Method for obtaining detection limits of 23 perfluorinated compounds in water

Abstract

A method for obtaining the detection limit of 23 perfluorinated compounds in water relates to the technical field of pollutant detection, and comprises the following steps: step S1, taking a sufficient amount of a water sample and placing the water sample in a fluoride-free volumetric flask to obtain a water sample containing methanol; s2, preparing a water quality sample to be detected; s3, detecting the water quality sample to be detected by adopting a high performance liquid chromatography tandem mass spectrometer; s4, setting an elution program of a mobile phase; and S5, testing, and calculating the concentrations of 23 perfluorinated compounds in the water quality sample to be detected. According to the method, the detection limits of 23 perfluorinated compounds in water are obtained by utilizing a liquid chromatography-triple quadrupole mass spectrometer and adopting an online solid-phase extraction method, so that the detection efficiency is improved, the personal error is reduced, and the consumption of an organic solvent and the use of a traditional solid-phase extraction column are reduced.

Description

Technical Field

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

[0002] Perfluorinated compounds are synthetic chemical substances. The carbon-fluorine bonds of these compounds are very stable and difficult to form through natural processes, and there is no natural source in nature. Perfluorinated compounds mainly come from human activities, such as industrial emissions from factories that manufacture and use perfluorinated compounds; products containing perfluorinated compounds, such as non-stick pans and waterproof materials, which enter water bodies after use and disposal; fire-fighting foams used in fire training and accidents contain perfluorinated compounds and are easily infiltrated into groundwater; wastewater treatment plants cannot completely remove perfluorinated compounds, resulting in their entry into natural water bodies, etc. Due to different pollution situations, the distribution of perfluorinated compounds in water quality shows an extremely uneven pattern. The content of perfluorinated compounds in untreated water samples in relevant production and use activity areas is relatively high, but the proportion of areas related to perfluorinated compound activities in the total national area is less than 0.1%. Therefore, the content of perfluorinated compounds in water quality in most areas is at a low concentration level. However, due to the harmful effects of perfluorinated compounds such as persistent pollution, bioaccumulation, immune system damage, developmental effects, and cancer risk, the detection of low concentration levels of perfluorinated compounds has practical significance.

[0003] In the prior art, such as the local standard of Jiangsu Province, DB 32 / T 4004-2021, "Determination of 17 perfluorinated compounds in water quality - High performance liquid chromatography - Tandem mass spectrometry", the enrichment function is achieved by manual solid-phase extraction method. The liquid phase is used to separate the components to be measured, and a triple quadrupole mass spectrometer is used to determine 17 perfluorinated compounds in surface water. Specifically, an internal standard working solution is added to 0.2 - 0.5 L of the sample. On the solid-phase extraction device, 4 mL of 0.1% ammonia / methanol solution, 4 mL of methanol, and 4 mL of pure water are added in sequence, and the column head is kept wet during the addition of the solvent. The upper end of the solid-phase extraction column is connected to a universal adapter, and the sample is absorbed under negative pressure through a pipeline, with the flow rate controlled at about 1 drop / second. The solid-phase extraction column is rinsed with 4 mL of 25 mmol / L ammonium acetate aqueous solution to fix 17 perfluorinated compounds on the solid-phase extraction column, and the previous sample and rinse solution are discarded. After the solid-phase extraction column is dried at low temperature with a vacuum freeze dryer, it is rinsed with 4 mL of methanol and 4 mL of ammonia / methanol solution in sequence, and the rinse solution is collected with a 15 mL polypropylene centrifuge tube. The collected rinse solution is concentrated with nitrogen on a nitrogen blowing instrument, fixed to 1 mL with methanol, filtered through a 0.22 μm filter membrane, and then placed in a 1.5 mL brown injection vial and stored at 4°C for measurement. The gradient elution process of the liquid chromatography mobile phase is as follows: the mobile phase is 2 mmol / L ammonium acetate aqueous solution and acetonitrile. At the starting time of elution, the volume percentage of ammonium acetate aqueous solution is 80% and the volume percentage of acetonitrile is 20%. Within 14 minutes, the volume percentage of ammonium acetate aqueous solution decreases uniformly from 80% to 10%, and the volume percentage of acetonitrile increases uniformly from 20% to 90%, and it is maintained for 2 minutes. At 16.01 minutes, the volume percentage of ammonium acetate aqueous solution increases from 10% to 80%, and the volume percentage of acetonitrile decreases from 90% to 20%, and it is maintained for 4 minutes. Among them, 0 - 14 minutes is the gradient elution process, 14 - 16 minutes is the isocratic elution process, and 16 - 20 minutes is the chromatographic column re-equilibration process.

[0004] During the above experimental operation process, the manual solid-phase extraction process is complex, 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 testing personnel. The manual solid-phase extraction process requires the preparation of a variety of solvents, which are repeatedly added quantitatively to the solid-phase extraction column, all of which require manual operation by experimental personnel, and the consumption of organic solvents is large. The sample enrichment amount is large between 0.2 - 0.5 L, the flow rate is controlled at about 1 drop / second during column passing, and it takes more than 1 hour for all samples to pass through the solid-phase extraction column, which takes a long time, the operation efficiency is low, and the methods such as freeze drying, nitrogen blowing instrument and vacuum pumping are cumbersome and time-consuming, and the required instrument equipment occupies a large area and has energy consumption. Summary of the Invention

[0005] In view of the above-mentioned disadvantages and deficiencies of the prior art, the present invention provides a method for obtaining the detection limits of 23 perfluorinated compounds in water quality. By using a liquid chromatography-triple quadrupole mass spectrometer and the on-line solid phase extraction method, the detection limits of 23 perfluorinated compounds in water quality are obtained, the detection efficiency is improved, and the human error, the consumption of organic solvents and the use of traditional solid phase extraction columns are reduced.

[0006] In order to achieve the above object, the main technical solutions adopted by the present invention include: A method for obtaining the detection limits of 23 perfluorinated compounds in water quality, comprising the following steps: Step S1: Take a sufficient amount of water quality sample and place it in a fluorine-free volumetric flask, add methanol so that the volume content of methanol is 10% of the water quality sample, and obtain a water quality sample containing methanol; Step S2: Add an isotope internal standard mixed use solution to the water quality sample containing methanol to prepare a water quality sample to be tested; Step S3: Use a high performance liquid chromatography-tandem mass spectrometer to detect the water quality sample to be tested. In the high performance liquid chromatography-tandem mass spectrometer, a solid phase extraction column is connected to the mass detector through a switching valve, and the on-line solid phase extraction method is adopted. The solid phase extraction column is used to load the sample in the reverse direction and elute the enriched components to be detected in the forward direction through the switching valve; Step S4: Set the elution program of the mobile phase: The mobile phase includes 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 respectively pumped into the high performance liquid chromatography-tandem mass spectrometer by a first pump, a second pump, a third pump, and a fourth pump; during the test stage from 0 min to 2.5 min, the switching valve is located at the position for loading the solid phase extraction column, that is, the loading position; from 2.51 min to 14 min, the switching valve is located at the position for the water quality sample in the solid phase extraction column to enter the mass detector, that is, the detection position; at 14.1 min, the switching valve is located at the loading position until the end of an injection cycle; At the start stage 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 are 85% and 15%. The first mobile phase and the second mobile phase are pumped into the high performance liquid chromatography-tandem mass spectrometer and maintained for 2.5 min. The whole process flow rate is 0.3 mL / min. During the time period from 2.51 min to 12.51 min, the volume percentages of the first mobile phase pumped by the first pump and the second mobile phase pumped by the second pump are gradually and uniformly adjusted to 2% and 98%. The first mobile phase and the second mobile phase are pumped into the solid phase extraction column and then enter the mass detector, and are maintained until the 16th minute. When it is 16.1 min, the volume percentages of the first mobile phase pumped by the first pump and the second mobile phase pumped by the second pump are restored to 85% and 15%, and are maintained until the end of an injection cycle; At the start of the test, the volume percentages of the third mobile phase pumped by the third pump and the fourth mobile phase pumped by the fourth pump are 0% and 100% respectively. 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 for sampling and is held for 2.5 min. The flow rate at this stage is 0.6 mL / min. When it reaches 2.51 min, the volume percentages of the third mobile phase pumped by the third pump and the fourth mobile phase pumped by the fourth pump are adjusted to 100% and 0% respectively, and the flow rate is 1.5 mL / min. The third mobile phase and the fourth mobile phase are pumped into the waste liquid and held until the 10th minute; when it reaches 10.1 min, the third pump and the fourth pump are stopped, and the flow rates of the third pump and the fourth pump are 0 mL / min; when it reaches 14.1 min, the third pump and the fourth pump are started. At this time, the flow rates of the third pump and the fourth pump are 0.1 mL / min. The volume percentages of the third mobile phase pumped by the third pump and the fourth mobile phase pumped by the fourth pump are 0% and 100% respectively. The flow rate is uniformly increased to 0.3 mL / min within 2 min and held until the end of an injection cycle; Step S5: Conduct the test according to the program set in step S4, quantitatively determine and calculate the concentrations of 23 perfluorinated compounds in the water quality sample to be tested by a high-performance liquid chromatograph, and then obtain the detection limits of the 23 perfluorinated compounds in the water quality sample to be tested.

[0007] Further, in step S1, if the water quality sample contains suspended matter or insoluble matter, sample after centrifugation.

[0008] Further, in step S2, add an isotope internal standard mixed working solution to the water quality sample containing methanol so that the concentration of the internal standard is 10 ng / L.

[0009] Further, in step S2, after adding the isotope internal standard mixed working solution to the water quality sample containing methanol, filter it through a filter membrane to prepare the water quality sample to be tested.

[0010] Further, 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-dioxo-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-chloro-20-fluoro-3-oxoundecane-1-sulfonic acid, perfluorotetradecanoic acid, perfluorohexadecanoic acid, perfluorooctadecanoic acid.

[0011] Further, the solid-phase extraction column is a hydrophilic-lipophilic balanced solid-phase extraction column.

[0012] Further, step S5 also includes calculating the detection limit according to the following formula: MDL = t ( n-1,0.99) × S ; In the formula: MDL is the detection limit, n is the number of parallel determinations; t is the one-sided t distribution value when the degree of freedom is n - 1 and the confidence level is 99%; S is n the standard deviation of m parallel determinations.

[0013] Furthermore, the switching valve is a ten-way valve.

[0014] Furthermore, the high performance liquid chromatography tandem mass spectrometer is a liquid chromatography-triple quadrupole mass spectrometer.

[0015] The beneficial effects of the present invention are: The method for obtaining the detection limits of 23 perfluorinated compounds in water quality of the present invention uses a liquid chromatography-triple quadrupole mass spectrometer and an on-line solid phase extraction method to obtain the detection limits of 23 perfluorinated compounds in water quality, reduces the detection limits of perfluorinated compounds in water quality, and is more suitable for the detection of actual water samples.

[0016] In the method for obtaining the detection limits of 23 perfluorinated compounds in water quality of the present invention, the on-line solid phase extraction method is adopted, which improves the detection efficiency and automation degree, enhances the sample treatment efficiency, optimizes the solvent use, reduces the consumption of organic solvents. The solid phase extraction column used in this method can be reused, reducing the generation of laboratory solid waste, and being more environmentally friendly in the long term by reducing the experimental cost. It reduces human error, reduces experimental deviation, improves experimental reproducibility, reduces the risk of sample loss and pollution, saves time and cost without the need for separate sample treatment, improves sensitivity and detection limit, can enrich the target compounds more efficiently by the on-line solid phase extraction method, reduces matrix interference, and enhances the flexibility of the method. It reduces the personnel cost, and at the same time avoids the potential toxicity of unknown samples during the operation process from posing an exposure risk to the inspection personnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic diagram of the sample loading position on the ten-way valve; Figure 2 is a schematic diagram of the detection position on the ten-way valve; Figure 3 is the total ion chromatogram of the analyte in Example 1.

[0018] 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 spectrometry detector, 18 is a trapping column, and 19 is an analytical column. Detailed implementation mode

[0019] For better explanation of the present invention for easy understanding, the present invention will be described in detail below in conjunction with the drawings through specific implementation modes.

[0020] The present invention provides a method for obtaining the detection limits of 23 perfluorinated compounds in water quality, including the following steps: Step S1: Take a sufficient amount of water quality sample and place it in a fluorine-free volumetric flask, add methanol so that the volume content of methanol is 10% of the water quality sample to obtain a water quality sample containing methanol. If the water quality sample contains suspended matter or insoluble matter, sample after centrifugation.

[0021] Step S2: Add an isotope internal standard mixed solution to the water quality sample containing methanol so that the concentration of the internal standard is 10 ng / L, and prepare a water quality sample to be measured after filtration through a filter membrane.

[0022] Step S3: Use a high performance liquid chromatography tandem mass spectrometer to detect the water quality sample to be measured. Set the solid phase extraction column 16 in the high performance liquid chromatography tandem mass spectrometer to be connected to the mass spectrometry detector 17 through a switching valve, and use the on-line solid phase extraction method. The solid phase extraction column 16 is used to enrich the components to be measured by reverse loading and forward elution through the switching valve. Specifically, the high performance liquid chromatography tandem mass spectrometer is a liquid chromatography-triple quadrupole mass spectrometer.

[0023] Step S4: Set the elution program of the mobile phase: The mobile phase includes 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 respectively pumped into the high performance liquid chromatography tandem mass spectrometer through the first pump 12, the second pump 13, the third pump 14, and the fourth pump 15. At 0 min to 2.5 min in the test stage, the switching valve is located at the position for loading the solid phase extraction column 16, that is, the loading position; at 2.51 min to 14 min, the switching valve is located at the position for the water quality sample to be measured in the solid phase extraction column 16 to enter the mass spectrometry detector 17, that is, the detection position; at 14.1 min, the switching valve is located at the loading position until the end of one injection cycle.

[0024] Specifically, a trapping 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 components to be measured can be provided between the mass spectrometry detector 17 and the switching valve. Specifically, the packing of the trapping column 18 can be C18, and the packing of the analytical column 19 can be C18. The packing of the solid-phase extraction column is a hydrophilic-lipophilic balanced solid-phase extraction column HLB. The switching valve can be a ten-port valve 1. When the ten-port valve 1 is in the sample loading position, as Figure 1 shown, the first mobile phase and the second mobile phase are respectively connected to the sixth hole position 7 of the ten-port valve 1 through the first pump 12, the second pump 13 and pipelines. The sixth hole position 7 is connected to the seventh hole position 8, the seventh hole position 8 is connected to the tenth hole position 11, the tenth hole position 11 is connected to the first hole position 2, and the first hole position 2 is connected to the injection end of the mass spectrometry detector 17 through the analytical column 19. The third mobile phase and the fourth mobile phase are respectively connected to the third hole position 4 of the ten-port valve 1 through the trapping column 18, the third pump 14, the fourth pump 15 and pipelines. The third hole position 4 is connected to the second hole position 3, the second hole position 3 is connected to the fifth hole position 6 through the solid-phase extraction column 16, the fifth hole position 6 is connected to the fourth hole position 5, the fourth hole position 5 is connected to the ninth hole position 10, and the ninth hole position 10 is connected to the eighth hole position 9. During the test stage from 0 min to 2.5 min, the ten-port valve 1 is in the sample loading position. The first mobile phase and the second mobile phase are respectively pumped into the sixth hole position 7, the seventh hole position 8, the tenth hole position 11, and the first hole position 2 of the ten-port valve 1 through the first pump 12 and the second pump 13, and then enter the mass spectrometry detector 17 through the analytical column 19. The third mobile phase and the fourth mobile phase are respectively pumped into the third hole position 4, the second hole position 3, the solid-phase extraction column 16, the fifth hole position 6, the fourth hole position 5, the ninth hole position 10, and the eighth hole position 9 of the ten-port valve 1 through the trapping column 18, the third pump 14, and the fourth pump 15, and then flow out as waste liquid. During this process, the third mobile phase and the fourth mobile phase drive the water quality sample to be measured to be loaded on the solid-phase extraction column 16.

[0025] When the ten-port valve 1 is in the detection position, as Figure 2As shown in the figure, the first mobile phase and the second mobile phase are respectively connected to the sixth hole position 7 of the ten-port valve 1 through the first pump 12, the second pump 13 and pipelines. The sixth hole position 7 is connected to the fifth hole position 6. The fifth hole position 6 is connected to the second hole position 3 through the solid-phase extraction column 16. The second hole position 3 is connected to the first hole position 2. The first hole position 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 position 4 of the ten-port valve 1 through the trapping column 18, the third pump 14, the fourth pump 15 and pipelines. The third hole position 4 is connected to the fourth hole position 5. The fourth hole position 5 is connected to the ninth hole position 10. The ninth hole position 10 is connected to the tenth hole position 11. The tenth hole position 11 is connected to the seventh hole position 8. The seventh hole position 8 is connected to the eighth hole position 9. At 2.51 min to 14 min, the ten-port valve 1 is in the detection position. The first mobile phase and the second mobile phase are respectively pumped into the sixth hole position 7, the fifth hole position 6, the solid-phase extraction column 16, the second hole position 3, the first hole position 2 of the ten-port valve 1 through the first pump 12 and the second pump 13, and then enter the mass spectrometer detector 17 through the analytical column 19. During this process, the first mobile phase and the second mobile phase elute the water quality sample to be measured on the solid-phase extraction column 16 and enter the mass spectrometer detector 17. The third mobile phase and the fourth mobile phase are respectively pumped into the third hole position 4, the fourth hole position 5, the ninth hole position 10, the tenth hole position 11, the seventh hole position 8, the eighth hole position 9 of the ten-port valve 1 through the trapping column 18, the third pump 14, the fourth pump 15, and then flow out as waste liquid. At 14.1 min, the ten-port valve 1 is switched to the sample loading position again until the end of one injection cycle.

[0026] The specific test procedure is set as follows: At the initial stage 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 are 85% and 15%. The first mobile phase and the second mobile phase are pumped into the high-performance liquid chromatography-tandem mass spectrometer and maintained for 2.5 min. The overall flow rate is 0.3 mL / min. During the time period of 2.51 min to 12.51 min, 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 are gradually and uniformly adjusted to 2% and 98%. The first mobile phase and the second mobile phase are pumped into the solid-phase extraction column and then enter the mass spectrometer detector 17, and are maintained until the 16th min. When it is 16.1 min, 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 are restored to 85% and 15%, and are maintained until the end of one injection cycle.

[0027] During the initial stage of the test, the volume percentages of the third mobile phase pumped by the third pump 14 and the fourth mobile phase pumped by the fourth pump 15 are 0% and 100% respectively. 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 sample to be tested enters the solid phase extraction column for sampling and is held for 2.5 minutes. The flow rate at this stage is 0.6 mL / min. When it reaches 2.51 minutes, the volume percentages of the third mobile phase pumped by the third pump 14 and the fourth mobile phase pumped by the fourth pump 15 are adjusted to 100% and 0% respectively, and the flow rate is 1.5 mL / min. The third mobile phase and the fourth mobile phase are pumped into the waste liquid and held until the 10th minute; when it reaches 10.1 minutes, 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 it reaches 14.1 minutes, the third pump 14 and the fourth pump 15 are started. At this time, the flow rates of the third pump 14 and the fourth pump 15 are 0.1 mL / min. The volume percentages of the third mobile phase pumped by the third pump 14 and the fourth mobile phase pumped 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 held until the end of an injection cycle.

[0028] Step S5: Conduct the test according to the program set in step S4, quantitatively determine and calculate the concentrations of 23 perfluorinated compounds in the water sample to be tested by a high performance liquid chromatograph, and then obtain the detection limits of the 23 perfluorinated compounds in the water sample to be tested.

[0029] Specifically, according to Appendix A of Technical Guidelines for Formulating Environmental Monitoring Analytical Method Standards HJ168—2020, the detection limits of 23 perfluorinated compounds are determined. The target substances are detected in the blank test repeated n times. In this specific embodiment, n = 11. According to steps S1 - S5, the measurement results are converted into the concentrations or contents in the sample, and the standard deviation of n parallel measurements is calculated. The detection limit is calculated according to the following formula.

[0030] MDL = t ( n-1,0.99) × S ; In the formula: MDL is the detection limit, n is the number of parallel measurements; t is the one-sided t distribution value when the degree of freedom is n - 1 and the confidence level is 99%; S is n the standard deviation of n parallel measurements.

[0031] Among them, the t value when the degree of freedom is n - 1 and the confidence level is 99% can be obtained by referring to Table A.1 of HJ168—2020. When n = 11, t = 2.764.

[0032] Specifically, the 23 perfluorinated compounds in the 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-dioxo-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)ethane sulfonic acid (6:2 ClPFAES), perfluorononane sulfonic acid (PFNS), perfluorododecanoic acid (PFDoDA), perfluorodecane sulfonic acid (PFDS), perfluorotridecanoic acid (PFTrDA), 11-chloroeicosadecafluoro-3-oxoundecane-1-sulfonic acid (8:2ClPFAES), perfluorotetradecanoic acid (PFTeDA), perfluorohexadecanoic acid (PFHxDS), perfluorooctadecanoic acid (PFODA).

[0033] Example 1 Take 4 mL of the water quality sample and place it in a 5 mL fluorine-free volumetric flask. Add 0.5 mL of methanol, and make up the volume to the scale with the water quality sample and mix well to obtain a water quality sample containing methanol. Add 50 μL of the isotope internal standard mixed use solution to the water quality sample containing methanol, mix well, filter through a 0.22 μm filter membrane, and place it in a 4.5 mL injection vial. The measured injection volume is 1 mL, meeting the requirements of detection sensitivity and detection limit. Requirements for the auto-sampler: The injection tray is equipped with 4.5 mL sample vials, and the injection volume of the injection needle and quantitative loop meets 100 - 5000 μL. Test according to the test method steps of the present invention, and the test results are as Figure 3 shown, and the figure contains 23 perfluorinated compounds and related internal standard components.

[0034] According to the "Technical Guidelines for the Formulation of Environmental Monitoring Analytical Method Standards" HJ168—2020 Appendix A, determine the detection limits of 23 perfluorinated compounds. Repeatedly measure the target substances detected in n blank tests. In this example, n = 11. Perform the determination according to the steps of the present invention, convert each measurement result into the concentration or content in the sample, calculate the standard deviation of n parallel measurements, and calculate the detection limit according to the detection limit calculation formula, as shown in Table 1-5.

[0035] Table 1 shows the detection limit determination data of PFBA, PFPeA, PFHxA, PFBS, and PFHpA: .

[0036] Table 2 shows the detection limit determination data of PFPeS, ADONA, PFOA, PFHxS, and PFNA: .

[0037] Table 3 shows the detection limit determination data for PFHpS, PFDA, PFOS, PFUnDA, and 6:2ClPFAES: 。

[0038] Table 4 shows the detection limit determination data for PFNS, PFDoDA, PFDS, PFTrDA, and 8:2ClPFAES: 。

[0039] Table 5 shows the detection limit determination data for PFTeDA, PFHxDA, and PFODA: 。

[0040] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limitations of the present invention. Modifications, alterations, substitutions, and variations made by those of ordinary skill in the art to the above embodiments all fall within the scope of the present invention.

Claims

1. A method for obtaining the detection limits of 23 perfluorinated compounds in water quality, characterized in that, It includes the following steps: Step S1: Take a sufficient amount of water quality sample and place it in a fluorine-free volumetric flask, add methanol so that the volume content of methanol is 10% of the water quality sample, and obtain a water quality sample containing methanol; Step S2: Add an isotope internal standard mixed solution to the water quality sample containing methanol to prepare a water quality sample to be tested; Step S3: Use a high performance liquid chromatography-tandem mass spectrometer to detect the water quality sample to be tested. Set a solid phase extraction column in the high performance liquid chromatography-tandem mass spectrometer to be connected to the mass detector through a switching valve. Adopt the on-line solid phase extraction method, and use the solid phase extraction column to load the sample in the reverse direction and elute in the forward direction to enrich the component to be tested; Step S4: Set the elution program of the mobile phase: The mobile phase includes 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 respectively pumped into the high performance liquid chromatography-tandem mass spectrometer by a first pump, a second pump, a third pump, and a fourth pump; during the test stage from 0 min to 2.5 min, the switching valve is located at the position for loading the sample on the solid phase extraction column, that is, the loading position; From 2.51 min to 14 min, the switching valve is located at the position for the water quality sample in the solid phase extraction column to enter the mass detector, that is, the detection position; at 14.1 min, the switching valve is located at the loading position until the end of an injection cycle; At the start stage 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 are 85% and 15%. The first mobile phase and the second mobile phase are pumped into the high performance liquid chromatography-tandem mass spectrometer and kept for 2.5 min. The whole process flow rate is 0.3 mL / min. During the time period from 2.51 min to 12.51 min, the volume percentages of the first mobile phase pumped by the first pump and the second mobile phase pumped by the second pump are gradually and uniformly adjusted to 2% and 98%. The first mobile phase and the second mobile phase are pumped into the solid phase extraction column and then enter the mass detector, and are maintained until the 16th minute. When it is 16.1 min, the volume percentages of the first mobile phase pumped by the first pump and the second mobile phase pumped by the second pump are restored to 85% and 15%, and are kept until the end of an injection cycle; At the initial stage of the test, the volume percentages of the third mobile phase pumped by the third pump and the fourth mobile phase pumped by the fourth pump are 0% and 100% respectively. 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 for sampling and is held for 2.5 min. The flow rate at this stage is 0.6 mL / min. When it reaches 2.51 min, the volume percentages of the third mobile phase pumped by the third pump and the fourth mobile phase pumped by the fourth pump are adjusted to 100% and 0% respectively, and the flow rate is 1.5 mL / min. The third mobile phase and the fourth mobile phase are pumped into the waste liquid and held until the 10th min; when it reaches 10.1 min, the third pump and the fourth pump are stopped, and the flow rates of the third pump and the fourth pump are 0 mL / min; when it reaches 14.1 min, the third pump and the fourth pump are started. At this time, the flow rates of the third pump and the fourth pump are 0.1 mL / min. The volume percentages of the third mobile phase pumped by the third pump and the fourth mobile phase pumped by the fourth pump are 0% and 100% respectively. The flow rate is uniformly increased to 0.3 mL / min within 2 min and held until the end of an injection cycle; Step S5: Conduct the test according to the program set in step S4, quantitatively determine and calculate the concentrations of 23 perfluorinated compounds in the water quality sample to be tested by a high-performance liquid chromatography instrument, and then obtain the detection limits of 23 perfluorinated compounds in the water quality sample to be tested.

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

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

4. A method for obtaining the detection limits of 23 perfluorinated compounds in water quality according to claim 1 or 3, characterized in that: In step S2, after adding the isotope internal standard mixed working solution to the water quality sample containing methanol, filter it through a filter membrane to prepare the water quality sample to be tested.

5. A method for obtaining the detection limits of 23 perfluorinated compounds in water quality according to claim 1, characterized in that: The 23 perfluorinated compounds in water quality are perfluorobutyric acid, perfluoropentanoic acid, perfluorohexanoic acid, perfluorobutane sulfonic acid, perfluoroheptanoic acid, perfluoropentane sulfonic acid, 4,8-dioxo-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-chloro-20-fluoro-3-oxoundecane-1-sulfonic acid, perfluorotetradecanoic acid, perfluorohexadecanoic acid, perfluorooctadecanoic acid.

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

7. A method for obtaining the detection limits of 23 perfluorinated compounds in water quality 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 is the one-sided t distribution value when the degree of freedom is n - 1 and the confidence level is 99%; S is n the standard deviation of n parallel determinations.

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

9. A method for obtaining the detection limits of 23 perfluorinated compounds in water quality 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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