Pretreatment method and application of silage corn

Abstract

The invention belongs to the technical field of feed quality control, and particularly relates to a pretreatment method and application of silage corn. The pretreatment method comprises the following steps: (1) extracting silage corn by using an organic solvent, and centrifuging to obtain supernate; (2) distilling and concentrating the supernate to obtain a concentrated solution; and (3) eluting the concentrated solution by using a solid-phase extraction column and an elution solvent to obtain a pretreatment solution, wherein the solid-phase extraction column is selected from a Cleanert-TPT column. According to the pretreatment method, no obvious pigment is generated after treatment, and the recovery rate of pesticide residues such as parachloropropham, phorate, terbufos, methidathion, bifenthrin, ethofenprox and deltamethrin is high; and the accuracy of pesticide residue detection is high.

Description

Technical Field

[0001] The invention belongs to the technical field of feed quality control, and particularly relates to a pretreatment method for silage corn and application thereof. Background Art

[0002] In recent years, dairy products have been loved by more and more people, which has led to a period of rapid development of the dairy industry. As people's demand for dairy products increases, their requirements for milk quality are also increasing. In the process of dairy cow breeding, there are many factors that affect milk quality, mainly including breed, environment, feed nutrition, age, parity, lactation period and health status. Among them, nutrients play a key role in milk quality because they can directly, quickly and effectively regulate milk quality.

[0003] In the production of dairy cows, 60%-100% of their daily diet is green roughage. As the most important green roughage in my country, the quality of silage corn is one of the key factors that determine whether ruminants can achieve the best production performance, especially the pesticide residues in it directly affect the quality and safety of livestock products.

[0004] At present, there are few studies on pesticide residues in silage corn at home and abroad. Generally, silage corn needs to be pre-treated before detecting pesticide residues. The existing technology will extract pigments during the pre-treatment, which affects the accuracy of subsequent detection. Therefore, it is necessary to develop a pre-treatment method that can reduce pigments when extracting silage corn and facilitate pesticide residue detection. Summary of the invention

[0005] In view of the above problems, one of the objects of the present invention is to provide a pretreatment method for silage corn, which can reduce the extraction of pigments in silage corn and improve the recovery rate of pesticide residues by selecting a suitable solid phase extraction column Cleanert-TPT column for elution, which is conducive to improving the accuracy of subsequent pesticide residue detection.

[0006] In order to achieve the above object, the present invention can adopt the following technical solutions:

[0007] The present invention provides a method for pre-treating silage corn, comprising: (1) extracting the silage corn using an organic solvent and centrifuging to obtain a supernatant; (2) distilling and concentrating the supernatant to obtain a concentrated solution; (3) eluting the concentrated solution using a solid phase extraction column and an elution solvent to obtain a pre-treatment solution, wherein the solid phase extraction column is selected from a Cleanert-TPT column.

[0008] Another aspect of the present invention provides a method for detecting pesticide residues in silage corn, wherein the pesticide residues include one or more of chlorpropham, phorate, terbufos, methidathion, bifenthrin, ethomethrin and deltamethrin, and the detection method comprises: (1) pre-treating the silage corn using the above-mentioned silage corn pre-treatment method to obtain a pre-treatment liquid; and (2) detecting the pesticide residues in the pre-treatment liquid using gas chromatography-mass spectrometry.

[0009] The beneficial effects of the present invention include at least: the pretreatment method of silage corn provided by the present invention has no obvious pigment after treatment, and has a high recovery rate for pesticide residues such as chlorpropham, phorate, terbufos, methidathion, bifenthrin, ethomethrin and deltamethrin; and the accuracy of detecting pesticide residues is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 The extract was purified by ENVI-18 column;

[0011] Figure 2 The extract was purified by Sep-Pak aminopropyl column;

[0012] Figure 3 The extract was purified by Envi-Carb activated carbon column and ENVI-18 column;

[0013] Figure 4 The extract was purified by Cleanert-TPT column;

[0014] Figure 5 The matrix blank solution, sample and spiked sample are shown in Figure 1. No. 1 is the matrix blank solution, No. 2 is the sample, and No. 3 is the spiked sample.

[0015] Figure 6 is the standard curve of chlorpropham;

[0016] Figure 7 is the standard curve of phorate;

[0017] Figure 8 is the standard curve of terbuthion;

[0018] Fig. 9 is the standard curve of methidathion;

[0019] Fig.10 is the standard curve of bifenthrin;

[0020] Fig.11 is the standard curve of ethomethrin;

[0021] Fig.12 is the standard curve of deltamethrin;

[0022] Fig.13 Detection chromatogram for substrate;

[0023] Fig.14 The mass spectrum of chlorpheniramine in substrate detection;

[0024] Fig.15 This is the mass spectrum of phorate in substrate detection;

[0025] Fig.16 This is the mass spectrum of terbuthion in substrate detection;

[0026] Fig.17 This is the mass spectrum of thiophanate-methyl in substrate detection;

[0027] Fig.18 This is the mass spectrum of bifenthrin in substrate detection;

[0028] Fig.19 This is the mass spectrum of ethoxyfenpropathrin in substrate detection;

[0029] Fig. 20 This is the mass spectrum of deltamethrin in substrate detection;

[0030] Fig.21 Detect chromatogram for sample 1;

[0031] Fig. 22 Detect chromatogram for sample 2;

[0032] Fig.23 Detection chromatogram for sample 3;

[0033] Fig.24 Detection chromatogram for sample 4. DETAILED DESCRIPTION

[0034] The examples are provided to better illustrate the present invention, but the present invention is not limited to the examples. Therefore, those skilled in the art may make non-essential improvements and adjustments to the implementation scheme according to the above invention content, which still fall within the protection scope of the present invention.

[0035] The terms used herein are only used to describe specific embodiments and are not intended to limit the present disclosure. Unless the context has a significantly different meaning, expressions in the singular include expressions in the plural. As used herein, it should be understood that terms such as "include", "have", "include" are intended to indicate the presence of features, numbers, operations, components, parts, elements, materials or combinations. The terms of the present invention are disclosed in the specification, and are not intended to exclude the possibility that one or more other features, numbers, operations, components, parts, elements, materials or combinations thereof may exist or may be added. As used herein, " / " may be interpreted as "and" or "or", depending on the circumstances.

[0036] The term "silage" in the present invention refers to a storage technology or method in which fresh plant species are compacted and sealed to isolate the stored green fodder from the external air, causing internal hypoxia and leading to anaerobic fermentation, thereby producing organic acids, which can preserve the fresh fodder for a long time and can reduce nutrient loss and facilitate animal digestion and absorption.

[0037] The term "silage corn" in the present invention includes corn varieties specifically used for feed that are silaged as a whole, and also includes corn stalks that are silaged after edible tender corn is removed.

[0038] The term "extraction" in the present invention refers to the preparation of useful components (such as constituents or juice) from a substance by solvent treatment, distillation, dehydration, pressure or centrifugal force, or other chemical or mechanical processes.

[0039] The term "purification" in the present invention refers to removing unnecessary or harmful impurities to make the items reach the level of purity.

[0040] The embodiment of the present invention provides a method for processing silage corn, comprising: (1) extracting the silage corn using an organic solvent and centrifuging to obtain a supernatant; (2) distilling and concentrating the supernatant to obtain a concentrated solution; (3) eluting the concentrated solution using a solid phase extraction column and an elution solvent to obtain a pretreatment solution, wherein the solid phase extraction column is selected from a Cleanert-TPT column.

[0041] It should be noted that the solid phase extraction column selected in the present invention, the Cleanert-TPT column, can adsorb the pigment in the above-mentioned concentrated solution, so that there is almost no pigment in the eluted extract, and the Cleanert-TPT column has an excellent recovery rate for pesticide residues such as chlorpropham, phorate, terbufos, methidathion, bifenthrin, ethomethrin and cypermethrin in silage corn, which is beneficial to the subsequent detection of pesticide residues.

[0042] In some specific embodiments, the elution solvent may preferably be a mixed solvent of acetonitrile and toluene or acetonitrile. It should be noted that different elution solvents have an effect on the recovery rate of pesticide residues such as chlorpropamide, phorate, terbufos, methidathion, bifenthrin, ethomethrin and deltamethrin in silage corn, and a mixed solvent of acetonitrile and toluene or acetonitrile is preferred, and the organic solvent has a good recovery rate for the above-mentioned pesticide residues.

[0043] In some specific embodiments, the elution solvent may preferably be a mixed solvent of acetonitrile and toluene, and the volume ratio of acetonitrile to toluene is preferably 3:1. It should be noted that different volume ratios of acetonitrile to toluene have different effects on the recovery of pesticide residues. When acetonitrile-toluene (3:1) is selected as the extraction solvent, the recovery rates of terbuthion, bifenthrin and deltamethrin are higher than those of other ratios; the recovery ratio of ethomethrin is second only to acetonitrile, much higher than other elution solvents; the recovery ratio of phorate is second only to acetonitrile-toluene (4:1) and acetonitrile-toluene (5:1), much higher than other elution solvents; the recovery ratio of methidathion is second only to acetonitrile-toluene (1:1) and acetonitrile-toluene (2:1), much higher than other elution solvents; and when acetonitrile-toluene (3:1) is used as the extraction solvent, the spiked recovery rate meets the requirements of GB / T27404-2008 laboratory quality control specification. Therefore, taking comprehensive considerations, acetonitrile-toluene (3:1) can be preferably used as the elution solvent in the present invention.

[0044] In some specific embodiments, the organic solvent may preferably be acetonitrile. It should be noted that when acetonitrile is selected as the extraction solvent, the recovery rates of chlorpropamide, phorate, terbufos, methidathion, bifenthrin, ethomethrin and deltamethrin are better than those of other solvents, such as n-hexane and acetone:n-hexane (1:1).

[0045] In some specific embodiments, in the above step (1), the silage corn is crushed before extraction with an organic solvent. It should be noted that the silage corn can be crushed before extraction to improve the extraction efficiency; in addition, the crushing method is a method known in the art.

[0046] Another embodiment of the present invention provides a method for detecting pesticide residues in silage corn, wherein the pesticide residues include one or more of chlorpropham, phorate, terbufos, methidathion, bifenthrin, ethomethrin and deltamethrin, comprising: (1) pre-treating the silage corn using the above-mentioned silage corn pre-treatment method to obtain a pre-treatment liquid; and (2) detecting the pesticide residues in the pre-treatment liquid using gas chromatography-mass spectrometry.

[0047] It should be noted that the accuracy of pesticide residue detection can be improved by subjecting the pretreatment liquid obtained after extracting silage corn using the above-mentioned pretreatment method to gas chromatography-mass spectrometry detection.

[0048] In some specific embodiments, in the above step (2), the pretreatment liquid is concentrated to dryness, the residue is dissolved with n-hexane, filtered through a 0.2 μm microporous filter membrane, and then the pesticide residue is detected by gas chromatography-mass spectrometry. It should be noted that in order to improve the accuracy of the detection, the above pretreatment liquid can be concentrated to dryness, dissolved and filtered, and then subjected to gas chromatography-mass spectrometry detection.

[0049] In some specific embodiments, the above-mentioned gas chromatography-mass spectrometry detection conditions may include: column box temperature: 60°C for 1 min, heated to 170°C at 40°C / min, heated to 310°C at 10°C / min, and maintained for 3 min; carrier gas: helium, purity ≥99.999%, flow rate 1mL / min; injection port temperature: 280°C; injection volume: 1μL; injection mode: non-split injection; EI source: 70eV; ion source temperature: 280°C; transmission line temperature: 280°C.

[0050] It should be noted that the gas chromatography-mass spectrometry detection conditions may preferably be the above-mentioned conditions. Under the above-mentioned gas chromatography-mass spectrometry detection conditions, qualitative and quantitative detection of pesticide residues such as chlorpropham, phorate, terbufos, methidathion, bifenthrin, ethomethrin and cypermethrin can be achieved at very low content (60 ppm).

[0051] It should also be noted that in the above-mentioned gas chromatography-mass spectrometry detection, the mass spectrometer used is a triple quadrupole mass spectrometer.

[0052] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with specific examples, but the content of the present invention is not limited to the following examples.

[0053] In the following examples, according to the characteristics of the instrument used and the method development procedure of dMRM, the instrument reference conditions were obtained as shown in Table 1 below.

[0054] Table 1 Gas chromatography-mass spectrometry detection conditions

[0055]

[0056] In addition, according to the establishment procedure of the dMRM method, the retention time, qualitative and quantitative ion pairs of each pesticide residue compound were obtained, as shown in Table 2 below.

[0057] Table 2 Retention time, qualitative and quantitative ion pairs of pesticide residues

[0058]

[0059] In the following examples, the silage corn used was produced by Liangjiang Dairy Farm of Chongqing Tianyou Zongheng Animal Husbandry Development Co., Ltd., batch number 20220818.

[0060] 1. Silage Corn Extraction

[0061] In the embodiment of the present invention, the silage corn pretreatment is carried out according to the following steps:

[0062] (1) crushing the silage corn with a crusher;

[0063] (2) Extraction: Weigh 10 g of sample (accurate to 0.001 g) into a 50 mL stoppered centrifuge tube, add 30 mL of extraction solvent, extract at 300 r / min on an air oscillator for 1 min, centrifuge at 10,000 r / min for 5 min, and transfer the supernatant to a distillation flask; repeat the extraction once, add the supernatant to the distillation flask, place in a 45°C water bath, rotate and concentrate to about 0.5 mL, and add 1 mL of elution solvent to wash to obtain the concentrate.

[0064] (3) Purification: Add about 2 cm of anhydrous sodium sulfate to the concentrated solution in the solid phase extraction column, pre-wash the column with 5 mL of elution solvent, discard the effluent, and connect the distillation flask; when the liquid level reaches the top of the anhydrous sodium sulfate, transfer the liquid to be purified to the solid phase extraction column, wash it with 5 mL of elution solvent, and transfer it all to the solid phase extraction column. Repeat this process 4 times and collect all the effluent as the pre-treatment solution.

[0065] In the embodiment of the present invention, the laboratory quality control specification GB / T27404-2008 is as shown in Table 3 below.

[0066] Table 3 GB / T27404-2008 Laboratory Quality Control Specifications

[0067]

[0068] Example 1 Solid Phase Extraction Column Screening

[0069] (1) Color screening

[0070] In the embodiment of the present invention, acetonitrile is used as the extraction solvent, the elution solvent is composed of acetonitrile-toluene (3:1) and different solid phase extraction columns (see Table 4) are used to extract the silage corn according to the above-mentioned silage corn extraction method to obtain different pretreatment liquids, and the colors of the different pretreatment liquids are observed. The results are shown in Table 2 below (in the table, Envi-Carb activated carbon column and ENVI-18 column refer to the Envi-Carb column with about 2 cm high anhydrous sodium sulfate added, the column is connected to the top of the Sep-Pak aminopropyl column, and the series column is connected to a conical flask.).

[0071] Table 4 Different colors of extracts extracted from different solid phase extraction columns

[0072] serial number Extraction solvent Elution solvent Solid Phase Extraction Column Condition 1-1 Acetonitrile Acetonitrile-toluene (3:1) Cleanert-TPT column Figure 1 1-2 Acetonitrile Acetonitrile-toluene (3:1) ENVI-18 column Figure 2 1-3 Acetonitrile Acetonitrile-toluene (3:1) Sep-Pak Aminopropyl Columns Figure 3 1-4 Acetonitrile Acetonitrile-toluene (3:1) Envi-Carb activated carbon columns and ENVI-18 columns Figure 4

[0073] From the above table 1 and Figures 1 to 4 It can be seen that after ENVI-18 solid phase extraction column ( Figure 2 ) and Sep-Pak aminopropyl columns ( Figure 3) after purification, the pigment content of the pretreatment liquid is very high, which is easy to clog the chromatographic column, contaminate the liner and the ion source; after purification by Envi-Carb activated carbon column and ENVI-18 column, the pigment of the pretreatment liquid is significantly reduced, but the pigment still exists; after purification by Cleanert-TPT column, the pretreatment liquid has no obvious pigment; Cleanert-TPT column (specification: 2.0g, 10mL) is selected as the solid phase extraction column in the present invention.

[0074] (2) Spike recovery test

[0075] In an embodiment of the present invention, silage corn is treated according to the above-mentioned silage corn pretreatment method to obtain a concentrated solution, and 240 μL of a mixed standard of chlorpropham, phorate, terbufos, methidathion, bifenthrin, ether cypermethrin and cypermethrin with a concentration of 0.5 ppm is added to the concentrated solution to obtain a concentrated-standard solution, and the concentrated-standard solution is purified using different solid phase extraction columns (see Table 5) to obtain different pretreatment solutions, and the pretreatment solution is fixed to 2 mL; the pretreatment solution is loaded on the machine, and the detection is performed according to the above-mentioned gas chromatography-mass spectrometry detection parameters, and the spiked recovery rate is calculated, as shown in Table 5 below.

[0076] Table 5 Spiked recovery of each component in different purification columns

[0077]

[0078] It can be seen from Table 5 above that the Cleanert-TPT column has a high recovery rate for chlorpropham, phorate, terbufos, methidathion, bifenthrin, ethomethrin and deltamethrin, and the spiked recovery rate meets the requirements of GB / T27404-2008 laboratory quality control specification.

[0079] In summary, the recovery rate of some pesticide residues using Cleanert-TPT column is not as good as other columns, but the recovery rate of terbuthion, bifenthrin and deltamethrin is the highest; and the recovery rate of chlorpropamide, methidathion and ethomethrin is second only to ENVI-18 column, and much higher than other columns; the recovery rate of phorate is not the lowest. And the recovery rate of all pesticide residues meets the requirements of GB / T27404-2008 laboratory quality control specification; and it is the only column that can obviously remove pigments, so Cleanert-TPT column is selected for pretreatment in the present invention.

[0080] Example 2 Pretreatment with different extraction solvents

[0081] In an embodiment of the present invention, silage corn is crushed according to the above-mentioned silage corn pretreatment method to obtain crushed silage corn, and 240 μL of a mixed standard of chlorpropham, phorate, terbufos, methidathion, bifenthrin, ether cypermethrin and cypermethrin with a concentration of 0.5 ppm is added, and different extraction solvents (see Table 6) are used for subsequent extraction and purification (the elution solvent is acetonitrile-toluene (3:1), and the solid phase extraction column is a Cleanert-TPT column) to obtain different pretreatment liquids, and the pretreatment liquid is fixed to 2 mL; the pretreatment liquid is loaded on the machine, and the detection is performed according to the above-mentioned gas chromatography-mass spectrometry detection parameters, and the spiked recovery rate is calculated, as shown in Table 7 below.

[0082] Table 6 Extraction results of different extraction solvents

[0083] serial number Extraction solvent Elution solvent Solid Phase Extraction Column 2-1 Acetonitrile Acetonitrile-toluene (3:1) Cleanert-TPT column 2-2 n-Hexane Acetonitrile-toluene (3:1) Cleanert-TPT column 2-3 Acetone:n-hexane (1:9) Acetonitrile-toluene (3:1) Cleanert-TPT column

[0084] Table 7 Spiked recovery of each component in different pretreatment solutions

[0085]

[0086] It can be seen from Table 7 above that when acetonitrile is selected as the extraction solvent, the recoveries of 4-chlorpropamine, phorate, terbufos, methidathion, bifenthrin, ethomethrin and deltamethrin are better than those of n-hexane and acetone: n-hexane (1:1), and the spiked recoveries meet the requirements of GB / T27404-2008 laboratory quality control specification; therefore, acetonitrile can be preferably used as the extraction solvent in the present invention.

[0087] Example 3 Pretreatment with different elution solvents

[0088] In an embodiment of the present invention, the silage corn is treated according to the above-mentioned silage corn pretreatment method (the extraction solvent is acetonitrile) to obtain a concentrated solution, and the concentrated solution is added with 240 μL of a mixed standard solution of chlorpropham, phorate, terbufos, methidathion, bifenthrin, ether cypermethrin and cypermethrin with a concentration of 0.5 ppm to obtain a concentrated-standard solution, and the concentrated-standard solution is purified using different elution solvents (see Table 8) and Cleanert-TPT columns to obtain different pretreatment solutions, and the pretreatment solution is fixed to 2 mL; the pretreatment solution is loaded on the machine, and the detection is performed according to the above-mentioned gas chromatography-mass spectrometry detection parameters, and the spiked recovery rate is calculated, as shown in Table 9 below.

[0089] Table 8 Extraction results with different elution solvents

[0090] serial number Extraction solvent Elution solvent Solid Phase Extraction Column 3-1 Acetonitrile Acetonitrile Cleanert-TPT column 3-2 Acetonitrile Acetonitrile-toluene (1:1) Cleanert-TPT column 3-3 Acetonitrile Acetonitrile-toluene (2:1) Cleanert-TPT column 3-4 Acetonitrile Acetonitrile-toluene (3:1) Cleanert-TPT column 3-5 Acetonitrile Acetonitrile-toluene (4:1) Cleanert-TPT column 3-6 Acetonitrile Acetonitrile-toluene (5:1) Cleanert-TPT column

[0091] Table 9 Spiked recovery of each component in different elution solvents

[0092]

[0093]

[0094] It can be seen from Table 9 that when acetonitrile-toluene (3:1) is selected as the extraction solvent, the recovery rates of terbuthion, bifenthrin and deltamethrin are higher than those of other ratios; the recovery ratio of ethomethrin is second only to acetonitrile, much higher than other elution solvents; the recovery ratio of phorate is second only to acetonitrile-toluene (4:1) and acetonitrile-toluene (5:1), much higher than other elution solvents; the recovery ratio of methidathion is second only to acetonitrile-toluene (1:1) and acetonitrile-toluene (2:1), much higher than other elution solvents; and when acetonitrile-toluene (3:1) is used as the extraction solvent, the spiked recovery rate meets the requirements of the laboratory quality control specification of GB / T27404-2008. Therefore, considering comprehensively, acetonitrile-toluene (3:1) is preferably used as the elution solvent in the present invention.

[0095] In addition, the colors of the matrix blank solution, samples, and spiked samples were observed. Figure 5 As shown, the results show that the matrix blank solution, sample and spiked sample have no obvious pigment. Among them, the matrix blank solution is the pre-treatment solution obtained by pre-treating the silage corn using the above-mentioned silage corn pre-treatment method; the sample is the same as the pre-treatment solution; the spiked sample is the solution obtained by adding a known amount of the standard to the sample.

[0096] 2. Detection of pesticide residues by gas chromatography-mass spectrometry

[0097] (I) Construction of standard curve

[0098] The silage corn was treated according to the above silage corn pretreatment method to obtain a pretreatment liquid, wherein the extraction solvent was acetonitrile, the elution solvent was a mixed solvent of acetonitrile-toluene (volume ratio 3:1), and the solid phase extraction column was a Cleanert-TPT column.

[0099] The extract was added with chlorpropham, phorate, terbufos, methidathion, bifenthrin, ethomethrin and deltamethrin standards to prepare standard matrix standards with concentrations of 20 ppb, 40 ppb, 60 ppb, 80 ppb and 100 ppb, respectively, and then injected. The samples were tested according to the above-mentioned gas chromatography-mass spectrometry detection conditions. The standard curves of chlorpropham, phorate, terbufos, methidathion, bifenthrin, ethomethrin and deltamethrin were constructed according to the instrument (Agilent 8890GC-7000D) "Quantitative Analysis Software" ("QQQ Quantitative Analysis"), and the results were as follows: Figure 6 , Figure 7 , Figure 8 , Fig. 9 , Fig.10 , Fig.11 and Fig.12 shown.

[0100] (II) Substrate injection test

[0101] The silage corn was treated according to the above silage corn pretreatment method to obtain a pretreatment solution, wherein the extraction solvent was acetonitrile, the elution solvent was a mixed solvent of acetonitrile-toluene (volume ratio 3:1), and the solid phase extraction column was a Cleanert-TPT column. The above pretreatment solution was injected and tested according to the above gas chromatography-mass spectrometry detection conditions. The results are shown in Table 10, and the detection chromatogram is shown in Fig.13 shown.

[0102] Table 10 Gas chromatography-mass spectrometry detection of the substrate

[0103] name RT(min) response Final concentration (ppb) Chlorpheniramine 7.128 48 0 Phorate 7.458 291 0 Ethofenprox 16.844 14418 12.6423

[0104] In addition, the mass spectrometry detection results of chlorpropham, phorate, terbufos, methidathion, bifenthrin, ethomethrin and deltamethrin are as follows: Fig.14 , Fig.15 , Fig.16 , Fig.17 , Fig.18 , Fig.19 and Fig. 20 shown.

[0105] (III) Sample injection testing

[0106] In the embodiment of the present invention, the silage corn is crushed according to the above-mentioned silage corn pretreatment method to obtain crushed silage corn, and then 240 μL of a mixed standard solution of chlorpropham, phorate, terbufos, methidathion, bifenthrin, ether cypermethrin and cypermethrin with a concentration of 0.5 ppm is added; then the silage corn pretreatment method is extracted (the extraction solvent is acetonitrile), purified (the elution solvent is acetonitrile-toluene (volume ratio 3: 1) mixed solvent, and the solid phase extraction column is Cleanert-TPT column) to obtain a pretreatment liquid (sample 1), and the pretreatment liquid is fixed to 2 mL; the pretreatment liquid is loaded on the machine and detected according to the above-mentioned gas chromatography-mass spectrometry detection parameters. The specific detection situation is shown in Table 11, and the color spectrum is as shown in Table 11. Fig.21 shown.

[0107] Table 11 Gas chromatography-mass spectrometry detection of sample 1

[0108] name RT(min) response Final concentration (ppb) Chlorpheniramine 7.121 7797 48.7462 Phorate 7.481 11435 57.5257 Terbuthion 8.134 16347 61.0614 Methidathion 11.019 17368 52.0920 Bifenthrin 13.944 70058 64.0721 Ethofenprox 16.793 68188 63.4999 Deltamethrin 18.127 52248 65.7363

[0109] In addition, three other parallel tests were performed according to the above method to obtain Sample 2, Sample 3 and Sample 4. The test results are shown in Table 12, Table 13 and Table 14, respectively, and the chromatograms are shown in Table 14, respectively. Fig. 22 , Fig.23 and Fig.24 shown.

[0110] Table 12 Gas chromatography-mass spectrometry detection of sample 2

[0111]

[0112]

[0113] Table 13 Gas chromatography-mass spectrometry detection of sample 3

[0114] name RT(min) response Final concentration (ppb) Chlorpheniramine 7.121 6584 40.6178 Phorate 7.485 9540 47.7086 Terbuthion 8.138 13577 50.5601 Methidathion 11.023 14828 44.1389 Bifenthrin 13.941 59894 54.3102 Ethofenprox 16.793 59463 55.1939 Deltamethrin 18.131 43682 55.4589

[0115] Table 14 Gas chromatography-mass spectrometry detection of sample 4

[0116] name RT(min) response Final concentration (ppb) Chlorpheniramine 7.121 7003 43.4265 Phorate 7.481 9664 48.3512 Terbuthion 8.138 13858 51.6264 Methidathion 11.019 14552 43.2757 Bifenthrin 13.941 61261 55.6230 Ethofenprox 16.793 57171 53.0792 Deltamethrin 18.131 41542 52.8917

[0117] The spiked recoveries of the above samples were calculated, as shown in Table 15 below.

[0118] Table 15 Recovery rate of spiked samples

[0119]

[0120] It can be seen from Table 15 that the extraction method of the present invention can achieve a good spiked recovery rate (the recovery rate of all pesticide residues meets the requirement of 60%-120% stipulated in the laboratory quality control specification GB / T27404-2008), and the subsequent detection of 7 pesticide residues in silage corn also achieved excellent test results at very low content (60ppm).

[0121] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be covered by the scope of the claims of the present invention.

Claims

1. A method for pre-treating silage corn, characterized in that: include: (1) extracting silage corn with an organic solvent and centrifuging to obtain a supernatant; (2) distilling and concentrating the supernatant to obtain a concentrated solution; (3) eluting the concentrated solution with a solid phase extraction column and an elution solvent to obtain a pretreatment solution, wherein the solid phase extraction column is selected from a Cleanert-TPT column.

2. The pretreatment method for silage corn according to claim 1, characterized in that: The elution solvent is a mixed solvent of acetonitrile and toluene or acetonitrile.

3. The pretreatment method for corn silage according to claim 2, characterized in that: The elution solvent is a mixed solvent of acetonitrile and toluene, and the volume ratio of acetonitrile to toluene is 3:

1.

4. The method for pre-treating corn silage according to any one of claims 1 to 3, characterized in that: The organic solvent selected was acetonitrile.

5. The method for pre-treating corn silage according to any one of claims 1 to 3, characterized in that: In step (1), the silage corn is crushed before extraction with an organic solvent.

6. The method for pre-treating corn silage according to claim 4, characterized in that: In step (1), the silage corn is crushed before extraction with an organic solvent.

7. A method for detecting pesticide residues in silage corn, wherein the pesticide residues include one or more of chlorpropham, phorate, terbufos, methidathion, bifenthrin, ethomethrin and deltamethrin, characterized in that: include: (1) Pre-treating silage corn using the silage corn pre-treatment method according to any one of claims 1 to 6 to obtain a pre-treatment liquid; (2) detecting pesticide residues in the pre-treatment liquid using gas chromatography-mass spectrometry.

8. The method for detecting pesticide residues in silage corn according to claim 7, characterized in that: The extract was concentrated to dryness, and the residue was dissolved in n-hexane. After filtering through a 0.2 μm microporous filter membrane, the pesticide residues were detected by gas chromatography-mass spectrometry.

9. The method for detecting pesticide residues in silage corn according to claim 7 or 8, characterized in that: The gas chromatography-mass spectrometry detection conditions include: column box temperature: 60°C for 1 min, heated to 170°C at 40°C / min, heated to 310°C at 10°C / min, and maintained for 3 min; carrier gas: helium, purity ≥99.999%, flow rate 1 mL / min; injection port temperature: 280°C; injection volume: 1 μL; injection mode: splitless injection; EI source: 70 eV; ion source temperature: 280°C; transmission line temperature: 280°C.

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