Method for pre-analysis treatment of microplastics

Abstract

To provide a microplastic pre-analysis treatment method which reduces the influence of a specific gravity separation solution in test results.SOLUTION: A microplastic pre-analysis treatment method is provided, comprising a step (S3) of placing microplastic separated by specific gravity separation treatment (S2) into a sieve, a step (S4) of immersing the sieve with the microplastic thereon into pure water of a depth shallower than the height of the sieve, and a step (S5) of drying the sieve (and the microplastic) using a constant temperature dryer after taking the sieve out of the pure water.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a pretreatment method for the analysis of microplastics.

Background Art

[0002] Microplastics refer to fine plastic waste (5 mm or less). There are concerns about the impact on the ecosystem as the chemical substances contained or adsorbed by microplastics are incorporated into the food chain.

[0003] In order to study and countermeasure the impact of such microplastics, it is necessary to analyze microplastics. For example, Japanese Patent No. 6811370 (Patent Document 1) discloses a technique related to sample production for analyzing microplastics.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] For example, when performing component analysis of microplastics, a Fourier Transform Infrared Spectrophotometer (FTIR) is generally used. When performing such analysis, pretreatment is carried out before analysis to remove contaminants from environmental water collected from rivers and oceans and extract only microplastics by density separation using sodium iodide.

[0006] However, there were problems such as the fact that components of the specific gravity separation solution, such as sodium iodide, affected the measurement results of the Fourier transform infrared spectrophotometer, and that if the sample was not sufficiently dried after pretreatment, the water peaks would overlap, requiring a long drying time.

[0007] This disclosure aims to provide a method for pre-treating microplastics for analysis that can reduce the influence of specific gravity separation solutions in the detection results. [Means for solving the problem]

[0008] A first aspect of this disclosure relates to a method for pre-treatment of microplastics obtained by specific gravity separation. The method for pre-treatment of microplastics comprises the steps of: placing the microplastics separated by specific gravity separation into a sieve; immersing the sieve containing the microplastics in pure water to a depth shallower than the height of the sieve; and drying the sieve in a constant-temperature dryer after removing it from the pure water. [Effects of the Invention]

[0009] The microplastic analysis pretreatment method described herein is useful for obtaining analytical results that reduce the influence of specific gravity separation solutions such as sodium iodide. [Brief explanation of the drawing]

[0010] [Figure 1] This is a diagram illustrating analysis using a Fourier transform infrared spectrophotometer (FTIR). [Figure 2] This is a process diagram showing each step in the pretreatment method for analyzing microplastics. [Figure 3] This is an external view of the sieve used in step S3 of Figure 3. [Figure 4] This is a diagram to explain the water peak. [Figure 5] This figure shows the analysis results obtained from comparison samples without pretreatment. [Figure 6] This figure shows the analysis results obtained from pre-treated samples. [Figure 7] This figure shows the waveforms from Figure 5 and Figure 6 superimposed on each other. [Modes for carrying out the invention]

[0011] The embodiments will be described in detail below with reference to the drawings. Note that the same or corresponding parts in the drawings are denoted by the same reference numerals, and their descriptions will not be repeated.

[0012] When analyzing the components of microplastics, a Fourier transform infrared spectrophotometer is generally used. A Fourier transform infrared spectrophotometer is primarily used to estimate the structure of organic compounds. When infrared light is shone on a molecule, the infrared light corresponding to the vibrational energy between the atoms constituting the molecule is absorbed. By examining this degree of absorption, the Fourier transform infrared spectrophotometer uses infrared spectroscopy to estimate and quantify the structure of compounds.

[0013] Figure 1 is a diagram illustrating analysis using a Fourier transform infrared spectrophotometer (FTIR). The Fourier transform infrared spectrophotometer 1 comprises a light source 3, an interferometer 2, a detector 5, and a computer 6. The interferometer 2 includes a movable mirror 21, a beam splitter 22, and a fixed mirror 23.

[0014] Infrared light emitted from the light source 3 into the interferometer 2 is separated by the beam splitter 22 into two beams: one from a fixed mirror and the other from a moving mirror. The fixed mirror 23 does not move, only the moving mirror 21 moves. The light reflected by the fixed mirror 23 and the moving mirror 21 returns and is combined. This combined light is an interference wave (interferogram) with a phase difference of light depending on the distance the moving mirror 21 moves. This interference wave is irradiated onto the sample, and the transmitted light is detected by the detector 5.

[0015] When infrared light is irradiated onto the sample 4 with this configuration, the light intensity detected by the detector differs depending on the movement distance of the moving mirror 21. An infrared spectrum is obtained by performing a Fourier transform on the output of the detector 5 using the computer 6. The following describes the pretreatment method for the sample 4 to be set in the Fourier transform infrared spectrophotometer 1.

[0016] Figure 2 is a process diagram showing each step of the pretreatment method for microplastic analysis. First, in step S1, an acid hydrolysis treatment for removing organic substances with hydrogen peroxide water or the like is performed on the microplastics collected from environmental water.

[0017] Once this is dehydrated, in the subsequent step S2, a specific gravity separation treatment is performed by pouring an aqueous sodium iodide solution to float the microplastics. Note that an aqueous sodium chloride solution may be used instead of the aqueous sodium iodide solution.

[0018] And in step S3, a particle size separation treatment is performed by scooping up the floating microplastics with a sieve (300 μm) by pouring an aqueous sodium iodide solution or an aqueous sodium chloride solution.

[0019] Figure 3 is an external view of the sieve used in step S3 of Figure 3. The microplastics after specific gravity separation are collected with a stainless sieve as shown in Figure 3. Note that in Figure 3, an example with an opening of 300 μm is shown, but the opening may be appropriately changed according to the particle size of the microplastics to be analyzed.

[0020] Returning to Figure 2 again, in the subsequent step S4, a sodium iodide removal treatment is performed. In step S4, the sieve is immersed in pure water at a depth shallower than the height of the sieve and left for about 1 minute. Then, the sieve is gently lifted from the pure water. At this time, since there is a possibility that the microplastics will pass through the mesh of the sieve due to water pressure when water is poured from above, it is important to immerse it in the pure water stored in the container. In this way, the sodium iodide used in the specific gravity separation treatment is removed. Note that when an aqueous sodium chloride solution is used instead of the aqueous sodium iodide solution, sodium chloride is removed.

[0021] Next, the drying process in step S5 is carried out. For the drying process, the sieve containing the microplastics is left in a constant-temperature dryer (without a fan) set to approximately 30°C to 50°C for several hours. If the temperature is raised too high, the microplastics may deteriorate. Also, if there is a fan in the dryer, the microplastics may be scattered. Drying should be carried out with these points in mind.

[0022] Figure 4 illustrates the water peak. If drying is insufficient, the water peak shown in Figure 4 will be superimposed on the detection results. Therefore, it is important to completely dry the microplastics in a constant-temperature dryer to remove moisture.

[0023] Subsequently, in step S6, the sieve is removed from the dryer, and a single microplastic particle is picked out from the sieve using tweezers. This is then placed in an FTIR detector and analyzed.

[0024] The following describes a comparison of the results when the pretreatment method of this embodiment is performed and when it is not. Figure 5 shows the analysis results obtained from a sample without pretreatment (before washing with water). Figure 6 shows the analysis results obtained from a sample with pretreatment according to this embodiment. Figure 7 shows the waveforms of Figure 5 and Figure 6 superimposed.

[0025] The sodium iodide peaks, which are visible in the areas indicated by the arrows in Figures 5 and 7, are reduced in Figure 6. In Figure 6, the wavelength of 1000 cm, which was the original target for detection, is reduced. -1 The peak is clearly visible, and data unaffected by sodium iodide and water can be obtained.

[0026] [Aspect] Those skilled in the art will understand that the exemplary embodiments described above are specific examples of the following embodiments.

[0027] (Section 1) A first aspect of this disclosure relates to a method for pre-treatment of microplastics obtained by specific gravity separation. The method for pre-treatment of microplastics comprises the steps of: placing the microplastics separated by specific gravity separation into a sieve; immersing the sieve containing the microplastics in pure water to a depth shallower than the height of the sieve; and drying the sieve in a constant-temperature dryer after removing it from the pure water.

[0028] (Section 2) In the method for pretreatment of microplastics for analysis described in Section 1, the specific gravity separation treatment comprises the step of injecting a sodium iodide solution or a sodium chloride solution into the microplastics.

[0029] According to the microplastic analysis pretreatment method of this embodiment, when analysis is performed by FTIR, data can be obtained that is free from the influence of specific gravity separation solutions such as sodium iodide and water.

[0030] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0031] 1. Fourier transform infrared spectrophotometer, 2. Interferometer, 3. Light source, 4. Sample, 5. Detector, 6. Computer, 21. Mobile mirror, 22. Beam splitter, 23. Fixed mirror.

Claims

[Claim 1] A pre-analysis treatment method performed before analyzing microplastics obtained by specific gravity separation treatment with an infrared spectrometer, The gravity separation process includes the step of injecting a sodium iodide solution or a sodium chloride solution into the microplastic. The aforementioned pre-analysis treatment method is: A step of putting the microplastics separated by the specific gravity separation process into a sieve, A step of immersing the sieve containing the microplastics in pure water at a depth shallower than the height of the sieve, A method for pretreatment of microplastics for analysis, comprising the steps of removing the sieve from pure water and then drying the sieve containing the microplastics in a constant-temperature dryer.

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