Method for determining five ultra-short-chain perfluorinated compounds in agricultural products

Abstract

This invention relates to a method for determining five ultrashort-chain perfluorinated compounds in agricultural products, comprising the following steps: S1, weighing 1.00~5.00g of homogenized sample into a first centrifuge tube, adding a certain amount of internal standard and 1~5 mL of ultrapure water, and vortexing for 1 min; S2, adding 10 mL of 2% formic acid acetonitrile, homogenizing at high speed for 1 min, adding the QuEChERS pretreatment package, quickly vortexing and centrifuging at high speed for 5 min; S3, transferring the upper acetonitrile layer to a second centrifuge tube containing a purification agent, vortexing thoroughly, and centrifuging at high speed for 5 min; S4, taking 5 mL of the supernatant into a third centrifuge tube, blowing it dry with nitrogen at 45℃, adding 1 mL of methanol-water solution with a volume ratio of 1:1 to make up to volume, centrifuging at high speed at 12000 r / min for 10 min, and filtering the supernatant through a 0.22 μm filter membrane; S5, detecting the supernatant after filtration in step S4 by liquid chromatography-tandem mass spectrometry. Because of the above-mentioned technical solution, the method for determining five ultra-short-chain perfluorinated compounds in agricultural products described in this invention can simultaneously determine five ultra-short-chain perfluorinated compounds in agricultural products.

Description

Technical Field

[0001] This invention relates to the field of agricultural product testing technology, specifically to a method for determining five ultrashort-chain perfluorinated compounds in agricultural products. Background Technology

[0002] Perfluorinated compounds (PFOCs) are a class of fluorinated organic compounds in which some or all of the hydrogen atoms attached to the alkyl carbon chain are replaced by fluorine. Due to their remarkable thermal and chemical stability, they are widely used in industrial and commercial sectors. In recent years, the high persistence, mobility, and bioaccumulation characteristics of PFOCs have led to strong concerns that their use has exceeded the limits of environmental sustainability. The Stockholm Conventions of 2009 and 2017 banned the production and use of long-chain PFOCs (chain length >7, i.e., perfluorooctanoic acid and perfluorooctane sulfonic acid). However, to compensate for the shortage of long-chain PFOCs, ultra-short-chain (chain length: 1-3) and short-chain (chain length: 4-7) homologues have been produced and used in large quantities as substitutes, leading to their continuous accumulation in the environment and their gradual emergence as a major type of pollution.

[0003] Ultrashort-chain PFAAs refer to perfluorocarboxylic acids and perfluorosulfonic acids with fewer than four carbon atoms, including trifluoroacetic acid (TFA), perfluoropropionic acid (PFPrA), trifluoromethanesulfonic acid (TFMS), perfluoroethanesulfonic acid (PFEtS), and perfluoropropanesulfonic acid (PFPrS). These compounds are found in water, soil, air, and organisms due to their small molecular size, high polarity, and good water solubility, and their concentrations are typically higher than those of long-chain compounds.

[0004] Concentrations of ultrashort-chain PFAAs in various environmental matrices (such as water, soil, and air) have been reported, and all five ultrashort-chain PFAAs have been detected in aquatic environments in Europe, North America, and Asia. Ultrashort-chain PFAAs have also been widely detected in plant, animal, human, and other biological samples.

[0005] However, in the existing technology, no method has been found that can simultaneously determine the above five ultrashort chain PFAAs in agricultural products. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a method for determining five ultra-short-chain perfluorinated compounds in agricultural products, so as to solve the technical problem that no method has been found in the prior art that can simultaneously determine five ultra-short-chain PFAAs in agricultural products.

[0007] This invention is achieved through the following technical solution: A method for determining five ultrashort-chain perfluorinated compounds in agricultural products includes the following steps: S1. Weigh 1.00~5.00g of homogeneous sample into the first centrifuge tube, add a certain amount of internal standard and 1~5 mL of ultrapure water, and vortex mix for 1 min. S2. Continue to add 10 mL of 2% formic acid acetonitrile, homogenize at high speed for 1 min, add QuEChERS pretreatment package, vortex quickly to mix, and centrifuge at high speed for 5 min. S3. Transfer the upper layer of acetonitrile to the second centrifuge tube containing the purifying agent, vortex thoroughly, and centrifuge at high speed for 5 minutes. S4. Take 5 mL of supernatant into the third centrifuge tube, blow it dry with nitrogen at 45℃, add 1 mL of methanol-water solution with a volume ratio of 1:1 to make up the volume, centrifuge at 12000 r / min for 10 min, and filter the supernatant through a 0.22 μm filter membrane. S5. The supernatant after filtration in step S4 is detected by liquid chromatography-tandem mass spectrometry.

[0008] The beneficial effects of this invention are as follows: The method for determining five ultrashort-chain perfluorinated compounds in agricultural products described in this invention can simultaneously determine five ultrashort-chain perfluorinated compounds in agricultural products. Attached Figure Description

[0009] Figure 1 This is a process flow diagram of the method for determining five ultrashort-chain perfluorinated compounds in agricultural products according to the present invention; Figure 2-6 This is a punctuation diagram of five ultrashort-chain perfluorinated compounds in the method for determining five ultrashort-chain perfluorinated compounds in agricultural products according to the present invention; Figure 7 The chromatograms of the five ultrashort-chain perfluorinated compounds in the method for determining five ultrashort-chain perfluorinated compounds in agricultural products according to the present invention are shown. Figure 8 This is a schematic diagram of the fourth centrifuge tube in the method for determining five ultrashort-chain perfluorinated compounds in agricultural products according to the present invention; Figure 9 This is a top view of the fourth centrifuge tube in the method for determining five ultrashort-chain perfluorinated compounds in agricultural products according to the present invention; Figure 10 for Figure 9 AA section view; Figure 11 for Figure 10 Enlarged view of 'a' in the middle; Figure 12 This is a schematic diagram of the dispensing device in the method for determining five ultrashort-chain perfluorinated compounds in agricultural products according to the present invention; Figure 13 for Figure 12 Enlarged view of b in the middle; Figure 14This is a schematic diagram of the dispensing device in the method for determining five ultrashort-chain perfluorinated compounds in agricultural products according to the present invention, omitting the second cylinder; Figure 15 for Figure 14 Enlarged view of C in the middle; Figure 16 This is a top view of the dispensing apparatus in the method for determining five ultrashort-chain perfluorinated compounds in agricultural products according to the present invention; Figure 17 for Figure 16 BB cross-sectional view; Figure 18 for Figure 17 Enlarged view of d in the middle; Figure 19 This is a top view of the combination of the support seat, sliding plate, connecting strip, counterweight and sealing component in the dispensing device of the method for determining five ultra-short chain perfluorinated compounds in agricultural products according to the present invention. Figure 20 for Figure 19 CC section view.

[0010] In the diagram: Connecting channel-1; Insertion tube-2; Channel section-3; Centrifuge tube body-4; Centrifuge tube cap-5; Through hole-6; Round hole-7; First cylinder-8; Sealing plug-9; Fixing plate-10; Helical spring-11; Second cylinder-12; Sliding cavity-13; Sliding plate-14; Perforation-15; Base-16; Bearing seat-17; Rotating shaft-18; Support plate-19; Sealing component-20; Vent hole-21; Second adhesive tape-22; Connecting strip-23; Counterweight-24; Strip groove-25; Slide groove-26; Connecting plate-27; Insert rod-28; Slider-29; Protruding plate-30; Limiting rod-31; Fixing rod-32. Detailed Implementation

[0011] Example 1 Please refer to Figure 1 This invention provides a technical solution: a method for determining five ultrashort-chain perfluorinated compounds in agricultural products. This embodiment targets agricultural products, and the method described in this invention is used to process these products. The specific method is as follows: Materials and reagents The standard trifluoroacetic acid (TFA), perfluoropropionic acid (PFPrA), trifluoromethanesulfonic acid (TFMS), perfluoroethanesulfonic acid (PFEtS), and perfluoropropanesulfonic acid (PFPrS) were all purchased at a concentration of 100 μg / mL, and the internal isotope standard (13C-PFPrA) was purchased at a concentration of 10 μg / mL. All were purchased from Medica (Tianjin) Technology Co., Ltd.; methanol and acetonitrile (chromatographic grade, Merck, Germany); formic acid (chromatographic grade); ammonium acetate; QuEChERS pretreatment kit; and purification tubes (150 mg C18 and 900 mg anhydrous magnesium sulfate, Hunan Bickman Holding Co., Ltd.).

[0012] Instruments and equipment AB 5500 High Performance Liquid Chromatography-Tandem Mass Spectrometer (Sciex Corporation, USA); Advantage A10 Ultra Pure water system (Millipore, USA); vortex mixer; homogenizer (Omni); high-speed refrigerated centrifuge (Sigma); nitrogen blower (Ruico).

[0013] S1. Weigh 1.00~5.00g of homogenized Chinese cabbage sample into a 50mL polypropylene centrifuge tube, add a certain amount of internal standard and 1~5 mL of ultrapure water, and vortex mix for 1min. The preferred mass of the homogeneous sample is 5.00 g, with a weighing accuracy of 0.01 g. The internal standard is specifically perfluoropropionic acid internal standard-13C, and the preferred amount and concentration of the added internal standard is 20 µL 100 ppb. The preferred amount of added ultrapure water is 5 mL.

[0014] S2. Continue to add 10 mL of 2% formic acid acetonitrile, homogenize at high speed for 1 min, add the QuEChERS pretreatment package (specifically, the QuEChERS extraction salt package), vortex quickly to mix, and centrifuge at high speed for 5 min; the QuEChERS pretreatment package is specifically the QuEChERS extraction salt package.

[0015] S3. Transfer the upper layer of acetonitrile to a second centrifuge tube containing a purifying agent, vortex thoroughly, and then centrifuge at high speed for 5 minutes. The purifying agent is preferably 150 mg PSA adsorbent and 900 mg anhydrous magnesium sulfate, and the centrifuge tube body is preferably a 15 ml centrifuge tube body.

[0016] S4. Take 5 mL of supernatant into the third polypropylene centrifuge tube, blow it dry with nitrogen at 45℃, add 1 mL of methanol-water solution with a volume ratio of 1:1 to make up the volume, centrifuge at 12000 r / min for 10 min, and filter the supernatant through a 0.22 μm filter membrane. S5. The supernatant after filtration in step S4 is detected by liquid chromatography-tandem mass spectrometry.

[0017] Preparation of standard solutions Accurately measure appropriate amounts of a mixed standard solution of five ultrashort-chain perfluorinated compounds and an internal standard solution, and dilute them with a methanol-water solution at a volume ratio of 1:1 to prepare a series of standard working solutions with concentrations of 0.05 μg / L, 0.10 μg / L, 0.50 μg / L, 1.00 μg / L, 2.00 μg / L, 5.00 μg / L, and 10.00 μg / L, each containing an internal standard of 1.00 μg / L, for determination by liquid chromatography-tandem mass spectrometry.

[0018] Liquid chromatography-tandem mass spectrometry detection In step S5, the liquid chromatography conditions are as follows: Chromatographic column: The chromatographic column is a Chemalink PFP column with parameters of 4.6 mm × 250 mm and a particle size of 5.0 μm; Mobile phase A: 5 mmol ammonium acetate solution, which contains 0.1% formic acid; Mobile phase B: Methanol; Flow rate: 0.5 mL / min; Injection volume: 5 μL; Column temperature: 40 ℃; Gradient elution was used.

[0019] Table 1 Gradient elution program In step S5, the mass spectrometry conditions are as follows: Ion source: Electrospray ionization (ESI); Scanning method: Negative ion scanning; Electrospray voltage: 4500V; Atomizer pressure: 65 psi; Air curtain pressure: 30 psi; Auxiliary air pressure: 60 psi; Ion source temperature: 450 ℃; Acquisition method: Mass spectrometry multiple reaction monitoring (MRM).

[0020] Table 2 Retention times and mass spectrometry parameters of five ultrashort-chain perfluorinated compounds and internal standards Table 3. Spiking recoveries and precision of five ultrashort-chain perfluorinated compounds Development and quantitative analysis of standard working curves Five ultrashort-chain perfluorinated compounds and their internal standard mixed working solution were detected under the above-mentioned liquid chromatography and mass spectrometry conditions. The detection chromatograms are shown below. Figure 7 As shown, regression analysis was performed on the peak areas of the target analytes and their corresponding concentrations (for perfluoropropionic acid, the ratio of the peak area of ​​the characteristic ion chromatographic peak to the peak area of ​​the corresponding internal standard characteristic ion chromatographic peak was used as the ordinate, and the corresponding standard solution concentration ratio was used as the abscissa for regression analysis). This yielded standard working curves and their regression equations for five ultrashort-chain perfluorinated compounds, as shown below. Figures 2-6 As shown.

[0021] The results showed that the target compound exhibited good linearity in the concentration range of 0.05 μg / L to 10.0 μg / L, with correlation coefficients r greater than 0.998.

[0022] In this embodiment, the detection limit for the five ultrashort-chain perfluorinated compounds was 0.05 μg / kg, which indicates high sensitivity.

[0023] In this embodiment, when the concentration of the Chinese cabbage sample was added was 0.05 μg / kg to 0.5 μg / kg, the recovery rates of trifluoromethanesulfonic acid were between 85.33% and 91.81%, trifluoroacetic acid between 83.73% and 102.00%, perfluoropropionic acid between 90.85% and 94.40%, perfluoroethanesulfonic acid between 97.09% and 106.53%, and perfluoropropanesulfonic acid between 94.60% and 101.47%, which achieved high recovery rates and met the detection requirements for ultra-short-chain perfluorinated compounds. See Table 3 for details.

[0024] In this embodiment, the relative standard deviation of the seven independent test results obtained under repeatability conditions ranged from 1.15% to 17.01%, meeting the precision requirements of GB / T 27404 "Laboratory Quality Control Standard for Physicochemical Testing of Food", indicating high precision. See Table 3 for details.

[0025] Example 2 Please refer to Figure 1 This invention provides a technical solution: a method for determining five ultrashort-chain perfluorinated compounds in agricultural products. This embodiment targets livestock and poultry products. The livestock and poultry products are processed according to the method of this invention, as detailed below: Materials and reagents The standard trifluoroacetic acid (TFA), perfluoropropionic acid (PFPrA), trifluoromethanesulfonic acid (TFMS), perfluoroethanesulfonic acid (PFEtS), and perfluoropropanesulfonic acid (PFPrS) were all purchased at a concentration of 100 μg / mL, and the internal isotope standard (13C-PFPrA) was purchased at a concentration of 10 μg / mL. All were purchased from Medica (Tianjin) Technology Co., Ltd.; methanol and acetonitrile (chromatographic grade, Merck, Germany); formic acid (chromatographic grade); ammonium acetate; QuEChERS pretreatment kit; and purification tubes (150 mg C18 and 900 mg anhydrous magnesium sulfate, Hunan Bickman Holding Co., Ltd.).

[0026] Instruments and equipment AB 5500 High Performance Liquid Chromatography-Tandem Mass Spectrometer (Sciex Corporation, USA); Advantage A10 Ultra Pure water system (Millipore, USA); vortex mixer; homogenizer (Omni); high-speed refrigerated centrifuge (Sigma); nitrogen blower (Ruico).

[0027] S1. Weigh 1.00~5.00g of homogenized pork sample into a 50mL polypropylene centrifuge tube, add a certain amount of internal standard and 1~5 mL of ultrapure water, and vortex mix for 1min. The preferred mass of the homogeneous sample is 5.00 g, with a weighing accuracy of 0.01 g. The internal standard is specifically perfluoropropionic acid internal standard-13C, and the preferred amount and concentration of the added internal standard is 20 µL 100 ppb. The preferred amount of added ultrapure water is 5 mL.

[0028] S2. Continue to add 10 mL of 2% formic acid acetonitrile, homogenize at high speed for 1 min, add the QuEChERS pretreatment package (specifically, the QuEChERS extraction salt package), vortex quickly to mix, and centrifuge at high speed for 5 min; the QuEChERS pretreatment package is specifically the QuEChERS extraction salt package.

[0029] S3. Transfer the upper layer of acetonitrile to a second centrifuge tube containing a purifying agent, vortex thoroughly, and then centrifuge at high speed for 5 minutes. The purifying agent is preferably 150 mg PSA adsorbent and 900 mg anhydrous magnesium sulfate, and the centrifuge tube body is preferably a 15 ml centrifuge tube body.

[0030] S4. Take 5 mL of supernatant into the third polypropylene centrifuge tube, blow it dry with nitrogen at 45℃, add 1 mL of methanol-water solution with a volume ratio of 1:1 to make up the volume, centrifuge at 12000 r / min for 10 min, and filter the supernatant through a 0.22 μm filter membrane. S5. The supernatant after filtration in step S4 is detected by liquid chromatography-tandem mass spectrometry.

[0031] Preparation of standard solutions Accurately measure appropriate amounts of a mixed standard solution of five ultrashort-chain perfluorinated compounds and an internal standard solution, and dilute them with a methanol-water solution at a volume ratio of 1:1 to prepare a series of standard working solutions with concentrations of 0.05 μg / L, 0.10 μg / L, 0.50 μg / L, 1.00 μg / L, 2.00 μg / L, 5.00 μg / L, and 10.00 μg / L, each containing an internal standard of 1.00 μg / L, for determination by liquid chromatography-tandem mass spectrometry.

[0032] Liquid chromatography-tandem mass spectrometry detection In step S5, the liquid chromatography conditions are as follows: Chromatographic column: The chromatographic column is a Chemalink PFP column with parameters of 4.6 mm × 250 mm and a particle size of 5.0 μm; Mobile phase A: 5 mmol ammonium acetate solution, which contains 0.1% formic acid; Mobile phase B: Methanol; Flow rate: 0.5 mL / min; Injection volume: 5 μL; Column temperature: 40 ℃; Gradient elution was used.

[0033] Table 4 Gradient elution program In step S5, the mass spectrometry conditions are as follows: Ion source: Electrospray ionization (ESI); Scanning method: Negative ion scanning; Electrospray voltage: 4500V; Atomizer pressure: 65 psi; Air curtain pressure: 30 psi; Auxiliary air pressure: 60 psi; Ion source temperature: 450 ℃; Acquisition method: Mass spectrometry multiple reaction monitoring (MRM).

[0034] Table 5. Retention times and mass spectrometry parameters of five ultrashort-chain perfluorinated compounds and internal standards. Table 6. Spiking recoveries and precision of five ultrashort-chain perfluorinated compounds Development and quantitative analysis of standard working curves Five ultrashort-chain perfluorinated compounds and their internal standard mixed working solution were detected under the above-mentioned liquid chromatography and mass spectrometry conditions. The detection chromatograms are shown below. Figure 7 As shown, regression analysis was performed on the peak areas of the target analytes and their corresponding concentrations (for perfluoropropionic acid, the ratio of the peak area of ​​the characteristic ion chromatographic peak to the peak area of ​​the corresponding internal standard characteristic ion chromatographic peak was used as the ordinate, and the corresponding standard solution concentration ratio was used as the abscissa for regression analysis). This yielded standard working curves and their regression equations for five ultrashort-chain perfluorinated compounds, as shown below. Figures 2-6 As shown.

[0035] The results showed that the target compound exhibited good linearity in the concentration range of 0.05 μg / L to 10.0 μg / L, with correlation coefficients r greater than 0.998.

[0036] In this embodiment, the detection limit for the five ultrashort-chain perfluorinated compounds was 0.05 μg / kg, which indicates high sensitivity.

[0037] In this embodiment, when the concentration of the pork sample added was 0.05 μg / kg to 0.5 μg / kg, the recoveries of trifluoromethanesulfonic acid were between 76.53% and 91.73%, trifluoroacetic acid between 86.84% and 106.73%, perfluoropropionic acid between 85.09% and 101.33%, perfluoroethanesulfonic acid between 87.07% and 102.57%, and perfluoropropanesulfonic acid between 114.13% and 119.80%, which achieved relatively high recovery rates and met the detection requirements for ultra-short-chain perfluorinated compounds. See Table 6 for details.

[0038] In this embodiment, the relative standard deviation of the seven independent test results obtained under repeatability conditions is between 0.59% and 9.31%, which meets the precision requirements of GB / T 27404 "Laboratory Quality Control Standard for Physicochemical Testing of Food", indicating high precision. See Table 6 for details.

[0039] Example 3 Please refer to Figure 1 This invention provides a technical solution: a method for determining five ultrashort-chain perfluorinated compounds in agricultural products. This embodiment targets aquatic products, which are processed according to the method of this invention. The specific method is as follows: Materials and reagents The standard trifluoroacetic acid (TFA), perfluoropropionic acid (PFPrA), trifluoromethanesulfonic acid (TFMS), perfluoroethanesulfonic acid (PFEtS), and perfluoropropanesulfonic acid (PFPrS) were all purchased at a concentration of 100 μg / mL, and the internal isotope standard (13C-PFPrA) was purchased at a concentration of 10 μg / mL. All were purchased from Medica (Tianjin) Technology Co., Ltd.; methanol and acetonitrile (chromatographic grade, Merck, Germany); formic acid (chromatographic grade); ammonium acetate; QuEChERS pretreatment kit; and purification tubes (150 mg C18 and 900 mg anhydrous magnesium sulfate, Hunan Bickman Holding Co., Ltd.).

[0040] Instruments and equipment AB 5500 High Performance Liquid Chromatography-Tandem Mass Spectrometer (Sciex Corporation, USA); Advantage A10 Ultra Pure water system (Millipore, USA); vortex mixer; homogenizer (Omni); high-speed refrigerated centrifuge (Sigma); nitrogen blower (Ruico).

[0041] S1. Weigh 1.00~5.00g of homogenized sea bass sample into a 50mL polypropylene centrifuge tube, add a certain amount of internal standard and 1~5 mL of ultrapure water, and vortex mix for 1min. The preferred mass of the homogeneous sample is 5.00 g, with a weighing accuracy of 0.01 g. The internal standard is specifically perfluoropropionic acid internal standard-13C, and the preferred amount and concentration of the added internal standard is 20 µL 100 ppb. The preferred amount of added ultrapure water is 5 mL.

[0042] S2. Continue to add 10 mL of 2% formic acid acetonitrile, homogenize at high speed for 1 min, add the QuEChERS pretreatment package (specifically, the QuEChERS extraction salt package), vortex quickly to mix, and centrifuge at high speed for 5 min; the QuEChERS pretreatment package is specifically the QuEChERS extraction salt package.

[0043] S3. Transfer the upper layer of acetonitrile to a second centrifuge tube containing a purifying agent, vortex thoroughly, and then centrifuge at high speed for 5 minutes. The purifying agent is preferably 150 mg PSA adsorbent and 900 mg anhydrous magnesium sulfate, and the centrifuge tube body is preferably a 15 ml centrifuge tube body.

[0044] S4. Take 5 mL of supernatant into the third polypropylene centrifuge tube, blow it dry with nitrogen at 45℃, add 1 mL of methanol-water solution with a volume ratio of 1:1 to make up the volume, centrifuge at 12000 r / min for 10 min, and filter the supernatant through a 0.22 μm filter membrane. S5. The supernatant after filtration in step S4 is detected by liquid chromatography-tandem mass spectrometry.

[0045] Preparation of standard solutions Accurately measure appropriate amounts of a mixed standard solution of five ultrashort-chain perfluorinated compounds and an internal standard solution, and dilute them with a methanol-water solution at a volume ratio of 1:1 to prepare a series of standard working solutions with concentrations of 0.05 μg / L, 0.10 μg / L, 0.50 μg / L, 1.00 μg / L, 2.00 μg / L, 5.00 μg / L, and 10.00 μg / L, each containing an internal standard of 1.00 μg / L, for determination by liquid chromatography-tandem mass spectrometry.

[0046] Liquid chromatography-tandem mass spectrometry detection In step S5, the liquid chromatography conditions are as follows: Chromatographic column: The chromatographic column is a Chemalink PFP column with parameters of 4.6 mm × 250 mm and a particle size of 5.0 μm; Mobile phase A: 5 mmol ammonium acetate solution, which contains 0.1% formic acid; Mobile phase B: Methanol; Flow rate: 0.5 mL / min; Injection volume: 5 μL; Column temperature: 40 ℃; Gradient elution was used.

[0047] Table 7 Gradient elution program In step S5, the mass spectrometry conditions are as follows: Ion source: Electrospray ionization (ESI); Scanning method: Negative ion scanning; Electrospray voltage: 4500V; Atomizer pressure: 65 psi; Air curtain pressure: 30 psi; Auxiliary air pressure: 60 psi; Ion source temperature: 450 ℃; Acquisition method: Mass spectrometry multiple reaction monitoring (MRM).

[0048] Table 8 Retention times and mass spectrometry parameters of five ultrashort-chain perfluorinated compounds and internal standards Table 9. Spiking recoveries and precision of five ultrashort-chain perfluorinated compounds Development and quantitative analysis of standard working curves Five ultrashort-chain perfluorinated compounds and their internal standard mixed working solution were detected under the above-mentioned liquid chromatography and mass spectrometry conditions. The detection chromatograms are shown below. Figure 7 As shown, regression analysis was performed on the peak areas of the target analytes and their corresponding concentrations (for perfluoropropionic acid, the ratio of the peak area of ​​the characteristic ion chromatographic peak to the peak area of ​​the corresponding internal standard characteristic ion chromatographic peak was used as the ordinate, and the corresponding standard solution concentration ratio was used as the abscissa for regression analysis). This yielded standard working curves and their regression equations for five ultrashort-chain perfluorinated compounds, as shown below. Figures 2-6 As shown.

[0049] The results showed that the target compound exhibited good linearity in the concentration range of 0.05 μg / L to 10.0 μg / L, with correlation coefficients r greater than 0.998.

[0050] In this embodiment, the detection limit for the five ultrashort-chain perfluorinated compounds was 0.05 μg / kg, which indicates high sensitivity.

[0051] In this embodiment, when the concentration of the sea bass sample was 0.05 μg / kg to 0.5 μg / kg, the recoveries of trifluoromethanesulfonic acid were between 86.73% and 95.67%, trifluoroacetic acid between 89.65% and 110.35%, perfluoropropionic acid between 93.56% and 106.52%, perfluoroethanesulfonic acid between 98.67% and 107.56%, and perfluoropropanesulfonic acid between 104.67% and 107.98%, which achieved high recovery rates and met the detection requirements for ultra-short-chain perfluorinated compounds. See Table 9 for details.

[0052] In this embodiment, the relative standard deviation of the seven independent test results obtained under repeatability conditions is between 1.21% and 8.53%, which meets the precision requirements of GB / T 27404 "Laboratory Quality Control Standard for Physicochemical Testing of Food" and has high precision. See Table 9 for details.

[0053] Example 4 In step S2 of the above embodiments one to three, before centrifuging the mixture formed after adding the QuEChERS pretreatment package, the mixture in the first centrifuge tube is dispensed into two fourth centrifuge tubes through a dispensing device, and the amount of mixture in the two fourth centrifuge tubes is the same.

[0054] When centrifuging the mixture formed after adding the QuEChERS pretreatment package in step S2, two fourth centrifuge tubes containing the same amount of the mixture are inserted into two centrifuge tube holes of the same diameter on the centrifuge rotor, and then the mixture in the two fourth centrifuge tubes can be centrifuged. This method achieves centrifuge balancing, making the centrifuge rotor less prone to shaking during centrifugation, thus reducing wear and extending the centrifuge's service life.

[0055] Please refer to Figure 8-20 In this embodiment, the dispensing device includes a support base, a connecting channel 1, a partition, and two insert tubes 2. The upper side of the support base is horizontal. The connecting channel 1 is formed inside the support base. The partition is disposed on the support base. The partition is used to divide the connecting channel 1 into two channel segments 3. The partition is also used to connect the two channel segments 3. Both insert tubes 2 are fixed on the support base and are arranged vertically. The lower ends of the two insert tubes 2 are connected to the two ends of the connecting channel 1 respectively. The upper ends of the insert tubes 2 protrude from the upper side of the support base. The fourth centrifuge tube includes a centrifuge tube body 4, a centrifuge tube cap 5, and a switch. The centrifuge tube cap 5 is threaded onto the centrifuge tube body 4. The bottom wall of the centrifuge tube body 4 has an insertion hole in the middle that connects the inner cavity of the centrifuge tube body 4 to the outside. The insertion hole cooperates with the insertion tube 2. The switch is located inside the centrifuge tube body 4. The switch is used to open the insertion hole during the insertion of the insertion tube 2, so that the inner cavity of the insertion tube 2 is connected to the inner cavity of the centrifuge tube body 4. The switch is also used to close the insertion hole during the removal of the insertion tube 2 from the insertion hole.

[0056] Before dispensing the mixture from the first centrifuge tube into the two fourth centrifuge tubes, the centrifuge tube caps 5 are removed from the centrifuge tube bodies 4, so that the lower ends of both centrifuge tube bodies 4 are supported on the upper side of the support base. While the lower ends of both centrifuge tube bodies 4 are supported on the upper side of the support base, the upper ends of the two insertion tubes 2 are inserted one-to-one into the insertion holes of the two centrifuge tube bodies 4. During this process, the switch opens the insertion holes, so that the inner cavity of the insertion tube 2 communicates with the inner cavity of the centrifuge tube body 4. After the lower ends of both centrifuge tube bodies 4 are supported on the upper side of the support base, the two centrifuge tube bodies 4 are in a state where they are connected by the connecting channel 1 and the two insertion tubes 2.

[0057] The mixture in the first centrifuge tube is then poured into one of the centrifuge tube bodies 4. The mixture in one centrifuge tube body 4 can then enter the other centrifuge tube body 4 via the connecting channel 1 and the two insertion tubes 2. According to the principle of communicating vessels, after a certain period of time, once the liquid levels in both centrifuge tube bodies 4 have stabilized, the liquid levels in both centrifuge tube bodies 4 will be the same, at which point the amount of mixture in both centrifuge tube bodies 4 will be the same. When dispensing the mixture from the first centrifuge tube into two fourth centrifuge tubes, it is relatively easy to ensure that the amount of mixture in the two fourth centrifuge tubes is the same.

[0058] After the liquid levels in both centrifuge tube bodies 4 have stabilized, the connecting channel 1 is divided into two channel segments 3 by the partition, at which point the two centrifuge tube bodies 4 are no longer connected. Then, the two centrifuge tube bodies 4 are moved upward, and the insertion tube 2 is gradually pulled out from the insertion hole. During this process, the switch part closes the insertion hole, and the mixture in the centrifuge tube body 4 cannot leak out from the centrifuge tube body 4.

[0059] Then, the centrifuge tube cap 5 is reinstalled onto the centrifuge tube body 4, and the two centrifuge tube bodies 4 can then be placed on the centrifuge rotor to centrifuge the mixture in the two fourth centrifuge tubes. The fourth centrifuge tubes can be installed on the centrifuge rotor in the same way as existing ordinary centrifuge tubes are installed on existing ordinary centrifuge rotors; no specially designed centrifuge rotor for use with the fourth centrifuge tubes is required.

[0060] In this embodiment, the upper end of the insertion tube 2 is closed, and a through hole 6 is provided on the upper side wall of the insertion tube 2; A circular hole 7 is formed on the bottom wall of the centrifuge tube body 4. A first cylinder 8 is provided inside the centrifuge tube body 4. The lower end of the first cylinder 8 is fixed to the bottom wall of the centrifuge tube body 4. The first cylinder 8 surrounds the circular hole 7. The circular hole 7 and the inner cavity of the first cylinder 8 form the insertion hole. The switching part includes a sealing plug 9, a fixing plate 10, and a helical spring 11. The sealing plug 9 is inserted into the upper end of the first cylinder 8 and closes the upper end of the first cylinder 8. The fixing plate 10 is fixed to the upper end of the sealing plug 9, and the edge of the fixing plate 10 protrudes beyond the edge of the sealing plug 9. The helical spring 11 is sleeved on the first cylinder 8. The upper end of the helical spring 11 is fixedly connected to the fixing plate 10, and the lower end is fixedly connected to the bottom wall of the centrifuge tube body 4.

[0061] During the process of inserting the upper end of the insertion tube 2 into the insertion hole on the centrifuge tube body 4, the upper end of the insertion tube 2 passes through the circular hole 7 and inserts into the inner cavity of the first cylinder 8, pushing the sealing plug 9 and the fixing plate 10 upward. The helical spring 11 is gradually stretched. After the sealing plug 9 and the fixing plate 10 are pushed upward a certain distance, the lower end of the centrifuge tube body 4 is supported on the upper side of the support base. At this time, the through hole 6 connects the inner cavity of the insertion tube 2 and the inner cavity of the centrifuge tube body 4. The switch can thus open the insertion hole during the insertion of the insertion tube 2, so that the inner cavity of the insertion tube 2 connects to the inner cavity of the centrifuge tube body 4.

[0062] During the process of pulling the upper end of the insertion tube 2 out of the insertion hole on the centrifuge tube body 4, the helical spring 11 elastically resets and pulls down the fixing plate 10 and the sealing plug 9, so that the sealing plug 9 is re-inserted into the upper end of the first cylinder 8 and seals the upper end of the first cylinder 8. After the upper end of the insertion tube 2 is pulled out of the insertion hole on the centrifuge tube body 4, the insertion hole is in a closed state. The switch unit can thus close the insertion hole during the process of pulling the insertion tube 2 out of the insertion hole.

[0063] The switch can open the socket simply by inserting the tube 2 into the socket on the centrifuge tube body 4, and it can automatically close the socket simply by pulling the tube 2 out of the socket on the centrifuge tube body 4. It is convenient to open and close the socket using the switch.

[0064] In this embodiment, the dispensing device further includes two fixing parts, which are used to fix the two centrifuge tube bodies 4 to the upper side of the support base in a one-to-one correspondence. It can be understood that in other embodiments, the centrifuge tube bodies 4 can also be pressed downwards and fixed to the upper side of the support base by hand.

[0065] After the lower ends of both centrifuge tube bodies 4 are supported on the upper side of the support base, the two centrifuge tube bodies 4 are fixed to the upper side of the support base one-to-one by the two fixing parts. At this time, the centrifuge tube bodies 4 will not move upward and detach from the upper side of the support base under the action of the helical spring 11, and the lower ends of both centrifuge tube bodies 4 can be kept supported on the upper side of the support base in a relatively convenient way.

[0066] In this embodiment, the fixing part includes a second cylinder 12 and a first adhesive tape (not shown in the figure). The second cylinder 12 is fixed on the upper side of the support base. The second cylinder 12 is coaxially arranged with the insertion tube 2. The inner cavity of the second cylinder 12 cooperates with the centrifuge tube body 4. The lower end of the first adhesive tape is pasted and fixed to the outer peripheral surface of the second cylinder 12, and the upper end of the first adhesive tape is used to paste and fix to the outer peripheral surface of the centrifuge tube body 4.

[0067] After inserting the centrifuge tube body 4 into the second cylinder 12 and supporting its lower end on the upper side of the support base, the upper end of the first adhesive tape is attached and fixed to the outer circumferential surface of the centrifuge tube body 4. This fixing part thus secures the centrifuge tube body 4 to the upper side of the support base. Tearing off the upper end of the first adhesive tape from the outer circumferential surface of the centrifuge tube body 4 releases the fixing part from the centrifuge tube body 4, allowing it to be removed from the support base.

[0068] In this embodiment, a sliding cavity 13 is formed inside the support base; The partition includes a sliding plate 14, which is slidably fitted into the sliding cavity 13. A through hole 15 is formed on the sliding plate 14. When the upper end of the sliding plate 14 abuts against the upper side wall of the sliding cavity 13, the sliding plate 14 divides the connecting channel 1 into two channel segments 3. When the lower end of the sliding plate 14 abuts against the lower side wall of the sliding cavity 13, the through hole 15 connects the two channel segments 3.

[0069] When the dispensing device is in its initial state, the lower end of the sliding plate 14 abuts against the lower side wall of the sliding cavity 13, and the perforation 15 connects the two channel sections 3. At this time, the partition can connect the two channel sections 3.

[0070] Move the sliding plate 14 so that its upper end abuts against the upper sidewall of the sliding cavity 13. At this time, the perforation 15 is completely offset from the two channel segments 3, and the sliding plate 14 divides the connecting channel 1 into two channel segments 3. The partition thus divides the connecting channel 1 into two channel segments 3.

[0071] In this embodiment, the support base includes a base 16, a bearing seat 17, and two support parts. The upper side of the bearing seat 17 is the upper side of the support base, and the two support parts are respectively used to support the two opposite ends of the bearing seat 17 above the base 16. The two opposite ends of the bearing seat 17 are each fixed with a rotating shaft 18. The two rotating shafts 18 are arranged with the same axis, and the axis of the two rotating shafts 18 and the axis of the two insertion tubes 2 are located on the same vertical plane. The support includes a support plate 19 and a limiting component. The two rotating shafts 18 are rotatably connected to the support plates 19 of the two support parts in a one-to-one correspondence. The limiting component is used to fix the angle of the rotating shaft 18 so that the rotating shaft 18 cannot rotate on the support plate 19. When the limiting component fixes the angle of the rotating shaft 18, the upper side of the bearing seat 17 is in a horizontal state. The limiting component can also release the fixation of the angle of the rotating shaft 18. The two channel segments 3 are symmetrically arranged on both sides of the sliding plate 14. Both channel segments 3 are inclined vertically, and the upper ends of the two channel segments 3 are connected to the lower ends of the two insertion tubes 2 in a one-to-one correspondence. The support 17 also has two air inlets, the upper ends of the two air inlets are connected to the lower ends of the two channel segments 3 respectively, and the lower ends of the two air inlets are connected to the outer surface of the support 17. A sealing member 20 is detachably fixedly connected inside the two air inlets, and the sealing member 20 is used to block the corresponding air inlet. The lower end of the centrifuge tube body 4 is provided with an exhaust hole 21. A second adhesive tape 22 is attached and fixed to the centrifuge tube body 4. The second adhesive tape 22 seals the exhaust hole 21. A clearance hole is formed on the second cylinder 12 at the position corresponding to the second adhesive tape 22.

[0072] Specifically, the connecting channel 1 is formed inside the support 17, the partition is provided on the support 17, both insertion tubes 2 are fixed on the support 17 and are arranged vertically, and the two fixing parts are used to fix the two centrifuge tube bodies 4 to the upper side of the support 17 in a one-to-one correspondence.

[0073] When the dispensing device is in its initial state, the limiting component fixes the angle of the rotating shaft 18, the rotating shaft 18 cannot rotate on the support plate 19, and the upper side of the bearing seat 17 is in a horizontal state.

[0074] After the liquid levels in both centrifuge tube bodies 4 have stabilized, centrifuge tube caps 5 are placed on both centrifuge tube bodies 4 fixed to the support base 17. The fixing of the angle of the rotating shaft 18 by the limiting component is released, and then the two rotating shafts 18 are rotated on the two support plates 19 respectively. The support base 17 and the two centrifuge tube bodies 4 rotate with the rotating shafts 18. During the rotation of the support base 17 and the two centrifuge tube bodies 4 with the rotating shafts 18, the sliding plate 14 is moved so that the sliding plate 14 divides the connecting channel 1 into two channel segments 3. After the centrifuge tube bodies 4 rotate to face downwards, the angle of the rotating shaft 18 is re-limited by the limiting component, so that the rotating shaft 18 cannot rotate on the support plate 19.

[0075] Then, the two sealing components 20 are removed from the two air inlets one by one, and the second adhesive tape 22 on the two centrifuge tube bodies 4 is torn off through the clearance hole. At this time, the mixture in the two insertion tubes 2 can enter the two centrifuge tube bodies 4 one by one, and the mixture in the two channel sections 3 can also enter the two centrifuge tube bodies 4 one by one. This can reduce the amount of mixture remaining in the connecting channel 1 and the insertion tubes 2, so that the total amount of mixture in the two centrifuge tube bodies 4 is close to the amount of mixture poured out from the first centrifuge tube. This can reduce the possibility that the amount of mixture is insufficient for the operation steps of the measurement method.

[0076] After no more mixture continues to flow out of the insertion tube 2, the second adhesive tape 22 is reattached to the centrifuge tube body 4, so that the second adhesive tape 22 re-seals the vent hole 21. Then the centrifuge tube body 4 can be removed from the support 17.

[0077] Since the centerlines of the two rotating shafts 18 and the two insertion tubes 2 are located on the same vertical plane, during the rotation of the bearing seat 17 and the two centrifuge tube bodies 4, the two centrifuge tube bodies 4 can always maintain the same height, and the amount of mixture in the two centrifuge tube bodies 4 can always remain the same.

[0078] In this embodiment, the air inlet has an internal thread, and the sealing member 20 is a bolt. Screwing the bolt into the air inlet seals it, and unscrewing it releases the seal.

[0079] In this embodiment, the upper side of the support seat 17 is recessed downward to form a channel, and the lower end of the channel is connected to the sliding cavity 13. The partition also includes a connecting strip 23 that slides within the channel and a counterweight 24 fixed to the upper end of the connecting strip 23. The lower end of the connecting strip 23 is fixedly connected to the sliding plate 14. When the lower end of the sliding plate 14 abuts against the lower side wall of the sliding cavity 13, the lower side of the counterweight 24 abuts against the upper side of the bearing seat 17.

[0080] The sliding plate 14 can be moved within the sliding cavity 13 by moving the counterweight 24, which makes it convenient to move the sliding plate 14 within the sliding cavity 13.

[0081] When the centrifuge tube body 4 is facing upward, under the gravity of the counterweight 24, the lower end of the sliding plate 14 can more stably hold against the lower side wall of the sliding cavity 13, and the perforation 15 can more stably maintain the connection between the two channel segments 3.

[0082] During the rotation of the support seat 17, the counterweight 24 can rotate with the support seat 17. When the upper side of the support seat 17 rotates to face downwards, the counterweight 24 can drive the sliding plate 14 to slide under its own weight. After the sliding plate 14 slides a certain distance, the sliding plate 14 divides the connecting channel 1 into two channel segments 3. During the rotation of the support seat 17, the sliding plate 14 can be moved automatically, and the sliding plate 14 can be automatically divided into two channel segments 3.

[0083] In this embodiment, the upper side of the support plate 19 is recessed downward to form a strip groove 25. The strip grooves 25 on the support plates 19 of the two support parts are directly opposite each other. The support plate 19 also has a plurality of horizontal insertion holes. The insertion holes connect the two opposite sides of the support plate 19. The plurality of insertion holes are arranged sequentially at intervals along the vertical direction. The insertion holes are set perpendicular to the axis of the rotating shaft 18. The outer side of the support plate 19 is also recessed to form a vertical sliding groove 26. The support part also includes a connecting plate 27 and multiple insert rods 28. One end of each of the multiple insert rods 28 is fixedly connected to the connecting plate 27. The ends of the multiple insert rods 28 are located on the same vertical plane. The multiple insert rods 28 are slidably fitted into the multiple insert rod holes in a one-to-one correspondence. In each pair of adjacent insert rods 28, the length of the lower insert rod 28 is greater than the length of the upper insert rod 28. The rotating shaft 18 is located within the strip groove 25 and cooperates with the strip groove 25. The rotating shaft 18 is supported on the uppermost insert rod 28. A first hole is formed on the rotating shaft 18. The first hole is perpendicular to the rotating shaft 18 and is horizontally arranged. The limiting component includes a slider 29, a protruding plate 30, and a limiting rod 31. The slider 29 is slidably fitted in the groove 26, the protruding plate 30 is fixed on the slider 29, and a second hole is formed on the protruding plate 30. The limiting rod 31 is inserted into the first hole and the second hole.

[0084] Since the rotating shaft 18 is located within and cooperates with the strip groove 25, the rotating shaft 18 is supported on the uppermost insert rod 28, and the rotating shaft 18 can thus be rotatably connected to the support plate 19.

[0085] When the limiting rod 31 is inserted into the first hole and the second hole, the rotating shaft 18 cannot rotate. At this time, the limiting component can fix the angle of the rotating shaft 18, so that the rotating shaft 18 cannot rotate on the support plate 19. When the limiting rod 31 is pulled out from the first hole, the limiting component can release the fixation of the angle of the rotating shaft 18.

[0086] After the mixture is poured into one of the centrifuge tube bodies 4, the connecting plates 27 of the two supports can be pulled simultaneously, causing the two connecting plates 27 to move away from the corresponding support plates 19 at the same time. The connecting plates 27 can drive the multiple insert rods 28 connected to them to move, and the multiple insert rods 28 arranged sequentially from top to bottom can be completely removed from the strip groove 25 in sequence. In each pair of adjacent inserts 28, when the upper insert 28 moves out of the slot 25, the rotating shaft 18 supported on the upper insert 28 can move downward within the slot 25. After the rotating shaft 18 moves downward a certain distance, it can strike and support the lower insert 28. When the rotating shaft 18 strikes the lower insert 28, both the bearing seat 17 and the centrifuge tube body 4 can quickly stop moving downward. The mixture in one centrifuge tube body 4 can quickly enter the other centrifuge tube body 4 through the connecting channel 1 and the two inserts 2 under the action of inertia, so that the amount of mixture in the two centrifuge tube bodies 4 can reach the same amount more quickly.

[0087] After the centrifuge tube body 4 is rotated downwards, and the sealing member 20 is released from the air inlet, and the second adhesive tape 22 is peeled off the centrifuge tube body 4, the connecting plates 27 of the two support parts can be pulled simultaneously, causing the two connecting plates 27 to move away from the corresponding support plates 19 at the same time. The connecting plates 27 can drive the multiple insertion rods 28 connected to them to move, and the multiple insertion rods 28 arranged sequentially from top to bottom can be completely removed from the strip groove 25 in sequence. In each pair of adjacent insertion rods 28, when the upper insertion rod 28 moves out of the strip groove 25, the rotating shaft 18 supported on the upper insertion rod 28 can move downward within the strip groove 25. After the rotating shaft 18 moves downward a certain distance, it can strike and support the lower insertion rod 28. When the rotating shaft 18 strikes the lower insertion rod 28, both the bearing seat 17 and the centrifuge tube body 4 can quickly stop moving downward, and the mixed liquid in the channel section 3 and the insertion tube 2 can enter the centrifuge tube body 4 more quickly under the action of inertia.

[0088] During the downward movement of the rotating shaft 18, the slider 29 can move downward within the groove 26, and the limiting rod 31 can remain inserted and engaged within the first hole and the second hole. During the downward movement of the rotating shaft 18, the limiting component can maintain the angle of the rotating shaft 18 so that the rotating shaft 18 will not rotate during the downward movement.

[0089] In this embodiment, the dispensing device further includes a fixing rod 32, with both ends of the fixing rod 32 fixedly connected to the two connecting plates 27. By pulling the fixing rod 32, the connecting plates 27 of the two supporting parts can be pulled synchronously, making it more convenient to pull the connecting plates 27 of the two supporting parts synchronously.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for determining five ultrashort-chain perfluorinated compounds in agricultural products, characterized in that, Includes the following steps: S1. Weigh 1.00-5.00g of homogeneous sample into the first centrifuge tube, add a certain amount of internal standard and 1-5 mL of ultrapure water, and vortex mix for 1 min. S2. Continue to add 10 mL of 2% formic acid acetonitrile, homogenize at high speed for 1 min, add QuEChERS pretreatment package, vortex quickly to mix, and centrifuge at high speed for 5 min. S3. Transfer the upper layer of acetonitrile to the second centrifuge tube containing the purifying agent, vortex thoroughly, and centrifuge at high speed for 5 minutes. S4. Take 5 mL of supernatant into the third centrifuge tube, blow it dry with nitrogen at 45℃, add 1 mL of methanol-water solution with a volume ratio of 1:1 to make up the volume, centrifuge at 12000 r / min for 10 min, and filter the supernatant through a 0.22 μm filter membrane. S5. Detect the supernatant after filtration in step S4 by liquid chromatography-tandem mass spectrometry; In step S2, before centrifuging the mixture formed after adding the QuEChERS pretreatment package, the mixture in the first centrifuge tube is divided into two fourth centrifuge tubes by a dispensing device, and the amount of mixture in the two fourth centrifuge tubes is the same. The dispensing device includes a support base, a connecting channel, a partition, and two inserts. The upper side of the support base is horizontal. The connecting channel is formed inside the support base. The partition is disposed on the support base and is used to divide the connecting channel into two channel segments. The partition is also used to connect the two channel segments. Both inserts are fixed on the support base and are arranged vertically. The lower ends of the two inserts are connected to the two ends of the connecting channel respectively. The upper ends of the inserts protrude from the upper side of the support base. The fourth centrifuge tube includes a centrifuge tube body, a centrifuge tube cap, and a switch. The centrifuge tube cap is threaded onto the centrifuge tube body. The bottom wall of the centrifuge tube body has an insertion hole in the middle that connects the inner cavity of the centrifuge tube body to the outside. The insertion hole cooperates with the insertion tube. The switch is located inside the centrifuge tube body. The switch is used to open the insertion hole during the insertion of the insertion tube, so that the inner cavity of the insertion tube is connected to the inner cavity of the centrifuge tube body. The switch is also used to close the insertion hole during the insertion of the insertion tube from the insertion hole. The upper end of the cannula is closed, and a through hole is provided on the upper side wall of the cannula; A circular hole is formed on the bottom wall of the centrifuge tube body. A first cylinder is provided inside the centrifuge tube body. The lower end of the first cylinder is fixed to the bottom wall of the centrifuge tube body. The first cylinder surrounds the circular hole. The circular hole and the inner cavity of the first cylinder form the insertion hole. The switching part includes a sealing plug, a fixing plate, and a helical spring. The sealing plug is inserted into the upper end of the first cylinder and closes the upper end of the first cylinder. The fixing plate is fixed to the upper end of the sealing plug, and the edge of the fixing plate protrudes beyond the edge of the sealing plug. The helical spring is sleeved on the first cylinder, and the upper end of the helical spring is fixedly connected to the fixing plate, and the lower end is fixedly connected to the bottom wall of the centrifuge tube body. A sliding cavity is formed within the support base; The partition includes a sliding plate that can slide up and down in the sliding cavity. A perforation is formed on the sliding plate. When the upper end of the sliding plate abuts against the upper side wall of the sliding cavity, the sliding plate divides the connecting channel into two channel segments. When the lower end of the sliding plate abuts against the lower side wall of the sliding cavity, the perforation connects the two channel segments. The support includes a base, a bearing seat, and two support parts. The upper side of the bearing seat is the upper side of the support, and the two support parts are respectively used to support the two opposite ends of the bearing seat above the base. The two opposite ends of the bearing seat are each fixed with a rotating shaft, the two rotating shafts are arranged with the same center line, and the center lines of the two rotating shafts and the center lines of the two insertion tubes are located on the same vertical plane; The support includes a support plate and a limiting component. The two rotating shafts are rotatably connected to the support plates of the two support parts in a one-to-one correspondence. The limiting component is used to fix the angle of the rotating shaft so that the rotating shaft cannot rotate on the support plate. When the limiting component fixes the angle of the rotating shaft, the upper side of the bearing seat is in a horizontal state. The limiting component can also release the fixation of the angle of the rotating shaft. The two channel segments are symmetrically arranged on both sides of the sliding plate. Both channel segments are inclined vertically, and the upper ends of the two channel segments are connected to the lower ends of the two insertion tubes in a one-to-one correspondence. The support base also has two air inlets, the upper ends of the two air inlets are connected to the lower ends of the two channel sections respectively, and the lower ends of the two air inlets are connected to the outer surface of the support base. A sealing component is detachably fixedly connected inside the two air inlets, and the sealing component is used to block the corresponding air inlet. The lower end of the centrifuge tube body is provided with an exhaust hole, and a second adhesive tape is attached and fixed to the centrifuge tube body to seal the exhaust hole. A clearance hole is formed on the second cylinder at the position corresponding to the second adhesive tape.

2. The method for determining five ultrashort-chain perfluorinated compounds in agricultural products according to claim 1, characterized in that, In step S5, the liquid chromatography conditions are as follows: Chromatographic column: The chromatographic column is a Chemalink PFP column with parameters of 4.6 mm × 250 mm and a particle size of 5.0 μm; Mobile phase A: 5 mmol ammonium acetate solution, which contains 0.1% formic acid; Mobile phase B: Methanol; Flow rate: 0.5 mL / min; Injection volume: 5 μL; Column temperature: 40 ℃.

3. The method for determining five ultrashort-chain perfluorinated compounds in agricultural products according to claim 1, characterized in that, In step S5, the mass spectrometry conditions are as follows: Ion source: Electrospray ionization source; Scanning method: Negative ion scanning; Electrospray voltage: 4500V; Atomizer pressure: 65 psi; Air curtain pressure: 30 psi; Auxiliary air pressure: 60 psi; Ion source temperature: 450 ℃; Acquisition method: Mass spectrometry multiple reaction monitoring.

4. The method for determining five ultrashort-chain perfluorinated compounds in agricultural products according to claim 1, characterized in that: The dispensing device also includes two fixing parts, which are used to fix the two centrifuge tube bodies to the upper side of the support base in a one-to-one correspondence.

5. The method for determining five ultrashort-chain perfluorinated compounds in agricultural products according to claim 1, characterized in that: Alternatively, the centrifuge tube body can be pressed down and fixed to the upper side of the support by hand.

6. The method for determining five ultrashort-chain perfluorinated compounds in agricultural products according to claim 1, characterized in that: The upper side of the support plate is recessed downward to form a strip groove. The strip grooves on the support plates of the two support parts are directly opposite each other. The support plate also has a plurality of horizontal insertion holes. The insertion holes connect the two opposite sides of the support plate. The plurality of insertion holes are arranged sequentially at intervals in the vertical direction. The insertion holes are set perpendicular to the axis of rotation. The outer side of the support plate is also recessed to form a vertical sliding groove. The support part also includes a connecting plate and multiple insert rods. One end of each insert rod is fixedly connected to the connecting plate. The ends of the multiple insert rods are located on the same vertical plane. The multiple insert rods are slidably fitted into the multiple insert rod holes in a one-to-one correspondence. In each pair of adjacent insert rods, the length of the lower insert rod is greater than the length of the upper insert rod. The rotating shaft is located in the strip groove and cooperates with the strip groove. The rotating shaft is supported on the uppermost insert rod. A first hole is formed on the rotating shaft. The first hole is perpendicular to the rotating shaft and is set horizontally. The limiting component includes a slider, a convex plate, and a limiting rod. The slider is slidably fitted in a groove, the convex plate is fixed on the slider, and a second hole is formed on the convex plate. The limiting rod is inserted into the first hole and the second hole.

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