A method for obtaining detection limits of 23 perfluorinated compounds in water

Abstract

A method for obtaining the detection limits of 23 perfluorinated compounds in water, relating to the field of pollutant detection technology, comprises the following steps: Step S1, taking a sufficient amount of water sample and placing it in a fluorine-free volumetric flask to obtain a water sample containing methanol; Step S2, preparing a water sample to be tested; Step S3, testing the water sample using a high-performance liquid chromatography-tandem mass spectrometer; Step S4, setting an elution program for the mobile phase; Step S5, conducting a test and calculating the concentrations of the 23 perfluorinated compounds in the water sample to be tested. The present invention utilizes a liquid chromatography-triple quadrupole mass spectrometer and an online solid-phase extraction method to obtain the detection limits of the 23 perfluorinated compounds in water, thereby improving detection efficiency, reducing human error, and reducing the consumption of organic solvents and the use of traditional solid-phase extraction columns.

Description

Technical Field

[0001] The present invention relates to the technical field of pollutant detection, and in particular to a method for obtaining detection limits of 23 perfluorinated compounds in water. Background Art

[0002] Perfluorinated compounds (PFAs) are artificially synthesized chemicals whose carbon-fluorine bonds are extremely stable, difficult to form naturally, and they do not occur naturally. PFCs primarily originate from human activities, such as industrial emissions from factories that manufacture and use PFCs; products containing PFCs, such as non-stick pans and waterproofing materials, enter water bodies after use and disposal; firefighting foam used in fire drills and accidents contains PFCs, which easily seep into groundwater; and wastewater treatment plants are unable to completely remove PFCs, leading to their entry into natural water bodies. Due to varying contamination patterns, the distribution of PFCs in water quality is highly uneven. Untreated water samples from areas with relevant production and use activities have elevated levels of PFCs. However, areas with PFC-related activities account for less than 0.1% of the country's total land area, resulting in low concentrations of PFCs in water quality across most regions. However, due to the hazards of PFCs, such as persistent pollution, bioaccumulation, immune system damage, developmental effects, and cancer risks, detecting low concentrations of PFCs is of practical significance.

[0003] In the existing technology, such as the Jiangsu Provincial Local Standard DB 32 / T 4004-2021 "Determination of 17 Perfluorinated Compounds in Water Quality by High Performance Liquid Chromatography Tandem Mass Spectrometry", the enrichment function is achieved through manual solid-phase extraction, the components to be tested are separated by liquid phase, and 17 perfluorinated compounds in surface water are determined using a triple quadrupole mass spectrometer. Specifically, an internal standard solution is added to 0.2~0.5L of sample, and 4mL of 0.1% ammonia / methanol solution, 4mL of methanol and 4mL of pure water are added to the solid-phase extraction device in sequence. The column head is always kept wet during the addition of solvents. A universal adapter is connected to the top of the solid-phase extraction column, and the sample is absorbed under negative pressure through the pipeline, and the flow rate is controlled at about 1 drop / second. The solid-phase extraction column is rinsed with 4mL of 25mmol / L ammonium acetate aqueous solution to fix the 17 perfluorinated compounds on the solid-phase extraction column. The previous samples and eluents are discarded. After drying the solid-phase extraction column in a vacuum freeze dryer, the column was sequentially eluted with 4 mL of methanol and 4 mL of an aqueous ammonia / methanol solution. The eluent was collected in a 15 mL polypropylene centrifuge tube. The collected eluent was concentrated with nitrogen in a nitrogen blow dryer, diluted to 1 mL with methanol, passed through a 0.22 μm filter, and placed in a 1.5 mL brown injection vial. The sample was stored at 4°C until analysis. The liquid chromatography mobile phase gradient elution process consisted of 2 mmol / L aqueous ammonium acetate and acetonitrile. At the start of the elution, the volume percentages of aqueous ammonium acetate and acetonitrile were 80% and 20% respectively. Over 14 minutes, the volume percentage of aqueous ammonium acetate was steadily decreased from 80% to 10%, while the volume percentage of acetonitrile was steadily increased from 20% to 90% and maintained for 2 minutes. At 16.01 minutes, the volume percentage of aqueous ammonium acetate was increased from 10% to 80%, while the volume percentage of acetonitrile was decreased from 90% to 20% and maintained for 4 minutes. The 0-14 min period was the gradient elution process, the 14-16 min period was the isocratic elution process, and the 16-20 min period was the column re-equilibration process.

[0004] During the above-mentioned experimental operation, the manual solid-phase extraction process is complicated, the sample demand is large, the human operation error is large, the operation efficiency is low, the consumption of organic solvents is large, and the potential toxicity of unknown samples may pose an exposure risk to the inspectors. The manual solid-phase extraction process requires the preparation of multiple solvents, which are repeatedly and quantitatively added to the solid-phase extraction column. Both require manual operation by the experimenter, and the consumption of organic solvents is large. The sample enrichment volume is between 0.2-0.5L, and the flow rate is controlled at about 1 drop / second when passing through the column. It takes more than 1 hour for all samples to pass through the solid-phase extraction column, which requires a long time and low operation efficiency. Freeze drying, nitrogen blow dryer and vacuum pumping are cumbersome and time-consuming. The required instruments and equipment occupy a large area and consume energy. Summary of the Invention

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a method for obtaining the detection limits of 23 perfluorinated compounds in water quality. The method utilizes a liquid chromatography-triple quadrupole mass spectrometer and adopts an online solid-phase extraction method to obtain the detection limits of 23 perfluorinated compounds in water quality, thereby improving detection efficiency, reducing human errors, and reducing the consumption of organic solvents and the use of traditional solid-phase extraction columns.

[0006] In order to achieve the above objectives, the main technical solutions adopted by the present invention include:

[0007] A method for obtaining the detection limits of 23 perfluorinated compounds in water comprises the following steps:

[0008] Step S1, taking a sufficient amount of water sample and placing it in a fluorine-free volumetric flask, adding methanol so that the volume content of methanol is 10% of the water sample, to obtain a water sample containing methanol;

[0009] Step S2, adding an isotope internal standard mixed solution to a water sample containing methanol to prepare a water sample to be tested;

[0010] Step S3: Detecting the water quality sample using a high performance liquid chromatography-tandem mass spectrometer. A solid phase extraction column is set in the high performance liquid chromatography-tandem mass spectrometer and connected to a mass spectrometer detector via a switching valve. An online solid phase extraction method is used to enrich the components to be tested by using the solid phase extraction column through reverse loading and forward elution via a switching valve.

[0011] Step S4, setting the elution program of the mobile phase:

[0012] The mobile phases include a first mobile phase of 2 mmol / L ammonium acetate aqueous solution, a second mobile phase of acetonitrile, a third mobile phase of acetonitrile, and a fourth mobile phase of 0.1% formic acid aqueous solution. The first mobile phase, the second mobile phase, the third mobile phase, and the fourth mobile phase are pumped into the high performance liquid chromatography tandem mass spectrometer through a first pump, a second pump, a third pump, and a fourth pump, respectively. During the test phase from 0 min to 2.5 min, the switching valve is located at a position for loading the solid phase extraction column, i.e., a loading position; during the test phase from 2.51 min to 14 min, the switching valve is located at a position for allowing the water quality sample to be tested in the solid phase extraction column to enter the mass spectrometer detector, i.e., a detection position; at 14.1 min, the switching valve is located at the loading position until one injection cycle is completed.

[0013] At the start of the test, the volume percentages of the first mobile phase pumped by the first pump and the second mobile phase pumped by the second pump were 85% and 15%, respectively. The first mobile phase and the second mobile phase were pumped into the high performance liquid chromatography tandem mass spectrometer and maintained for 2.5 minutes with a full flow rate of 0.3 mL / min. During the time period of 2.51 minutes to 12.51 minutes, the volume percentages of the first mobile phase pumped by the first pump and the second mobile phase pumped by the second pump were gradually and uniformly adjusted to 2% and 98%, respectively. The first mobile phase and the second mobile phase were pumped into the solid phase extraction column and then into the mass spectrometry detector and maintained until the 16th minute. At 16.1 minutes, the volume percentages of the first mobile phase pumped by the first pump and the second mobile phase pumped by the second pump were restored to 85% and 15%, respectively, and maintained until the end of one injection cycle.

[0014] At the start of the test, the volume percentages of the third mobile phase pumped in by the third pump and the fourth mobile phase pumped in by the fourth pump are 0% and 100%, and the third mobile phase and the fourth mobile phase are pumped into the solid phase extraction column and then flow into the waste liquid. The water quality sample to be tested enters the solid phase extraction column and is loaded for 2.5 minutes. The flow rate in this stage is 0.6 mL / min. At 2.51 minutes, the volume percentages of the third mobile phase pumped in by the third pump and the fourth mobile phase pumped in by the fourth pump are adjusted to 100% and 0%, and the flow rate is 1.5 mL / min. The mobile phase and the fourth mobile phase were pumped into the waste liquid and maintained until the 10th minute; at 10.1 minutes, the third pump and the fourth pump were stopped, and the flow rates of the third pump and the fourth pump were 0 mL / min; at 14.1 minutes, the third pump and the fourth pump were turned on, and the flow rates of the third pump and the fourth pump were 0.1 mL / min, and the volume percentages of the third mobile phase pumped in by the third pump and the fourth mobile phase pumped in by the fourth pump were 0% and 100%, respectively. The flow rate was uniformly increased to 0.3 mL / min within 2 minutes and maintained until the end of one injection cycle;

[0015] Step S5: Perform the test according to the procedure set in step S4, quantitatively determine and calculate the concentrations of the 23 perfluorinated compounds in the water sample to be tested using the high performance liquid chromatography, and then obtain the detection limits of the 23 perfluorinated compounds in the water sample to be tested.

[0016] Furthermore, in step S1, if the water sample contains suspended matter or insoluble matter, sampling is performed after centrifugation.

[0017] Furthermore, in step S2, an isotope internal standard mixed solution is added to the water sample containing methanol so that the internal standard concentration is 10 ng / L.

[0018] Furthermore, in step S2, an isotope internal standard mixed solution is added to the water sample containing methanol and then filtered through a filter membrane to prepare a water sample to be tested.

[0019] Furthermore, the 23 perfluorinated compounds in the water quality are perfluorobutyric acid, perfluoropentanoic acid, perfluorohexanoic acid, perfluorobutane sulfonic acid, perfluoroheptanoic acid, perfluoropentane sulfonic acid, 4,8-dioxa-3-H-perfluorononanoic acid, perfluorooctanoic acid, perfluorohexane sulfonic acid, perfluorononanoic acid, perfluoroheptane sulfonic acid, perfluorodecanoic acid, perfluorooctane sulfonic acid, perfluoroundecanoic acid, perfluoro 2-((6-chlorohexyl)oxy)ethane sulfonic acid, perfluorononane sulfonic acid, perfluorododecanoic acid, perfluorodecane sulfonic acid, perfluorotridecanoic acid, 11-chloroticosanoic acid, perfluorotetradecanoic acid, perfluorohexadecanoic acid, and perfluorooctadecanoic acid.

[0020] Furthermore, the solid phase extraction column is a hydrophilic-lipophilic equilibrium solid phase extraction column.

[0021] Furthermore, step S5 further includes calculating the detection limit according to the following formula:

[0022] MDL = t ( n-1,0.99) × S ;

[0023] Where: MDL is the detection limit, n is the number of parallel determinations; t For a one-sided test with n-1 degrees of freedom and 99% confidence level t distribution value; S for n Standard deviation of the replicates.

[0024] Furthermore, the switching valve is a ten-way valve.

[0025] Furthermore, the high performance liquid chromatography tandem mass spectrometer is a liquid chromatography-triple quadrupole mass spectrometer.

[0026] The beneficial effects of the present invention are:

[0027] The method for obtaining the detection limits of 23 perfluorinated compounds in water quality of the present invention utilizes a liquid chromatography-triple quadrupole mass spectrometer and adopts an online solid phase extraction method to obtain the detection limits of the 23 perfluorinated compounds in water quality, thereby reducing the detection limits of perfluorinated compounds in water quality and being more suitable for actual water sample detection.

[0028] In the method for obtaining the detection limits of 23 perfluorinated compounds in water quality of the present invention, an online solid-phase extraction method is adopted, which improves the detection efficiency and the degree of automation, enhances the sample processing efficiency, optimizes the use of solvents, and reduces the consumption of organic solvents. The solid-phase extraction column used in this method can be reused, which reduces the generation of laboratory solid waste. Long-term use reduces experimental costs and is more environmentally friendly. It reduces human errors, reduces experimental deviations, improves experimental reproducibility, reduces sample loss and contamination risks, does not require separate sample processing, saves time and costs, improves sensitivity and detection limits, and the online solid-phase extraction method can more efficiently enrich the target, reduce matrix interference, and enhance method flexibility. It reduces personnel costs and avoids the exposure risk of unknown samples to testers due to their potential toxicity during operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the sample loading position of the ten-way valve;

[0030] Figure 2 This is a schematic diagram of the detection position of the ten-way valve;

[0031] Figure 3 This is the total ion current diagram of the component to be measured in Example 1.

[0032] In the figure: 1 is a ten-way valve, 2 is the first hole position, 3 is the second hole position, 4 is the third hole position, 5 is the fourth hole position, 6 is the fifth hole position, 7 is the sixth hole position, 8 is the seventh hole position, 9 is the eighth hole position, 10 is the ninth hole position, 11 is the tenth hole position, 12 is the first pump, 13 is the second pump, 14 is the third pump, 15 is the fourth pump, 16 is a solid phase extraction column, 17 is a mass spectrometer detector, 18 is a capture column, and 19 is an analytical column. DETAILED DESCRIPTION

[0033] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation methods in conjunction with the accompanying drawings.

[0034] The present invention provides a method for obtaining the detection limits of 23 perfluorinated compounds in water, comprising the following steps:

[0035] Step S1: Take a sufficient amount of water sample and place it in a fluorine-free volumetric flask. Add methanol so that the methanol content is 10% by volume of the water sample to obtain a water sample containing methanol. If the water sample contains suspended matter or insoluble matter, centrifuge and then take a sample.

[0036] Step S2: adding an isotope internal standard mixed solution to the water sample containing methanol to make the internal standard concentration be 10 ng / L, and filtering through a filter membrane to prepare a water sample to be tested.

[0037] Step S3: Detect the water quality sample using a high-performance liquid chromatography-tandem mass spectrometer. A solid-phase extraction column 16 is provided in the high-performance liquid chromatography-tandem mass spectrometer and connected to a mass spectrometer detector 17 via a switching valve. Online solid-phase extraction is employed, with the solid-phase extraction column 16 being used to enrich the components to be detected by reverse loading and forward elution via a switching valve. Specifically, the high-performance liquid chromatography-tandem mass spectrometer is a liquid chromatography-triple quadrupole mass spectrometer.

[0038] Step S4, setting the elution program of the mobile phase:

[0039] The mobile phases included a first mobile phase of 2 mmol / L ammonium acetate aqueous solution, a second mobile phase of acetonitrile, a third mobile phase of acetonitrile, and a fourth mobile phase of 0.1% formic acid aqueous solution. The first, second, third, and fourth mobile phases were pumped into the high-performance liquid chromatography-tandem mass spectrometer via a first pump 12, a second pump 13, a third pump 14, and a fourth pump 15, respectively. During the test phase, from 0 to 2.5 minutes, the switching valve was positioned to load the solid phase extraction column 16, i.e., the loading position. From 2.51 to 14 minutes, the switching valve was positioned to load the water quality sample in the solid phase extraction column 16 into the mass spectrometer detector 17, i.e., the detection position. At 14.1 minutes, the switching valve was positioned to the loading position until the end of the injection cycle.

[0040] Specifically, a capture column 18 for removing system impurities can be provided between the third pump 14, the fourth pump 15 and the switching valve, and an analytical column 19 for separating the components to be tested can be provided between the mass spectrometer detector 17 and the switching valve. Specifically, the packing of the capture column 18 can be C18, and the packing of the analytical column 19 can be C18. The solid phase extraction column packing is a hydrophilic lipophilic balance solid phase extraction column HLB. The switching valve can be a ten-way valve 1. When the ten-way valve 1 is in the sample loading position, as shown in FIG. Figure 1As shown, the first mobile phase and the second mobile phase are respectively connected to the sixth hole 7 of the ten-way valve 1 through the first pump 12, the second pump 13 and the pipeline, the sixth hole 7 is connected to the seventh hole 8, the seventh hole 8 is connected to the tenth hole 11, the tenth hole 11 is connected to the first hole 2, and the first hole 2 is connected to the injection end of the mass spectrometer detector 17 through the analytical column 19. The third mobile phase and the fourth mobile phase are respectively connected to the third hole 4 of the ten-way valve 1 through the capture column 18, the third pump 14, the fourth pump 15 and the pipeline, the third hole 4 is connected to the second hole 3, the second hole 3 is connected to the fifth hole 6 through the solid phase extraction column 16, the fifth hole 6 is connected to the fourth hole 5, the fourth hole 5 is connected to the ninth hole 10, and the ninth hole 10 is connected to the eighth hole 9. During the test phase from 0 to 2.5 minutes, ten-way valve 1 is in the sample loading position. The first and second mobile phases are sequentially pumped into the sixth hole 7, seventh hole 8, tenth hole 11, and first hole 2 of ten-way valve 1 by first pump 12 and second pump 13, respectively. They then pass through analytical column 19 and enter mass spectrometer detector 17. The third and fourth mobile phases are sequentially pumped into the third hole 4, second hole 3, solid-phase extraction column 16, fifth hole 6, fourth hole 5, ninth hole 10, and eighth hole 9 of ten-way valve 1 by capture column 18, third pump 14, and fourth pump 15, respectively, before flowing out as waste. During this process, the third and fourth mobile phases drive the water quality sample to be tested onto solid-phase extraction column 16.

[0041] When the ten-way valve 1 is in the detection position, such as Figure 2As shown, the first mobile phase and the second mobile phase are respectively connected to the sixth hole 7 of the ten-way valve 1 through the first pump 12, the second pump 13 and the pipeline, the sixth hole 7 is connected to the fifth hole 6, the fifth hole 6 is connected to the second hole 3 through the solid phase extraction column 16, the second hole 3 is connected to the first hole 2, and the first hole 2 is connected to the liquid inlet end of the mass spectrometer detector 17 through the analytical column 19. The third mobile phase and the fourth mobile phase are respectively connected to the third hole 4 of the ten-way valve 1 through the capture column 18, the third pump 14, the fourth pump 15 and the pipeline, the third hole 4 is connected to the fourth hole 5, the fourth hole 5 is connected to the ninth hole 10, the ninth hole 10 is connected to the tenth hole 11, the tenth hole 11 is connected to the seventh hole 8, and the seventh hole 8 is connected to the eighth hole 9. From 2.51 to 14 minutes, ten-way valve 1 is in the detection position. The first and second mobile phases are sequentially pumped into the sixth hole 7, fifth hole 6, solid phase extraction column 16, second hole 3, and first hole 2 of ten-way valve 1 via first pump 12 and second pump 13, respectively. They then pass through analytical column 19 and enter mass spectrometer detector 17. During this process, the first and second mobile phases elute the water quality sample on solid phase extraction column 16 and enter mass spectrometer detector 17. The third and fourth mobile phases are sequentially pumped into the third hole 4, fourth hole 5, ninth hole 10, tenth hole 11, seventh hole 8, and eighth hole 9 of ten-way valve 1 via capture column 18, third pump 14, and fourth pump 15, respectively, before flowing out as waste liquid. At 14.1 minutes, ten-way valve 1 switches back to the loading position until one injection cycle is complete.

[0042] The specific test procedure is set as follows:

[0043] At the start of the test, the volume percentages of the first mobile phase pumped by the first pump 12 and the second mobile phase pumped by the second pump 13 were 85% and 15%, respectively. The first mobile phase and the second mobile phase were pumped into the high performance liquid chromatography tandem mass spectrometer and maintained for 2.5 minutes with a full flow rate of 0.3 mL / min. In the time period of 2.51 minutes to 12.51 minutes, the volume percentages of the first mobile phase pumped by the first pump 12 and the second mobile phase pumped by the second pump 13 were gradually and uniformly adjusted to 2% and 98%, respectively. After being pumped into the solid phase extraction column, the first mobile phase and the second mobile phase entered the mass spectrometry detector 17 and were maintained until the 16th minute. At 16.1 minutes, the volume percentages of the first mobile phase pumped by the first pump 12 and the second mobile phase pumped by the second pump 13 were restored to 85% and 15%, respectively, and maintained until the end of one injection cycle.

[0044] At the start of the test, the volume percentages of the third mobile phase pumped in by the third pump 14 and the fourth mobile phase pumped in by the fourth pump 15 are 0% and 100%, and the third mobile phase and the fourth mobile phase are pumped into the solid phase extraction column and then flow into the waste liquid. The water quality sample to be tested enters the solid phase extraction column and is loaded for 2.5 minutes. The flow rate in this stage is 0.6 mL / min. At 2.51 minutes, the volume percentages of the third mobile phase pumped in by the third pump 14 and the fourth mobile phase pumped in by the fourth pump 15 are adjusted to 100% and 0%, and the flow rate is 1.5 mL / min. The third mobile phase and the fourth mobile phase are pumped into the solid phase extraction column and the waste liquid flows into the waste liquid. The water quality sample to be tested enters the solid phase extraction column and is loaded for 2.5 minutes. The flow rate in this stage is 0.6 mL / min. The mobile phase is pumped into the waste liquid and maintained until the 10th minute; when 10.1 minutes have passed, the third pump 14 and the fourth pump 15 are stopped, and the flow rates of the third pump 14 and the fourth pump 15 are 0 mL / min; when 14.1 minutes have passed, the third pump 14 and the fourth pump 15 are started, and the flow rates of the third pump 14 and the fourth pump 15 are 0.1 mL / min, and the volume percentages of the third mobile phase pumped in by the third pump 14 and the fourth mobile phase pumped in by the fourth pump 15 are 0% and 100%, respectively. The flow rate is uniformly increased to 0.3 mL / min within 2 minutes and maintained until the end of one injection cycle.

[0045] Step S5: Perform the test according to the procedure set in step S4, quantitatively determine and calculate the concentrations of the 23 perfluorinated compounds in the water sample to be tested using the high performance liquid chromatography, and then obtain the detection limits of the 23 perfluorinated compounds in the water sample to be tested.

[0046] Specifically, according to Appendix A of the "Technical Guidelines for the Development of Environmental Monitoring Analytical Method Standards" HJ168-2020, the detection limits of 23 perfluorinated compounds were determined, and the target objects were detected in repeated n blank tests. In this specific implementation, n=11. According to steps S1-S5, each measurement result was converted into the concentration or content in the sample, and the standard deviation of n parallel measurements was calculated. The detection limit was calculated according to the following formula.

[0047] MDL = t ( n-1,0.99) × S ;

[0048] Where: MDL is the detection limit, n is the number of parallel determinations; t For a one-sided test with n-1 degrees of freedom and 99% confidence level t distribution value; S for n Standard deviation of the replicates.

[0049] Among them, when the degrees of freedom is n-1 and the confidence level is 99%, the t value can be referred to Table A.1 of HJ168-2020. When n=11, t=2.764.

[0050] Specifically, the 23 perfluorinated compounds in water quality are perfluorobutyric acid (PFBA), perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluorobutane sulfonic acid (PFBS), perfluoroheptanoic acid (PFHpA), perfluoropentane sulfonic acid (PFPeS), 4,8-dioxa-3-H-perfluorononanoic acid (ADONA), perfluorooctanoic acid (PFOA), perfluorohexane sulfonic acid (PFHxS), perfluorononanoic acid (PFNA), perfluoroheptane sulfonic acid (PFHpS), perfluorodecanoic acid (PFDA), perfluorooctane sulfonic acid (PFOS), perfluoroundecanoic acid (PFUnDA), perfluoro 2-((6-chlorohexyl)oxy)ethanesulfonic acid (6:2) ClPFAES), perfluorononanesulfonic acid (PFNS), perfluorododecanoic acid (PFDoDA), perfluorodecanesulfonic acid (PFDS), perfluorotridecanoic acid (PFTrDA), 11-chloroticofluoro-3-oxaundecane-1-sulfonic acid (8:2ClPFAES), perfluorotetradecanoic acid (PFTeDA), perfluorohexadecanoic acid (PFHxDS), and perfluorooctadecanoic acid (PFODA).

[0051] Example 1

[0052] Take 4mL of water sample and place it in a 5mL fluorine-free volumetric flask, add 0.5mL of methanol, add the water sample to the scale and mix to obtain a water sample containing methanol. Add 50μL of isotope internal standard mixed solution to the water sample containing methanol, mix well, filter through a 0.22 μm filter membrane, and place it in a 4.5mL injection bottle. The injection volume to be tested is 1mL, which meets the detection sensitivity and detection limit requirements. Automatic sampler requirements: the injection plate is equipped with a 4.5mL sample bottle, and the injection volume of the injection needle and quantitative loop meets 100-5000μL. The test was carried out according to the test method steps of the present invention, and the test results are as follows Figure 3 As shown, the figure contains 23 perfluorinated compounds and their associated internal standard components.

[0053] According to Appendix A of the "Technical Guidelines for the Development of Environmental Monitoring Analytical Method Standards" HJ168-2020, the detection limits of 23 perfluorinated compounds were determined, and the target object was detected in the blank test by repeated determination n times. In this embodiment, n=11. The determination was performed according to the steps of the present invention, and each measurement result was converted into the concentration or content in the sample. The standard deviation of the n parallel determinations was calculated, and the detection limit was calculated according to the detection limit calculation formula, as shown in Table 1-5.

[0054] Table 1 shows the detection limit data of PFBA, PFPeA, PFHxA, PFBS and PFHpA:

[0055] .

[0056] Table 2 shows the detection limit data of PFPeS, ADONA, PFOA, PFHxS and PFNA:

[0057] .

[0058] Table 3 shows the detection limit data of PFHpS, PFDA, PFOS, PFUnDA, and 6:2ClPFAES:

[0059] .

[0060] Table 4 shows the detection limit data of PFNS, PFDoDA, PFDS, PFTrDA, and 8:2ClPFAES:

[0061] .

[0062] Table 5 shows the detection limit data of PFTeDA, PFHxDA and PFODA:

[0063] .

[0064] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limiting the present invention. Any changes, modifications, substitutions and variations of the above embodiments by a person skilled in the art fall within the scope of the present invention.

Claims

1. A method for obtaining the detection limits of 23 perfluorinated compounds in water, characterized in that: The steps include: Step S1, taking a sufficient amount of water sample and placing it in a fluorine-free volumetric flask, adding methanol so that the volume content of methanol is 10% of the water sample, to obtain a water sample containing methanol; Step S2, adding an isotope internal standard mixed solution to a water sample containing methanol to prepare a water sample to be tested; Step S3: Detecting the water quality sample using a high performance liquid chromatography-tandem mass spectrometer. A solid phase extraction column is set in the high performance liquid chromatography-tandem mass spectrometer and connected to a mass spectrometer detector via a switching valve. An online solid phase extraction method is used to enrich the components to be tested by using the solid phase extraction column through reverse loading and forward elution via a switching valve. Step S4, setting the elution program of the mobile phase: The mobile phases included a first mobile phase of 2 mmol / L ammonium acetate aqueous solution, a second mobile phase of acetonitrile, a third mobile phase of acetonitrile, and a fourth mobile phase of 0.1% formic acid aqueous solution. The first mobile phase, the second mobile phase, the third mobile phase, and the fourth mobile phase were pumped into the high performance liquid chromatography tandem mass spectrometer via a first pump, a second pump, a third pump, and a fourth pump, respectively. During the test phase from 0 min to 2.5 min, the switching valve was located at the solid phase extraction column loading position, i.e., the loading position. From 2.51min to 14min, the switching valve is in the position where the water quality sample to be tested in the solid phase extraction column enters the mass spectrometer detector, that is, the detection position; at 14.1min, the switching valve is in the loading position until one injection cycle is completed; At the start of the test, the volume percentages of the first mobile phase pumped by the first pump and the second mobile phase pumped by the second pump were 85% and 15%, respectively. The first mobile phase and the second mobile phase were pumped into the high performance liquid chromatography tandem mass spectrometer and maintained for 2.5 minutes with a full flow rate of 0.3 mL / min. During the time period of 2.51 minutes to 12.51 minutes, the volume percentages of the first mobile phase pumped by the first pump and the second mobile phase pumped by the second pump were gradually and uniformly adjusted to 2% and 98%, respectively. The first mobile phase and the second mobile phase were pumped into the solid phase extraction column and then into the mass spectrometry detector and maintained until the 16th minute. At 16.1 minutes, the volume percentages of the first mobile phase pumped by the first pump and the second mobile phase pumped by the second pump were restored to 85% and 15%, respectively, and maintained until the end of one injection cycle. At the start of the test, the volume percentages of the third mobile phase pumped in by the third pump and the fourth mobile phase pumped in by the fourth pump are 0% and 100%, and the third mobile phase and the fourth mobile phase are pumped into the solid phase extraction column and then flow into the waste liquid. The water quality sample to be tested enters the solid phase extraction column and is loaded for 2.5 minutes. The flow rate in this stage is 0.6 mL / min. At 2.51 minutes, the volume percentages of the third mobile phase pumped in by the third pump and the fourth mobile phase pumped in by the fourth pump are adjusted to 100% and 0%, and the flow rate is 1.5 mL / min. The mobile phase and the fourth mobile phase were pumped into the waste liquid and maintained until the 10th minute; at 10.1 minutes, the third pump and the fourth pump were stopped, and the flow rates of the third pump and the fourth pump were 0 mL / min; at 14.1 minutes, the third pump and the fourth pump were turned on, and the flow rates of the third pump and the fourth pump were 0.1 mL / min, and the volume percentages of the third mobile phase pumped in by the third pump and the fourth mobile phase pumped in by the fourth pump were 0% and 100%, respectively. The flow rate was uniformly increased to 0.3 mL / min within 2 minutes and maintained until the end of one injection cycle; Step S5: Perform the test according to the procedure set in step S4, quantitatively determine and calculate the concentrations of the 23 perfluorinated compounds in the water sample to be tested using the high performance liquid chromatography, and then obtain the detection limits of the 23 perfluorinated compounds in the water sample to be tested.

2. The method for obtaining the detection limits of 23 perfluorinated compounds in water according to claim 1, characterized in that: In step S1, if the water sample contains suspended matter or insoluble matter, sampling is performed after centrifugation.

3. The method for obtaining the detection limits of 23 perfluorinated compounds in water according to claim 1, characterized in that: In step S2, an isotope internal standard mixed solution is added to the water sample containing methanol so that the internal standard concentration is 10 ng / L.

4. A method for obtaining the detection limits of 23 perfluorinated compounds in water according to claim 1 or 3, characterized in that: In step S2, an isotope internal standard mixed solution is added to a water sample containing methanol and the mixture is filtered through a filter membrane to prepare a water sample to be tested.

5. The method for obtaining the detection limits of 23 perfluorinated compounds in water according to claim 1, characterized in that: The 23 perfluorinated compounds in the water quality are perfluorobutyric acid, perfluoropentanoic acid, perfluorohexanoic acid, perfluorobutane sulfonic acid, perfluoroheptanoic acid, perfluoropentane sulfonic acid, 4,8-dioxa-3-H-perfluorononanoic acid, perfluorooctanoic acid, perfluorohexane sulfonic acid, perfluorononanoic acid, perfluoroheptane sulfonic acid, perfluorodecanoic acid, perfluorooctane sulfonic acid, perfluoroundecanoic acid, perfluoro 2-((6-chlorohexyl)oxy)ethane sulfonic acid, perfluorononane sulfonic acid, perfluorododecanoic acid, perfluorodecane sulfonic acid, perfluorotridecanoic acid, 11-chloroticosanoic acid, perfluoroundecanoic acid, and perfluorooctadecanoic acid.

6. The method for obtaining the detection limits of 23 perfluorinated compounds in water according to claim 1, characterized in that: The solid phase extraction column is a hydrophilic-lipophilic equilibrium solid phase extraction column.

7. The method for obtaining the detection limits of 23 perfluorinated compounds in water according to claim 1, characterized in that: Step S5 also includes calculating the detection limit according to the following formula: MDL = t ( n-1,0.99) × S ； Where: MDL is the detection limit, n is the number of parallel determinations; t For a one-sided test with n-1 degrees of freedom and 99% confidence level t distribution value; S for n Standard deviation of the replicates.

8. The method for obtaining the detection limits of 23 perfluorinated compounds in water according to claim 1, characterized in that: The switching valve is a ten-way valve.

9. The method for obtaining the detection limits of 23 perfluorinated compounds in water according to claim 1, characterized in that: The high performance liquid chromatography tandem mass spectrometer is a liquid chromatography-triple quadrupole mass spectrometer.

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