Method for dual-mode extraction of perfluoroalkanoic acid in water sample

Abstract

The invention provides a method for dual-mode extraction of perfluoroalkanoic acid in a water sample, and belongs to the technical field of perfluoroalkanoic acid pollutant residue detection. The method provided by the invention comprises the following steps: carrying out first vortex mixing on a water sample solution containing perfluoroalkyl acid substances and layered double hydroxides, and centrifuging to obtain a lower-layer precipitate; mixing the lower precipitate with an acidic solution, adding a switchable polarity eutectic solvent solution, and carrying out second vortex mixing to obtain a homogeneous system; mixing the homogeneous system with an alkaline solution, and carrying out induced phase separation to obtain a lower-layer switchable polarity eutectic solvent phase; and diluting the lower-layer switchable polarity eutectic solvent phase, and carrying out quantitative analysis through a high performance liquid chromatography-tandem mass spectrometer. According to the method provided by the invention, the efficient enrichment and detection of trace perfluoroalkanoic acid in the environmental water sample are realized by utilizing the synergistic effect of the layered double hydroxide and the switchable polarity deep-eutectic solvent.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of perfluoroalkanoic acid residue detection, and particularly relates to a method for extracting perfluoroalkanoic acid in water samples by using layered double hydroxide and switchable polarity deep eutectic solvent in a double mode. BACKGROUND

[0002] Perfluoroalkyl acids (PFAAs) as a new type of persistent organic pollutants (POPs) have unique hydrophobic and oleophobic properties and chemical stability, and are widely used in industrial production and consumer products (such as non-stick coatings, fire-fighting foams, etc.). However, the persistence, long-distance migration and bioaccumulation of perfluoroalkanoic acid in the environment are also a cause for concern. Studies have shown that perfluoroalkanoic acid can be accumulated through the food chain, interfere with the endocrine system of the human body, and induce health risks such as hepatotoxicity and immunosuppression. The extremely low toxicological threshold (ng / L level) poses a severe challenge to the sensitivity and selectivity of the analysis method. Therefore, it is of great importance to develop efficient and accurate detection technology for trace PFAAs in environmental water for environmental pollution prevention and control and health risk assessment.

[0003] In the existing analysis technology, the pretreatment technology for harmful residues mainly includes solid phase extraction (SPE), dispersive solid phase extraction (d-SPE) method, etc. For example, the Chinese invention patent with the authorization announcement number CN116399965B provides a method for extracting and analyzing triazole fungicides by using switchable polarity deep eutectic solvent (SHDES). The method realizes the reversible switching of the polarity of the solvent by adjusting the pH, reduces the use of organic solvents to a certain extent, and improves the enrichment efficiency of the target substance. However, the method still has some limitations: first, it mainly relies on the polarity switching mechanism of a single solvent system, and has limited anti-interference ability for coexisting anions (such as sulfate, dodecyl sulfate, etc.) in complex matrix; second, the patent method is aimed at triazole fungicides, and its mechanism is mainly based on hydrogen bonding and hydrophobic interaction, so the selective enrichment ability is insufficient for perfluoroalkanoic acid substances with strong fluorophobicity; third, the method does not introduce functional material assisted extraction, which may result in that the sensitivity and selectivity cannot meet the detection requirements of ultra-trace PFAAs in actual water sample analysis. SUMMARY

[0004] Therefore, the present application provides a method for extracting perfluoroalkanoic acid in water samples in a double mode. The method provided by the present application realizes efficient enrichment and detection of trace perfluoroalkanoic acid (PFAAs) in environmental water samples by using the synergistic effect of layered double hydroxide and switchable polarity deep eutectic solvent.

[0005] In order to solve the above technical problems, the present application provides the following technical solutions:

[0006] The application provides a method for extracting perfluoroalkanoic acids from water samples in a dual mode, comprising the following steps:

[0007] The water sample solution containing perfluoroalkanoic substances is mixed with layered double hydroxides for the first vortex mixing, centrifuged to obtain a lower precipitate;

[0008] After the lower precipitate is mixed with an acidic solution, a switchable polarity deep eutectic solvent solution is added, and the second vortex mixing is performed to obtain a homogeneous system;

[0009] The homogeneous system is mixed with an alkaline solution to induce phase separation, and a lower switchable polarity deep eutectic solvent phase is obtained;

[0010] After diluting the lower switchable polarity deep eutectic solvent phase, quantitative analysis is performed by high performance liquid chromatography-tandem mass spectrometry.

[0011] Preferably, the mass-volume ratio of the layered double hydroxide to the water sample solution containing perfluoroalkanoic substances is (1-10) mg:10 mL.

[0012] Preferably, the layered double hydroxide is zinc-aluminum layered double hydroxide.

[0013] Preferably, the volume ratio of the switchable polarity deep eutectic solvent solution to the water sample solution containing perfluoroalkanoic substances is (0.015-0.04):1.

[0014] Preferably, the switchable polarity deep eutectic solvent is prepared by mixing hexafluoroisopropanol and dipropylamine; the molar ratio of the hexafluoroisopropanol to the dipropylamine is (2-1):(1-5).

[0015] Preferably, the perfluoroalkanoic substances in the water sample solution containing perfluoroalkanoic substances include one or more of perfluorobutyric acid, perfluoropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid and perfluorobutane sulfonic acid.

[0016] Preferably, the acidic solution includes one of sulfuric acid, hydrochloric acid and nitric acid; the concentration of the acidic solution is 4 mol / L-8 mol / L.

[0017] Preferably, the alkaline solution includes one of sodium carbonate, sodium hydroxide and potassium hydroxide; the concentration of the alkaline solution is 2 mol / L-6 mol / L.

[0018] Preferably, the time of the first vortex mixing is 5 min-25 min, and the time of the second vortex mixing is 10 s-20 s.

[0019] Preferably, the analysis conditions of the high performance liquid chromatography-tandem mass spectrometry include:

[0020] Chromatographic column: Waters C18 column, 100mm × 3.5mm, 3.5μm;

[0021] Mobile phase: A is water, B is acetonitrile, wherein the water contains 0.1% formic acid, and the acetonitrile contains 0.1% formic acid;

[0022] Gradient elution: 0 min - 4 min, 10% - 85% B; 4 min - 7 min, 85% - 10% B;

[0023] Flow rate: 0.45 mL / min; injection volume: 10 μL; ion source: electrospray ion source, negative ion mode; nebulizer gas pressure: 55 psi, curtain gas pressure: 35 psi; monitoring mode: multiple reaction monitoring.

[0024] This invention provides a dual-mode extraction method for perfluoroalkyl acids (PFAAs) from water samples, comprising the following steps: mixing a water sample solution containing PFAAs with a layered double hydroxide in a first vortex, centrifuging to obtain a lower precipitate; mixing the lower precipitate with an acidic solution, adding a switchable polar eutectic solvent solution, and performing a second vortex to obtain a homogeneous system; mixing the homogeneous system with an alkaline solution and inducing phase separation to obtain a lower switchable polar eutectic solvent phase; diluting the lower switchable polar eutectic solvent phase and performing quantitative analysis using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS / MS). The method provided by this invention selects a layered double hydroxide for dispersive micro-solid-phase extraction and utilizes a switchable polar eutectic solvent for homogeneous liquid-liquid microextraction. The synergistic effect of these two methods maximizes the efficient enrichment of PFAAs and minimizes the influence of coexisting anions (such as sulfate and dodecyl sulfate) in complex matrices.

[0025] Furthermore, the method provided by this invention exhibits significant comprehensive advantages in the enrichment and detection of perfluoroalkyl compounds in environmental water and food samples.

[0026] This method achieves preliminary and efficient capture of perfluoroalkyl compounds through the unique layered structure of layered double hydroxides and electrostatic and hydrogen bonding interactions. Its acidic solubility eliminates the elution step in traditional solid-phase extraction, greatly simplifying the operation process.

[0027] This invention employs a switchable polarity eutectic solvent composed of hexafluoroisopropanol and dipropylamine as the extraction medium. Its intelligent polarity switching characteristics enable precise control of homogeneous extraction and phase separation, virtually eliminating the need for volatile organic solvents, embodying a green and environmentally friendly analytical approach. Furthermore, hexafluoroisopropanol achieves efficient capture of perfluoroalkyl acids through specific fluorine-fluorine interactions. This invention utilizes pH as an external stimulus, precisely controlling the polarity of the difluoroisopropanol (DES) through a reversible chemical reaction (protonation / deprotonation of amines), achieving intelligent switching from "homogeneous extraction" to "two-phase separation." The process is simple, efficient, and fully controllable; the entire switching process is based on a well-defined chemical equilibrium, which can be precisely controlled by adjusting the amount of sodium carbonate added. The method exhibits good reproducibility and is simple to operate.

[0028] This invention innovatively combines the initial enrichment of layered double hydroxides with secondary extraction using a switchable polar eutectic solvent. This method exhibits excellent resistance to matrix interference. Through pH optimization and sodium carbonate-induced phase separation, it effectively separates the target analyte from anionic interfering components such as dodecyl sulfate and sulfate in complex matrices, significantly outperforming traditional single-mode extraction methods.

[0029] The dual-mode extraction method for perfluoroalkyl acids in water samples provided by this invention is simple and efficient, requiring only vortexing, centrifugation, and pH adjustment. It not only provides an efficient and green technical means to solve the problem of detecting trace perfluoroalkyl compounds in the environment, but also has significant scientific value and application potential. This method can be further extended to the analysis and detection of other perfluorinated compounds, anionic pesticides, and other pollutants, showing a wide range of applicability prospects. Attached Figure Description

[0030] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0031] Figure 1 This is a schematic diagram of a dual-mode synergistic extraction method based on zinc-aluminum layered double hydroxides and a switchable polar eutectic solvent.

[0032] Figure 2 In the image, 2a and 2b are scanning electron microscope images of zinc-aluminum layered double hydroxides; 2c is an infrared spectrum; 2d is an X-ray diffraction pattern; 2e is a nitrogen adsorption desorption curve; and 2f is an X-ray electron spectrum.

[0033] Figure 3 The figure shows the optimization of extraction efficiency for perfluoroalkyl acids, where 3a is the amount of adsorbent, 3b is the adsorption time, 3c is the volume of sulfuric acid added, 3d is the volume of switchable polarity eutectic solvent added, 3e is the volume of sodium carbonate added, and 3f is the effect of pH value. Detailed Implementation

[0034] This invention provides a method for dual-mode extraction of perfluoroalkyl acids from water samples, comprising the following steps:

[0035] A water sample solution containing perfluoroalkyl acids was mixed with a layered double hydroxide in a first vortex, and then centrifuged to obtain the lower precipitate.

[0036] After mixing the lower precipitate with an acidic solution, a switchable polarity eutectic solvent solution is added, and a second vortex mixing is performed to obtain a homogeneous system.

[0037] The homogeneous system is mixed with an alkaline solution to induce phase separation, resulting in a lower layer of switchable polar eutectic solvent phase.

[0038] After diluting the lower layer of switchable polar eutectic solvent phase, quantitative analysis was performed using high performance liquid chromatography-tandem mass spectrometry.

[0039] In this invention, an aqueous solution containing perfluoroalkyl acids is mixed with a layered double hydroxide in a first vortex, and then centrifuged to obtain a lower precipitate.

[0040] In this invention, the pH value of the aqueous solution containing perfluoroalkyl acids is preferably 2-10, more preferably 4; the perfluoroalkyl acids in the aqueous solution containing perfluoroalkyl acids include one or more of perfluorobutyric acid, perfluorovalerate, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid and perfluorobutyric acid.

[0041] In this invention, the preferred mass-to-volume ratio of the layered double hydroxide to the aqueous solution containing perfluoroalkyl acids is (1-10) mg:10 mL, more preferably (4-6) mg:10 mL, and most preferably 5 mg:10 mL.

[0042] In this invention, the layered double hydroxide is a zinc-aluminum layered double hydroxide. Preferably, the zinc-aluminum layered double hydroxide is prepared by a method comprising the following steps: dissolving 2.679 g of zinc nitrate hexahydrate and 1.12 g of aluminum nitrate nonahydrate in 100 mL of deionized water to obtain a salt solution; dissolving 0.48 g of sodium hydroxide and 0.32 g of sodium carbonate in 100 mL of deionized water to obtain an alkaline solution; slowly adding the alkaline solution to the salt solution in a 60°C water bath, maintaining pH = 11, stirring overnight, washing until neutral, and then drying in a 60°C oven.

[0043] In this invention, due to the advantages of layered double hydroxides (LDHs) having a good layered structure and simple and convenient synthesis, LDH is used as a solid adsorbent for dispersed micro solid-phase extraction by utilizing its excellent electrostatic and hydrogen bonding interactions. It can selectively capture perfluoroalkyl acids in the sample. At the same time, the solubility of LDH under acidic conditions (pH<4) eliminates the desorption process in traditional material extraction, greatly simplifying the extraction steps, saving pretreatment time, and making it green and environmentally friendly as no organic reagents are used in the entire extraction process.

[0044] In this invention, the preferred time for the first vortex mixing is 5-25 minutes, more preferably 10-20 minutes, and most preferably 15 minutes. This invention does not impose any particular limitation on the method of the first vortex mixing; any vortex mixing method well-known to those skilled in the art can be used. This invention achieves sufficient adsorption and enrichment of perfluoroalkyl acids in an aqueous solution containing perfluoroalkyl acids through vortex mixing.

[0045] In a preferred embodiment of the present invention, the amount of the layered double hydroxide is 5 mg, the first vortex mixing time is 15 min, and the optimal pH of the aqueous solution is 4. As a solid adsorbent, the layered double hydroxide gradually increases in adsorption efficiency with increasing adsorption time, reaching a peak at 15 min, and then reaching an equilibrium state. Initially, there are a large number of unoccupied active sites on the surface of the adsorbent, which allows the target substance to be rapidly adsorbed. As the adsorption time extends, the target analyte is completely adsorbed by the adsorbent through electrostatic interactions and van der Waals forces, reaching adsorption equilibrium.

[0046] In this invention, the centrifugal force is preferably 3600g-4000g, more preferably 3622g; the centrifugation time is preferably 1min-5min, more preferably 1min. This invention preferably discards the supernatant obtained after centrifugation. This invention does not have a specific limitation on the centrifugation method; any centrifugation method well known to those skilled in the art can be used.

[0047] After obtaining the lower precipitate, the present invention mixes the lower precipitate with an acidic solution, adds a switchable polarity eutectic solvent solution, and performs a second vortex mixing to obtain a homogeneous system.

[0048] In this invention, the acidic solution preferably includes one of sulfuric acid, hydrochloric acid, and nitric acid, more preferably sulfuric acid; the concentration of the acidic solution is preferably 4 mol / L-8 mol / L, more preferably 6 mol / L; the volume ratio of the acidic solution to the aqueous solution containing perfluoroalkanoic acid is preferably (0.01-0.03):1, more preferably 0.02:1.

[0049] This invention does not impose any particular limitation on the mixing method; any mixing method well known to those skilled in the art can be used. This invention involves mixing the lower precipitate with an acidic solution to dissolve the layered double hydroxides in the lower precipitate.

[0050] In this invention, the switchable polar eutectic solvent is preferably prepared by mixing hexafluoroisopropanol and dipropylamine, specifically preferably by the following steps: mixing hexafluoroisopropanol (HFIP) and dipropylamine (DPA), and stirring the resulting mixture at 60°C until it is homogeneous and transparent; the molar ratio of hexafluoroisopropanol to dipropylamine is preferably (2-1):(1-5); the volume ratio of the switchable polar eutectic solvent solution to the aqueous solution containing perfluoroalkyl substances is preferably (0.015-0.04):1, more preferably 0.02:1.

[0051] In this invention, the second vortex mixing time is preferably 10s-20s, more preferably 15s. This invention does not impose any particular limitation on the method of the second vortex mixing; any vortex mixing method well-known to those skilled in the art can be used. After the second vortex mixing, the solution system is in a homogeneous state. At this point, a polar eutectic solvent can be switched to fully contact the target analyte, achieving thorough homogeneous liquid-liquid microextraction through specific FF interactions and hydrogen bonding.

[0052] After obtaining the homogeneous system, the present invention mixes the homogeneous system with an alkaline solution to induce phase separation, thereby obtaining a lower layer of switchable polar eutectic solvent phase.

[0053] In this invention, the alkaline solution preferably comprises one of sodium carbonate, sodium hydroxide, and potassium hydroxide, more preferably sodium carbonate; the concentration of the alkaline solution is preferably 2 mol / L-6 mol / L, more preferably 4 mol / L; the volume ratio of the alkaline solution to the aqueous sample solution containing perfluoroalkyl acids is preferably (0.02-0.04):1, more preferably 0.03:1. This invention involves adding alkaline sodium carbonate solution to a homogeneous system to induce phase separation, achieving separation of the aqueous phase from the switchable polarity eutectic solvent phase through pH switching; the addition of alkaline sodium carbonate solution changes the eutectic solvent system from hydrophilic to hydrophobic, allowing for rapid separation of the solvent and water, and enriching the perfluoroalkyl acids in the aqueous sample solution within the eutectic solvent system.

[0054] After obtaining the lower layer switchable polar eutectic solvent phase, the present invention dilutes the lower layer switchable polar eutectic solvent phase and performs quantitative analysis by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS / MS).

[0055] In this invention, the diluent is preferably acetonitrile; the dilution ratio of the switchable polar eutectic solvent phase to acetonitrile is preferably 2-1:1-2, more preferably 1:1. In the embodiments of this invention, 50 μL of the switchable polar eutectic solvent phase is preferably diluted with acetonitrile (50-200 μL), and the best chromatographic effect is obtained when 100 μL of acetonitrile is used. This invention does not impose any special limitations on the dilution method; any dilution and mixing method well known to those skilled in the art can be used.

[0056] In this invention, the preferred analytical conditions for the high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS / MS) include:

[0057] Chromatographic column: Waters C18 column, 100mm × 3.5mm, 3.5μm;

[0058] Mobile phase: A is water, B is acetonitrile, wherein the water contains 0.1% formic acid, and the acetonitrile contains 0.1% formic acid;

[0059] Gradient elution: 0 min - 4 min, 10% - 85% B; 4 min - 7 min, 85% - 10% B;

[0060] Flow rate: 0.45 mL / min; injection volume: 10 μL; ion source: electrospray ionization (ESI), negative ion mode; nebulizer gas pressure: 55 psi, curtain gas pressure: 35 psi; monitoring mode: multiple reaction monitoring (MRM).

[0061] The present invention preferably involves centrifuging the mixed solution during quantitative analysis, with the larger eutectic solvent system located in the lower layer of the centrifuge tube, thereby facilitating the separation of the lower layer solution of perfluoroalkyl acid from the centrifuge tube and improving detection efficiency and accuracy.

[0062] This invention provides a dual-mode extraction method for perfluoroalkyl acids (PFAAs) from water samples based on the synergistic effect of layered double hydroxides (LDHs) and switchable polar eutectic solvents (SHDES), for the efficient enrichment and detection of trace PFAAs in environmental water samples. The method utilizes the excellent electrostatic and hydrogen bonding interactions of LDHs to selectively adsorb PFAAs. Subsequently, an acidic solution is added to dissolve the LDHs and trigger a polarity reversal in the switchable polar eutectic solvent, forming a homogeneous system for efficient mass transfer. Finally, under alkaline conditions, the switchable polar eutectic solvent is induced to regain its hydrophobicity, and phase separation is used to enrich PFAAs.

[0063] This invention combines the electrostatic and hydrogen bonding interactions of layered double hydroxides with the fluorine-fluorine specific interactions of a switchable polar eutectic solvent to construct a synergistic dual-mode extraction platform. The optimal conditions determined through system optimization are: 5 mg of layered double hydroxide adsorbent, 15 min of adsorption time, sample pH = 4, 200 μL (6 mol / L) of sulfuric acid, 300 μL of the switchable polar eutectic solvent, and 300 μL (4 mol) of sodium carbonate. Under these conditions, the dual-mode extraction method for perfluoroalkyl acids (PFAAs) in water samples has been successfully applied to the analysis of actual samples such as drinking water and milk, demonstrating high sensitivity, high selectivity, strong anti-interference ability, and good reproducibility. Furthermore, the entire process requires almost no organic solvents, conforming to the principles of green analytical chemistry, and providing an efficient and reliable solution for the detection of trace PFAAs in the environment.

[0064] The following detailed description of the dual-mode extraction method for perfluoroalkyl acids from water samples provided by the present invention, with reference to specific embodiments, should not be construed as limiting the scope of protection of the present invention.

[0065] Example 1

[0066] 1. Synthesis of layered double hydroxides and switchable polarity eutectic solvents

[0067] 1.1 Synthesis of layered double hydroxides: Zinc nitrate hexahydrate (2.679 g) and aluminum nitrate nonahydrate (1.12 g) were dissolved in 100 mL of deionized water. Sodium hydroxide (0.48 g) and sodium carbonate (0.32 g) were also dissolved in 100 mL of deionized water. The alkaline solution was slowly added to the salt solution in a 60 °C water bath, maintaining pH = 11. The mixture was stirred overnight, washed until neutral, and then dried in a 60 °C oven.

[0068] The synthesized layered double hydroxide ZnAl-LDH material was characterized by a combination of characterization techniques, including scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption-desorption isotherms. Figure 2 a and Figure 2 bSEM images show that the layered double hydroxide material is formed by stacking multiple layers of sheet-like units to form irregular blocky or flower-like aggregates, exhibiting a typical three-dimensional nanostructure of LDH. Stepped edges and clear interlayer gaps are visible between the sheets, indicating that it has a high specific surface area and abundant active sites. The thickness of a single sheet is about tens of nanometers, the lateral size is up to the micrometer level, the size range is 1-5 μm, and the edges are sharp without structural damage, proving that the synthesis process did not destroy the crystal integrity.

[0069] according to Figure 2The characteristic crystal plane diffraction peaks (003), (006), and (009) appearing in the dX-ray diffraction pattern confirm its perfect layered crystal structure.

[0070] according to Figure 2 As can be seen from the infrared spectrum, the Fourier transform infrared spectrum is at 3460 cm⁻¹. -1 and 1620cm -1 The characteristic vibrational peak of hydroxyl groups was detected at 1370 cm⁻¹. -1 Vibrational signals of carbonate ions were observed at the surface, indicating that the material surface is rich in various oxygen-containing functional groups.

[0071] X-ray photoelectron spectroscopy (XPS) was used to analyze the synthesized zinc-aluminum layered double hydroxide material to comprehensively characterize its surface elemental composition, chemical state, and electronic structure. The results are as follows: Figure 2 As shown in f: the wide-scan XPS spectrum clearly shows the photoelectron peaks of core elements such as Zn, Al, C, and O, confirming that the material surface is mainly composed of these elements. No other impurity elements were detected, indicating that the synthesized product has high purity.

[0072] Nitrogen adsorption-desorption tests showed that the material exhibited a type IV isotherm and an H3 hysteresis loop, with a BET specific surface area of ​​43.808 m². 2 / g, BJH pore volume is 0.181cm³ 3 / g, with its predominantly mesoporous pore structure, provides an efficient transport channel for pollutant adsorption.

[0073] These characterization results fully demonstrate that layered double hydroxide materials possess excellent crystal structure, rich surface chemical properties, and well-developed pore structure, providing a solid guarantee for their application in the field of environmental pollutant adsorption.

[0074] 1.2 Synthesis of switchable polarity eutectic solvent: The switchable polarity eutectic solvent is prepared by mixing hexafluoroisopropanol (HFIP) and dipropylamine (DPA) in a molar ratio (2-1:1-5) and stirring at 60°C until a homogeneous and transparent eutectic solvent is formed.

[0075] 2. Preparation of standard aqueous sample solutions

[0076] Appropriate amounts of perfluorobutyric acid (PFBA), perfluorovalerate (PFPeA), perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), and perfluorobutyric acid (PFBS) were dissolved in acetonitrile to prepare eight standard stock solutions with a concentration of 100 μg / mL. These solutions were stored in the dark at 4°C before use. The stock solutions of the eight model compounds were diluted with acetonitrile to prepare a mixed working solution with a concentration of 1 μg / mL.

[0077] 3. A method for dual-mode extraction of perfluoroalkyl acids from water samples, comprising the following steps:

[0078] Add 10 mL of the sample aqueous solution to a 15 mL centrifuge tube, then add 5 mg of zinc-aluminum layered double hydroxide and mix thoroughly. Shake the mixture on a vortex mixer for 15 min, centrifuge at 3622 g for 1 min, and collect the lower precipitate. Slowly add 200 μL of 6.0 mol / L sulfuric acid solution to fully dissolve the zinc-aluminum layered double hydroxide material, then add 300 μL of a switchable polar eutectic solvent, and vortex for 15 s to form a homogeneous phase.

[0079] Then, 300 μL of 4 mol / L sodium carbonate is slowly injected, and a foaming reaction occurs immediately, generating a large number of bubbles, achieving phase separation and separating the lower layer containing the target analyte in a switchable polar eutectic solvent.

[0080] The bottom phase (50 μL) was collected using a microsyringe and transferred to a 1.5 mL centrifuge tube. It was then diluted with 100 μL of acetonitrile to improve chromatographic separation. Finally, 10 μL of the mixture was injected into an HPLC-MS / MS system for quantitative analysis.

[0081] Chromatographic column: Waters C18 column, 100mm × 3.5mm, 3.5μm;

[0082] Mobile phase: A is water, B is acetonitrile, wherein the water contains 0.1% formic acid, and the acetonitrile contains 0.1% formic acid;

[0083] Gradient elution: 0 min - 4 min, 10% - 85% B; 4 min - 7 min, 85% - 10% B;

[0084] Flow rate: 0.45 mL / min; injection volume: 10 μL; ion source: electrospray ionization (ESI), negative ion mode; nebulizer gas pressure: 55 psi, curtain gas pressure: 35 psi; monitoring mode: multiple reaction monitoring (MRM).

[0085] This embodiment 1 uses a dual-mode synergistic extraction process based on zinc-aluminum layered double hydroxides and a switchable polarity eutectic solvent, as follows: Figure 1 As shown.

[0086] 4. Selection of extraction method and process conditions

[0087] A: The effect of adsorbent dosage

[0088] (1) Experimental method: First, add 10 mL of water sample solution to a 15 mL centrifuge tube, then add zinc-aluminum layered double hydroxide and mix thoroughly. Shake the mixture on a vortex mixer to allow for full adsorption. Then, centrifuge at 3622 g for 1 min and collect the lower precipitate.

[0089] Slowly add 6.0 mol / L sulfuric acid solution to fully dissolve the zinc-aluminum layered double hydroxide material, then add a switchable polarity eutectic solvent, and vortex for 15 seconds to form a homogeneous phase.

[0090] Finally, 4 mol / L sodium carbonate is slowly injected, and an immediate foaming reaction occurs, generating a large number of bubbles to achieve phase separation. The lower layer containing the target analyte is separated by a switchable polar eutectic solvent. The bottom phase (50 μL) is collected using a microsyringe and transferred to a 1.5 mL centrifuge tube. Then, it is diluted with 100 μL of acetonitrile to improve the chromatographic separation effect.

[0091] Experimental results are as follows Figure 3 As shown in Figure a, when the adsorbent dosage is between 1 and 5 mg, the adsorption efficiency increases with increasing adsorbent dosage. This trend may be because a lower adsorbent dosage provides fewer active sites, resulting in fewer opportunities for perfluoroalkanoic acid pollutants to interact with the material. With increasing adsorbent dosage, more active sites become available, leading to increased adsorption efficiency. When the adsorbent dosage reaches 5 mg, the residual perfluoroalkanoic acid pollutants in the aqueous solution are completely adsorbed. Further increasing the adsorbent dosage does not result in a significant adsorption effect. Therefore, in subsequent experiments, 5 mg was selected as the optimal adsorbent dosage.

[0092] B: Effect of adsorption time

[0093] (1) Experimental method: The method is the same as that in Example 1, except that different adsorption times are set to compare the adsorption effects.

[0094] (2) Experimental results are as follows Figure 3 As shown in b, the adsorption efficiency was recorded at 5, 10, 15, 20, and 25 min. With increasing adsorption time, the adsorption efficiency gradually increased, reaching a peak at 15 min, and then reaching equilibrium. Initially, the adsorbent surface had a large number of unoccupied active sites, allowing the target substance to be rapidly adsorbed. As the adsorption time prolonged, the target analyte was completely adsorbed by the adsorbent, reaching adsorption equilibrium; therefore, 15 min was determined to be the optimal adsorption time.

[0095] C: Effect of sulfuric acid volume

[0096] (1) Experimental method: The method is the same as in Example 1, except that different volumes of sulfuric acid were used for extraction (100-300 μL).

[0097] (2) Experimental results: such as Figure 3 The results shown in Figure c indicate that preliminary experiments revealed that sulfuric acid concentrations below 6 mol / L were insufficient to completely convert the hydrophobic phase to the hydrophilic phase, and even failed to completely dissolve the zinc-aluminum layered double hydroxide material. Therefore, this invention selected a sulfuric acid concentration of 6 mol / L. Further investigation was conducted on the effect of sulfuric acid volume on the extraction efficiency, with the sulfuric acid volume ranging from 100 to 300 μL. Figure 3 As shown in Figure c, the peak area of ​​the analyte gradually increased with increasing sulfuric acid volume, reaching a peak at 200 μL, and then slightly decreased. This is likely because as the sulfuric acid volume gradually increases, the reaction with excess sodium carbonate produces more bubbles, significantly increasing the contact area and thus significantly improving the extraction effect. After the reaction is complete, further increasing the sulfuric acid volume may produce a dilution effect. Therefore, 200 μL of sulfuric acid was determined to be the optimal volume for subsequent studies.

[0098] D: The effect of the amount of switchable polarity eutectic solvent used

[0099] (1) Experimental method: The method is the same as in Example 1, except that different volumes of switchable polar eutectic solvents (150-400 μL) were used for extraction.

[0100] (2) Experimental results: such as Figure 3 As shown in Figure d, when the volume of the switchable polar eutectic solvent is less than 150 μL, it is difficult to collect the switchable polar eutectic solvent layer as the bottom phase. Therefore, in order to investigate the effect of the volume of the switchable polar eutectic solvent on the extraction efficiency, different volumes of switchable polar eutectic solvent were tested in the range of 150 to 400 μL. The optimal enrichment efficiency was achieved when the volume of the switchable polar eutectic solvent was 300 μL. As the volume of the switchable polar eutectic solvent increased, the peak area response of all analytes gradually decreased. This phenomenon can be explained by the dilution effect. Therefore, 300 μL of switchable polar eutectic solvent was used in subsequent experiments.

[0101] E: Effect of sodium carbonate dosage

[0102] (1) Experimental method: The method is the same as in Example 1, except that the amount of sodium carbonate added is different (200-400 μL).

[0103] (2) Experimental Results: The switchable polar eutectic solvent can be converted to a hydrophilic state by adding sulfuric acid, but it can be restored to its inherent hydrophobic form in alkaline solutions by pH adjustment. The bubble phenomenon generated by the acid-base reaction can increase the contact area between perfluoroalkane contaminants and the droplets of the switchable polar eutectic solvent, thereby significantly improving the extraction efficiency; therefore, different volumes of sodium carbonate solution (4 mol / L), ranging from 200 to 400 μL, were studied to induce the deprotonation of the switchable polar eutectic solvent; such as Figure 3 As shown in Figure e, with the increase of sodium carbonate volume, the volume of the bottom hydrophobic phase after switching also increases. Due to the dilution effect, the extraction performance of all analytes shows a decreasing trend. Based on the results, 300 μL of sodium carbonate (4 mol / L) was selected.

[0104] F: Effect of pH

[0105] (1) Experimental method: The method is the same as in Example 1, except that the pH value of the water sample solution is different.

[0106] (2) Experimental results: The results of the study on the pH value (2-10) of the working solution are as follows Figure 3 As shown in f, the enrichment efficiency of PFAAs is highest when the pH value is 4. This is because there is an electrostatic interaction between the anions in perfluoroalkyl acids and the cations on the surface of zinc-aluminum layered double hydroxides. Low pH values ​​are not conducive to the formation of perfluoroalkyl acid anions because their pKa (0.17-3.31) is low. High pH values ​​may weaken the protonation of primary amines. Therefore, pH = 4 is preferably used in the embodiments of the present invention.

[0107] This invention also compared the dual-mode extraction method with some publicly available literature analysis methods, and the comparison results are shown in Table 1.

[0108]

[0109] As shown in Table 1, compared with the technical solutions disclosed in the literature, the method of the present invention is superior to or comparable to other methods with similar analytical objectives in terms of recovery rate and limit of detection (LOD). Furthermore, in previous existing methods, a large amount of solid adsorbent was used, and a large amount of organic solvent was often used during elution, which was time-consuming and labor-intensive. In the present invention, acidic solvent direct dissolution is used instead of traditional organic solvent elution, and elution can be completed within seconds, which is highly efficient and rapid. This technology minimizes sample loss, improves the accuracy and reproducibility of analysis, and reduces energy consumption, which is in line with the sustainable development goals of green analysis.

[0110] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for dual-mode extraction of perfluoroalkyl acids from water samples, comprising the following steps: A water sample solution containing perfluoroalkyl acids was mixed with a layered double hydroxide in a first vortex, and then centrifuged to obtain the lower precipitate. After mixing the lower precipitate with an acidic solution, a switchable polarity eutectic solvent solution is added, and a second vortex mixing is performed to obtain a homogeneous system. The homogeneous system is mixed with an alkaline solution to induce phase separation, resulting in a lower layer of switchable polar eutectic solvent phase. After diluting the lower layer of switchable polar eutectic solvent phase, quantitative analysis was performed using high performance liquid chromatography-tandem mass spectrometry.

2. The method according to claim 1, characterized in that, The mass-to-volume ratio of the layered double hydroxide to the aqueous solution containing perfluoroalkyl acids is (1-10) mg: 10 mL.

3. The method according to claim 1 or 2, characterized in that, The layered double hydroxide is a zinc-aluminum layered double hydroxide.

4. The method according to claim 1, characterized in that, The volume ratio of the switchable polarity eutectic solvent solution to the aqueous solution containing perfluoroalkyl acids is (0.015-0.04):

1.

5. The method according to claim 1 or 4, characterized in that, The switchable polar eutectic solvent is prepared by mixing hexafluoroisopropanol and dipropylamine; the molar ratio of hexafluoroisopropanol to dipropylamine is (2-1):(1-5).

6. The method according to claim 1, characterized in that, The perfluoroalkyl acids in the aqueous solution containing perfluoroalkyl acids include one or more of perfluorobutyric acid, perfluorovaleric acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid, and perfluorobutyric acid.

7. The method according to claim 1, characterized in that, The acidic solution includes one of sulfuric acid, hydrochloric acid, and nitric acid; the concentration of the acidic solution is 4 mol / L-8 mol / L.

8. The method according to claim 1, characterized in that, The alkaline solution includes one of sodium carbonate, sodium hydroxide, and potassium hydroxide; the concentration of the alkaline solution is 2 mol / L to 6 mol / L.

9. The method according to claim 1, characterized in that, The mixing time of the first vortex is 5 min-25 min, and the mixing time of the second vortex is 10 s-20 s.

10. The method according to claim 1, characterized in that, The analytical conditions for the high-performance liquid chromatography-tandem mass spectrometry include: Chromatographic column: Waters C18 column, 100mm × 3.5mm, 3.5μm; Mobile phase: A is water, B is acetonitrile, wherein the water contains 0.1% formic acid, and the acetonitrile contains 0.1% formic acid; Gradient elution: 0 min - 4 min, 10% - 85% B; 4 min - 7 min, 85% - 10% B; Flow rate: 0.45 mL / min; injection volume: 10 μL; ion source: electrospray ion source, negative ion mode; nebulizer gas pressure: 55 psi, curtain gas pressure: 35 psi; monitoring mode: multiple reaction monitoring.

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