A method for determining the residual amount of perfluoroalkyl acid pollutants in vegetables

Abstract

The present invention relates to a method for determining the residual amount of perfluoroalkyl acid pollutants in vegetables. The present invention aims to solve the problems of cumbersome operation, low efficiency, poor accuracy, significant matrix effect, and weak matrix applicability in existing methods and technologies for analyzing perfluoroalkyl acid pollutants in vegetables, and establishes a new method through innovative inventions and technical optimization in the pretreatment and instrumental analysis process. The established method will be suitable for rapid screening and precise quantitative analysis of perfluoroalkyl acid pollutants in vegetables with large sample volumes and on a large scale, and will greatly improve the efficiency of analysis and detection, and effectively improve accuracy.

Description

Technical Field

[0001] The invention belongs to the field of detection technology, and in particular relates to a method for determining the residual amount of perfluoroalkyl acid pollutants in vegetables. Background Art

[0002] The information disclosed in the background of the invention is only intended to enhance the understanding of the overall background of the invention and should not be necessarily regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Perfluoroalkyl acids (PFAAs) are a class of artificially synthesized chemicals that are thermally stable, chemically stable, and surface active, and are widely used in industrial products and daily necessities. However, they easily release pollution into the environment and are not easy to decompose, thus entering the food chain and being ingested by humans. Studies have found that perfluoroalkyl acids have a variety of acute and chronic toxicities to the human body, and are easily combined with protein substances in the human body to produce enrichment. In recent years, some studies have detected perfluoroalkyl acid contamination in vegetables, and found that there is a certain correlation between the consumption of vegetables by the population and the level of human exposure to perfluoroalkyl acids.

[0004] In the existing detection methods of perfluoroalkyl acids in vegetables, solid phase extraction technology is mostly used for sample pretreatment, and the extractants include weak anion exchange (WAX), hydrophilic-lipophilic balance (HLB) and graphitized carbon black (Envi-Carb). Although it has the advantages of high enrichment multiple and good purification effect, it also has the disadvantages of using too many types of solvents, cumbersome operation and long time consumption. In recent years, a quick, easy, cheap, effective, rugged and safe pretreatment technology (QuEChERS) has received extensive attention and research. It can quickly extract, purify and concentrate trace substances in food, is suitable for organic mass spectrometry analysis, and greatly shortens the sample processing time. At present, there are many perfluoroalkyl acid detection methods based on QuEChERS technology, but most of them are for animal products such as fish, animal offal, eggs, oils and honey; while the detection method for vegetable matrix is ​​still blank at home and abroad. Therefore, it is necessary to develop a detection method based on the improved QuEChERS technology for large-scale screening and accurate quantitative analysis of perfluoroalkyl acid pollutants in vegetables that is rapid, easy to operate, highly sensitive, and has strong matrix applicability. Summary of the invention

[0005] In view of the above technical problems, the present invention aims to solve the problems of cumbersome operation, low efficiency, poor accuracy, significant matrix effect, and weak matrix applicability in the existing analysis methods and technologies of perfluoroalkyl acid pollutants in vegetables, and establish a new method through innovative inventions and technical optimization in the pretreatment and instrument analysis process. The established method will be suitable for large-scale rapid screening and precise quantitative analysis of perfluoroalkyl acid pollutants in vegetables with large sample volumes, and will greatly improve the efficiency of analysis and detection, and effectively improve accuracy.

[0006] One of the purposes of the present invention is to invent a purification tube suitable for pre-treatment of detection of 13 kinds of perfluoroalkyl acids in vegetables.

[0007] The second purpose of the present invention is to provide a method for detecting the residual amounts of 13 perfluoroalkyl acids in vegetables based on the pretreatment of the purification tube.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A purification tube suitable for pre-treatment of 13 perfluoroalkyl acids in vegetables, the purification tube comprising: (1) a through-type purification tube body; and (2) a matrix-dispersed purifier encapsulated therein, the matrix-dispersed purifier being composed of a uniform mixture of five solid powders: 100 mg N-propylethylenediamine (PSA), 80 mg octadecyl silica gel (C18), 50 mg graphitized carbon black (GCB), 50 mg multi-walled carbon nanotubes (MWCNTs), and 800 mg anhydrous magnesium sulfate.

[0010] The specific preparation method is as follows: (1) weighing 100 mg of N-propylethylenediamine, 80 mg of octadecyl silica gel, 50 mg of graphitized carbon black, 50 mg of multi-walled carbon nanotubes, and 800 mg of anhydrous magnesium sulfate, mixing them evenly, and transferring them into the lumen of a through-type purification tube; (2) placing a sieve plate of a matching size of the purification tube into the lumen from above, and using a press to compact the filler to obtain the purification tube.

[0011] A method for detecting the residual amount of perfluoroalkyl acids in vegetables based on the above purification tube. The method comprises:

[0012] (1) Sample pretreatment: add formic acid-acetonitrile extract and internal standard working solution to the crushed and homogenized vegetable sample, vortex mix, add dehydrating salt, shake and extract, centrifuge to separate the solid, aqueous phase and organic phase, and obtain the sample to be tested;

[0013] (2) Purification and concentration: Take the purification tube, insert it into the pretreatment centrifuge tube and slowly press down to filter and purify the upper organic phase, dissolve it with methanol after nitrogen blowing, and filter it;

[0014] (3) Using liquid chromatography-mass spectrometry / mass spectrometry, quantitative analysis and detection of perfluoroalkyl acids in the sample to be tested.

[0015] Furthermore, the formic acid-acetonitrile extract is an acetonitrile solution containing 0.5% formic acid (v:v).

[0016] Furthermore, the internal standard working solution is a methanol solution of 8 isotopic internal standards at a concentration of 10 ng / mL, including 13 C4-PFBA, 13 C2-PFHxA, 13 C3-PFOA, 13 C4-PFNA, 13 C2-PFDA, 13 C2-PFUdA, 13 C2-PFDoA, 13 C4-PFOS.

[0017] Furthermore, the dehydrated salt is a mixture of 1.5 g of sodium chloride and 6 g of anhydrous magnesium sulfate.

[0018] Furthermore, the vortex mixing time was 1 min, the shaking time was 1 min, the centrifugation time was 5 min, and the rotation speed was 4000 r / min.

[0019] Further, after inserting the pretreatment centrifuge tube, press it by hand until the bottom is about 0.5 cm from the top of the liquid surface of the supernatant, and then slowly press down the purification tube at a rate of 1 mm / s; press until the height of the filtered solution exceeds 5 cm and the volume exceeds 6 mL; use a pipette to transfer 5 mL of the purified solution from the filtered solution to a 15 mL centrifuge tube, and blow dry it with a nitrogen flow of 6-8 psi in a 40°C water bath; accurately draw 1 mL of methanol into the dried centrifuge tube, vortex for 0.5 min to dissolve the dried residue, and then pass it through a 0.22 μm filter membrane and transfer it to a sample injection bottle for testing.

[0020] Furthermore, the perfluoroalkyl acid includes perfluorobutyric acid, perfluoropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorodecanoic acid, perfluorononanoic acid, perfluoroundecanoic acid, perfluorododecanoic acid, perfluorotridecanoic acid, perfluorotetradecanoic acid, perfluorohexadecanoic acid, and perfluorooctane sulfonic acid.

[0021] Further, the liquid chromatography conditions for instrumental analysis include:

[0022] Chromatographic column: Aglient Eclipse Plus C18 column (2.1×100mm, 1.8μm);

[0023] Column temperature: 25°C;

[0024] Flow rate: 0.3 mL / min;

[0025] Injection volume: 5 μL;

[0026] Mobile phase: phase A is water, phase B is methanol; 5mmol / L ammonium acetate and 0.5% formic acid are added to phases A and B;

[0027] The gradient elution program is as follows:

[0028] 0min: mobile phase A 90.0%, mobile phase B 10.0%;

[0029] 3.0min: mobile phase A 30.0%, mobile phase B 70.0%;

[0030] 6.0min: mobile phase A 0%, mobile phase B 100%;

[0031] 6.5 min: mobile phase A 0%, mobile phase B 100%;

[0032] 6.6min: mobile phase A 90.0%, mobile phase B 10.0%;

[0033] 7.5min: mobile phase A 90.0%, mobile phase B 10.0%;

[0034] Furthermore, the mass spectrometry conditions for instrumental analysis include:

[0035] Ion source: electrospray ionization ESI (-);

[0036] Curtain air (CUR): 10psi;

[0037] Ionization voltage (IS): -4500V;

[0038] Temperature (TEM): 550 °C;

[0039] Spray gas (GS1): 50psi;

[0040] Auxiliary heating gas (GS2): 50psi;

[0041] Scan mode: Multiple reaction monitoring (MRM).

[0042] Beneficial effects of the present invention:

[0043] 1. The method of the present invention adopts the QuEChERS purification technology to carry out pretreatment, which overcomes the problems of the existing solid phase extraction method such as the use of a lot of solvents, many solvent conversions and extraction operations, and cumbersome pretreatment. The purification time is shortened by more than 80% compared with the solid phase extraction method, and the number of solution additions / transfers in the purification process is reduced from more than 6 times to 1 time, which is significantly fast, simple, and efficient.

[0044] 2. Compared with the existing detection methods, the method described in the present invention has better spike recovery range and matrix effect evaluation results, and has good precision, accuracy and low matrix effect.

[0045] 3. The method described in the present invention can simultaneously detect 14 kinds of perfluoroalkyl acids in vegetables such as leek, eggplant, lettuce, cucumber, and tomato. The applicable range of the matrix and the range of detection targets are higher than those of existing methods, and it is more suitable for risk assessment screening, monitoring and analysis of perfluoroalkyl acid pollutants in various vegetables. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0047] Figure 1 The effect of the amount of PSA and C18 purifier used on the recovery rate of PFAAs;

[0048] Figure 2 The effect of formic acid addition level in the extraction solvent on the recovery of PFAAs;

[0049] Figure 3 Select the ion chromatogram for the PFAA mixed standard solution. DETAILED DESCRIPTION

[0050] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0051] Example 1

[0052] A method for detecting the residual amounts of 13 perfluoroalkyl acids in vegetables based on a pass-through purification technology. The method comprises:

[0053] (1) Sample pretreatment: Add formic acid-acetonitrile extract and internal standard working solution to the crushed and homogenized sample, vortex mix, add dehydrating salt and shake to extract, centrifuge to separate the solid, aqueous and organic phases.

[0054] The specific ratio of the formic acid-acetonitrile extract is an acetonitrile solution containing 0.5% formic acid (v:v); the internal standard working solution is a methanol solution of 8 isotopic internal standards with a concentration of 10 ng / mL, including 13 C4-PFBA, 13 C2-PFHxA, 13 C3-PFOA, 13 C4-PFNA, 13 C2-PFDA,13 C2-PFUdA, 13 C2-PFDoA, 13 C4-PFOS; the dehydrated salt is a mixture of 1.5 g sodium chloride and 6 g anhydrous magnesium sulfate; the vortex mixing time is 1 min, and the shaking time is 1 min; the centrifugal time is 5 min, and the rotation speed is 4000 r / min.

[0055] (2) Purification and concentration: Take a pass-through purification tube, insert it into the pretreatment centrifuge tube, and slowly press down to filter and purify the upper organic phase. After nitrogen blowing, dissolve it with methanol and filter it.

[0056] The purification tube comprises: (1) a through-type purification tube body; (2) a plurality of matrix-dispersed purification agents encapsulated therein, which are composed of five solid powders mixed evenly, including 100 mg N-propylethylenediamine (PSA), 80 mg octadecyl silica gel (C18), 50 mg graphitized carbon black (GCB), 50 mg multi-walled carbon nanotubes (MWCNTs), and 800 mg anhydrous magnesium sulfate. The specific implementation method is as follows: (1) weighing 100 mg N-propylethylenediamine, 80 mg octadecyl silica gel, 50 mg graphitized carbon black, 50 mg multi-walled carbon nanotubes, and 800 mg anhydrous magnesium sulfate, mixing them evenly and transferring them into the lumen of the through-type purification tube; (2) using a special device, placing a sieve plate of a suitable size on the purification tube, pressing it, and obtaining a through-type QuEChERS purification tube.

[0057] After inserting the pretreatment centrifuge tube, press it by hand until the bottom is about 0.5 cm from the top of the supernatant liquid surface, and then slowly press down the purification tube at a rate of 1 mm / s; press until the height of the filtered solution exceeds 5 cm and the volume exceeds 6 mL; use a pipette to transfer 5 mL of the purified solution from the filtered solution to a 15 mL centrifuge tube, and blow dry with a nitrogen flow of 6 to 8 psi in a 40°C water bath; accurately draw 1 mL of methanol into the dried centrifuge tube, vortex for 0.5 min to dissolve the dried residue, then filter through a 0.22 μm filter membrane and transfer to the injection bottle for testing.

[0058] (3) Using liquid chromatography-mass spectrometry / mass spectrometry, quantitative analysis and detection of 13 perfluoroalkyl acids in the sample prepared by the above steps.

[0059] Among them, 13 perfluoroalkyl acids include perfluorobutyric acid, perfluoropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorodecanoic acid, perfluorononanoic acid, perfluoroundecanoic acid, perfluorododecanoic acid, perfluorotridecanoic acid, perfluorotetradecanoic acid, perfluorohexadecanoic acid, and perfluorooctane sulfonic acid;

[0060] The LC conditions for instrumental analysis included:

[0061] Chromatographic column: Aglient Eclipse Plus C18 column (2.1×100mm, 1.8μm);

[0062] Column temperature: 25°C;

[0063] Flow rate: 0.3 mL / min;

[0064] Injection volume: 5 μL;

[0065] Mobile phase: Phase A is 5mmol / L ammonium acetate-0.5% formic acid-water, and phase B is 5mmol / L ammonium acetate-0.5% formic acid-methanol; the gradient elution program is as follows:

[0066] Table 1 Gradient elution program

[0067] Time / min Mobile phase A / % Mobile phase B / % 0 90.0 10.0 3.0 30.0 70.0 6.0 0 100.0 Instrument 6.5 0 100.0 6.6 90.0 10.0 7.5 90.0 10.0

[0068] The mass spectrometry conditions for the analysis included:

[0069] Ion source: electrospray ionization ESI (-);

[0070] Curtain air (CUR): 10psi;

[0071] Ionization voltage (IS): -4500V;

[0072] Temperature (TEM): 550 °C;

[0073] Spray gas (GS1): 50psi;

[0074] Auxiliary heating gas (GS2): 50psi;

[0075] Scan mode: Multiple reaction monitoring (MRM).

[0076] Each target detection substance and isotope internal standard is monitored using the following mass spectrometry parameters:

[0077] Table 2 Mass spectrometry parameters

[0078]

[0079] Example 2

[0080] Organic acids, chlorophyll, etc. rich in plant food matrices can not only cause contamination of liquid phase systems, ion sources and mass analyzers, but also produce matrix effects and matrix interferences that affect detection accuracy, so the pre-treatment process purification process is crucial. Among the commonly used purifiers selected in this embodiment, although PSA can effectively remove organic acids and other substances in vegetables, it has a certain adsorption to PFAAs that also contain organic acid groups; C18 can adsorb weak polar co-extraction interferences in the matrix, but it may affect the analysis of hydrophobic long carbon chain PFAAs; while GCB and MwCNTs can effectively adsorb pigments with planar structures and have little effect on chain-structured PFASs. Therefore, this embodiment focuses on optimizing the usage of PSA and C18. On the basis of the method in Example 1, the discussion addition amount of PSA is set to 0, 50, 100, 150, 200 mg, and C18 is set to 0, 40, 80, 120, 160 mg.

[0081] Depend on Figure 1 It can be seen that for PSA, the short carbon chain PFBA, PFHxA and PFOS have similar changes, which are manifested in the increase in the recovery rate after using PSA, and a significant decrease after the dosage exceeds 100 mg. Analysis shows that a small amount of PSA can purify polar interferences such as organic acids, thereby reducing the matrix effect inhibition of the electrospray ion source; and excessive use may lead to adsorption loss of the target, which increases with the decrease in the number of carbon atoms of PFAAs. The recovery rates of PFOA, PFUdA and PFHxDA with medium and long carbon chains tend to be stable under the condition of gradually increasing PSA, and are less affected. For C18, the use of a small amount has no obvious effect on the recovery rate of each component, but the recovery rate of the three substances with medium and long carbon chains shows a significant downward trend after the usage exceeds 80 mg. Taking into account the changes in the recovery rate of each substance, this embodiment determines the usage of 100 mg of PSA and 80 mg of C18.

[0082] Example 3

[0083] This embodiment adopts Sin-QuEChERS normal phase purification technology, which has higher analysis and processing efficiency than SPE reverse phase purification and traditional QuEChERS dispersion purification. A simple test compared the analysis time of the above-mentioned purification methods. Using the same extraction operation (same as Example 1), the extraction process of a batch (20) of samples from the beginning of weighing the sample to salting out and dehydration takes about 30 to 40 minutes; while the purification and concentration time from salting out and dehydration to the filtration membrane operation is quite different: Sin-QuEChERS purification technology takes about 15 minutes, WAX-SPE method takes about 80 minutes, and QuEChERS dispersion purification takes about 35 minutes. Under the premise of ensuring the recovery rate and stability of the spiked recovery, the present invention has a more obvious time advantage and significantly improves the detection efficiency.

[0084] Example 4

[0085] In the method of using QuEChERS technology to detect pesticide residues in vegetables in recent years, acetonitrile is often used as an extraction solvent for extraction. Compared with acetone, ethyl acetate and n-hexane, acetonitrile has a slightly stronger polarity and is more suitable for high-throughput synchronous extraction and analysis of compound groups with large polarity differences; compared with methanol, acetonitrile can separate from water layers in a saturated electrolyte environment to achieve liquid-liquid extraction and phase separation. Therefore, this embodiment combines the polar characteristics of 13 PFAAs and refers to recent research, and uses acetonitrile equal to the sample as the extraction solvent. Since PFAAs contain carboxyl or sulfonic acid groups in their molecular structure, they have a low dissociation constant and are easily extracted by organic phases under acidic conditions, so the effect of adding formic acid on the extraction efficiency was investigated. The specific experimental method is the same as in Example 1, except that the amount of formic acid added is selected to be 0%, 0.1%, 0.5%, 1% and 2%, and the pH after mixing with the solvent blank is 6.26, 3.74, 2.95, 2.57, and 2.35, respectively.

[0086] Depend on Figure 2 It can be seen that the extraction rates of PFBA, PFHxA and PFOS under different addition conditions are similar, and increase with the increase of the addition amount, and tend to be stable or slightly decrease after reaching 0.5%; while PFOA, PFUdA and PFHxDA reach the best extraction efficiency when adding 0.1% or 0.5% formic acid, and then decrease. Considering that PFBA, PFHxA and PFOA are the main pollutants in greenhouse vegetables, the present invention determines the addition amount of 0.5% formic acid in the extraction solvent.

[0087] Example 5

[0088] A 1.8 μm particle size chromatographic column was used, and a gradient elution procedure was established. By adding appropriate amounts of ammonium acetate and formic acid (5 mmol / L ammonium acetate and 0.5% formic acid), the retention capacity of the target on the C18 chromatographic column was improved, and a good peak shape was obtained. The effective separation of 13 PFAAs was achieved within 7.5 min, such as Figure 3 shown.

[0089] Example 6

[0090] In order to verify the scientificity, rationality and superiority of the present invention, the following methodological verification was carried out:

[0091] (1) The linear equation and linear range of each target were determined, as shown in the following table. The linear range of the calibration curves of most substances is 0.05-5 ng / mL, while PFBA and PFOA have a wider linear range. The correlation coefficients of the calibration curves of all substances are between 0.997 and 0.999, showing a good linear relationship. Referring to the requirements of the relevant EU standard SANTE / 11945 / 2015, the detection limit and quantification limit of each substance were determined by the triple signal-to-noise ratio (S / N) method and the ten-fold signal-to-noise ratio method. The detection limit of all substances is in the range of 0.004-0.008 μg / kg, and the quantification limit is in the range of 0.009-0.023 μg / kg.

[0092] Table 3 Linear equations and linear ranges of various targets

[0093]

[0094] (2) The precision and accuracy of the method were investigated, as shown in the following table. Common greenhouse vegetables such as cucumber, lettuce, tomato, eggplant and leek were selected, and three spike concentrations of 0.1, 0.5 and 2.5 μg / kg were used for testing in five vegetable matrices and blank solvent (acetonitrile) (n=6). The accuracy was investigated by the average value of the spike recovery rate, and the precision was investigated by the relative standard deviation (RSD) of each group, as shown in the following table. The overall spike recovery rates in the solvent matrix and sample matrix were in the range of 75.4% to 103.7%, with the highest RSD of 8.1%, which met the technical requirements of EU SANTE / 11945 / 2015 and GB / T 32465-2015 Requirements for Validation and Internal Quality Control of Chemical Analysis Methods.

[0095] Table 4 Precision and accuracy of the present invention

[0096]

[0097]

[0098]

[0099] (3) The matrix effect of the method was evaluated, as shown in the table above. The 65 groups of ME values ​​of each substance in different matrices were in the range of 0.82 to 1.15. Among them, 7 groups of values ​​were in the range of 0.8 to 0.9, showing a slight inhibitory effect; 3 groups of values ​​were in the range of 1.1 to 1.2, showing a slight enhancement effect; and 55 groups of values ​​were in the range of 0.9 to 1.1, and the matrix effect was negligible. Compared with the method established by Xiang et al., the present invention is less affected by the matrix effect as a whole, and the difference between matrices of the same substance is small. Therefore, the same matrix standard solution curve can be used for the analysis of different vegetable matrices in the detection, thereby improving the analysis and detection efficiency.

[0100] (4) Comparison with multiple existing similar methods is shown in the following table. In general, the present invention uses formic acid-acetonitrile extraction and a purification method using multiple purifiers to analyze PFAAs in vegetables, which is superior to published methods in many aspects. Compared with weak polar solvents such as tetrahydrofuran and MTBE used in early inspection methods, the toxicity and volatility of acetonitrile used in the present invention are lower, and it has a better effect on the extraction of targets of different polarities, and the liquid-liquid separation operation is convenient and efficient; solid phase extraction technology including Florisil, graphitized carbon and WAX are widely used, but compared with the present invention, it has shortcomings in terms of operation time, number of phase changes, flow rate control, solvent pH, etc. The quantitative limit level of the present invention is lower than that of multiple methods, has good sensitivity, and meets the requirements of trace analysis; compared with other methods, the recovery rate of the present invention is the best (close to 100%), which is because the isotope internal standard correction in the pretreatment greatly improves the accuracy and repeatability of the method.

[0101] Table 5 Comparison of different methods

[0102]

[0103] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for detecting the residual amount of perfluoroalkyl acids in vegetables based on a purification tube, characterized in that: The detection method comprises the following steps: (1) Sample pretreatment: add formic acid-acetonitrile extract and internal standard working solution to the crushed and homogenized vegetable sample, vortex mix, add dehydrating salt and shake to extract, centrifuge to separate the solid, aqueous phase and organic phase, and obtain the sample to be tested; the dehydrating salt is a mixture of 1.5 g sodium chloride and 6 g anhydrous magnesium sulfate; (2) Purification and concentration: Take the purification tube, insert it into the pretreatment centrifuge tube and slowly press down to filter and purify the upper organic phase, dissolve it with methanol after nitrogen blowing, and filter it; (3) Using liquid chromatography-mass spectrometry / mass spectrometry to quantitatively analyze and detect perfluoroalkyl acids in the sample to be tested; The purification tube is a purification tube suitable for pre-treatment of 13 perfluoroalkyl acids in vegetables, comprising: (1) a through-type purification tube body; (2) a matrix-dispersed purification agent encapsulated therein, wherein the matrix-dispersed purification agent is composed of five solid powders, namely, 100 mg N-propylethylenediamine PSA, 80 mg octadecyl silica gel C18, 50 mg graphitized carbon black GCB, 50 mg multi-walled carbon nanotubes MWCNTs, and 800 mg anhydrous magnesium sulfate, which are uniformly mixed; The perfluoroalkyl acids include perfluorobutyric acid, perfluoropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorodecanoic acid, perfluorononanoic acid, perfluoroundecanoic acid, perfluorododecanoic acid, perfluorotridecanoic acid, perfluorotetradecanoic acid, perfluorohexadecanoic acid and perfluorooctane sulfonic acid.

2. The detection method according to claim 1, characterized in that: The specific preparation method of the purification tube is as follows: (1) weighing 100 mg of N-propylethylenediamine, 80 mg of octadecyl silica gel, 50 mg of graphitized carbon black, 50 mg of multi-walled carbon nanotubes, and 800 mg of anhydrous magnesium sulfate, mixing them evenly, and transferring them into the lumen of a through-type purification tube; (2) placing a sieve plate of a matching size of the purification tube into the lumen from above, and using a press to compact the filler to obtain the purification tube.

3. The detection method according to claim 1, characterized in that: The formic acid-acetonitrile extract is an acetonitrile solution containing 0.5% formic acid by volume; The internal standard working solution is a methanol solution of 8 isotopic internal standards at a concentration of 10 ng / mL, including 13 C4-PFBA, 13 C2-PFHxA, 13 C3-PFOA, 13 C4-PFNA, 13 C2-PFDA, 13 C2-PFUdA, 13 C2-PFDoA, 13 C4-PFOS.

4. The detection method according to claim 1, characterized in that: The vortex mixing time was 1 min, the shaking time was 1 min, and the centrifugation time was 5 min at a speed of 4000 r / min.

5. The detection method according to claim 1, characterized in that: After inserting the pretreatment centrifuge tube, press it by hand until the bottom is 0.5 cm from the top of the supernatant liquid surface, and then slowly press down the purification tube at a rate of 1 mm / s; press until the height of the filtered solution exceeds 5 cm and the volume exceeds 6 mL; use a pipette to transfer 5 mL of the purified solution from the filtered solution to a 15 mL centrifuge tube, and blow dry with a nitrogen flow of 6-8 psi in a 40°C water bath; accurately draw 1 mL of methanol into the dried centrifuge tube, vortex for 0.5 min to dissolve the dried residue, then pass through a 0.22μm filter membrane and transfer to an injection bottle for testing.

6. The detection method according to claim 1, characterized in that: The LC conditions for instrumental analysis included: Chromatographic column: Aglient Eclipse Plus C18 column 2.1×100mm, 1.8μm; Column temperature: 25 °C; Flow rate: 0.3 mL / min; Injection volume: 5 μL; Mobile phase: Phase A was water and phase B was methanol; 5 mmol / L ammonium acetate and 0.5% formic acid were added to both phases A and B.

7. The detection method according to claim 6, characterized in that: The elution method is gradient elution, and the gradient elution procedure is as follows: 0min: mobile phase A 90.0%, mobile phase B 10.0%; 3.0min: mobile phase A 30.0%, mobile phase B 70.0%; 6.0min: mobile phase A 0%, mobile phase B 100.0%; 6.5min: mobile phase A 0%, mobile phase B 100.0%; 6.6min: mobile phase A 90.0%, mobile phase B 10.0%; 7.5min: Mobile phase A 90.0%, mobile phase B 10.0%.

8. The detection method according to claim 1, characterized in that: The mass spectrometry conditions for instrumental analysis included: Ion source: electrospray ionization ESI-; Curtain air CUR: 10 psi; Ionization voltage IS: -4500 V; Temperature TEM: 550°C; Spray gas GS1: 50 psi; Auxiliary heating gas GS2: 50 psi; Scan mode: Multiple reaction monitoring (MRM).

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