Method for simultaneously detecting various micro-plastics in water

Abstract

The invention provides a method for simultaneously detecting various micro-plastics in water, and belongs to the technical field of micro-plastic detection. The method comprises the steps of sample pretreatment, thermal cracking-gas chromatography-mass spectrometer measurement, qualitative analysis and quantitative analysis. The method comprises the following steps: taking a water sample, uniformly shaking, filtering with a filter membrane, taking the filtered filter membrane, adding acetone, carrying out ultrasonic elution, washing the filter membrane, and collecting an eluent; adding acetone into the eluted filter membrane, carrying out ultrasonic elution again, washing the filter membrane, collecting the eluent, combining the two eluents, heating and concentrating in a water bath, adding acetone, ultrasonically mixing, transferring into a cracking cup, heating and volatilizing, and determining by a thermal cracking-gas chromatography-mass spectrometer. Carrying out qualitative analysis through analysis of cracking products with different types of micro-plastic characteristics, and then carrying out quantification through an external standard method; the method provided by the invention can accurately quantify the six microplastics in the effluent, and has the advantages of simple pretreatment, small sampling amount, high accuracy and lowest detection limit of 0.012 [mu] g / L.

Description

Technical Field

[0001] The invention relates to a method for simultaneously detecting multiple microplastics in water, belonging to the technical field of microplastic determination. Background Art

[0002] Microplastics refer to plastic particles with a diameter of less than 5 mm, which have a relatively long life in the environment and are difficult to degrade. At present, my country has not yet issued a special national standard for the quantitative detection of microplastics. The quantitative analysis reported in domestic and foreign literature mainly relies on thermal analysis and mass spectrometry, namely pyrolysis-gas chromatography-mass spectrometry (PY-GCMS) and thermal desorption-gas chromatography-mass spectrometry (ATD-GCMS), to achieve quantitative analysis of microplastics in water.

[0003] Since microplastics have a large specific surface area and will absorb organic matter in the water, pretreatment is required for detection. Most methods use digestion to remove other impurities. The digestion methods mainly include acid digestion, alkaline digestion, oxidative digestion, enzyme digestion and UTS (urea / thiourea / sodium hydroxide) method. Among them, oxidative digestion is the most commonly used, but the digestion efficiency of simple hydrogen peroxide (H2O2) is low, so some researchers use Fenton's reagent instead of single H2O2. Studies have shown that H2O2 treatment may cause degradation and discoloration of microplastics, and whether it is acid, alkaline digestion, or oxidative digestion, it will lead to the loss of particle fluorescence and strong agglomeration of particles, which may affect the final test results.

[0004] In addition, the current pretreatment method is relatively complicated and involves more reagents, which will also affect the test results. Moreover, the current detection method can detect only a few types of microplastics in water.

[0005] Therefore, there is an urgent need to provide a method with simple pre-treatment and the ability to qualitatively and quantitatively detect more types of microplastics. Summary of the invention

[0006] The purpose of the present invention is to overcome some defects in the prior art and provide a method for simultaneously detecting multiple microplastics in water.

[0007] In order to achieve the above technical purpose, the technical solution adopted by the present invention is as follows:

[0008] The present invention first provides a method for simultaneously detecting multiple microplastics in water, and the detection method comprises the following steps:

[0009] (1) Sample pretreatment: Take a water sample and filter it with a filter membrane. After filtering, immerse the filter membrane in acetone, perform ultrasonic elution at room temperature, rinse the filter membrane with acetone, and collect the eluate; immerse the filter membrane in acetone again, perform ultrasonic elution at room temperature, rinse the filter membrane with acetone, and collect the eluate; repeat the elution several times according to the above operation, then combine the eluates and heat and concentrate them in a water bath to obtain a solid product, which is the concentrated product. Then add acetone and ultrasonically mix it, transfer it to a cracking cup, and heat and evaporate it to obtain the water sample to be tested after pretreatment;

[0010] Wherein, the filter membrane in step (1) comprises a glass fiber filter membrane and a stainless steel filter membrane, preferably a stainless steel filter membrane; the number of elutions is not less than 2 times, preferably 2 times; the time of ultrasonic elution is not less than 30 minutes, preferably 30 minutes.

[0011] In the above pretreatment process, the filter membrane is immersed in acetone after the first filtration and the filter membrane is immersed in acetone after the second filtration, and the volume ratio of acetone used twice and the water sample is: 5mL:4mL:2L; the volume of acetone used for washing the filter membrane is 1mL, and the amount of acetone added in the ultrasonic mixing step is 1mL.

[0012] (2) Pyrolysis-gas chromatography-mass spectrometry detection: Pyrolysis-gas chromatography-mass spectrometry is used to perform qualitative and quantitative detection on pre-treated water samples;

[0013] Among them, in the thermal pyrolysis-gas chromatography-mass spectrometry detection process: the pyrolysis temperature is 600°C, the pyrolysis time is 0.3min;

[0014] The detection used a chromatographic column SH-I-5Sil MS, and the column oven temperature program was an initial temperature of 40°C for 2 minutes, then heated to 280°C at 20°C / min and held for 10 minutes, and then heated to 320°C at 20°C / min and held for 10 minutes. The injection method was split injection with a split ratio of 10:1.

[0015] During the detection process, the carrier gas was high-purity nitrogen, the chromatographic column flow rate was 1.78 mL / min, the ionization mode was electron impact EI, the ion source temperature was 300° C., the interface temperature was 280° C., the acquisition method was full scan, and the scan range was 35-350 m / z.

[0016] (3) Qualitative analysis: Based on the results of pyrolysis-gas chromatography-mass spectrometry, the types of microplastics in the sample to be tested are determined by comparing them with the characteristic pyrolysis product standards corresponding to different microplastics;

[0017] (4) Quantitative analysis: Based on the results of pyrolysis-gas chromatography-mass spectrometry, a standard curve is established with the quantitative ion peak area of ​​microplastics as the vertical coordinate and the mass of microplastics as the horizontal coordinate to calculate the mass of microplastics in the water sample to be tested; then the content of microplastics in the water sample to be tested is calculated.

[0018] Wherein, the content of microplastics in the water sample to be tested in step (4) is calculated according to formula (1):

[0019] x=(C-C0) / V…………(1),

[0020] Where:

[0021] x——the content of microplastics in the sample, in micrograms per liter (μg / L);

[0022] C0——The mass of microplastics in the blank test (without filtering the water sample, directly testing the acetone eluate of the blank filter membrane) obtained from the standard curve, in micrograms (μg);

[0023] C——The mass of microplastics in the sample (target water sample to be tested) obtained from the standard curve, in micrograms (μg);

[0024] V is the volume of the sample, in liters (L).

[0025] In the detection described in the present invention, the microplastics include polymethyl methacrylate (PMMA), polypropylene (PP), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyethylene (PE), and polystyrene (PS), and the corresponding characteristic pyrolysis products include methyl methacrylate MMA, 2,4-dimethyl-1-heptene C9', naphthalene Nap, benzophenone BP, 1,20-octadecadiene C18', and styrene trimer SSS.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) In the method of the present invention, only acetone is used as a reagent during the pretreatment process. The background content of microplastics contained in pesticide-grade acetone is low, and acetone has a low boiling point and is volatile, which can greatly shorten the pretreatment time. The present invention further uses acetone and a stainless steel filter membrane combined with an ultrasonic elution method to pretreat the sample, which simplifies the pretreatment steps and effectively reduces the cost. The pretreatment method for water samples in the prior art requires a digestion step, which either uses high temperature or a strong oxidant, and the cost is relatively high. The reagent involved in the sample pretreatment method of the present invention is mainly acetone, and the operation is mainly ultrasonic elution. The entire treatment method is simple to operate and the cost is low, and the stainless steel filter membrane of the present invention can be recycled.

[0028] (2) The method for detecting microplastics in water provided by the present invention can realize rapid and accurate qualitative and quantitative analysis of polymethyl methacrylate (PMMA), polypropylene (PP), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyethylene (PE), and polystyrene (PS), and can simultaneously detect multiple types of microplastics, which is more than the existing technology.

[0029] (3) The detection limit of the method provided by the present invention is 0.012-0.40 μg / L, and the quantitative limit of the method is 0.039-1.32 μg / L. The method of the present invention has the characteristics of low detection limit, high sensitivity, high accuracy and high precision. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the glass filtration device involved in the embodiment and a diagram of the self-assembled device. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the technical solution of the present invention, the preferred embodiments of the present invention are described in detail below, but the following embodiments do not limit the protection scope of the present invention.

[0032] In the embodiments of the present invention, those that are not described in detail are all completed by conventional experimental methods, and those processes involved in the embodiments that are not described in detail are all understandable and easily implementable by those skilled in the art based on the product instructions or basic knowledge in the field, and therefore are not described in detail again.

[0033] In the embodiment, the acetone used is of pesticide residue grade and needs to be filtered through a glass fiber filter membrane with a pore size of 0.3 μm before use. The water used for the spiked water sample is first-grade water that complies with the provisions of GB / T 6682.

[0034] The 12 kinds of microplastics mixed standard MPs-CaCO3-L designed in the embodiment were purchased from Shimadzu Corporation of Japan. The 12 kinds of microplastics include polypropylene (PP), polyethylene (PE), polystyrene (PS), polyethylene terephthalate (PET), polyurethane (PU), polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), nylon-6 (PA6), nylon-6,6 (PA66), polycarbonate (PC), styrene-butadiene rubber (SBR), and acrylonitrile-butadiene-styrene copolymer (ABS).

[0035] Example 1: Optimization of water sample pretreatment conditions

[0036] In the present invention, a method for pre-treatment of a water sample is first provided, comprising the following steps:

[0037] Take a water sample, shake it evenly, and then filter it with a filter membrane. After filtration, immerse the filter membrane in acetone, perform ultrasonic elution at room temperature, rinse the filter membrane with acetone, and collect the eluate; immerse the filter membrane in acetone again, perform ultrasonic elution at room temperature, rinse the filter membrane with acetone, and collect the eluate; repeat the elution several times according to the above operation, then combine the eluates and heat them in a water bath to concentrate them to near dryness to obtain a concentrated product, add acetone and ultrasonically mix them, transfer them to a lysis cup, heat and evaporate them to obtain the water sample to be tested after pretreatment.

[0038] In the pre-treatment process, the filter membrane material and ultrasonic conditions are optimized for the accuracy of subsequent detection and to eliminate interference.

[0039] (1) Optimization of filter membrane material

[0040] Based on the different materials of the filter membrane, the surface smoothness and strength of the filter membrane are also different. There are many commonly used filter membranes at present, among which glass fiber filter membrane does not contain plastic, but the surface smoothness and mechanical strength are low. When ultrasonically extracting microplastics in organic solvents, the glass fiber filter membrane is very easy to fall off. The filter membranes made of polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) have good surface smoothness and high strength, but it is difficult to customize a filter membrane with a pore size of 10μm. The filter membrane made of nylon material has good surface smoothness and high strength. Although it belongs to plastic, it is not within the scope of detection of the present invention, so it can be used. The mechanical strength of stainless steel filter membrane is high and can be reused. Therefore, the present invention selects glass fiber filter membrane, nylon filter membrane and stainless steel filter membrane for comparative experiments.

[0041] Except for the different filter membrane materials, other experimental conditions remain unchanged. Three different filter membranes are used to filter spiked water samples (polystyrene PS with a particle size of 10 μm is added to Wahaha pure water). After ultrasonic extraction, the recovery rates of different experimental groups are measured by a machine (pyrolysis-gas chromatography-mass spectrometer). The measurement results are shown in Table 1. As can be seen from Table 1, the recovery rates of glass fiber filter membranes and stainless steel filter membranes both meet the requirements of 60-130%, while nylon filter membranes do not meet the requirements. Stainless steel filter membranes can be reused, and the pore size is not affected by pressure, so stainless steel filter membranes were finally selected in this experiment.

[0042] The parameters of the pyrolysis-gas chromatography-mass spectrometer are as follows:

[0043] Thermal cracking: The cracking temperature is 600℃ and the cracking time is 0.3min.

[0044] Gas chromatography: the injection port temperature was 300°C, the carrier gas was high-purity nitrogen (purity > 99.999%), the chromatographic column was SH-I-5Sil MS (purchased from Shimadzu Corporation of Japan; specifications: 30m*0.25mm*0.25μm), the chromatographic column flow rate was 1.78mL / min, and the column oven temperature program was an initial temperature of 40°C for 2min, then heated to 280°C at 20°C / min and held for 10min, then heated to 320°C at 20°C / min and held for 10min, the injection mode was split injection, and the split ratio was 10:1.

[0045] Mass spectrometry: ionization mode was electron impact EI, ionization energy was 70 eV, ion source temperature was 300°C, interface temperature was 280°C, acquisition mode was full scan (Scan), and scan range was 35-350 m / z.

[0046] Table 1. Effects of different filter membrane materials on the measurement results

[0047]

[0048] (2) Optimization of ultrasonic elution times

[0049] This example investigates the effect of the number of elutions on the elution rate of microplastics on the filter membrane surface, and evaluates it by adding a spike. The results are shown in Table 2. The sum of the peak areas of the three eluates was taken as the content of microplastics in the sample, and the elution rates of the first and first two times were evaluated. The elution rates of the second time were increased by 3.97% to 30.61% compared with the elution rate of the first time. The results show that the number of elutions of two times can meet the detection requirements.

[0050] Table 2. Effects of different ultrasound times on the measurement results

[0051]

[0052] (3) Optimization of ultrasonic elution time

[0053] This example investigates the effect of ultrasonic elution time on the elution rate of microplastics on the filter membrane surface, and adopts a spiked method for evaluation. The measurement results are shown in Table 3. When the ultrasonic elution time is less than 30 minutes, the elution rates of the six microplastics are in the range of 58.42% to 88.59%. When the ultrasonic elution time is 30 minutes, the elution rates of the six microplastics are all greater than 95%, so the ultrasonic time of 30 minutes can meet the detection requirements.

[0054] Table 3. Effects of different ultrasound times on the test results

[0055]

[0056] Through the optimization of the above conditions, in the sample pretreatment process designed in the present invention, a stainless steel filter membrane is selected for treatment, the elution times are preferably 2 times, and the elution time is preferably 30 minutes.

[0057] Example 2: Detection method of microplastics in water

[0058] This embodiment provides a method for simultaneously detecting multiple microplastics in water, which specifically includes the following steps:

[0059] (1) Pretreatment of microplastics in water

[0060] Use stainless steel tweezers to pick up a stainless steel filter membrane with a pore size of 10 μm and a diameter of 25 mm and place it in a glass filtration device (the filter membrane was purchased from Jiuding High-Tech Filtration Equipment (Beijing) Co., Ltd., and the schematic diagram of the glass filtration device is shown in the figure). Figure 1 ) on the surface of the sand core, take 2L of water sample after thorough shaking and mixing, and then transfer the stainless steel filter membrane to a custom-sized glass test tube (30mm in diameter and 100mm in length) with stainless steel tweezers. Add 5mL of acetone, ultrasonically elute at room temperature for 30min, and then rinse the filter membrane with 1mL of acetone; then add 4mL of acetone, ultrasonically elute at room temperature for 30min, and then rinse the filter membrane with 1mL of acetone; combine the two acetone eluates, heat in a water bath and concentrate until nearly dry; add 1mL of acetone, ultrasonically and vortex to mix, and then transfer all to the cracking cup, and heat at 70℃ to evaporate. After the acetone is completely evaporated, add glass wool (to prevent the sample from splashing out when the cracking cup falls freely to the cracking furnace and contaminating the cracking tube), and analyze on the machine.

[0061] The glass filtering device involved in the present invention comprises a circulating water multi-purpose vacuum pump, a cylindrical graduated filter cup, a fixing clamp, a sand core filter head, and a water sample collection bottle, wherein the cylindrical graduated filter cup is used to filter the water sample to be tested, and the lower end is connected to the sand core filter head. After the cylindrical graduated filter cup and the sand core filter head are tightened with the fixing clamp, the sand core filter head is connected to the water sample collection bottle, and the stainless steel filter membrane is placed on the sand core surface of the glass filtering device.

[0062] (2) Instrument conditions

[0063] The parameters of the pyrolysis-gas chromatography-mass spectrometer are as follows:

[0064] Thermal cracking: The cracking temperature is 600℃ and the cracking time is 0.3min.

[0065] Gas chromatography: the injection port temperature was 300°C, the carrier gas was high-purity nitrogen (purity > 99.999%), the chromatographic column was SH-I-5Sil MS (purchased from Shimadzu Corporation of Japan; specifications: 30m*0.25mm*0.25μm), the chromatographic column flow rate was 1.78mL / min, and the column oven temperature program was an initial temperature of 40°C for 2min, then heated to 280°C at 20°C / min and held for 10min, then heated to 320°C at 20°C / min and held for 10min, the injection mode was split injection, and the split ratio was 10:1.

[0066] Mass spectrometry: ionization mode was electron impact EI, ionization energy was 70 eV, ion source temperature was 300°C, interface temperature was 280°C, acquisition mode was full scan (Scan), and scan range was 35-350 m / z.

[0067] (3) Characterization of microplastics

[0068] The characteristic peak of the polymer is determined by the monomer structure and polymerization mode of the polymer, and is not affected by the degree of polymerization or the later extrusion process. However, in a mixed sample, too much component information will cause interference. In order to accurately quantify and quantify, it is necessary to find the characteristic small molecules corresponding to each high molecular polymer. In this embodiment, 6 kinds of microplastics are detected, including polymethyl methacrylate (PMMA), polypropylene (PP), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyethylene (PE), and polystyrene (PS). The characteristic substances selected in this embodiment are representative, can well eliminate the interference of other substances, and have good stability and reproducibility, and are universal in the identification of microplastic structures. The characteristic pyrolysis products of the 6 kinds of microplastics detected by the target of the present invention, as well as the quantitative ion and qualitative ion information are shown in Table 4.

[0069] Table 4. Characteristic fragmentation products of microplastics and quantitative and qualitative ions

[0070]

[0071] If the retention time of the target microplastic chromatographic peak in the tested sample is compared with the retention time of the standard chromatographic peak of the corresponding characteristic pyrolysis product, the relative error is within ±0.1min; and the mass-to-charge ratio of the mass spectrometric fragment ions corresponding to the target microplastic in the tested sample is consistent with the mass spectrum of the standard (the mass spectrum contains the mass-to-charge ratio and relative ion abundance), and the relative abundance of ions with the corresponding mass-to-charge ratio compared with the standard should be consistent with Table 5, then the target compound can be qualitatively identified.

[0072] Table 5. Maximum allowable deviation of relative ion abundance for qualitative confirmation by gas chromatography-mass spectrometry

[0073] Relative ion abundance ＞100％ 50%~100%(inclusive) 10%~50%(inclusive) ≤10％ Allowable relative deviation ±25％ ±30％ ±35％ ±50％

[0074] Here, relative deviation = (relative ion abundance in sample - relative ion abundance in standard) / relative ion abundance in standard * 100%.

[0075] (4) Quantification of microplastics

[0076] A series of 12 kinds of microplastic mixed standards (MPs-CaCO3-L, purchased from Shimadzu (Shanghai) Laboratory Equipment Co., Ltd.) with different masses (from low to high) were weighed using a 1 / 100,000 balance, namely 0.10 mg, 0.20 mg, 0.50 mg, 1.00 mg, 2.00 mg, 5.00 mg, and 10.00 mg, and then measured on the machine (the mixed standards were directly placed in the lysis cup and sampled for detection). The linear regression equation was established with the quantitative ion peak area (Y) of the microplastics as the ordinate and the mass of the microplastics (X, μg) as the abscissa.

[0077] The results are shown in Table 6. The six types of microplastics have a wide linear range and a good linear relationship. The correlation coefficients are all greater than 0.99, which meets the requirements of the analysis method.

[0078] Table 6. Instrument linear range related parameters for 6 types of microplastics

[0079] Microplastic Name English abbreviation Linear regression equation Correlation coefficient / R Linear range / μg Polymethyl methacrylate PMMA Y=1593515X+173291.9 0.9979 0.013-2.034 Polypropylene PP Y=48666.27X+10965.24 0.9967 0.109-9.965 Polyvinyl chloride PVC Y=324460.3X+778064.1 0.9979 0.075-10.074 Polyethylene terephthalate PET Y=179399.3X+18460.96 0.9992 0.009-17.544 Polyethylene PE Y=54714.54X+57031.24 0.9943 0.386-19.442 Polystyrene PS Y=500409.0X+258014.9 0.9963 0.024-9.223

[0080] The content of microplastics in the target sample to be tested is finally calculated according to formula (1):

[0081] x=(C-C0) / V…………(1)

[0082] Where:

[0083] x——the content of microplastics in the sample, in micrograms per liter (μg / L);

[0084] C0——The mass of microplastics in the blank test (without filtering the water sample, directly testing the acetone eluate of the blank filter membrane) obtained from the standard curve, in micrograms (μg);

[0085] C——The mass of microplastics in the sample (target water sample to be tested) obtained from the standard curve, in micrograms (μg);

[0086] V is the volume of the sample, in liters (L).

[0087] (5) Detection limit and quantification limit of the method of the present invention

[0088] The quantitative limit of the method was determined by measuring the signal-to-noise ratio (S / N = signal intensity of the sample / noise signal intensity) of the spiked sample (1.1 mg of microplastic mixed standard MPs-CaCO3-L, added to 2.0 L of Wahaha water sample). At least 6 parallel samples were tested, and the recovery rate (60%-120%) and precision (RSD≤20%) met the requirements.

[0089] In this example, 6 microplastic mixed standards of about 1.1 mg MPs-CaCO3-L were weighed with a 1 / 100,000 balance and added to a beaker containing 2.0 L of Wahaha water sample. After stirring and mixing with a glass rod, the sample was pre-treated and then measured on the machine. The method detection limit (LOD) of this method is 0.012-0.40 μg / L, and the limit of quantification (LOQ) is 0.039-1.32 μg / L, as shown in Table 7.

[0090] The spiked amount of PMMA (0.078 μg) is PMMA with a particle size of more than 10 μm in 1.1 mg of mixed standard (MPs-CaCO3-L), and the signal-to-noise ratio S / N measured on the machine is 38.56. Affected by the accuracy of the balance, the sample weight cannot be reduced any further, so it is impossible to accurately weigh the mass of the standard with a PMMA signal-to-noise ratio of approximately 10 to do the spike experiment. Based on the fact that the signal-to-noise ratio ratio is equal to the mass ratio, the method quantification limit of PMMA is 0.01 μg / L, which is much lower than the quantification limits of the other six microplastics. From a toxicological point of view, the method quantification limit is too low and has little practical significance. Therefore, the quantification of PMMA is finally limited to 0.078 μg of PMMA with a particle size of more than 10 μm in 1.1 mg of mixed standard (MPs-CaCO3-L), which is 0.039 μg / L compared to the sampling volume of 2.0 L of water.

[0091] Table 7. Method LOD and method LOQ for 6 microplastics

[0092]

[0093] (6) Accuracy and precision of the detection method of the present invention

[0094] The accuracy and precision of the method were evaluated by examining the spike recovery results of the actual sample (1.1 mg of microplastic mixed standard MPs-CaCO3-L, added to 2.0 L of tap water). Tap water was used for 3 levels (1.1 mg, 2.3 mg, 4.5 mg of microplastic mixed standard MPs-CaCO3-L; the addition levels were LOQ, 2LOQ and 5LOQ) and 6 parallel spike experiments. That is, 6 1.1 mg, 6 2.3 mg, and 6 4.5 mg of microplastic mixed standard MPs-CaCO3-L were weighed with a one-hundred-thousandth balance, and added to a beaker containing 2.0 L of tap water, respectively. After stirring and mixing with a glass rod, the sample was pre-treated and then measured on the machine. The recovery rate and precision of the experimental results were calculated to evaluate the accuracy and precision of the method. The experimental results are shown in Tables 8 and 9.

[0095] Recovery rate (%) = (measured concentration - sample background concentration) * constant volume / spiked amount * 100%

[0096] Precision (RSD) (%) = standard deviation / average value * 100%

[0097] Among them, the sample background concentration is the concentration of microplastics contained in the sample itself.

[0098] Table 8. Accuracy and precision test results (n=6)

[0099]

[0100] Table 9. Accuracy and precision test results (n=6)

[0101]

[0102] By analyzing the experimental data, it can be seen that the recoveries at different spiked levels are between 69.73% and 111.21%, and the precision (RSD) is between 2.78% and 12.56%, which meets the requirements of methodological recovery (60-120%) and precision (≤20%).

[0103] Example 3: Detection of microplastics in actual samples

[0104] The quantitative analysis and detection method for microplastics in water established based on Example 2 has a wide linear range and an extremely low detection limit, an average spiked recovery rate of ≥60%, and a precision of ≤20%. It can realize the quantitative detection of 6 types of microplastics in different water sources such as commercially available bottled water, groundwater, and tap water.

[0105] The present embodiment collected 2 batches of tap water (randomly collected), 2 batches of pure water, groundwater (randomly collected), first-level RO pure water, second-level RO pure water, commercially available Nongfu Spring, and commercially available Baishuishan water samples, and used the pretreatment and quantitative and qualitative analysis methods of the present invention to detect microplastics in the water.

[0106] The results obtained after testing are shown in Table 10. Through analysis, the method of the present invention can detect 6 types of microplastics at the same time, the qualitative test results are consistent with the theoretical prediction, and the quantitative test results are not much different from the public data.

[0107] Table 10. Detection results of microplastics in 9 batches of water samples

[0108]

[0109] The above results fully verify the advantages of the pretreatment method of the present invention, as well as the feasibility, accuracy and precision of the detection method of the present invention, and provide new ideas for the detection of microplastics in the environment.

[0110] The above embodiments are detailed descriptions of the preferred embodiments of the present invention, but the embodiments are not intended to limit the scope of the patent application of the present invention. For those skilled in the art, any modifications made without departing from the content, spirit and scope of the present invention are within the protection scope of the present invention.

Claims

1. A method for simultaneously detecting multiple microplastics in water, characterized in that: The detection method comprises the following steps: (1) Sample pretreatment: Take a water sample and filter it with a filter membrane. After filtering, immerse the filter membrane in acetone, perform ultrasonic elution at room temperature, rinse the filter membrane with acetone, and collect the eluate; immerse the filter membrane in acetone again, perform ultrasonic elution at room temperature, rinse the filter membrane with acetone, and collect the eluate; repeat the elution several times according to the above operation, then combine the eluates and heat and concentrate them in a water bath to obtain a solid product, which is the concentrated product. Then add acetone and ultrasonically mix it, transfer it to a cracking cup, and heat and evaporate it to obtain the water sample to be tested after pretreatment; (2) Pyrolysis-gas chromatography-mass spectrometry detection: Pyrolysis-gas chromatography-mass spectrometry is used to perform qualitative and quantitative detection on pre-treated water samples; (3) Qualitative analysis: Based on the results of pyrolysis-gas chromatography-mass spectrometry, the types of microplastics in the sample to be tested are determined by comparing them with the characteristic pyrolysis product standards corresponding to different microplastics; (4) Quantitative analysis: Based on the results of pyrolysis-gas chromatography-mass spectrometry, a standard curve is established with the quantitative ion peak area of ​​microplastics as the vertical coordinate and the mass of microplastics as the horizontal coordinate to calculate the mass of microplastics in the water sample to be tested; then the content of microplastics in the water sample to be tested is calculated.

2. The detection method according to claim 1, characterized in that: The filter membrane in step (1) includes a glass fiber filter membrane and a stainless steel filter membrane, preferably a stainless steel filter membrane.

3. The detection method according to claim 1, characterized in that: The number of elutions in step (1) is no less than 2 times, preferably 2 times.

4. The detection method according to claim 1, characterized in that: The time of ultrasonic elution in step (1) is not less than 30 min, preferably 30 min.

5. The detection method according to claim 1, characterized in that: In step (1), the filter membrane is immersed in acetone after the first filtration and the filter membrane is immersed in acetone after the second filtration, and the volume ratio of acetone used twice to the water sample is: 5mL:4mL:2L; the volume of acetone used for washing the filter membrane is 1mL, and the amount of acetone added in the ultrasonic mixing step is 1mL.

6. The detection method according to claim 1, characterized in that: In the thermal pyrolysis-gas chromatography-mass spectrometry detection in step (2), the pyrolysis temperature is 600° C. and the pyrolysis time is 0.3 min.

7. The detection method according to claim 1, characterized in that: In the pyrolysis-gas chromatography-mass spectrometry detection process described in step (2), the chromatographic column is SH-I-5Sil MS, and the column oven heating program is an initial temperature of 40°C for 2 min, then heated to 280°C at 20°C / min and held for 10 min, and then heated to 320°C at 20°C / min and held for 10 min. The injection mode is split injection, and the split ratio is 10:

1.

8. The detection method according to claim 1, characterized in that: In the thermal pyrolysis-gas chromatography-mass spectrometry detection process described in step (2), the carrier gas is high-purity nitrogen, the chromatographic column flow rate is 1.78 mL / min, the ionization mode is electron bombardment EI, the ion source temperature is 300° C., the interface temperature is 280° C., the acquisition mode is full scan, and the scanning range is 35-350 m / z.

9. The detection method according to claim 1, characterized in that: The microplastics include polymethyl methacrylate (PMMA), polypropylene (PP), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyethylene (PE), and polystyrene (PS).

10. The detection method according to claim 1, characterized in that: The content of microplastics in the water sample to be tested in step (4) is calculated according to formula (1): x=(C-C0) / V…………(1), Where: x——the content of microplastics in the sample, in micrograms per liter (μg / L); C0——The mass of microplastics in the blank test (without filtering the water sample, directly testing the acetone eluate of the blank filter membrane) obtained from the standard curve, in micrograms (μg); C——The mass of microplastics in the sample (target water sample to be tested) obtained from the standard curve, in micrograms (μg); V is the volume of the sample, in liters (L).

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