Method for detecting environmentally persistent free radicals in a body of water

Abstract

The application discloses a kind of detection methods of environmental persistent free radicals in tire wear particle aqueous solution, including centrifugal treatment to tire wear particle aqueous solution, and the solid and supernatant are obtained after solid-liquid separation;The obtained solid is dispersed in organic dispersant, and the solution after dispersion is vacuum dried, and the measured solid particles are obtained;The supernatant obtained after centrifugation is first extracted by solid-phase extraction with organic solvent, and the extract is concentrated by high-throughput parallel vacuum concentrator, and the concentrated solution is vacuum deoxygenated to obtain the measured solution;The content of environmental persistent free radicals in the obtained measured solid particles and the obtained measured solution is determined by electron spin resonance spectrometer.The method of the present application can accurately determine the content of tire wear particles and environmental persistent free radicals in water, with high detection accuracy and good sample recovery rate.

Description

Technical Field

[0001] This invention relates to a method for detecting persistent environmental free radicals in water, belonging to the field of detection and analysis of new pollutants in complex environmental samples. Background Technology

[0002] Persistent environmental free radicals (PARs) are a class of novel pollutants with long half-lives and stable existence. They can induce reactive oxygen species (ROS) in the environment, promoting oxidative stress and causing oxidative damage, posing a significant threat to biological health and environmental safety. Currently, PARs have been detected in solid particles such as plastics, atmospheric particulate matter, wood, combustion particulate matter, and biochar. Tire abrasion particles, generated from the friction between motor vehicle or non-motor vehicle tires and the road surface, are characterized by small particle size, high yield, and wide distribution. The environmental pollution and hazards they cause are significant. While some researchers have detected PARs on tire abrasion particles, most of these particles eventually enter the aquatic environment through road runoff. ROS are also more easily detected and transformed in water, but the threat of PARs in the aquatic environment where these particulate pollutants reside has not been investigated. Traditional PAR detection methods only target solid particles, and their pretreatment methods are direct drying, which can cause particle aggregation, affecting particle size and reducing the accuracy of PAR detection. Furthermore, there are currently almost no methods for detecting the content of persistent environmental free radicals (PFRs) in aqueous solutions of tire wear particles. There are also no well-defined methods for extracting and detecting PFRs in water. Direct detection of PFRs in aqueous solutions is susceptible to interference from the highly polar water and oxygen in the water. PFRs in water present challenges in extraction and detection due to numerous interfering factors compared to those on particles. Therefore, given the current lack of methods for testing the content of PFRs generated by tire wear particles in water, there is an urgent need to develop a separation and detection method for PFRs that offers good extraction efficiency and is easy to operate. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a method for the separation and detection of persistent environmental free radicals in water. After centrifugation of the water, an organic dispersant is added to the solid for pre-drying treatment, effectively preventing particle aggregation during subsequent drying and ensuring the true particle size of the sample as much as possible. The separated solution is first extracted with a mixed solution of isopropanol and n-hexane, and the extract is then concentrated and deoxygenated under vacuum. Electron spin resonance spectroscopy is used to detect both particles and the solution, achieving high detection rates and good sample recovery rates. This method is simple to operate, efficient, and widely applicable to the separation and detection of persistent environmental free radicals in water.

[0004] To achieve the above objectives, the present invention provides a method for detecting persistent environmental free radicals in water, the method comprising the following steps:

[0005] (1) Centrifugation: The water body is centrifuged to separate the solid and liquid and obtain solid and liquid.

[0006] (2) Preparation of solid particles: The solid in step (1) is dispersed in an organic dispersant, and the dispersed solution is vacuum dried to obtain solid particles.

[0007] (3) Processing of the test solution: The liquid obtained in step (1) is first extracted with an organic solvent. The extract is then concentrated by a high-throughput parallel vacuum concentrator. The concentrate is then deoxygenated under vacuum to obtain the test solution.

[0008] (4) Environmental persistent free radical content test: The content of environmental persistent free radicals in the solid particles obtained in step (2) and the test solution obtained in step (3) was determined using an electron spin resonance spectrometer.

[0009] In this invention, the water is first centrifuged to separate the liquid and solid components. The resulting solid particles are then dispersed in an organic dispersant to ensure uniform dispersion. After dispersion, the water is vacuum-dried to prevent particle aggregation during direct drying, thus increasing detection accuracy. The separated liquid is first extracted with an organic solvent, primarily to extract persistent environmental free radicals. This liquid is then vacuum-concentrated to obtain a test solution with a high concentration of persistent environmental free radicals. Vacuum deoxygenation removes oxygen from the water, reducing interference with the test signal.

[0010] In one embodiment of the present invention, the water body is selected from one of the water samples such as surface water, soil water, and groundwater.

[0011] In one embodiment of the present invention, the centrifugation speed is 3000-5000 r / min, preferably 4000 r / min, and the time is 10-20 min, preferably 15 min.

[0012] In one embodiment of the present invention, in step (1), the solid after centrifugation is first filtered by standing with filter paper with a pore size of 3 μm until the moisture content is <40%.

[0013] In one embodiment of the present invention, in step (2), the solid particles are tire wear particles with a particle size of less than 150 μm.

[0014] In one embodiment of the present invention, in step (2), the organic dispersant is a mixture of zinc stearate and microcrystalline wax.

[0015] In one embodiment of the present invention, in step (2), the mass ratio of zinc stearate to microcrystalline wax in the organic dispersant is 1:2 to 2:1, preferably 1:1.

[0016] In one embodiment of the present invention, in step (2), the amount of organic dispersant added is 0.01 to 0.03 mL / mg, preferably 0.01 mL / mg.

[0017] In one embodiment of the present invention, the preparation step of the organic dispersant includes: using pre-cooled xylene solvent to fully dissolve zinc stearate and microcrystalline wax to prepare an organic dispersant.

[0018] In one embodiment of the present invention, in step (2), the vacuum degree during vacuum drying is -0.07 to -0.09 MPa, preferably -0.085 MPa; the drying time is 3h to 5h, preferably 4h.

[0019] In one embodiment of the present invention, in step (3), the organic solvent is a mixture of isopropanol and n-hexane.

[0020] In one embodiment of the present invention, in step (3), the mass ratio of isopropanol to n-hexane is 3:1 to 2:2, preferably 2:1.

[0021] In one embodiment of the present invention, in step (3), the volume of the concentrated solution is 3% to 8% of the volume of the solution before concentration, preferably 5%.

[0022] In one embodiment of the present invention, in step (3), the vacuum deoxygenation process is as follows: after the liquid in the sealed reaction flask has been completely cooled, the gas in the reaction flask is extracted for 2-3 minutes using a diaphragm vacuum pump. The concentrate needs to be placed in a liquid nitrogen tank first, and the solution is immersed in liquid nitrogen to be completely cooled before vacuuming. Then it is taken out to thaw, and this step is repeated 2-3 times.

[0023] In one embodiment of the present invention, the environmentally persistent free radical includes at least one of the following: aromatic free radicals centered on carbon atoms, semiquinone free radicals centered on oxygen atoms, and carbon-centered free radicals with oxygen-containing functional groups near lone electrons.

[0024] Environmental persistent free radicals can be classified into three categories based on the electron paramagnetic resonance spectroscopy parameter factor g. Free radicals with g < 2.0030 are carbon-centered free radicals, including cyclopentadienyl radicals, aromatic radicals, anthrone radicals, etc. Free radicals with g > 2.0040 are oxygen-centered free radicals, including semiquinone radicals and quinone radicals, etc. There are two types of free radicals with 2.0030 < g < 2.0040. One is a mixture of carbon-centered free radicals and oxygen-centered free radicals, and the other is a carbon-centered free radical with oxygen-containing functional groups near the unpaired electron.

[0025] In one embodiment of the present invention, in step (4), when measuring the content of environmental persistent free radicals in the test solution obtained in step (3), 20 μL of the test solution is aspirated with a capillary tube, and the other end is sealed with grease. The lower end is slowly placed in a nuclear magnetic resonance tube without leakage, and the nuclear magnetic resonance tube is immediately inserted into the instrument cavity for measurement.

[0026] In one embodiment of the present invention, in step (4), the working conditions of the electron spin resonance spectrometer are: modulation frequency is 1.0 G, scanning width is 100 G, time constant is 0.01 ms, scanning time is 30.0 s, and scanning times are 3 times.

[0027] In one embodiment of the present invention, the method comprises the following steps:

[0028] (1) Water sample pretreatment: The taken water body is placed in a centrifugal device and centrifuged at a speed of 4000 r / min for 15 min. After standing for separation, the supernatant is left for treatment. The lower-layer solid is first statically filtered through a 3-μm quantitative filter paper until the water content < 40%;

[0029] (2) Preparation of solid particles: Zinc stearate and microcrystalline wax are fully dissolved in a pre-cooled xylene solvent to prepare an organic dispersant. The organic dispersant is dropped into the wet solid particles and mixed evenly. After standing for 1 h, it is placed in a vacuum drying oven at 35 °C and dried thoroughly for 4 h to obtain solid particles. The addition amount of the organic dispersant is 0.01 - 0.03 mL / mg, preferably 0.01 mL / mg;

[0030] (3) Treatment of the test solution: The supernatant after static separation in step (1) is subjected to solid-phase extraction using an organic solvent (isopropanol: n-hexane = 2:1). The extraction column is first activated with 5 mL of isopropanol and 5 mL of deionized water at a flow rate of 2 mL / min. The solution is injected at a flow rate of 5 mL / min. After the injection is completed, 4 mL of isopropanol and 6 mL of organic solvent (isopropanol: n-hexane = 2:1) are used to elute sequentially at a flow rate of 2 mL / min. The eluent is placed in a high-throughput parallel vacuum concentrator for concentration. The volume of the concentrated solution is 5% of the volume before concentration. The concentrated solution is brought to a final volume with n-hexane and placed in a liquid nitrogen tank. After the solution is completely cooled, a vacuum is drawn, and then the solution is taken out and thawed. This step is repeated 2-3 times.

[0031] (4) Environmental persistent free radical content test: The solid particles dried in step (2) are slowly placed into the NMR tube and finally inserted into the cavity of the ESR instrument for measurement; 20 μL of the solution after vacuum deoxygenation in step (3) is drawn with a capillary tube and the other end is sealed with grease. The lower end is slowly placed into the NMR tube and no leakage is allowed. The NMR tube is immediately inserted into the cavity of the instrument for measurement. The working conditions of the electron spin resonance spectrometer are: modulation frequency of 1.0 G, scanning width of 100 G, time constant of 0.01 ms, scanning time of 30.0 s, and scanning times of 3.

[0032] The beneficial effects of this invention are:

[0033] 1. The method of this invention can be used to determine persistent environmental free radicals in water, with good accuracy and high recovery rate of solid and liquid samples separated from water.

[0034] 2. This invention utilizes zinc stearate and microcrystalline wax to prepare an organic dispersant, which is added to solid particles for pre-drying treatment. This effectively avoids particle aggregation during subsequent drying, ensures the true particle size, and improves the detection accuracy of persistent environmental free radical content in solid particles.

[0035] 3. This invention utilizes a mixture of isopropanol and n-hexane as an organic solvent for solid-phase extraction of the solution. The extract is then concentrated and deoxygenated under vacuum, and the results are determined using an electron spin resonance spectrometer. This method has a high detection rate and good sample spike recovery rate. Attached Figure Description

[0036] Figure 1 This is a flowchart of the method for detecting persistent environmental free radicals in an aqueous solution of tire wear particles in Example 1;

[0037] Figure 2 The graph shows the concentration of persistent free radicals and the spiked recovery rate of tire wear particles under the working conditions of the dispersant in Example 2.

[0038] Figure 3 The graph shows the concentration of persistent environmental free radicals and the spiked recovery rate in the supernatant of tire wear particles in Example 3.

[0039] Figure 4 This is a comparison chart of the concentrations of persistent environmental free radicals detected after solid-phase extraction of the supernatant of tire wear particles using different organic solvents in Example 4.

[0040] Figure 5 This is a graph showing the concentration of persistent environmental free radicals detected after solid-phase extraction of the supernatant of tire wear particles using mixtures of different proportions of isopropanol and n-hexane in Example 5.

[0041] Figure 6 This is a graph showing the environmental persistence concentration of the tire wear particle supernatant after different treatment processes, as shown in Example 6.

[0042] Figure 7 This is a graph showing the concentration of persistent environmental free radicals and the spiked recovery rate after dispersing tire wear particles using different organic dispersants, as shown in Example 7.

[0043] Figure 8 The graph shows the concentration of persistent environmental free radicals and the spiked recovery rate of tire wear particles when no organic dispersant was used, as shown in Comparative Example 1. Detailed Implementation

[0044] The method described in this invention will be further illustrated below through specific embodiments.

[0045] This invention provides a method for detecting persistent environmental free radicals in water, which can be used to separate, extract, and quantitatively analyze the content of persistent environmental free radicals in particles containing persistent environmental free radicals and their solutions. The following instruments and reagents are used:

[0046] Instruments: Grinding mill (Hettich Hardware Accessories Co., Ltd.), centrifuge (Eppendorf), ultrapure water system (ELGALabWater, UK), electronic balance (Mettler Toledo, Switzerland), vacuum drying oven (Shanghai Boxun Industrial Co., Ltd.), fully automated solid phase extraction system (AutoSPE-06D, Reeko), high-throughput parallel vacuum concentrator (FSE 1100, Reeko), vacuum diaphragm pump (GEMINI), electron spin resonance spectrometer (Bruck GmbH, Germany).

[0047] Reagents: Ultrapure water, deionized water, n-hexane, isopropanol, acetone and dichloromethane were all chromatographic grade, dimethyl sulfoxide and ethanol were analytical grade, zinc stearate (99%), microcrystalline wax (99.9%), xylene (99.9%), 2,2-biphenyl-1-picrylhydrazyl (>96%).

[0048] The water used in this embodiment is an aqueous solution containing tire wear particles. The method for preparing the aqueous solution containing tire wear particles includes the following steps:

[0049] (1) Preparation of tire wear particles: The collected tires were cleaned with anhydrous ethanol and ultrapure water and then cut into fragments smaller than 1×1cm. The fragments were frozen with liquid nitrogen and then ground into fine particles with a small grinder. After continuous grinding and sieving, tire wear particle samples with a particle size of <150μm were prepared.

[0050] (2) Preparation of the aqueous solution of tire wear particles: Weigh 1.0g of tire wear particles using an electronic balance, soak them in an Erlenmeyer flask containing 100mL of ultrapure water, and mechanically stir at 2000r / min for 24h to prepare the aqueous solution of tire wear particles.

[0051] Example 1: Detection of environmentally persistent free radicals in aqueous solution of tire wear particles

[0052] A method for detecting persistent environmental free radicals in an aqueous solution of tire wear particles, comprising the following steps:

[0053] (1) Water sample pretreatment: Take 100 mL of the water solution of tire wear particles and put it into a 100 mL glass centrifuge tube. Centrifuge at 4000 r / min at room temperature for 15 min. After centrifugation, take it out and let it stand for 10 min. After the solution is separated into layers, slowly pour out all the supernatant into the centrifuge tube for further processing. The lower solid layer is filtered by using filter paper with a pore size of 3 μm. After the water content of the solid particles is <40%, put it into a beaker for further processing. The filtered solution is also poured into the centrifuge tube containing the supernatant.

[0054] (2) Preparation of solid particles: Weigh 0.5g of zinc stearate and 0.5g of microcrystalline wax into a 25mL beaker, add 10mL of xylene solvent pre-cooled at 4℃ to dissolve them to prepare an organic dispersant, weigh 1g of solid sample with a water content of <40% after centrifugation and filtration in step (1), add 10mL of dispersant to it and stir thoroughly. After the particles and organic dispersant are mixed evenly and allowed to stand for 1h, put the dispersed solid particles into a vacuum drying oven at 35℃ and dry for 2h to obtain the solid particles to be tested.

[0055] (3) Treatment of the test solution: The 100 mL supernatant from step (1) was subjected to solid-phase extraction using an organic solvent (isopropanol: n-hexane = 2:1). The extraction column was first activated with 5 mL of isopropanol and 5 mL of deionized water at a flow rate of 2 mL / min. The test solution was injected at a flow rate of 5 mL / min. After the injection was completed, 4 mL of isopropanol and 6 mL of organic solvent (isopropanol: n-hexane = 2:1) were used to elute the solution at a flow rate of 2 mL / min. After the elution was completed, 10 mL of the extract was placed in a high-throughput parallel vacuum concentrator for concentration. The volume of the concentrated solution was 5% of the volume before concentration. The concentrated solution was brought to a final volume of 1 mL with n-hexane and placed in a liquid nitrogen tank. After the solution was completely cooled, a vacuum was drawn, and the solution was taken out and thawed. This step was repeated 2-3 times.

[0056] (4) Environmental persistent free radical content test: The solid particles dried in step (2) are slowly placed into the NMR tube and inserted into the cavity of the ESR instrument for measurement; 20 μL of the solution after vacuum deoxygenation in step (3) is drawn with a capillary tube and the other end is sealed with grease. The lower end is slowly placed into the NMR tube and no leakage is allowed. The NMR tube is immediately inserted into the cavity of the instrument for measurement. The working conditions of the electron spin resonance spectrometer are: modulation frequency of 1.0 G, scanning width of 100 G, time constant of 0.01 ms, scanning time of 30.0 s, and scanning times of 3.

[0057] The final measured content of persistent environmental free radicals in the solid particles was 1.65 × 10⁻⁶. 17 The concentration of persistent environmental free radicals in the test solution was 1.39 × 10⁻⁶ spins / g. 17 The total environmentally persistent free radical content in the aqueous solution of tire wear particles was 3.04 × 10⁻⁶ spins / g. 17 spins / g.

[0058] Example 2: Accuracy assessment of the content of environmentally persistent free radicals in solid particles

[0059] The determination of the content of persistent environmental free radicals in solid particles in an aqueous solution of tire wear particles includes the following steps:

[0060] (1) Water sample pretreatment: Take 100ml of tire wear particle aqueous solution and put it into a 100ml glass centrifuge tube. Centrifuge at 4000r / min at room temperature for 15min. After centrifugation, take it out and let it stand for 10min. After the solution is separated into layers, slowly pour out all the supernatant into the centrifuge tube for further processing. The lower solid layer is filtered by using filter paper with a pore size of 3μm. After the water content of the solid particles is <40%, put it into a beaker for further processing. After filtration, the solution is also poured into the centrifuge tube containing the supernatant.

[0061] (2) Preparation of solid particles: Weigh 0.5g of zinc stearate and 0.5g of microcrystalline wax into a 25mL beaker, add 10mL of xylene solvent pre-cooled at 4℃ to dissolve them to prepare an organic dispersant, weigh 1g of solid sample with a water content of <40% after centrifugation and filtration in step (1), add 10mL of organic dispersant to it, and stir thoroughly. After the particles and organic dispersant are mixed evenly and allowed to stand for 1h, put the dispersed solid particles into a vacuum drying oven at 35℃ and dry for 2h to obtain the solid particles to be tested.

[0062] (3) Determination of the content of environmental persistent free radicals in solid particles: 50 mg of the solid particles dried in step (2) were slowly placed into a nuclear magnetic resonance tube with an inner diameter of 4 mm. The nuclear magnetic resonance tube was gently shaken until there were no obvious gaps between the particles and the sample height was about 1 cm. The nuclear magnetic resonance tube was inserted into the cavity of the ESR instrument and measured using an electron spin resonance spectrometer. The working conditions of the electron spin resonance spectrometer were: modulation frequency of 1.0 G, center field of 3504.3 G, microwave power of 0.5 mW, scanning width of 100 G, time constant of 0.01 ms, scanning time of 30.0 s, and scanning times of 3 times.

[0063] The content of persistent environmental free radicals in the solid particles was determined to be 1.65 × 10⁻⁶. 17 The spins / g, i.e., the measured value of the sample, is 1.65 × 10⁻⁶. 17 spins / g.

[0064] The determination of the content of solid particles in the spiked solution includes the following steps:

[0065] (1) Preparation of spiking solution: Weigh 10 mg of 2,2-biphenyl-1-picrylhydrazine and dissolve it in 10 mL of dimethyl sulfoxide to prepare a 1 mg / mL free radical standard; take 100 mL of tire wear particle aqueous solution and add 100 μL of free radical standard to it to obtain the spiking solution;

[0066] (2) The solid particles to be tested in the spiked solution were prepared according to the methods of steps (1) and (2) in Example 1, and the content of environmental persistent free radicals in the solid particles to be tested in the spiked solution was determined according to the method of step (4), and named as the spiked sample test value.

[0067] The formula for calculating the spiked recovery rate is:

[0068] (Spiked sample test value - Sample test value) ÷ Spiked amount × 100%

[0069] 2,2-Biphenyl-1-picrylhydrazine is a stable free radical and can be used as a standard for detecting persistent environmental free radicals using electron spin resonance spectroscopy. In this embodiment, the milligram concentration of 2,2-biphenyl-1-picrylhydrazine is 15.3 × 10⁻⁶. 17 Based on the calculation, the content of the 2,2-biphenyl-1-picrylhydrazine standard substance added in this example is 1.53 × 10⁻⁶ mg / spins. 17 spins, i.e., the added scalar is 1.53 × 10⁻⁶. 17 The actual measured concentration of persistent environmental free radicals in the spiked solution was 3.14 × 10¹⁷ spins / g, and the calculated recovery rate was 97.39%. Test results are shown below. Figure 2 .

[0070] Therefore, the method of the present invention can accurately determine the content of persistent environmental free radicals in solid particles.

[0071] Example 3: Accuracy assessment of the content of persistent environmental free radicals in the supernatant

[0072] A method for testing the content of persistent environmental free radicals in supernatant includes the following steps:

[0073] (1) Water sample pretreatment: The aqueous solution of tire wear particles was centrifuged according to the method in step (1) of Example 1 to obtain all the supernatant;

[0074] (2) Treatment of the test solution: Solid-phase extraction was performed on all the supernatant obtained in step (1) using a mixture of 6 mL isopropanol and n-hexane. During extraction, the extraction column was first activated with a mixture of 5 mL isopropanol and n-hexane, and then activated with 5 mL deionized water. The flow rates of both the organic solvent and deionized water during activation were 2 mL / min. The test solution was injected at a flow rate of 5 mL / min. After injection, 4 mL isopropanol was used for the first elution, and then 6 mL isopropanol and n-hexane was used for the second elution. The flow rate of the organic solvent during both the first and second elutions was 2 mL / min. After elution, the test solution was subjected to vacuum concentration and deoxygenation treatment sequentially according to the method in Example 1. The volume ratio of isopropanol to n-hexane in the mixture of isopropanol and n-hexane was 2:1.

[0075] (3) Test of environmental persistent free radical content: Take 20 μL of the solution after vacuum deoxygenation in step (2) with a capillary tube, and seal the other end with grease. Slowly place the lower end into the NMR tube without leakage. Immediately insert the NMR tube into the instrument cavity for measurement. The working conditions of the electron spin resonance spectrometer are: modulation frequency of 1.0 G, scanning width of 100 G, time constant of 0.01 ms, scanning time of 30.0 s, and scanning times of 3.

[0076] The concentration of persistent environmental free radicals in the supernatant was measured to be 1.39 × 10⁻⁶. 17 The spins / g, i.e., the measured value of the sample, is 1.39 × 10⁻⁶. 17 spins / g.

[0077] A method for testing the content of persistent environmental free radicals in a spiked solution includes the following steps:

[0078] (1) Preparation of spiking solution: Weigh 10 mg of 2,2-biphenyl-1-picrylhydrazine and dissolve it in 10 mL of dimethyl sulfoxide to prepare a 1 mg / mL free radical standard; take 100 mL of tire wear particle aqueous solution and add 100 μL of free radical standard to it to obtain the spiking solution;

[0079] (2) The test solution in the spiked solution was prepared according to the methods of steps (1) and (2) in Example 3, and the content of persistent free radicals in the test solution in the spiked solution was determined according to the method of step (3) in Example 3, and named as the spiked sample test value.

[0080] The formula for calculating the spiked recovery rate is: (Spiked sample value - Sample value) ÷ Spiked amount × 100%

[0081] 2,2-Biphenyl-1-picrylhydrazine is a stable free radical and can be used as a standard for detecting persistent environmental free radicals using electron spin resonance spectroscopy. In this embodiment, the concentration of the 2,2-biphenyl-1-picrylhydrazine free radical is 15.3 × 10⁻⁶. 17 Based on the calculation, the content of the 2,2-biphenyl-1-picrylhydrazine standard substance added in this example is 1.53 × 10⁻⁶ mg / spins. 17 spins, i.e., the added scalar is 1.53 × 10⁻⁶. 17 Spins; however, the actual measured content of persistent environmental free radicals in the supernatant of the spiked solution was 2.87 × 10⁻⁶. 17 The calculated recoveries were 96.73% (spins / g). See the test results below. Figure 3 .

[0082] Therefore, the method of the present invention can accurately determine the content of persistent environmental free radicals in the supernatant.

[0083] Example 4: The Influence of Organic Solvents on Test Results During Solution Solid-Phase Extraction

[0084] A method for testing the content of persistent environmental free radicals in supernatant includes the following steps:

[0085] (1) Water sample pretreatment: The aqueous solution of tire wear particles was centrifuged according to the method in step (1) of Example 1 to obtain all the supernatant;

[0086] (2) Treatment of the test solution: Solid phase extraction was performed on all the supernatant obtained in step (1) using 6 mL of a mixture of isopropanol and n-hexane, isopropanol, n-hexane, acetone and dichloromethane respectively. During extraction, the extraction column was first activated with 5 mL of a mixture of isopropanol and n-hexane, isopropanol, n-hexane, acetone, and dichloromethane, respectively. Then, 5 mL of deionized water was used to activate each of the above solutions. During activation, the flow rate of both the organic solvent and deionized water was 2 mL / min. The test solution was injected at a flow rate of 5 mL / min. After injection, a first elution was performed with 4 mL of isopropanol, isopropanol, n-hexane, acetone, and dichloromethane, respectively. A second elution was performed with 6 mL of a mixture of isopropanol and n-hexane, isopropanol, n-hexane, acetone, and dichloromethane, respectively. The flow rate of the organic solvent was 2 mL / min during both the first and second elutions. After elution, the test solution was sequentially subjected to vacuum concentration and deoxygenation treatment according to the method in Example 1. The volume ratio of isopropanol to n-hexane in the isopropanol and n-hexane mixture was 2:1.

[0087] (3) Environmental persistent free radical content test: Use a capillary tube to draw 1 cm of the solution after vacuum deoxygenation in step (2), and seal the other end with grease. Slowly place the lower end into the NMR tube without leakage. Immediately insert the NMR tube into the instrument cavity for measurement. The working conditions of the electron spin resonance spectrometer are: modulation frequency of 1.0 G, scanning width of 100 G, time constant of 0.01 ms, scanning time of 30.0 s, and scanning times of 3.

[0088] The results of the analysis of persistent environmental free radical content in the test solution after extraction with different organic solvents are shown below. Figure 4 ,from Figure 4 It can be seen that when using a mixture of isopropanol and n-hexane for extraction, the measured content of persistent environmental free radicals is higher, and the test is more accurate.

[0089] Example 5: Effect of the ratio of isopropanol to n-hexane in the organic solvent on the test results during solution solid-phase extraction.

[0090] The difference between Example 5 and Example 4 is that, during extraction, the organic solvent in step (2) is a mixed solution of isopropanol and n-hexane, wherein the volume ratios of isopropanol and n-hexane are 2:1, 1:1, 3:1, and 1:2, respectively. The extraction column is first activated sequentially with 5 mL of isopropanol and 5 mL of deionized water at a flow rate of 2 mL / min. The test solution is then injected at a flow rate of 5 mL / min. After the injection is completed, elution is performed sequentially with 4 mL of isopropanol and 6 mL of a mixed solution of isopropanol and n-hexane at a flow rate of 2 mL / min.

[0091] The results of the analysis of persistent environmental free radical content in the test solution after extraction with different organic solvents are shown below. Figure 5 ,from Figure 5 It can be seen that when using a mixture of isopropanol and n-hexane for extraction, the measured content of persistent environmental free radicals is higher and the test is more accurate when the volume ratio of isopropanol to n-hexane is 2:1.

[0092] Example 6: The Influence of the Treatment Process on the Test Results

[0093] A method for testing the content of persistent environmental free radicals in supernatant includes the following steps:

[0094] (1) Water sample pretreatment:

[0095] The spiked solution was prepared according to the steps of the spiked solution preparation in Example 2, and centrifuged according to the method of step (1) in Example 1 to obtain all the supernatant;

[0096] (2) Treatment of the test solution: Take 5 portions of the supernatant of the spiked solution, treat them according to the method in step (3) of Example 1, and then determine the content of environmental persistent free radicals in the test solution according to the test method in step (4) of Example 1.

[0097] Positive label: First, perform solid-phase extraction with organic solvents, then vacuum concentration and vacuum deoxygenation.

[0098] Concentration and standard removal: Direct vacuum concentration and vacuum deoxygenation treatment;

[0099] Solid-phase extraction with organic solvents is performed first, followed by direct vacuum deoxygenation.

[0100] Solid concentration standard: Organic solvent solid phase extraction followed by vacuum concentration, without deoxygenation;

[0101] Solid-phase extraction with organic solvents: The test results are as follows. Figure 6 As shown in the data, it is clear that the highest concentration of persistent environmental free radicals (PFRs) in the spiked solution after processing using all procedures of this invention was 2.87 × 10⁻⁶. 17The spiked solution with the highest spins / g showed the best recovery rate, reaching 96.73%. The spiked solution that only underwent concentration and deoxygenation processes had the lowest measured content and the worst recovery rate, indicating that effective extraction of the solution is an important step in obtaining detection results, while vacuum concentration and vacuum deoxygenation are also important factors affecting the detection results.

[0102] Example 7: Effect of Organic Dispersants on the Accuracy of Free Radical Content Test in Solid Particles

[0103] The determination of the environmental persistent free radical content in an aqueous solution of tire wear particles after treatment with different organic dispersants includes the following steps:

[0104] (1) Water sample pretreatment: Take 100ml of tire wear particle aqueous solution and put it into a 100ml glass centrifuge tube. Centrifuge at 4000r / min at room temperature for 15min. After centrifugation, take it out and let it stand for 10min. After the solution is separated into layers, slowly pour out all the supernatant into the centrifuge tube for further processing. The lower solid layer is filtered by using filter paper with a pore size of 3μm. After the water content of the solid particles is <40%, put it into a beaker for further processing. After filtration, the solution is also poured into the centrifuge tube containing the supernatant.

[0105] (2) Preparation of solid particles and dispersants: Weigh 0.5g of zinc stearate and 0.5g of microcrystalline wax into a 25mL beaker, add 10mL of xylene solvent pre-cooled at 4℃ to dissolve them to prepare organic dispersant 1. Weigh 1g of 4 solid samples with a water content of <40% after centrifugation and filtration in step (1), add 10mL of organic dispersant 1, 10mL of organic dispersant (barium stearate), 10mL of organic dispersant 3 (zinc stearate) and 10mL of organic dispersant 4 (microcrystalline wax) to each sample, and stir thoroughly. After the particles and organic dispersants are mixed evenly and allowed to stand for 1h, place the dispersed solid particles in a vacuum drying oven at 35℃ and dry for 2h to obtain the solid particles to be tested.

[0106] (3) Determination of the content of environmental persistent free radicals in solid particles: 50 mg of the solid particles dried in step (2) were slowly placed into a nuclear magnetic resonance tube with an inner diameter of 4 mm. The nuclear magnetic resonance tube was gently shaken until there were no obvious gaps between the particles and the sample height was about 1 cm. The nuclear magnetic resonance tube was inserted into the cavity of the ESR instrument and measured using an electron spin resonance spectrometer. The working conditions of the electron spin resonance spectrometer were: modulation frequency of 1.0 G, center field of 3504.3 G, microwave power of 0.5 mW, scanning width of 100 G, time constant of 0.01 ms, scanning time of 30.0 s, and scanning times of 3 times.

[0107] The measurement results are as follows Figure 7As shown, compared with the other three organic dispersants, the solid particles treated with organic dispersant 1 had the highest content of persistent environmental free radicals, at 1.65 × 10⁻⁶. 17 The spins / g indicates that the dispersant has a significant impact on the detection effect of particles.

[0108] Comparative Example 1: Solid particles without organic dispersant

[0109] The difference between Comparative Example 1 and Example 2 is that neither the preparation steps of the solid particles in the aqueous solution and the spiked solution of tire wear particles included a dispersion treatment step using an organic dispersant.

[0110] The results of the determination of solid particles in Comparative Example 1 are as follows: Figure 8 As shown, the content of persistent environmental free radicals in the solid particles of the aqueous solution and the spiked solution of tire wear particles was 1.28 × 10⁻⁶. 17 spins / g and 2.32×10 17 The spiked recoveries were 67.97% (spins / g). Compared to the solid particles using an organic dispersant in Example 1, this sample showed a lower spiked recoveries, indicating that the organic dispersant used in this invention has better detection performance.

Claims

1. A method for detecting persistent environmental free radicals in water, characterized in that, Includes the following steps: (1) Centrifugation: The water body is centrifuged to separate the solid and liquid and obtain solid and supernatant; (2) Preparation of solid particles: The solid in step (1) is dispersed in an organic dispersant, and the dispersed solution is vacuum dried to obtain the solid particles to be tested. (3) Treatment of the test solution: The supernatant obtained in step (1) is first extracted with an organic solvent. The extract is concentrated by a high-throughput parallel vacuum concentrator and then deoxygenated under vacuum to obtain the test solution. (4) Environmental persistent free radical content test: The content of environmental persistent free radicals in the solid particles to be tested obtained in step (2) and the solution to be tested obtained in step (3) was determined using an electron spin resonance spectrometer.

2. The detection method according to claim 1, characterized in that, In step (1), the rotation speed during centrifugation is 3000-5000 r / min and the time is 10-20 min.

3. The detection method according to claim 1, characterized in that, In step (1), the solid after centrifugation is first filtered by standing with qualitative filter paper with a pore size of 3 μm until the moisture content is <40%.

4. The detection method according to claim 1, characterized in that, In step (2), the solid particles include tire wear particles, and the organic dispersant is a mixture of zinc stearate and microcrystalline wax, wherein the mass ratio of zinc stearate to microcrystalline wax is 1:2 to 2:

1.

5. The detection method according to claim 1, characterized in that, In step (2), the amount of organic dispersant added is 0.01 to 0.03 mL / mg solid.

6. The detection method according to claim 1, characterized in that, In step (3), the organic solvent is a mixture of isopropanol and n-hexane, and the mass ratio of isopropanol to n-hexane is 3:1 to 2:

2.

7. The detection method according to claim 1, characterized in that, The environmentally persistent free radicals include at least one of the following: carbon-centered free radicals, oxygen-centered free radicals, mixtures of carbon-centered and oxygen-centered free radicals, and carbon-centered free radicals with oxygen-containing functional groups near lone electrons.

8. The detection method according to claim 1, characterized in that, In step (4), when determining the content of persistent environmental free radicals in the test solution obtained in step (3), 1 cm of the test solution is drawn with a capillary tube, and the other end is sealed with grease. The lower end is slowly placed in the NMR tube without leakage. The NMR tube is then immediately inserted into the instrument cavity for measurement.

9. The detection method according to claim 1, characterized in that, In step (4), the operating conditions of the electron spin resonance spectrometer are: modulation frequency of 1.0G, scanning width of 100G, time constant of 0.01ms, scanning time of 30.0s, and scanning times of 3.

10. The application of the detection method according to any one of claims 1 to 9 in the detection of persistent free radicals in the environment.

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