Method for micro-extraction analysis of perfluorooctanoic acid by using switchable eutectic solvent

Abstract

The invention relates to the technical field of liquid-liquid homogeneous microextraction, in particular to a method for microextraction analysis of perfluorooctanoic acid by using a switchable eutectic solvent. Comprising the following steps: step 1, mixing a hydrogen bond acceptor and a hydrogen bond donor according to a set proportion value, and stirring and mixing at a set temperature value to obtain a eutectic solvent; step 2, filtering the water sample through a water-based filter membrane, then adding a set amount of deep eutectic solvent, dropwise adding an alkaline solution, carrying out full vortex mixing through a mixer, and then adding an acidic solution to form an emulsion; according to the method, the high selectivity of the green solvent with a specific structure on perfluorooctanoic acid and the characteristic that the solvent is switched between hydrophilic and hydrophobic forms are utilized, so that the microextraction time is shortened, and the impurity removal and enrichment effects are enhanced. The method is simple and convenient to operate, green, environment-friendly, low in cost and good in effect, has the advantage of efficiently and rapidly pretreating the batch small-size complex matrix sample, and has a relatively good application prospect.

Description

Technical Field

[0001] The present invention relates to a method for detecting trace amounts of perfluorooctanoic acid (PFOA) in water, and in particular to a method for analyzing PFOA by microextraction using a switchable deep eutectic solvent. Background Art

[0002] Since the 1940s, perfluoroalkyl substances (PFAS) have been widely used in the production of various daily products and industrial applications due to their water- and grease-resistant properties. However, during their production and use, perfluoroalkyl substances (PFAS) are released directly or indirectly into the environment, and because they are not easily oxidized, photolyzed, hydrolyzed, or biodegraded, they continue to migrate and accumulate in the environment. Currently, perfluoroalkyl substances (PFAS) have been widely detected in the global atmosphere, sediments, organisms, and especially aquatic media, and some monomers can be enriched and amplified through the food chain. They have strong biological toxicity, pose a great threat to ecosystems and human health, and have attracted widespread attention from the international community. Perfluorooctanoic acid is one of the most common perfluorinated compounds. It can accumulate in the human body by binding to proteins and cause health hazards, such as kidney and liver damage, immunotoxicity, reproductive toxicity, and cancer.

[0003] Currently, the detection of trace levels of PFOA in water typically involves first enriching the water and then determining it using high-performance liquid chromatography (HPLC) or HPLC-tandem mass spectrometry (HPLC-MS / MS). Due to the complexity of the matrix in real water and the high cost and difficulty of analysis, pretreatment techniques to enrich trace levels of PFOA in water are crucial. Existing PFOA enrichment methods primarily include solid-phase extraction (SPE), liquid-phase extraction (LPE), and dispersive liquid-liquid microextraction (DL-LIQ).

[0004] The distribution and sources of traditional and emerging per- and polyfluoroalkyl substances in various environmental media in the Qiantang River Basin of China (RSC Advances, 2022, 12, 33, 21247-21254) were studied. Perfluoroalkyl substances (PFAS) were extracted from water samples using a WAX column with an analysis concentration range of 0.01 to 10.0 μg / L. However, the complex solid-phase extraction method used a large amount of hazardous organic solvents and the pretreatment time was lengthy.

[0005] For example, Chinese patent publication number CN117330664A discloses a method for simultaneously determining two types of new fluorine pollutants using liquid chromatography-tandem mass spectrometry. Solid-phase extraction is used for pretreatment, and then ultra-high performance liquid chromatography-tandem mass spectrometry is used for analysis. The analysis concentration range is 0.1 to 100 μg / L. Its complex solid-phase extraction also uses a large amount of hazardous organic solvents.

[0006] Chinese patent publication number CN118420487A discloses a perfluorooctanoic acid hapten, its preparation method, and application. A hybridoma cell line KND that secretes perfluorooctanoic acid monoclonal antibodies was cultivated. Anti-perfluorooctanoic acid monoclonal antibodies secreted by this cell line were obtained for use in food safety testing. The detection limit of perfluorooctanoic acid residues in the analysis is 1.13ug / mL, but the antibody production is complex and expensive.

[0007] Using deep eutectic solvents to quickly and efficiently remove perfluorooctanoic acid from water for sustainable water purification: An integrated experimental-modeling approach (Chemical Engineering Journal, 2024, 495: 153668) reported the use of a deep eutectic solvent (DES) of trioctyl phosphate and lauric acid to extract perfluorooctanoic acid from water, with an extraction efficiency of over 99%. However, this method can only extract perfluorooctanoic acid to a minimum concentration of 0.1000 mg / L, and its operation is not environmentally friendly. The extraction efficiency at low perfluorooctanoic acid concentrations is not ideal, which limits its use.

[0008] In general, existing methods require the use of large amounts of organic solvents, which can easily cause secondary environmental pollution, and the treatment process is complex and time-consuming. Therefore, there is an urgent need to establish efficient, rapid, highly sensitive, and low-detection-limit PFOA enrichment analysis methods for complex environmental matrices. This is of great significance for the comprehensive evaluation of PFOA contamination in environmental and biological samples.

[0009] Deep eutectic solvents (DES) are formed by hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs) through intermolecular hydrogen bonds. By selecting suitable hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs), the pH value can be adjusted to dynamically switch the formed deep eutectic solvent (DES) between hydrophobic and hydrophilic forms, forming a switchable deep eutectic solvent (DES). In the hydrophilic form, the switchable deep eutectic solvent (DES) is dispersed into the aqueous phase and can fully contact with the components to be measured. When switched to the hydrophobic form, the components to be measured are enriched in the organic phase, achieving efficient and rapid enrichment and separation of the components to be measured from the water body. Compared with traditional methods, microextraction using switchable deep eutectic solvents (DES) has better targeted adsorption and enrichment effects, uses fewer solvents and reagents, and has the advantage of being green and environmentally friendly.

[0010] In view of the deficiencies in the prior art, the present invention uses the natural product thymol as a hydrogen bond donor (HBD) and medium / long chain fatty alcohols as hydrogen bond acceptors (HBA), and the two constitute a switchable deep eutectic solvent (DES) for microextraction of perfluorooctanoic acid in water, and uses single factor experiments and Box-Behnken design response surface method to optimize the influencing factors of the microextraction process, reflecting excellent enrichment and separation performance. The present invention makes full use of the high selectivity of green solvents with specific chemical structures for the target and the characteristics of the solvent switching between hydrophilic / hydrophobic forms, shortens the microextraction time, and enhances the impurity removal and enrichment effects. The present invention is simple to operate, low in cost and effective, highly green, and has the advantages of efficient and rapid pretreatment of batch small-volume complex matrix samples, and has good application prospects. Summary of the Invention

[0011] In view of the shortcomings of existing methods for detecting perfluorooctanoic acid in water, the purpose of the present invention is to provide a method for analyzing perfluorooctanoic acid using pH-responsive switchable deep eutectic solvent microextraction.

[0012] The technical solution of the present invention is:

[0013] A method for analyzing perfluorooctanoic acid using switchable deep eutectic solvent microextraction, wherein perfluorooctanoic acid in a water sample is extracted using a deep eutectic solvent formed by a hydrogen bond acceptor and a hydrogen bond donor, and then analyzed by liquid chromatography-tandem mass spectrometry, comprising the following steps:

[0014] Step 1, mixing a hydrogen bond acceptor and a hydrogen bond donor in a set ratio, and stirring the mixture at a set temperature to obtain a deep eutectic solvent;

[0015] Step 2: The water sample is first filtered through a filter membrane, and then a set amount of a deep eutectic solvent is added, and an alkaline solution is added dropwise in a timely manner. After being fully vortex-mixed in a mixer, an acidic solution is added to form an emulsion. The emulsion is then centrifuged and separated. The upper liquid phase is collected with a microsyringe, diluted with methanol, and then filtered through an organic filter membrane to obtain the perfluorooctanoic acid extract solution to be determined.

[0016] Step 3. Qualitative and quantitative analysis of perfluorooctanoic acid in the extract solution was performed using liquid chromatography triple quadrupole mass spectrometry. The chromatographic conditions were as follows: a Phenomenex Kinetex F5 C18 column (100×3.0 mm, 2.6 μm), a column temperature of 40°C, a mobile phase consisting of a 0.01% formic acid aqueous solution (A)-methanol (B) gradient elution (0-0.5 min, 95% A; 0.5-3.0 min, 95%-5% A; 3.0-5.0 min, 5% A; 5.0-5.1 min, 5%-95% A; 5.1-7.0 min, 95% A), a flow rate of 0.3 mL / min, and an injection volume of 2 μL.

[0017] Mass spectrometry conditions: SCIEX Triple Quad TM The MS system was used in negative ion mode using an electrospray ionization source (ESI) in multiple reaction monitoring (MRM) mode. The spray voltage (IS) was -4500 V, the nebulizer gas pressure (GS1) was 50 psi, the curtain gas pressure (CUR) was 30 psi, the auxiliary gas pressure (GS2) was 50 psi, the ion source temperature (TEMP) was 500°C, and the collision gas pressure (CAD) was 8 psi. The mass spectrometry scan parameters are shown in Table 1.

[0018] Optionally, the hydrogen bond acceptor in step 1 is one or more of n-hexanol, n-octanol, n-decanol and n-dodecanol.

[0019] Optionally, the hydrogen bond donor in step 1 is thymol or carvacrol, preferably thymol.

[0020] Optionally, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor in step 1 is 4:1 to 1:2, preferably 3:1 to 2:1.

[0021] Optionally, the stirring temperature in step 1 is 20-30° C., and the stirring time is 1-2 min.

[0022] Optionally, the volume ratio of the water sample to the deep eutectic solvent in step 2 is 3000:25-35, 3000:28-29.

[0023] Optionally, the alkaline solution in step 2 is NaOH or KOH, preferably KOH.

[0024] Optionally, the concentration of the alkaline solution in step 2 is 3 to 6 mol / L, preferably 5 mol / L.

[0025] Optionally, the volume ratio of the KOH solution to the deep eutectic solvent in step 2 is 25:35 to 35:25, preferably 30:29 to 31:28.

[0026] Optionally, the vortex mixing time of the mixer in step 2 is 30 to 75 seconds, preferably 60 seconds.

[0027] Optionally, the acidic solution in step 2 is HCl or citric acid, preferably HCl.

[0028] Optionally, the concentration of the acidic solution in step 2 is 3 to 6 mol / L, preferably 4 to 5 mol / L.

[0029] Optionally, the volume ratio of the HCl solution to the deep eutectic solvent in step 2 is 55:25 to 45:35, preferably 50:28 to 49:29.

[0030] Optionally, the centrifugation time in step 2 is 120 to 240 seconds, and the centrifugal speed is 3000 to 5000 r / min.

[0031] Optionally, the methanol dilution ratio in step 2 is 10 or 100 times, preferably 10 times.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] The present invention synthesizes a green switchable DES with pH responsiveness as an extractant, which does not require the use of additional dispersants and emulsifiers, overcomes the problems of high solvent toxicity and large dosage in traditional methods, and has outstanding green and environmental protection advantages.

[0034] The liquid-liquid microextraction using switchable DES is a simple, fast, and efficient process, with the advantage of good processing effect on complex matrix samples, which can effectively reduce the analysis difficulty and cost of complex matrix samples.

[0035] No organic solvent is used in the entire sample pretreatment process, and the atomic utilization rate of the solvent synthesis process is 100%. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings, which are incorporated herein and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, further serve to explain the principles of the invention and to enable one skilled in the art to make and use the invention.

[0037] Figure 1 Schematic diagram of the process for analyzing perfluorooctanoic acid in water based on pH-responsive switchable DES microextraction established in the present invention;

[0038] Figure 2 is a typical total ion current diagram;

[0039] Figure 3 The infrared spectrum and differential scanning calorimetry diagram of the best extractant obtained by optimization;

[0040] Figure 4 This is the optimization result of the extractant type;

[0041] Figure 5 This is the optimization result of the extractant composition;

[0042] Figure 6 This is the optimization result of extraction time;

[0043] Figure 7 Response surface optimization results for base dosage, acid dosage and extractant dosage;

[0044] Figure 8 These are the test results of the extract phase of water samples with various concentrations of perfluorooctanoic acid after dilution with methanol. DETAILED DESCRIPTION

[0045] The present invention is further described below with reference to the embodiments and drawings, but the scope of protection of the present invention is not limited thereto and many variations are possible. If there are any points not particularly described in detail below, they can be understood by those skilled in the art according to conventional expressions or implemented according to existing technologies.

[0046] The present invention uses the natural product thymol as a hydrogen bond donor (HBD) and medium / long chain fatty alcohols as hydrogen bond acceptors (HBA). The two are configured in a set ratio to form a switchable DES to achieve efficient extraction of perfluorooctanoic acid in water, and then the extraction is determined by high performance liquid chromatography triple quadrupole mass spectrometry. The process is as follows: Figure 1 shown.

[0047] The chromatographic conditions of liquid chromatography triple quadrupole mass spectrometry were as follows: the chromatographic column was a Phenomenex Kinetex F5 C18 column (100×3.0 mm, 2.6 μm), the column temperature was 40°C, the mobile phase was a 0.01% formic acid aqueous solution (A)-methanol (B) gradient elution (0-0.5 min, 95% A; 0.5-3.0 min, 95%-5% A; 3.0-5.0 min, 5% A; 5.0-5.1 min, 5%-95% A; 5.1-7.0 min, 95% A), the flow rate was 0.3 mL / min, and the injection volume was 2 μL. TM The MS system was used in negative ion mode using an electrospray ionization source (ESI) in multiple reaction monitoring (MRM) mode. The spray voltage (IS) was -4500 V, the nebulizer gas pressure (GS1) was 50 psi, the curtain gas pressure (CUR) was 30 psi, the auxiliary gas pressure (GS2) was 50 psi, the ion source temperature (TEMP) was 500°C, and the collision gas pressure (CAD) was 8 psi. The mass spectrometry scan parameters are shown in Table 1.

[0048] Table 1 Mass spectrometry scanning parameters

[0049]

[0050] Typical total ion current diagram of mass spectrometry detection is as follows Figure 2 shown.

[0051] 1. Preparation and Characterization of Switchable Deep Eutectic Solvents

[0052] In the present invention, thymol was used as the HBD and four different medium- and long-chain fatty alcohols were synthesized at a molar ratio of 1:1 to synthesize four different switchable deep eutectic solvents (DES) (Table 2). In the hydrophobic state, all the switchable deep eutectic solvents (DES) were in the upper aqueous phase.

[0053] Table 2 Composition of switchable deep eutectic solvents (DES)

[0054]

[0055] The prepared switchable deep eutectic solvent (DES) was characterized by Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). Taking DES-2 as an example, the characterization results are as follows:

[0056] Step 1: FT-IR characterization

[0057] The hydrogen bonds of DES-2 were studied by FT-IR. Figure 3 As shown in a. It can be seen that the stretching vibration absorption peak of O–H changes from 3383.51 cm -1 and 3540cm of thymol (Thym) -1 Apparently shifted to DES-2's 3366.59 cm -1 The peaks are broadened, which can be attributed to the formation of hydrogen bonds within DES-2. The other absorption peaks of DES-2 are essentially consistent with those of Oct and Thmy in terms of peak shape and relative intensity, indicating that no chemical reaction occurs during the preparation of DES-2 and that hydrogen bonding is the primary driving force for DES formation.

[0058] Step 2: DSC characterization

[0059] Figure 3 b is the DSC graph of Oct, Thym and DES-2. It can be seen that the melting temperature of the eutectic mixture DES-2 shows a considerable decrease compared with the melting points of the two components, which is due to the specific hydrogen bonding interaction between them.

[0060] 2. Preparation of PFOA water sample

[0061] Accurately weigh 0.1 g of perfluorooctanoic acid solid, dissolve it in distilled water and dilute to 1 L to obtain a 0.1000 g / L perfluorooctanoic acid standard solution; then transfer 10 uL of the standard solution and dilute to 1 L with distilled water to obtain a 1.000 ug / L perfluorooctanoic acid water sample.

[0062] 3. Investigation of microextraction conditions

[0063] Take a set amount of perfluorooctanoic acid water sample, add a set amount of low eutectic solvent, and promptly add alkaline solution. After sufficient vortex mixing in a mixer, add acidic solution to form an emulsion. Then, centrifuge and separate the layers using a centrifuge. Collect the upper liquid phase with a microsyringe, dilute with methanol, and filter through an organic filter membrane to obtain the perfluorooctanoic acid extract solution to be measured.

[0064] Step 1: Screening of hydrogen bond acceptors and donors

[0065] 3 mL of perfluorooctanoic acid water sample was transferred, 29 μL of low eutectic solvent was added, 30 μL of 5 mol / L KOH solution was added dropwise, and the mixture was vortexed for 60 s to obtain a homogeneous solution. 45 μL of 5 mol / L HCl solution was added and centrifuged for 3 min to obtain the upper microextraction organic phase, and the perfluorooctanoic acid content in the upper solution was determined.

[0066] The microextraction effects of four deep eutectic solvents (DES-1, DES-2, DES-3 and DES-4) were investigated respectively. Figure 4 It can be seen that n-octanol-thymol has the best extraction effect on PFOA, which may be related to the hydrogen bonding interaction and hydrophobic interaction of the switchable DES.

[0067] Step 2: Molar ratio of hydrogen bond acceptor to hydrogen bond donor

[0068] 3 mL of perfluorooctanoic acid water sample was transferred, 29 μL of DES composed of n-octanol and thymol was added, 30 μL of 5 mol / L KOH solution was added dropwise, and the mixture was vortexed for 60 s to obtain a homogeneous solution. Then 45 μL of 5 mol / L HCl solution was added and centrifuged for 3 min to obtain the upper microextraction organic phase, and the perfluorooctanoic acid content in the upper solution was determined.

[0069] The effect of the molar ratio of octanol to thymol on the extraction of PFOA was investigated. Figure 5 As shown in the figure, the extraction recovery rate of PFOA gradually increases with increasing n-octanol ratio. The extraction effect is optimal when the molar ratio of n-octanol to thymol is 3:1. As the molar ratio continues to increase, the extraction recovery rate of PFOA decreases. This may be because the molar ratio of hydrogen bond acceptors to hydrogen bond donors affects the surface tension and dissociation degree of DES during the extraction process.

[0070] Step 3: Optimization of the vortex extraction time of the mixer:

[0071] 3 mL of perfluorooctanoic acid water sample was transferred, 29 μL of DES composed of n-octanol and thymol was added, 30 μL of 5 mol / L KOH solution was added dropwise, and a homogeneous solution was obtained by vortex mixing. Then 45 μL of 5 mol / L HCl solution was added and centrifuged for 3 min to obtain the upper microextraction organic phase, and the perfluorooctanoic acid content in the upper solution was determined.

[0072] The effect of vortex mixing time of the mixer on the extraction of perfluorooctanoic acid was investigated. Figure 6 As shown in the figure, the extraction recovery of PFOA increases with increasing vortex time. The highest extraction rate was achieved when the vortex time was 60 seconds. Further increases in vortex time increased the fluctuation in extraction recovery, which may be due to backmixing.

[0073] (4) Optimization of alkali, acid and extractant dosage

[0074] Due to the cross-influence of DES, KOH solution and hydrochloric acid solution in the experiment, in order to avoid the waste caused by a large number of repeated experiments in traditional single-factor experiments, the response surface curve method with BBD as the response surface model was used to optimize the volume of DES (25-35 μL), KOH solution volume (25-35 μL) and HCl solution volume (45-55 μL), as shown in the following example: Figure 7 The results show that the optimal extraction variables predicted by the response surface model are 28.86 μL of deep eutectic solvent, 30.22 μL of potassium hydroxide solution, and 49.82 μL of hydrochloric acid. The variables were rounded to 29 μL of DES, 30 μL of KOH solution, and 50 μL of HCl solution.

[0075] 4. Evaluation of the method for the determination of PFOA in aqueous samples under optimized conditions

[0076] Prepare a 0.05-10 μg / L perfluorooctanoic acid water sample, centrifuge, and filter through a 0.45 μm filter membrane. Transfer 3 mL of each concentration of water sample to a 5 mL centrifuge tube, add 29 μL of a deep eutectic solvent (n-octanol:n-thymol = 3:1), and immediately add 30 μL of a 5 mol / L KOH solution dropwise. Vortex the solution for 60 seconds to thoroughly mix, then add 50 μL of a 5 mol / L HCl solution to form an emulsion. Centrifuge at 4000 rpm for 3 minutes, then collect the upper phase with a microsyringe and transfer it to a 1.5 mL centrifuge tube. Dilute with methanol, filter through a 0.22 μm organic filter membrane into a sample injection vial, and analyze using liquid chromatography-tandem mass spectrometry.

[0077] Figure 8 The following are the test results for the extracts of various PFOA concentrations after dilution with methanol. (a) The extraction recovery of spiked water samples with concentrations of 0.05 to 1 μg / L at a 10-fold dilution with methanol; b) The extraction recovery of spiked water samples with concentrations of 0.5 to 10 μg / L at a 100-fold dilution with methanol. It can be seen that the dilution factor of the extract does not affect the analytical results.

[0078] The linear range (LR), correlation coefficient (R2), detection limit (LOD), quantification limit (LOQ), spike recovery (RR), intra-day precision and inter-day precision of the regression equation were obtained and are shown in Table 3.

[0079] Table 3 Detection limit parameters

[0080]

[0081] As can be seen, the method exhibits good linearity over the PFOA concentration range of 0.1-20 μg / L, with a correlation coefficient close to 1 (R² > 0.9999). The extraction recovery rate is 99.1%. The LOD and LOQ ranges for the entire method are 0.0015 μg / L and 0.005 μg / L, respectively, demonstrating high sensitivity and accuracy. Intra-day and inter-day precisions are 1.2% and 1.5%. This demonstrates the high reliability of the extraction method for the determination of PFOA in aqueous samples under these optimized conditions.

[0082] Example 1

[0083] In this study, wastewater sample A was used as a real sample to validate the applicability of the proposed method. PFOA was spiked into the real water sample at known concentration levels (0.00, 0.15, 0.30, and 0.60 μg / L) to determine the recoveries (RR) of PFOA. Unspiked and spiked samples were pretreated under optimized conditions.

[0084] Water samples were collected from the sewage outlet of Village A and spiked with a known concentration gradient of perfluorooctanoic acid (0.00, 0.15, 0.30, and 0.60 μg / L). After centrifugation, the samples were filtered through a 0.45 μm filter membrane. 3 mL of the water sample was transferred to a 5 mL centrifuge tube, 29 μL of a low eutectic solvent was added, and 30 μL of a 5 mol / L KOH solution was immediately added dropwise. The solution was vortexed for 60 seconds to thoroughly mix, and 49 μL of a 5 mol / L HCl solution was added to form an emulsion. After centrifugation at 4000 rpm for 3 minutes, the upper phase was collected with a microsyringe and transferred to a 1.5 mL centrifuge tube. The sample was diluted 10-fold with methanol and filtered through a 0.22 μm organic filter membrane into a sample injection bottle. The sample was then analyzed by liquid chromatography-tandem mass spectrometry.

[0085] The recoveries and actual concentrations of the spiked samples before enrichment were calculated. The recoveries of PFOA in the spiked water samples are shown in Table 4. PFOA was detected in the unspiked samples, and the recoveries of PFOA in the spiked water samples ranged from 94.33% to 100.0%.

[0086] Example 2

[0087] In this study, wastewater sample B was used as a real sample to validate the applicability of the proposed method. PFOA was spiked into the real water sample at known concentration levels (0.00, 0.15, 0.30, and 0.60 μg / L) to determine the recoveries (RR) of PFOA. Unspiked and spiked samples were pretreated under optimized conditions.

[0088] Water samples were collected from the sewage outlet of Village B and spiked with a known concentration gradient of perfluorooctanoic acid (0.00, 0.15, 0.30, and 0.60 μg / L). After centrifugation, the sample was filtered through a 0.45 μm filter membrane. 3000 μL of the water sample was transferred to a 5 mL centrifuge tube, 28 μL of a deep eutectic solvent was added, and 31 μL of a 5 mol / L KOH solution was immediately added dropwise. The solution was vortexed for 60 seconds to thoroughly mix, and 50 μL of a 5 mol / L HCl solution was added to form an emulsion. After centrifugation at 4000 rpm for 3 minutes, the upper phase was collected with a microsyringe and transferred to a 1.5 mL centrifuge tube. The sample was diluted 10-fold with methanol and filtered through a 0.22 μm organic filter membrane into a sample injection vial. The sample was analyzed by liquid chromatography-tandem mass spectrometry.

[0089] The recoveries and actual concentrations of the spiked samples before enrichment were calculated. The recoveries of PFOA in the spiked water samples are shown in Table 4. PFOA was detected in the unspiked samples, and the recoveries of PFOA in the spiked water samples ranged from 97.95% to 103.1%.

[0090] Table 4 Recovery of spiked PFOA in water samples

[0091]

Claims

1. A method for analyzing perfluorooctanoic acid (PFOA) using a switchable deep eutectic solvent microextraction method, wherein PFOA in a water sample is extracted using a deep eutectic solvent formed by a hydrogen bond acceptor and a hydrogen bond donor, and then analyzed by liquid chromatography-tandem mass spectrometry, characterized by: The steps include: Step 1, mixing a hydrogen bond acceptor and a hydrogen bond donor in a set ratio, and stirring the mixture at a set temperature to obtain a deep eutectic solvent; Step 2: The water sample is first filtered through an aqueous filter membrane, and then a set amount of a deep eutectic solvent is added, and an alkaline solution is added dropwise. After thorough vortex mixing in a mixer, an acidic solution is added to form an emulsion. The emulsion is then centrifuged and separated. The upper liquid phase is collected with a microsyringe, diluted with methanol, and then filtered through an organic filter membrane to obtain the perfluorooctanoic acid extract solution to be determined. Step 3: Use liquid chromatography triple quadrupole mass spectrometry to perform qualitative and quantitative analysis of perfluorooctanoic acid in the extraction solution.

2. The method for analyzing perfluorooctanoic acid using a switchable deep eutectic solvent microextraction according to claim 1, characterized in that: The hydrogen bond acceptor in step 1 is one or more of n-hexanol, n-octanol, n-decanol and n-dodecanol.

3. The method for analyzing perfluorooctanoic acid using a switchable deep eutectic solvent microextraction according to claim 1, wherein: The hydrogen bond donor in step 1 is thymol or carvacrol.

4. The method for analyzing perfluorooctanoic acid using a switchable deep eutectic solvent microextraction according to claim 1, wherein: The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor in step 1 is 4:1 to 1:

2.

5. The method for analyzing perfluorooctanoic acid using a switchable deep eutectic solvent microextraction according to claim 1, wherein: The stirring temperature in step 1 is 20-30° C., and the stirring time is 1-2 min.

6. The method for analyzing perfluorooctanoic acid using a switchable deep eutectic solvent microextraction according to claim 1, wherein: In step 2, the volume ratio of the water sample to the deep eutectic solvent is 3000:25-35.

7. The method for analyzing perfluorooctanoic acid using a switchable deep eutectic solvent microextraction according to claim 1, wherein: In step 2, the alkaline solution is NaOH or KOH with a concentration of 3 to 6 mol / L.

8. The method for analyzing perfluorooctanoic acid using a switchable deep eutectic solvent microextraction according to claim 1, wherein: In step 2, the volume ratio of the KOH solution to the deep eutectic solvent is 25:35 to 35:

25.

9. The method for analyzing perfluorooctanoic acid using a switchable deep eutectic solvent microextraction according to claim 1, wherein: The vortex mixing time of the mixer in step 2 is 30 to 75 seconds.

10. The method for analyzing perfluorooctanoic acid using a switchable deep eutectic solvent microextraction according to claim 1, wherein: The acidic solution in step 2 is HCl or citric acid with a concentration of 3 to 6 mol / L.

11. The method for analyzing perfluorooctanoic acid using a switchable deep eutectic solvent microextraction according to claim 1, wherein: In step 2, the volume ratio of the HCl solution to the deep eutectic solvent is 55:25 to 45:

35.

12. The method for analyzing perfluorooctanoic acid using a switchable deep eutectic solvent microextraction according to claim 1, wherein: The centrifugation time in step 2 is 120 to 240 seconds, and the centrifugal speed is 3000 to 5000 r / min.

13. The method for analyzing perfluorooctanoic acid using a switchable deep eutectic solvent microextraction according to claim 1, wherein: The dilution factor of methanol in step 2 is 10 or 100 times.

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