A method for reducing the degradation rates of p,p'-DDT and endrin during pesticide analysis

Abstract

The present invention discloses a method for reducing the degradation rates of p,p'-DDT and endrin during the pesticide analysis process, which relates to the technical field of chromatographic analysis and includes the following steps: S1. Introduce a gas containing unpaired electrons into the injection port of the pesticide analysis instrument and maintain it for 10 s - 60 s; S2. Send the pesticide detection sample into the injection port of the analysis instrument for sample analysis. 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 even below 10%, ensuring the stability of the analysis and greatly improving the accuracy of the analysis. At the same time, the present invention only needs to use a small amount of nitric oxide gas as a degradation inhibitor to simultaneously control the degradation rates of p,p'-DDT and endrin, with low cost, simple operation, greatly reducing the maintenance frequency of the chromatographic system, and effectively saving the analysis cost and time.

Description

Technical Field

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

[0002] Currently, during the gas chromatography or gas chromatography / mass spectrometry analysis of organochlorine pesticides, p,p'-DDT and endrin are extremely prone to degradation during the analysis, resulting in failed sample analysis. The reason for the degradation of p,p'-DDT and endrin is that when the injection port and chromatographic system contain a lot of impurities after long-term analysis, these impurities generate a lot of active sites. At a relatively high vaporization chamber temperature (such as 220°C to 280°C), a large number of highly active substances similar to hydrogen radicals are generated in the silanized chromatographic system at these active sites. These substances have characteristics similar to catalysts, 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 regulations of "HJ 921-2017 Determination of Organochlorine Pesticides in Soils and Sediments - 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), and 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 ≥ 15%, or the sum of the degradation rates of the two ≥ 30%, it indicates 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 keep the degradation rates of p,p'-DDT and endrin within 15% in each analysis.

[0004] This degradation reaction is essentially a free radical type of reduction reaction. On the quaternary carbon atoms of p,p'-DDT with 3 chlorine substitutions, due to the strong electron-withdrawing inductive effect of the chlorine atoms, the quaternary carbon atoms bonded to the chlorine atoms have relatively high activity. Under the combined action of high temperature and active sites, these active sites generate highly active substances similar to hydrogen radicals. These radicals either undergo a reduction reaction of halogenated hydrocarbons, replace the chlorine radicals on the quaternary carbon atoms connected to 3 chlorine atoms to generate p,p'-DDD, or undergo an elimination reaction to generate p,p'-DDE. Endrin is a relatively complex ring structure. Attacked by hydrogen radical active substances, it opens the ring to form endrin aldehyde, and the hydrogen radical replaces the chlorine radical to form endrin ketone.

[0005] At present, the traditional methods for controlling the degradation rates of p,p'-DDT and endrin to meet the standards during the analysis of organochlorine pesticides mainly involve the cleaning and maintenance of the chromatographic system. For example, cleaning the chromatographic injection port with organic reagents, silanizing or inerting the gas path, replacing the new split plate or inerting liner, cutting off the front 5 - 10 cm of the chromatographic column, re-aging the chromatographic column, and replacing the new chromatographic column. The purpose of these traditional methods is to reduce the active sites introduced or generated in the chromatographic system, thereby reducing the generation of hydrogen radicals by reducing the number of active sites, so as to stabilize the degradation rate at a relatively low level and ensure the smooth progress of the experiment. However, the problems with traditional methods are that the consumables are expensive, the cost is high, the maintenance is frequent, and the efficiency is low. Because the injection process of chromatography is a process of contaminating the chromatographic system, the impurities carried in the sample (such as macromolecular substances, humus, proteins, pigments, etc.) will inevitably generate active sites at high temperatures, leading to degradation. The continuous injection process is a process of continuously increasing the active sites in the system, and the degradation rates of p,p'-DDT and endrin will inevitably increase with the number of injections and the degree of contamination of the chromatographic system by the sample. To ensure that the degradation rates of p,p'-DDT and endrin always remain within 15%, continuous cleaning and maintenance of the chromatographic system are required. The excessively high maintenance frequency of the chromatographic system not only takes time and effort, has low sample analysis efficiency, but also has high consumable and labor costs, and it is difficult to guarantee the analysis accuracy.

[0006] The invention patent with the patent number CN201911169168.4 uses an organic compound with a halogen-containing strong electronegative group added during sample injection as a degradation inhibitor to maintain the degradation rate of p,p'-DDT below 15%. Compared with the above traditional methods, this invention ensures the stability of the analysis, improves the analysis accuracy, significantly reduces the maintenance frequency of the chromatographic system, effectively saves the consumable and labor costs of the analysis, and shortens the analysis time. However, since the outer electrons of chlorine atoms in the halogen-containing organic compound (such as CCl 4 ) have an 8-electron stable structure, its reaction ability with highly active substances similar to 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. Moreover, the liquid halogen-containing organic compound with a strong electronegative group needs to be completely vaporized at the chromatographic injection port before it can react with the highly active substances similar to hydrogen radicals generated at the active sites in the system, thereby inhibiting the reaction between p,p'-DDT and the highly active substances similar to hydrogen radicals and achieving the effect of reducing the degradation rate of p,p'-DDT. This is a competitive reaction process between the halogen-containing compound and p,p'-DDT for the highly active substances similar to hydrogen radicals. Therefore, when there are many sample impurities or a large number of active sites exist in the system, generating a large number of highly active substances similar to hydrogen radicals, or the vaporization process of the liquid halogen-containing organic compound becomes slow or incomplete, the inhibitory effect of the liquid halogen-containing organic compound on degradation will be 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 aldrin during the pesticide analysis process.

[0008] The object of the present invention is achieved by the following technical solutions:

[0009] A method for reducing the degradation rates of p,p'-DDT and aldrin during the pesticide analysis process, comprising the following steps:

[0010] S1. Introduce a gas containing unpaired electrons into the injection port of the pesticide analysis instrument and maintain it for 10 s - 60 s;

[0011] S2. Feed the pesticide detection sample into the injection port of the analysis instrument for sample analysis.

[0012] Specifically, the gas containing unpaired electrons is nitric oxide.

[0013] The pesticide analysis instrument is a gas chromatography / mass spectrometer or a gas chromatograph.

[0014] When using the gas containing unpaired electrons for pesticide analysis, it can also improve the linear relationship of the standard curves of organochlorine pesticides, organophosphorus pesticides and pyrethroids, and reduce the matrix effect in the analysis system.

[0015] The beneficial effects of the present invention are as follows:

[0016] The present invention utilizes the competitive reaction between nitric oxide gas and highly active substances similar to hydrogen radicals generated by active sites accumulated in the chromatographic system, thereby reducing the degradation rates of p,p'-DDT and aldrin. At the same time, since nitric oxide can significantly eliminate the free radicals generated in the chromatographic system, nitric oxide can also improve the linear relationship of the standard curves of some compounds with high activity, easy decomposition and poor chromatographic performance and improve the chromatographic matrix effect of these substances. And because nitric oxide itself is a gas and does not need to be vaporized during injection, introducing nitric oxide gas in advance to consume the active substances can further ensure the reduction of the degradation rates of p,p'-DDT and aldrin.

[0017] The present invention makes up for the problem that the invention patent with the patent number CN201911169168.4 cannot solve the degradation problem of aldrin during the chromatographic analysis of organochlorine pesticides, and adopts gaseous nitric oxide to avoid the problem that the degradation inhibition effect on p,p'-DDT is weakened when the vaporization of liquid halogenated organic compounds is unfavorable or incomplete.

[0018] 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 even below 10% (there is still a considerable distance from the red line), ensuring the stability of the analysis and greatly improving the accuracy of the analysis. At the same time, the present invention only needs to use a small amount of nitric oxide gas as a degradation inhibitor to simultaneously control the degradation rates of p,p'-DDT and endrin, with low cost and simple operation, greatly reducing the maintenance frequency of the chromatographic system and effectively saving the analysis cost and time. Description of the Drawings

[0019] Figure 1 It is a chromatogram of the degradation rate of p,p'-DDT without introducing nitric oxide in Example 1;

[0020] Figure 2 It is a chromatogram of the degradation rate of p,p'-DDT when introducing nitric oxide in Example 1;

[0021] Figure 3 It is a chromatogram of the degradation rate of endrin without introducing nitric oxide in Example 1;

[0022] Figure 4 It is a chromatogram of the degradation rate of endrin when introducing nitric oxide in Example 1;

[0023] In the figure, 1 - p,p'-DDT, 2 - p,p'-DDD, 3 - p,p'-DDE, 4 - endrin, 5 - endrin aldehyde, 6 - endrin ketone. Detailed Embodiments

[0024] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0025] According to the provisions of "HJ 921-2017 Determination of Organochlorine Pesticides in Soils and Sediments - 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), and 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 ≥ 15%, or the sum of the degradation rates of the two ≥ 30%, it indicates 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 keep the degradation rates of p,p'-DDT and endrin within 15% in each analysis. 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 during the analysis process are both kept within 15%, so as to obtain true analysis results.

[0026] The main technical means adopted by the present invention is that before injecting the test sample, nitric oxide is introduced into the gas chromatography injection port through the gas chromatography carrier gas flow path and kept for a period of time, and then the test sample of organochlorine pesticides is sampled through a liquid injector and enters the chromatographic system for analysis. The nitric oxide maintained in the injection port realizes the inhibition of the degradation of p,p'-DDT and endrin.

[0027] Example 1

[0028] An experiment on the reduction of the degradation rates of p,p'-DDT and endrin by nitric oxide in the mixed test of p,p'-DDT and endrin with other organochlorine pesticide components. Seven kinds of organochlorine pesticide mixtures (α666, hexachlorobenzene, β666, pentachloronitrobenzene, γ666, δ666, heptachlor) containing P,P'-DDT and endrin and without P,P'-DDT and endrin and their degradation products p,p'-DDD, P,P'-DDE, endrin aldehyde and endrin ketone were respectively prepared (concentration: 10 μg / mL). During the detection, first introduce nitric oxide gas into the injection port of the gas chromatography / mass spectrometry instrument and keep it for 30 s; then send the pesticide test sample into the injection port of the gas chromatography / mass spectrometry instrument for sample analysis.

[0029] The gas chromatography mass spectrometry analysis conditions are as follows:

[0030] Injection port temperature: 280 °C, split flow, split ratio: 5∶1;

[0031] Injection volume of standard solution: 1 μL

[0032] Nitric oxide introduction time: 30S

[0033] Column flow rate: 1.0 mL / min

[0034] Programmed temperature: Hold at 120 °C for 2 min, increase to 180 °C at 10 °C / min, hold for 2 min, increase to 260 °C at 20 °C / min, hold for 6 min, increase to 320 °C at 30 °C / min, hold for 3 min

[0035] GC-MS interface temperature: 280 °C

[0036] Mass spectrometry scan mode: SCAN, scan range: 45 - 500 mass numbers

[0037] Mass spectrometry tuning: Automatic tuning

[0038] Example 2

[0039] Prepare the calibration curves of 34 organochlorine pesticides, which are 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, tetrachlorometaxylene, α666, hexachlorobenzene, β666, pentachloronitrobenzene, γ666, δ666, heptachlor, aldrin, dicofol, heptachlor epoxide, exo-heptachlor epoxide, O,p’-DDE, γ-chlordane, α-chlordane, endosulfan 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 respectively. The concentration points of the calibration curves are 20 μg / L, 50 μg / L, 100 μg / L, 200 μg / L, 500 μg / L, 1000 μg / L, 2000 μg / L respectively. The internal standard is phenanthrene-d10 with a concentration of 200 μg / L. During detection, first introduce nitric oxide gas into the injection port of the gas chromatography / mass spectrometer and hold for 40 s; then send the pesticide detection sample into the injection port of the gas chromatography / mass spectrometer for sample analysis.

[0040] The gas chromatography - mass spectrometry analysis conditions are as follows:

[0041] Injection port temperature: 280 °C, split flow, split ratio: 5:1;

[0042] Nitric oxide introduction time: 40 S

[0043] Column flow rate: 1.0 mL / min

[0044] Programmed temperature: Hold at 120 °C for 2 min, increase to 180 °C at 10 °C / min, hold for 2 min, increase to 260 °C at 20 °C / min, hold for 6 min, increase to 320 °C at 30 °C / min, hold for 3 min

[0045] Temperament interface temperature: 280 °C

[0046] 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.

[0047] Mass spectrometry tuning: Automatic tuning

[0048] Example 3

[0049] Prepare calibration curves for 47 kinds of organophosphorus pesticides and pyrethroids. The 47 kinds of organophosphorus pesticides and pyrethroids are dichlorvos, mevinphos, cadusafos, demeton-S, phorate, sulprofos, phorate, demeton-O, dimethoate, diazinon, disulfoton, phosalone, methyl parathion, fenthion, malathion, chlorpyrifos, phorate sulfone, fenthion, parathion, triadimefon, crotoxyphos, trichloronate, fipronil, trans-permethrin, mecarbam, bensulide, insecticide, profenofos, defoliant, fosthiazate, fenthion sulfone, trithion, endosulfan sulfate, piperonyl butoxide, tetramethrin 1, bifenthrin, tetramethrin 2, EPN, bromopropylate, pyrethrin, bromfenvinfos, cis-permethrin, pyraclofos, permethrin 1, permethrin 2, coumaphos, cypermethrin 1, cypermethrin 2, cypermethrin 3, cypermethrin 4, fenvalerate 1, fenvalerate 2, deltamethrin. The concentration points of each 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. The internal standard is 1,2,4,5-tetrachloro-m-xylene with a concentration of 10.0 mg / L. During detection, first pass nitric oxide gas into the injection port of the gas chromatography / mass spectrometry instrument and keep it for 60 s; then send the pesticide detection sample into the injection port of the gas chromatography / mass spectrometry instrument for sample analysis.

[0050] The gas chromatography-mass spectrometry analysis conditions are as follows:

[0051] Injection port temperature: 280 °C, split flow, split ratio: 5:1;

[0052] Nitric oxide passing-in time: 60 S

[0053] Column flow rate: 1.0 mL / min

[0054] Programmed temperature rise: Keep at 120 °C for 2 min, rise to 180 °C at 10 °C / min, keep for 2 min, rise to 260 °C at 20 °C / min, keep for 6 min, rise to 320 °C at 30 °C / min, and keep for 3 min

[0055] Temperament interface temperature: 280 °C

[0056] Mass spectrometry scanning mode: SCAN

[0057] Mass spectrometry tuning: Automatic tuning

[0058] Comparative Example 1

[0059] Different from Example 1, no nitric oxide was introduced under the gas chromatography - mass spectrometry analysis conditions.

[0060] Comparative Example 2

[0061] Different from Example 2, no nitric oxide was introduced under the gas chromatography - mass spectrometry analysis conditions.

[0062] Comparative Example 3

[0063] Different from Example 3, no nitric oxide was introduced under the gas chromatography - mass spectrometry analysis conditions.

[0064] Comparing the experimental data of Example 1 and Comparative Example 1, the effects of nitric oxide on the degradation of p,p’ - DDT and aldrin in the case of mixing other organochlorine pesticide components are shown in Table 1:

[0065] Table 1 Effects of nitric oxide on the degradation of p,p’ - DDT and aldrin when other organochlorine pesticides are present

[0066]

[0067] As can be seen from Table 1, when other organochlorine pesticides are present, without nitric oxide, the degradation rate of p,p’ - DDT is 97.5% and the degradation rate of aldrin is 28.7%, exceeding the standard allowable range. After introducing nitric oxide at the injection port, the degradation rate of p,p’ - DDT is 3.6% and the degradation rate of aldrin is 5.5%. This shows that in the case of mixing other organochlorine pesticides, nitric oxide gas can still effectively reduce the degradation rates of p,p’ - DDT and aldrin during chromatographic analysis, meeting the method requirements.

[0068] 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:

[0069] Table 2 Influence of nitric oxide on the linear relationship of the calibration curve of organochlorine pesticides

[0070]

[0071] As shown in Table 2, in the presence of nitric oxide, the correlation coefficients of 34 organochlorine pesticides are better than those of 34 organochlorine pesticides without nitric oxide, indicating that the presence of nitric oxide does not react with p,p'-DDT or endrin or other compounds, does not interfere with the entire analysis process, and can improve the correlation coefficients of organochlorine pesticides. Especially for organochlorine pesticides starting from γ-chlordane, the correlation coefficients of their standard curves are significantly improved.

[0072] Comparing the experimental data of Example 3 and Comparative Example 3, the influence of nitric oxide on the linear relationship of the calibration curves of organophosphorus pesticides is shown in Table 3:

[0073] Table 3 Influence of nitric oxide on the linear relationship of the calibration curves of organophosphorus pesticides

[0074]

[0075] Continued Table 3

[0076]

[0077] As shown in Table 3, in the presence of nitric oxide, the linear relationships of most organophosphorus pesticides are basically the same as those without nitric oxide. However, for some organophosphorus pesticides such as diazinon, fipronil, sulfoxide of fenthion, and pyraclofos, the standard curves can be significantly improved in the presence of nitric oxide. Especially, nitric oxide can effectively improve the linear relationships of the standard curves of 10 pyrethroids, indicating that nitric oxide not only does not react with other compounds and does not interfere with the entire analysis process, but also can significantly improve the correlation coefficients of the standard curves of certain organophosphorus pesticides and pyrethroids.

[0078] Degradation rate test:

[0079] Connect a steel cylinder of nitric oxide standard gas with a concentration of 5000 μmol / mol to the carrier gas flow path of the gas chromatography-mass spectrometry injection port. Continuously pass the nitric oxide gas through the gas chromatography injection port, and then inject the standard solutions of p,p'-DDT and endrin in n-hexane phase (concentration: 10 μg / mL) to obtain the chromatograms 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 without passing nitric oxide. Figure 2 This is the chromatogram of the degradation rate of p,p'-DDT when passing nitric oxide. Figure 3 This is the chromatogram of the degradation rate of endrin without passing nitric oxide. Figure 4 This is the chromatogram of the degradation rate of endrin when passing nitric oxide. During detection, first pass the nitric oxide gas into the injection port of the gas chromatography / mass spectrometer and keep it for 20 s; then send the pesticide detection sample into the injection port of the gas chromatography / mass spectrometer for sample analysis.

[0080] The gas chromatography - mass spectrometry analysis conditions are as follows:

[0081] Injector temperature: 280 °C, split injection, split ratio: 5:1;

[0082] Injection volume of p,p'-DDT and endrin standard solutions in n - hexane phase: 1 μL

[0083] Nitric oxide introduction time: 20 s

[0084] Column flow rate: 1.0 mL / min

[0085] Programmed temperature rise: Hold at 120 °C for 2 min, rise to 180 °C at 10 °C / min, hold for 2 min, rise to 260 °C at 20 °C / min, hold for 6 min, rise to 320 °C at 30 °C / min, hold for 3 min

[0086] GC - MS interface temperature: 280 °C

[0087] Mass spectrometry scan mode: SCAN, scan range: 45 - 500 mass numbers

[0088] Mass spectrometry tuning: Automatic tuning

[0089] Comparison test: Prepare p,p'-DDT and endrin standard solutions in n - hexane phase (concentration is 10 μg / mL), and after separate injection analysis, obtain the degradation rates of p,p'-DDT and endrin without nitric oxide introduction. The gas chromatography - mass spectrometry analysis conditions are as follows:

[0090] Injector temperature: 280 °C, split injection, split ratio: 5:1;

[0091] Injection volume of p,p'-DDT and endrin standard solutions in n - hexane phase: 1 μL

[0092] Column flow rate: 1.0 mL / min

[0093] Programmed temperature rise: Hold at 120 °C for 2 min, rise to 180 °C at 10 °C / min, hold for 2 min, rise to 260 °C at 20 °C / min, hold for 6 min, rise to 320 °C at 30 °C / min, hold for 3 min

[0094] GC - MS interface temperature: 280 °C

[0095] Mass spectrometry scan mode: SCAN, scan range: 45 - 500 mass numbers

[0096] Mass spectrometry tuning: Automatic tuning

[0097] The influence of nitric oxide on the degradation of p,p'-DDT and endrin is shown in Table 4:

[0098] Table 4 Effects of Nitric Oxide on the Degradation of p,p’-DDT and Endrin

[0099]

[0100] As can be seen from Table 4, in the absence of nitric oxide, the degradation rate of p,p’-DDT was 98.5% and that of endrin was 27.0%, exceeding the standard allowable range. After introducing nitric oxide into the injection port, the degradation rate of p,p’-DDT was 4.3% and that of endrin was 6.1%, indicating that after introducing nitric oxide gas, the degradation problems of p,p’-DDT and endrin during chromatographic analysis can be effectively reduced, meeting the requirements.

[0101] Stability Test:

[0102] Connect a cylinder of nitric oxide standard gas with a concentration of 5000 μmol / mol to the carrier gas flow path of the injection port of the gas chromatography-mass spectrometry instrument. Continuously pass the nitric oxide gas through the gas chromatography injection port, and continuously inject the p,p’-DDT and endrin standard solutions 10 times to determine the stability of nitric oxide in reducing the degradation rates of p,p’-DDT and endrin under continuous injection conditions. During detection, first introduce the nitric oxide gas into the injection port of the gas chromatography / mass spectrometry instrument and keep it for 10 s; then send the pesticide detection sample into the injection port of the gas chromatography / mass spectrometry instrument for sample analysis.

[0103] The gas chromatography-mass spectrometry analysis conditions are as follows:

[0104] Injection port temperature: 280 °C, split, split ratio: 5∶1;

[0105] Injection volume of p,p’-DDT and endrin standard solutions in n-hexane phase: 1 μL

[0106] Nitric oxide introduction time: 10 S

[0107] Column flow rate: 1.0 mL / min

[0108] Programmed temperature rise: Hold at 120 °C for 2 min, rise to 180 °C at 10 °C / min, hold for 2 min, rise to 260 °C at 20 °C / min, hold for 6 min, rise to 320 °C at 30 °C / min, hold for 3 min

[0109] Gas chromatography-mass spectrometry interface temperature: 280 °C

[0110] Mass spectrometry scanning mode: SCAN, scanning range: 45 - 500 mass numbers

[0111] Mass spectrometry tuning: Automatic tuning

[0112] Comparative test: Prepare standard solutions of p,p'-DDT and endrin in n-hexane phase (concentration: 10 μg / mL). After separate injection analysis, the degradation rates of p,p'-DDT and endrin without adding nitric oxide are obtained.

[0113] The gas chromatography-mass spectrometry analysis conditions are as follows:

[0114] Injection port temperature: 280 °C, split injection, split ratio: 5:1;

[0115] Injection volume of the standard solutions of p,p'-DDT and endrin in n-hexane phase: 1 μL

[0116] Column flow rate: 1.0 mL / min

[0117] Programmed temperature rise: Hold at 120 °C for 2 min, rise to 180 °C at 10 °C / min, hold for 2 min, rise to 260 °C at 20 °C / min, hold for 6 min, rise to 320 °C at 30 °C / min, hold for 3 min

[0118] GC-MS interface temperature: 280 °C

[0119] Mass spectrometry scan mode: SCAN, scan range: mass numbers 45 - 500

[0120] Mass spectrometry tuning: Automatic tuning

[0121] The stability of nitric oxide in reducing the degradation rates of p,p'-DDT and endrin is shown in Table 5:

[0122] Table 5 Stability of nitric oxide in reducing the degradation rates of p,p'-DDT and endrin

[0123]

[0124] As shown in Table 5, under the condition of continuous injection, the degradation rate of p,p'-DDT decreases from 94.8% to 3.7% - 4.8%, and the degradation rate of endrin decreases from 24.5% to 5.0% - 6.3%, meeting the requirements. The degradation rates of p,p'-DDT and endrin always remain at low values, indicating that nitric oxide can continuously and stably maintain the degradation rates of p,p'-DDT and endrin at a very low level.

[0125] In summary, it can be seen that in the present invention, only by introducing nitric oxide gas into the pesticide analysis instrument for a period of time before injecting the sample to be tested, the degradation rates of p,p'-DDT and endrin can be reduced simultaneously, and the linear relationship and chromatographic matrix effect of highly active, unstable, and easily residual compounds can also be improved.

[0126] The above are only the preferred embodiments of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein, should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be changed within the scope of the concept described herein through the above teachings or the techniques or knowledge in related fields. And the changes and alterations made by those skilled in the art that do not depart from the spirit and scope of the present invention shall fall within the protection scope of the appended claims of 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, sending the pesticide test sample into the sampling port of the pesticide analysis instrument for sample analysis; The gas containing unpaired electrons is nitric oxide.

2. The method according to claim 1, characterized in that: The pesticide analysis instrument is a gas chromatograph-mass spectrometer or a gas chromatograph.

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