofos, permethrin 1, permethrin 2, coumaphos, cypermethrin 1, cypermethrin 2, cypermethrin 3, cypermethrin 4, fenvalerate 1, fenvalerate 2, deltamethrin, the concentration points of the calibration curve are 2.0 mg / L, 5.0 mg / L, 10.0 mg / L, 20.0 mg / L, 30.0 mg / L, 50.0 mg / L, and the internal standard is tetrachloro-m-xylene with a concentration of 10.0 mg / L. During the detection, nitric oxide gas is first introduced into the gas chromatograph / mass spectrometer injection port and maintained for 60 seconds; then the pesticide test sample is sent into the gas chromatograph / mass spectrometer injection port for sample analysis.

[0022] The gas chromatography-mass spectrometry analysis conditions were as follows: Inlet temperature: 280°C, split, split ratio: 5:1; Nitric oxide infusion time: 60S Column flow rate: 1.0mL / min Program temperature rise: 120℃ for 2 min, 10℃ / min to 180℃, hold for 2 min, 20℃ / min to 260℃, hold for 6 min, 30℃ / min to 320℃, hold for 3 min Gas-gas interface temperature: 280℃ Mass spectrometry scanning mode: SCAN Mass Spectrometry Tuning: Automatic Tuning Comparative Example 1 Different from Example 1, no nitric oxide is introduced during the gas chromatography-mass spectrometry analysis.

[0023] Comparative Example 2 Different from Example 2, no nitric oxide is introduced during the gas chromatography-mass spectrometry analysis.

[0024] Comparative Example 3 Different from Example 3, no nitric oxide is introduced during the gas chromatography-mass spectrometry analysis.

[0025] Comparing the experimental data of Example 1 and Comparative Example 1, the effect of nitric oxide on the degradation of p,p'-DDT and endrin when mixed with other organochlorine pesticide components is shown in Table 1: Table 1 Effect of nitric oxide on the degradation of p,p'-DDT and endrin in the presence of other organochlorine pesticides

[0026] As can be seen from Table 1, in the presence of other organochlorine pesticides, without nitric oxide, the degradation rate of p,p'-DDT was 97.5%, and the degradation rate of endrin was 28.7%, which exceeded the standard allowable range. After nitric oxide was introduced into the injection port, the degradation rate of p,p'-DDT was 3.6%, and the degradation rate of endrin was 5.5%, indicating that in the presence of other organochlorine pesticides, nitric oxide gas can still effectively reduce the degradation rate of p,p'-DDT and endrin during the chromatographic analysis process, meeting the method requirements.

[0027] Comparing the experimental data of Example 2 and Comparative Example 2, the influence of nitric oxide on the linear relationship of the calibration curve of organochlorine pesticides is shown in Table 2: Table 2 Effect of nitric oxide on the linear relationship of the calibration curve of organochlorine pesticides

[0028] As shown in Table 2, the correlation coefficients of the 34 organochlorine pesticides in the presence of nitric oxide are better than those in the absence of nitric oxide, indicating that the presence of nitric oxide will not react with p,p'-DDT or endrin or other compounds, nor will it interfere with the entire analysis process, and can improve the correlation coefficients of organochlorine pesticides, especially the correlation coefficients of the standard curves of organochlorine pesticides starting from γ-chlordane have been significantly improved.

[0029] Comparing the experimental data of Example 3 and Comparative Example 3, the influence of nitric oxide on the linear relationship of the calibration curve of organophosphorus pesticides is shown in Table 3: Table 3 Effect of nitric oxide on the linear relationship of the calibration curve of organophosphorus pesticides

[0030] Table 3

[0031] As shown in Table 3, in the presence of nitric oxide, the linear relationships of most organophosphorus pesticides are basically consistent with those in the absence of nitric oxide. However, the standard curves of some organophosphorus pesticides such as diazinon, fipronil, fenthion sulfone and pyraclostrobin can be significantly improved in the presence of nitric oxide. In particular, nitric oxide can effectively improve the linear relationship of the standard curves of 10 pyrethroids, indicating that nitric oxide not only does not react with other compounds and interfere with the entire analysis process, but also can significantly improve the correlation coefficients of the standard curves of some organophosphorus pesticides and pyrethroids.

[0032] Degradation rate test: A cylinder of nitric oxide standard gas with a concentration of 5000 μmol / mol was connected to the carrier gas flow path of the gas chromatography-mass spectrometry inlet, and nitric oxide gas was continuously passed through the gas chromatography inlet. Then, p,p'-DDT and endrin standard solutions in n-hexane phase (concentration of 10 μg / mL) were injected to obtain a chromatogram of the degradation of p,p'-DDT and endrin under the condition of passing nitric oxide. Figure 1 This is the chromatogram of the degradation rate of p,p'-DDT when no nitric oxide is introduced. Figure 2 This is the chromatogram of p,p'-DDT degradation rate when nitric oxide is introduced. Figure 3 This is the chromatogram of the degradation rate of endrin when no nitric oxide is introduced. Figure 4 The figure is a chromatogram of the degradation rate of endrin when nitric oxide is introduced. During the test, nitric oxide gas is first introduced into the injection port of the gas chromatograph / mass spectrometer and maintained for 20 seconds; then the pesticide test sample is sent into the injection port of the gas chromatograph / mass spectrometer for sample analysis.

[0033] The gas chromatography-mass spectrometry analysis conditions were as follows: Inlet temperature: 280°C, split, split ratio: 5:1; n-Hexane phase p,p'-DDT and endrin standard solution injection volume: 1μL Nitric oxide infusion time: 20S Column flow rate: 1.0mL / min Program temperature rise: 120℃ for 2 min, 10℃ / min to 180℃, hold for 2 min, 20℃ / min to 260℃, hold for 6 min, 30℃ / min to 320℃, hold for 3 min Gas-gas interface temperature: 280℃ Mass spectrometry scanning mode: SCAN, scanning range: 45~500 mass numbers Mass Spectrometry Tuning: Automatic Tuning Comparative test: Prepare standard solutions of p,p'-DDT and endrin in n-hexane phase (concentration of 10μg / mL), and analyze them separately to obtain the degradation rates of p,p'-DDT and endrin when no nitric oxide is introduced. The gas chromatography-mass spectrometry analysis conditions are as follows: Inlet temperature: 280°C, split, split ratio: 5:1; n-Hexane phase p,p'-DDT and endrin standard solution injection volume: 1μL Column flow rate: 1.0mL / min Program temperature rise: 120℃ for 2 min, 10℃ / min to 180℃, hold for 2 min, 20℃ / min to 260℃, hold for 6 min, 30℃ / min to 320℃, hold for 3 min Gas-gas interface temperature: 280℃ Mass spectrometry scanning mode: SCAN, scanning range: 45~500 mass numbers Mass Spectrometry Tuning: Automatic Tuning The effect of nitric oxide on the degradation of p,p'-DDT and endrin is shown in Table 4: Table 4 Effect of nitric oxide on the degradation of p,p'-DDT and endrin

[0034] It can be seen from Table 4 that in the absence of nitric oxide, the degradation rate of p,p'-DDT is 98.5%, and the degradation rate of endrin is 27.0%, which exceeds the standard allowable range. After nitric oxide is introduced into the injection port, the degradation rate of p,p'-DDT is 4.3%, and the degradation rate of endrin is 6.1%, indicating that after the introduction of nitric oxide gas, the degradation problem of p,p'-DDT and endrin in the chromatographic analysis process can be effectively reduced, meeting the requirements.

[0035] Stability test: Connect a nitric oxide standard gas cylinder with a concentration of 5000μmol / mol to the carrier gas flow path of the gas chromatography-mass spectrometry inlet, pass the nitric oxide gas through the gas chromatography inlet continuously, and continuously inject p,p'-DDT and endrin standard solutions 10 times to determine the stability of nitric oxide in reducing the degradation rate of p,p'-DDT and endrin under continuous injection conditions. During the test, first pass the nitric oxide gas into the gas chromatography / mass spectrometer inlet and keep it for 10s; then send the pesticide test sample into the gas chromatography / mass spectrometer inlet for sample analysis.

[0036] The gas chromatography-mass spectrometry analysis conditions were as follows: Inlet temperature: 280°C, split, split ratio: 5:1; n-Hexane phase p,p'-DDT and endrin standard solution injection volume: 1μL Nitric oxide infusion time: 10S Column flow rate: 1.0mL / min Program temperature rise: 120℃ for 2 min, 10℃ / min to 180℃, hold for 2 min, 20℃ / min to 260℃, hold for 6 min, 30℃ / min to 320℃, hold for 3 min Gas-gas interface temperature: 280℃ Mass spectrometry scanning mode: SCAN, scanning range: 45~500 mass numbers Mass Spectrometry Tuning: Automatic Tuning Comparative test: Prepare standard solutions of p,p'-DDT and endrin in n-hexane phase (concentration of 10μg / mL), and analyze them separately to obtain the degradation rates of p,p'-DDT and endrin when no nitric oxide is added.

[0037] The gas chromatography-mass spectrometry analysis conditions were as follows: Inlet temperature: 280°C, split, split ratio: 5:1; n-Hexane phase p,p'-DDT and endrin standard solution injection volume: 1μL Column flow rate: 1.0mL / min Program temperature rise: 120℃ for 2 min, 10℃ / min to 180℃, hold for 2 min, 20℃ / min to 260℃, hold for 6 min, 30℃ / min to 320℃, hold for 3 min Gas-gas interface temperature: 280℃ Mass spectrometry scanning mode: SCAN, scanning range: 45~500 mass numbers Mass Spectrometry Tuning: Automatic Tuning The stability of nitric oxide in reducing the degradation rate of p,p'-DDT and endrin is shown in Table 5: Table 5 Stability of nitric oxide in reducing the degradation rate of p,p'-DDT and endrin

[0038] As shown in Table 5, under the condition of continuous sampling, the degradation rate of p,p'-DDT dropped from 94.8% to 3.7%~4.8%, and the degradation rate of endrin dropped from 24.5% to 5.0%~6.3%, meeting the requirements. The degradation rates of p,p'-DDT and endrin remained low, indicating that nitric oxide can continuously and stably maintain the degradation rates of P,P'-DDT and endrin at an extremely low level.

[0039] In summary, it can be seen that the present invention only needs to pass nitric oxide gas into the pesticide analysis instrument for a period of time before the sample to be tested is injected, so as to simultaneously reduce the degradation rates of p,p'-DDT and endrin, and improve the linear relationship and chromatographic matrix effect of highly active, unstable, and easily residual compounds.

[0040] The above is only a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art shall not deviate from the spirit and scope of the present invention, and shall be within the scope of protection of the claims attached to the present invention.

Claims

1. A method for reducing the degradation rate of p,p'-DDT and endrin in the pesticide analysis process, characterized in that: The following steps are involved: S1. Pass the gas containing unpaired electrons into the inlet of the pesticide analyzer and keep it for 10s-60s; S2. Send the pesticide test sample into the sample inlet of the pesticide analysis instrument for sample analysis.

2. The method according to claim 1, characterized in that: The gas containing unpaired electrons is nitric oxide.

3. The method according to any one of claims 1 to 2, characterized in that: The pesticide analysis instrument is a gas chromatograph / mass spectrometer or a gas chromatograph.

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