Method for rapidly detecting concentration of perfluorooctanoic acid in water sample at low cost

Abstract

The invention provides a method for rapidly detecting the concentration of perfluorooctanoic acid in a water sample at low cost, and belongs to the technical field of pollutant detection. The method comprises the following steps: preparing a perfluorooctanoic acid solution containing interferents with the same concentration as a water sample to be detected; the perfluorooctanoic acid is partially converted into fluorine ions through treatment; determining the content of fluorine ions in the solution by using a fluorine ion selective electrode method; drawing a working curve; the fluorine ion concentration in the to-be-detected water sample is treated and measured by adopting the same method, and then the accurate perfluorooctanoic acid concentration in the to-be-detected sample is calculated through the working curve. The method disclosed by the invention is simple, convenient, rapid, good in repeatability, low in instrument requirement and low in detection cost, can resist interference of coexisting substances in a water body on a determination result, and can effectively improve the accuracy of concentration data of the perfluorooctanoic acid.

Description

Technical Field

[0001] The invention belongs to the technical field of pollutant detection, and specifically relates to a method for rapidly and low-costly detecting the concentration of perfluorooctanoic acid in a water sample. Background Art

[0002] Per- and polyfluoroalkyl substances (PFAS), as a new type of global organic pollutant, have attracted widespread attention in recent years. PFAS are a class of environmental pollutants with systemic and multi-organ toxicity. PFAS in the environment accumulate along the food chain and accumulate in organisms, eventually causing harm to human health.

[0003] Perfluorooctanoic acid (PFOA) is a type of perfluorinated compound with hydrophobic and oleophobic properties. Its chemical structure is more stable than other surfactants and is resistant to high temperatures and strong oxidants. Therefore, it is widely used in lubricants, fire extinguishers, surfactants, cleaning agents, cosmetics, textiles, interior decoration, leather products, etc. Its basic physical and chemical properties are shown in the table below.

[0004]

[0005] Studies have shown that PFOA exists in the global ecological environment and organisms, and the concentration level is increasing. PFOA shows strong resistance to chemical and biological degradation. So far, there has been no report of natural decomposition process. The Stockholm Convention regulates the global elimination of PFOA, its salts and related compounds. Since July 4, 2020, PFOA has been banned under the POPs regulations. In September 2020, the European Food Safety Authority set new safety thresholds for major perfluoroalkyl substances such as PFOA that accumulate in the body. In December 2022, my country officially released the "List of New Pollutants under Key Control (2023 Edition)", which also includes PFOA.

[0006] The properties of PFOA are determined by the structure of the fluorine element itself. Since the atomic radius of fluorine is very small and its polarizability is low, the bond energy of the carbon-fluorine bond is very strong. The fluorine atom with three non-bonding electron pairs effectively shields the carbon atom, further enhancing the stability of the carbon-fluorine bond. In addition, the carbon-fluorine chain structure of PFOA is very rigid, and the lack of electrophilic and nucleophilic attack makes the perfluorinated compound have excellent acid resistance, alkali resistance, heat resistance, reduction resistance, oxidation resistance, and resistance to biological invasion. These characteristics make PFOA show excellent performance in specific occasions, such as maintaining good stability in high temperature and high acid and alkali environments.

[0007] The existing detection method for perfluorooctanoic acid is mainly liquid chromatography-mass spectrometry (LC-MS / MS), which is a highly sensitive and selective analysis method. First, the perfluorooctanoic acid in the water sample can be extracted into a solid phase extraction column using solid phase extraction technology, and then analyzed using a liquid chromatography-mass spectrometry instrument to quantify the characteristic ions of perfluorooctanoic acid. Common chromatographic column materials such as C18 can be used for separation. Although liquid chromatography-mass spectrometry has high sensitivity and high selectivity, the instrument is expensive and the consumables are expensive, which leads to high analysis and testing costs. In addition, the equipment is complicated to operate and requires professional personnel to operate, and the detection cycle is long, which is not suitable for small laboratories to carry out analysis of such substances. Therefore, it is necessary to develop simpler, faster, and lower-cost detection methods to meet the needs of practical applications.

[0008] Existing derivatization reanalysis test methods include a derivatization method for detecting perfluorooctanoic acid using UV-HPLC, which reacts perfluorooctanoic acid with an acylating agent in an organic solvent at a certain temperature to obtain N-benzyl perfluorooctanoic acid imide, detects N-benzyl perfluorooctanoic acid imide with UV-HPLC, and then calculates the amount of perfluorooctanoic acid. There are also studies that use photocatalytic sodium persulfate to oxidize perfluorooctanoic acid, remove all fluoride ions in the perfluorooctanoic acid molecule, and obtain the concentration of perfluorooctanoic acid by testing the concentration of fluoride ions in the solution. Although the above-mentioned derivatization reanalysis test method can effectively detect the concentration of perfluorooctanoic acid, the reaction conditions are high, the derivatization steps are cumbersome, and the requirements for instruments and equipment are still very high. The chemical reagents used may also have adverse effects on the environment. In addition, the invention patent CN108828128B discloses a method for determining total organic fluorine in water samples and aqueous solutions. The method completely converts organic fluorine into inorganic fluorine through ultraviolet sulfite pretreatment, and the concentration of fluoride ions is measured to obtain the amount of total organic fluorine in the water sample. However, in reality, various interferences such as ions, organic compounds, and natural organic matter coexist in water bodies, which will inhibit the derivatization efficiency and affect the defluorination efficiency of PFOA, resulting in the measured PFOA concentration not being the actual concentration of PFOA. Summary of the invention

[0009] In view of the above shortcomings of the prior art, the present invention provides a method for quickly and cost-effectively detecting the concentration of perfluorooctanoic acid in water samples. The method is simple to operate, has good repeatability, and low detection cost. It can resist the interference of coexisting substances in the water body on the measurement results, and can quickly and accurately measure the actual concentration of perfluorooctanoic acid in the water sample.

[0010] To achieve the above purpose, the specific technical solutions of the present invention are as follows:

[0011] A method for rapidly and low-costly detecting the concentration of perfluorooctanoic acid in water samples comprises the following steps:

[0012] (1) Preparation of standard water sample: Prepare a perfluorooctanoic acid solution with a known concentration as a standard water sample;

[0013] (2) converting part of the perfluorooctanoic acid into fluoride ions by treatment;

[0014] (3) Determine the fluoride ion concentration in the treated solution;

[0015] (4) PFOA concentration (C PFOA ) as the horizontal axis, with fluoride ion concentration (C F ) as the vertical axis, draw the working curve of "perfluorooctanoic acid concentration-fluoride ion concentration";

[0016] (5) Treat the water sample to be tested according to steps (2)-(3), and substitute the fluoride ion concentration obtained by the test into the working curve of step (4) to calculate the perfluorooctanoic acid concentration in the water sample to be tested.

[0017] Preferably, the standard water sample prepared in step (1) contains the same concentration of interfering substances as that of the water sample to be tested.

[0018] Preferably, the concentration of the perfluorooctanoic acid solution in step (1) is ≤100 μmol / L.

[0019] Preferably, the treatment method of step (2) is: pouring the perfluorooctanoic acid solution into a reaction tube, adjusting the pH of the solution, and adding sulfite; passing an inert gas into the solution to deoxygenate, then sealing the reaction tube and irradiating it under a 185nm ultraviolet lamp.

[0020] Further preferably, the sulfite is added so that the concentration of the sulfite is 5-40 mmol / L.

[0021] Further preferably, the pH is 10-13, and the alkali used to adjust the pH includes but is not limited to sodium hydroxide or potassium hydroxide.

[0022] Further preferably, the sulfite includes but is not limited to sodium sulfite or potassium sulfite.

[0023] Further preferably, the reaction tube is a quartz glass vessel.

[0024] Further preferably, the introduced inert gas includes but is not limited to nitrogen or argon, and the purity of the gas is not limited.

[0025] Further preferably, the irradiation time is not less than 20 min.

[0026] More preferably, the irradiation time is 30 to 120 min.

[0027] Preferably, the fluoride ion concentration in step (3) is detected by a fluoride ion selective electrode method; the specific operation of the fluoride ion selective electrode method for determining fluoride ions is as follows: 5 mL of the solution after the light irradiation reaction is taken into a 50 mL volumetric flask, 5 mL of a total ion strength adjustment buffer solution is added thereto and the volume is fixed to 50 mL, all the solution in the volumetric flask is poured into a plastic beaker, a polytetrafluoroethylene magnet is added for stirring, a fluoride ion electrode, a reference electrode, and a temperature electrode are placed (stirring does not stop during the test), and the fluoride ion reading is read after the reading on the detector stabilizes; the total ion strength adjustment buffer solution is a TISBA III buffer solution: 1 mol / L hexamethylenetetramine-1 mol / L potassium nitrate-0.03 mol / L titanium iron reagent.

[0028] Preferably, the concentration of perfluorooctanoic acid in the water sample to be tested in step (5) is ≤100 μmol / L; samples with too high a concentration need to be diluted to bring their concentration within the effective range.

[0029] Preferably, the water sample to be tested in step (5) includes but is not limited to pure water, surface water, groundwater, tap water, and water samples containing various ions and / or organic compounds.

[0030] The technical principle of the method of the present invention is: using ultraviolet light to excite sulfite to generate hydrated electrons can reduce a certain proportion of CF bonds of perfluorooctanoic acid to CH and remove fluoride ions within a certain period of time. Under the conditions of different water matrices (i.e., coexisting ions and / or organic compounds and other interferents in the water body), standard curves are established based on the defluorination amount, and the accurate concentration of perfluorooctanoic acid in the sample to be tested can be calculated by detecting the fluoride ion concentration in the sample to be tested.

[0031] The method of the present invention uses a quartz glass reaction tube as a reaction container, so that ultraviolet light can pass through the quartz glass wall to cause a photoreaction in a water sample, and a sealing device such as a rubber stopper is installed on the quartz glass vessel, so that after an inert gas is introduced, the contact between the reaction liquid and oxygen can be isolated; under anaerobic and anoxic conditions, the reduction and defluorination conversion reaction speed of perfluorooctanoic acid is faster, and after 30 minutes of light reaction, perfluorooctanoic acid can be effectively defluorinated, and the perfluorooctanoic acid concentration in the water sample to be tested can be accurately calculated through a working curve; the method of the present invention controls the pH value within the range of 10-13, so that the efficiency of sulfite producing hydrated electrons under ultraviolet light excitation is higher, and then the reduction and defluorination efficiency of perfluorooctanoic acid is higher; when the fluoride ion selective electrode method is used to determine the fluoride ion concentration, a total ion strength adjustment buffer solution needs to be added to the solution to be tested, and the purpose is to omit the pH adjustment step before detection when the pH value of the current treatment solution is not greater than 13.

[0032] Compared with the prior art, the present invention is beneficial in that:

[0033] (1) The method of the present invention can quickly detect the concentration of perfluorooctanoic acid in water samples containing various interfering substances such as ions, organic compounds, and natural organic matter. The analysis and testing cost is low, which is conducive to the development of perfluorooctanoic acid concentration analysis and testing work in general laboratories;

[0034] (2) The method of the present invention adopts the fluoride ion selective electrode method as the final detection means. The fluoride ion detector used in the fluoride ion selective electrode method is commonly found in general analytical testing laboratories. Its simple operation and low analysis cost have expanded the application range of the instrument;

[0035] (3) The chemical reagents involved in the method of the present invention are all common reagents with low cost and small dosage, thus causing little secondary pollution;

[0036] (4) The method of the present invention takes corresponding measures to address various interfering substances such as ions, organic compounds, natural organic matter, etc. that affect the defluorination efficiency in the sample to be tested. By adding coexisting ions and / or organic compounds and other interfering substances to a perfluorooctanoic acid solution of known concentration, a standard curve is constructed to ensure the accuracy of the test results. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A flow chart for detecting the concentration of perfluorooctanoic acid in the water sample to be tested;

[0038] Figure 2 This is a diagram of the light reaction device;

[0039] Figure 3 This is the working curve drawn for Example 1. DETAILED DESCRIPTION

[0040] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] The present invention provides a method for rapidly and low-costly detecting the concentration of perfluorooctanoic acid in a water sample, comprising the following steps:

[0042] (1) Preparation of standard water sample: Prepare a perfluorooctanoic acid solution with a known concentration as a standard water sample;

[0043] (2) converting part of the perfluorooctanoic acid into fluoride ions by treatment;

[0044] (3) Determine the fluoride ion concentration in the treated solution;

[0045] (4) With the concentration of perfluorooctanoic acid as the horizontal axis and the concentration of fluoride ions as the vertical axis, draw a working curve of “perfluorooctanoic acid concentration-fluoride ion concentration”;

[0046] (5) Treat the water sample to be tested according to steps (2)-(3), and substitute the fluoride ion concentration obtained by the test into the working curve of step (4) to calculate the perfluorooctanoic acid concentration in the water sample to be tested.

[0047] In some examples, the standard water sample prepared in step (1) contains the same concentration of interfering substances as the water sample to be tested.

[0048] In some examples, the concentration of the perfluorooctanoic acid solution in step (1) is ≤100 μmol / L.

[0049] In the following specific embodiment, the treatment method is: pouring the perfluorooctanoic acid solution into a reaction tube, adjusting the pH of the solution, and adding sulfite; passing an inert gas into the solution to deoxygenate, then sealing the reaction tube and irradiating it under a 185nm ultraviolet lamp; the reaction tube is a quartz glass vessel.

[0050] In some examples, the sulfite is added so that the concentration of the sulfite is 5-40 mmol / L.

[0051] In some examples, the pH is 10-13, and the base used to adjust the pH includes but is not limited to sodium hydroxide or potassium hydroxide.

[0052] In some examples, the sulfite includes, but is not limited to, sodium sulfite or potassium sulfite.

[0053] In some examples, the introduced inert gas includes, but is not limited to, nitrogen or argon, and the purity of the gas is not limited.

[0054] In some examples, the irradiation time is no less than 20 min.

[0055] In some examples, the irradiation time is 30 to 120 min.

[0056] In some examples, the concentration of perfluorooctanoic acid in the water sample to be tested in step (5) is ≤100 μmol / L; samples with too high a concentration need to be diluted to bring their concentration within the effective range.

[0057] In some examples, the water sample to be tested in step (5) includes but is not limited to pure water, surface water, groundwater, tap water, and water samples containing various ions and / or organic compounds.

[0058] In the following specific embodiment, the fluoride ion concentration in step (3) is detected by the fluoride ion selective electrode method; the specific operation of the fluoride ion selective electrode method for determining fluoride ions is as follows: 5 mL of the solution after the light irradiation reaction is taken into a 50 mL volumetric flask, 5 mL of the total ion strength adjustment buffer solution is added thereto and the volume is fixed to 50 mL, all the solution in the volumetric flask is poured into a plastic beaker, a polytetrafluoroethylene magnet is added for stirring, a fluoride ion electrode, a reference electrode, and a temperature electrode are placed (stirring does not stop during the test), and the fluoride ion reading is read after the reading on the detector stabilizes; the total ion strength adjustment buffer solution is TISBA III buffer: 1 mol / L hexamethylenetetramine-1 mol / L potassium nitrate-0.03 mol / L titanium iron reagent.

[0059] Example 1

[0060] A method for rapid and low-cost detection of perfluorooctanoic acid concentration in water samples, the steps are as follows:

[0061] 1. Create a working curve

[0062] Prepare a 500 μmol / L perfluorooctanoic acid solution, pipette 0.04, 0.1, 0.2, 0.5, 1, 1.5, 2 mL of the solution into a quartz stoppered reaction tube, add different volumes of pure water to make the solution volume in the reaction tube 9 mL, and add 1 mL of 0.1 mol / L NaOH solution to make the total volume of the reaction solution 10 mL. At this time, the concentrations of perfluorooctanoic acid in each reaction tube are 2, 5, 10, 25, 50, 75, 100 μmol / L, and the pH of the reaction solution is 12. Then, for subsequent treatment, add 0.0252 g of sodium sulfite to make its concentration in the solution 20 mmol / L, then pass nitrogen into the quartz reaction tube for 10 min, deoxygenate, plug with a polytetrafluoroethylene stopper to seal, and place the reaction tube under a UV disinfection lamp for 60 min. After the reaction, the fluoride ion concentrations in the mixed solution were measured by fluoride ion selective electrode method to be 2.45, 6.01, 12.15, 29.27, 57.75, 86.25, and 110.50 μmol / L, respectively, that is, the defluorination rates of the perfluorooctanoic acid standard solutions were 81.8%, 80.0%, 81.0%, 78.1%, 77.0%, 76.7%, and 73.7%, respectively. The working curve was obtained by plotting the perfluorooctanoic acid concentration as the horizontal axis and the measured fluoride ion concentration as the vertical axis: C F (μmol / L) = 1.114×C PFOA (μmol / L) + 0.999, R 2 =0.9991(R 2It indicates the proportion of the variance of the dependent variable that can be explained by the independent variable. Its value range is between 0 and 1. The closer it is to 1, the better the model fits the data. The closer it is to 0, the worse the model fits the data. Figure 3 The method has good linearity in the concentration range of PFOA from 2 to 100 μmol / L.

[0063] 2. Precision determination

[0064] In 5 quartz stoppered reaction tubes, 10 mL of reaction solution containing 25 μmol / L perfluorooctanoic acid and pH 12 was prepared, and subsequent treatment was carried out: 0.0252 g of sodium sulfite was added to make its concentration in the solution 20 mmol / L, and then nitrogen was passed into the quartz reaction tube for 10 min. After deoxygenation, the polytetrafluoroethylene stopper was plugged to seal the tube, and the 5 reaction tubes were placed under the ultraviolet disinfection lamp for 60 min. After the reaction, the fluoride ion concentrations in the 5 mixed solutions were determined by the fluoride ion selective electrode method to be 29.27, 29.73, 28.03, 30.05, and 28.55 μmol / L, respectively. Substituting into the above working curve, the concentrations of perfluorooctanoic acid in the 5 parallel experiments were 101.5%, 103.1%, 97.2%, 104.2%, and 99.0%, respectively, with a standard deviation of 2.89%. It meets the requirements.

[0065] Example 2

[0066] Treatment effects under different pH conditions

[0067] In four quartz stoppered reaction tubes, a 25 μmol / L perfluorooctanoic acid standard solution was prepared, and 10 mL of the standard solution was transferred to the four quartz stoppered reaction tubes for subsequent treatment: the pH of the solution was adjusted to 10, 11, 12, and 13, and then 0.0252 g of sodium sulfite was added to make its concentration in the solution 20 mmol / L. Then nitrogen was passed into the quartz reaction tube for 10 minutes. After deoxygenation, the tube was sealed with a polytetrafluoroethylene stopper, and the reaction tube was placed under an ultraviolet disinfection lamp for 60 minutes. After the reaction, the fluoride ion concentrations in the four mixed solutions were determined by the fluoride ion selective electrode method to be 24.44, 26.60, 29.27, and 32.13 μmol / L, respectively, that is, the defluorination rates of perfluorooctanoic acid under each alkaline condition were 65.2%, 70.9%, 78.1%, and 85.7%, respectively. Substituting the solution into the working curve obtained in Example 1, the concentrations of perfluorooctanoic acid under the four pH conditions were 84.7%, 92.2%, 101.5% and 111.37%, respectively. When the pH was 12, the defluorination efficiency of this method was high, and the concentration of perfluorooctanoic acid could be determined more accurately.

[0068] Example 3

[0069] Treatment effects under different sodium sulfite concentrations

[0070] A standard solution of perfluorooctanoic acid with a concentration of 25 μmol / L was prepared, and 10 mL of the standard solution was transferred to 8 quartz stoppered reaction tubes for subsequent treatment: 0.004 g of NaOH particles was added to make the pH of the solution 12, and 0, 0.0013, 0.0025, 0.0063, 0.0126, 0.0189, 0.0252, and 0.0315 g of sodium sulfite were added, respectively, so that the concentrations in the solution were 0, 1, 2, 5, 10, 15, 20, and 25 mmol / L, respectively. Then, nitrogen was passed into the quartz reaction tube for 10 min. After deoxygenation, the tube was sealed with a polytetrafluoroethylene stopper, and the reaction tube was placed under a UV disinfection lamp for 60 min. After the reaction, the fluoride ion concentrations in the eight mixed solutions were determined by fluoride ion selective electrode method to be 3.88, 19.15, 24.28, 28.00, 29.27, 29.43, 30.13, and 30.63 μmol / L, respectively, that is, the defluorination rates of perfluorooctanoic acid under different sodium sulfite concentrations were 10.3%, 51.1%, 64.7%, 74.7%, 78.1%, 78.5%, 80.3%, and 81.7%, respectively. When the sodium sulfite concentration was greater than 2 mmol / L, the method had high defluorination efficiency and could accurately determine the concentration of perfluorooctanoic acid.

[0071] Example 4

[0072] Treatment effects under different light exposure durations

[0073] A standard solution of perfluorooctanoic acid with a concentration of 25 μmol / L was prepared, and 10 mL of the standard solution was transferred to 6 quartz stoppered reaction tubes for subsequent treatment: 0.004 g of NaOH particles was added to make the pH of the solution 12, and 0.0252 g of sodium sulfite was added to make its concentration in the solution 20 mmol / L. Then, nitrogen was passed into the quartz reaction tube for 10 min. After deoxygenation, the tube was sealed with a polytetrafluoroethylene stopper. The 6 reaction tubes were placed under a UV disinfection lamp and irradiated for 10, 20, 30, 60, 90, and 120 min, respectively. After the reaction, the fluoride ion concentrations in the six mixed solutions were measured by fluoride ion selective electrode method to be 18.19, 23.85, 26.18, 29.27, 30.41, and 30.72 μmol / L, respectively, that is, the defluorination rates of perfluorooctanoic acid under different illumination conditions were 48.5%, 63.6%, 69.8%, 78.1%, 81.1%, and 81.9%, respectively. When the photoreaction treatment was 30 minutes, perfluorooctanoic acid could be effectively defluorinated, so that a working curve could be established to accurately calculate its actual concentration.

[0074] Example 5

[0075] Effects of sodium ions and chloride ions

[0076] A 25 μmol / L perfluorooctanoic acid standard solution was prepared, which contained sodium chloride with concentrations of 0, 1, 2, 5, 10, and 20 mmol / L, respectively. 10 mL of each solution was transferred into 6 quartz stoppered reaction tubes for subsequent treatment: 0.004 g of NaOH particles was added to make the solution pH 12, and 0.0252 g of sodium sulfite was added to make its concentration in the solution 20 mmol / L. Then, nitrogen was passed into the quartz reaction tube for 10 min. After deoxygenation, the tubes were sealed with polytetrafluoroethylene stoppers. The 6 reaction tubes were placed under a UV disinfection lamp for 60 min. After the reaction, the fluoride ion concentrations in the six mixed solutions were measured by fluoride ion selective electrode method to be 29.27, 28.70, 29.27, 29.06, 28.86, and 28.98 μmol / L, respectively, that is, the defluorination rates of perfluorooctanoic acid under the influence of different concentrations of sodium chloride were 78.1%, 76.5%, 78.1%, 77.5%, 76.9%, and 77.3%, respectively. Sodium chloride had no obvious effect on the defluorination rate of perfluorooctanoic acid in the concentration range of 0-20 mmol / L.

[0077] Example 6

[0078] Effect of nitrate

[0079] A 25 μmol / L perfluorooctanoic acid standard solution was prepared, which contained sodium nitrate at concentrations of 0, 1, 2, 5, 10, and 20 mmol / L, respectively. 10 mL of each solution was transferred into 6 quartz stoppered reaction tubes for subsequent treatment: 0.004 g of NaOH particles was added to make the solution pH 12, and 0.0252 g of sodium sulfite was added to make its concentration in the solution 20 mmol / L. Nitrogen was then passed into the quartz reaction tube for 10 min. After deoxygenation, the tubes were sealed with polytetrafluoroethylene stoppers. The 6 reaction tubes were placed under a UV disinfection lamp for 60 min. After the reaction, the fluoride ion concentrations in the six mixed solutions were measured by fluoride ion selective electrode method to be 29.27, 24.13, 6.17, 0.99, 0.97, and 1.05 μmol / L, respectively, that is, the defluorination rates of perfluorooctanoic acid under the influence of different concentrations of sodium nitrate were 78.1%, 64.3%, 16.4%, 2.6%, 2.6%, and 2.8%, respectively. Sodium nitrate has a significant inhibitory effect on the defluorination rate of perfluorooctanoic acid in the concentration range of 0-20 mmol / L.

[0080] A standard curve was established for water samples containing 1 mmol / L sodium nitrate. The specific steps were as follows: prepare standard solutions of perfluorooctanoic acid with concentrations of 2, 5, 10, 20, 30, and 50 μmol / L, respectively, and make them contain 1 mmol / L sodium nitrate. Pipette 10 mL into 6 quartz stoppered reaction tubes for subsequent treatment: add 0.004 g NaOH particles to make the solution strongly alkaline, add 0.0252 g sodium sulfite to make its concentration in the solution 20 mmol / L, then pass nitrogen into the quartz reaction tube for 10 min, deoxygenate, plug with a polytetrafluoroethylene stopper to seal, and place the 6 reaction tubes under a UV disinfection lamp for 60 min. After the reaction, the fluoride ion concentrations in the six mixed solutions were determined by fluoride ion selective electrode method to be 1.98, 4.94, 9.83, 19.50, 28.80, and 47.78 μmol / L, respectively, and the defluorination rates were 66.1%, 65.8%, 65.5%, 65.0%, 64.0%, and 63.7%, respectively. The equation for the standard curve was C F (μmol / L) = 0.9528×C PFOA (μmol / L) +0.224, R 2 =0.9999. The result of the 25 μmol / L perfluorooctanoic acid solution in the same matrix and the fluoride ion content after treatment of 24.13 μmol / L was put into the newly established standard curve equation, and the measured perfluorooctanoic acid concentration was calculated to be 25.09 μmol / L, and the relative error of the detection result was 0.36%.

[0081] Example 7

[0082] Effect of magnesium ions

[0083] A 25 μmol / L perfluorooctanoic acid standard solution was prepared, which contained magnesium chloride at concentrations of 0, 1, 2, 5, 10, and 20 mmol / L, respectively. 10 mL of each solution was transferred into 6 quartz stoppered reaction tubes for subsequent treatment: 0.004 g of NaOH particles was added to make the solution pH 12, and 0.0252 g of sodium sulfite was added to make its concentration in the solution 20 mmol / L. Nitrogen was then passed into the quartz reaction tube for 10 min. After deoxygenation, the tubes were sealed with polytetrafluoroethylene stoppers. The 6 reaction tubes were placed under a UV disinfection lamp for 60 min. After the reaction, the fluoride ion concentrations in the six mixed solutions were measured by fluoride ion selective electrode method to be 29.27, 29.06, 28.82, 24.64, 22.00, and 19.87 μmol / L, respectively. That is, the defluorination rates of perfluorooctanoic acid under the influence of different concentrations of magnesium chloride were 78.1%, 77.5%, 76.9%, 65.7%, 58.7%, and 53.0%, respectively. Magnesium chloride has a significant inhibitory effect on the defluorination rate of perfluorooctanoic acid in the concentration range of 0-20 mmol / L.

[0084] A standard curve was established for water samples containing 10 mmol / L magnesium chloride. The specific steps were as follows: prepare standard solutions of perfluorooctanoic acid with concentrations of 2, 5, 10, 20, 30, and 50 μmol / L, respectively, and make them contain 10 mmol / L magnesium chloride. Pipette 10 mL into 6 quartz stoppered reaction tubes for subsequent treatment: add 0.004 g NaOH particles to make the solution pH 12, add 0.0252 g sodium sulfite to make its concentration in the solution 20 mmol / L, then pass nitrogen into the quartz reaction tube for 10 min, deoxygenate, plug with a polytetrafluoroethylene stopper to seal, and place the 6 reaction tubes under a UV disinfection lamp for 60 min. After the reaction, the fluoride ion concentrations in the six mixed solutions were determined by fluoride ion selective electrode method to be 1.81, 4.49, 8.91, 17.70, 26.19, and 43.35 μmol / L, respectively, and the defluorination rates were 60.2%, 59.9%, 59.4%, 59.0%, 58.2%, and 57.8%, respectively. The equation for the standard curve was C F (μmol / L) = 0.8647×C PFOA (μmol / L) +0.2127, R 2 =0.9999. The result of the perfluorooctanoic acid solution with a concentration of 25 μmol / L in the same matrix and the fluoride ion content of 22.00 μmol / L after the treatment was put into the newly established standard curve equation, and the perfluorooctanoic acid concentration was calculated to be 25.20 μmol / L, and the relative error of the detection result was 0.80%.

[0085] Example 8

[0086] Effect of Sodium Humate

[0087] A standard curve was established for water samples containing 5 mg / L sodium humate. The specific steps were as follows: prepare standard solutions of perfluorooctanoic acid with concentrations of 2, 5, 10, 20, 30, and 50 μmol / L, respectively, and make them contain 5 mg / L sodium humate. Pipette 10 mL into 6 quartz stoppered reaction tubes for subsequent treatment: add 0.004 g NaOH particles to make the solution pH 12, add 0.0252 g sodium sulfite to make its concentration in the solution 20 mmol / L, then pass nitrogen into the quartz reaction tube for 10 min, deoxygenate, plug with a polytetrafluoroethylene stopper to seal, and place the 6 reaction tubes under a UV disinfection lamp for 60 min. After the reaction, the fluoride ion concentrations in the six mixed solutions were determined by fluoride ion selective electrode method to be 1.85, 4.61, 9.17, 18.27, 26.91, and 44.63 μmol / L, respectively, and the defluorination rates were 61.6%, 61.5%, 61.1%, 60.9%, 59.8%, and 59.5%, respectively. The equation for the standard curve was C F (μmol / L) = 0.8901×C PFOA (μmol / L) +0.2145, R 2 =0.9999. The result of the 25 μmol / L perfluorooctanoic acid solution in the same matrix and the fluoride ion content after treatment of 22.69 μmol / L was put into the newly established standard curve equation, and the measured perfluorooctanoic acid concentration was calculated to be 25.25 μmol / L, and the relative error of the test result was 1.00%.

[0088] The above specific embodiments describe the implementation of the present invention in detail, but the present invention is not limited to the specific details in the above embodiments. Within the scope of the claims and technical concept of the present invention, the technical solution of the present invention can be modified and changed in many simple ways, and these simple modifications all belong to the protection scope of the present invention.

Claims

1. A method for rapidly and low-costly detecting the concentration of perfluorooctanoic acid in water samples, characterized in that: The steps include: (1) Preparation of standard water sample: Prepare a perfluorooctanoic acid solution with a known concentration as a standard water sample; (2) converting part of the perfluorooctanoic acid into fluoride ions by treatment; (3) Determine the fluoride ion concentration in the treated solution; (4) With the concentration of perfluorooctanoic acid as the horizontal axis and the concentration of fluoride ions as the vertical axis, draw a working curve of "perfluorooctanoic acid concentration-fluoride ion concentration"; (5) Treat the water sample to be tested according to steps (2)-(3), and substitute the fluoride ion concentration obtained by the test into the working curve of step (4) to calculate the perfluorooctanoic acid concentration in the water sample to be tested.

2. The method for rapid and low-cost detection of perfluorooctanoic acid concentration in water samples according to claim 1, characterized in that: The standard water sample prepared in step (1) contains the same concentration of interfering substances as that of the water sample to be tested.

3. The method for rapid and low-cost detection of perfluorooctanoic acid concentration in water samples according to claim 1, characterized in that: The concentration of the perfluorooctanoic acid solution in step (1) is ≤100 μmol / L.

4. The method for rapid and low-cost detection of perfluorooctanoic acid concentration in water samples according to claim 1, characterized in that: The treatment method of step (2) is as follows: pouring the perfluorooctanoic acid solution into a reaction tube, adjusting the pH of the solution, and adding sulfite; passing an inert gas into the solution to deoxygenate, then sealing the reaction tube and irradiating it under a 185nm ultraviolet lamp.

5. A method for rapid and low-cost detection of perfluorooctanoic acid concentration in water samples according to claim 4, characterized in that: The sulfite is added so that the concentration of the sulfite is 5-40 mmol / L.

6. The method for rapid and low-cost detection of perfluorooctanoic acid concentration in water samples according to claim 4, characterized in that: The pH is 10-13, and the alkali used to adjust the pH includes but is not limited to sodium hydroxide or potassium hydroxide.

7. A method for rapid and low-cost detection of perfluorooctanoic acid concentration in water samples according to claim 4, characterized in that: The sulfite includes, but is not limited to, sodium sulfite or potassium sulfite.

8. The method for rapid and low-cost detection of perfluorooctanoic acid concentration in water samples according to claim 4, characterized in that: The irradiation time is not less than 20 min.

9. The method for rapid and low-cost detection of perfluorooctanoic acid concentration in water samples according to claim 1, characterized in that: The concentration of perfluorooctanoic acid in the water sample to be tested in step (5) is ≤100 μmol / L.

10. The method for rapid and low-cost detection of perfluorooctanoic acid concentration in water samples according to claim 1, characterized in that: The water samples to be tested in step (5) include but are not limited to pure water, surface water, groundwater, tap water, and water samples containing various ions and / or organic compounds.

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