Micro-plastic detection method based on cyclic voltammetry electric incubation

Abstract

According to the micro-plastic detection method, a glassy carbon electrode is used as a working electrode, a platinum wire electrode is used as a counter electrode, an Ag / AgCl electrode is used as a reference electrode, and potassium ferricyanide / potassium ferrocyanide is used as an electrochemical signal molecule; the method comprises the following steps: putting a three-electrode system into a KCl electrolyte solution which contains a microplastic and contains a potassium ferricyanide / potassium ferrocyanide probe, connecting the three-electrode system into an electrochemical workstation, then carrying out electric incubation on a solution system by using a cyclic voltammetry method, and detecting the concentration of the microplastic by using a differential pulse voltammetry method after incubation is finished. According to the invention, the electrochemical technology is innovatively used for micro-plastic detection. By utilizing the characteristic that micro-plastic is easily adsorbed on the surface of a glassy carbon electrode, an electric incubation method is adopted to enhance adsorption and reduce response of signal molecules, so that an electrochemical sensing detection method is established. The method has the advantages of rapidness, simplicity, low cost and the like, can be used for effectively detecting the micro-plastics in a wider range and keeping good sensitivity, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of pollutant detection technology, specifically to a method for detecting microplastics based on cyclic voltammetry electro-incubation. Background Technology

[0002] Currently, plastic products are widely used in many industries, such as packaging, automobiles, construction, electronics, and agriculture. According to the European Plastics Association, global plastic production reached 390 million tons in 2021. While plastics have provided immense convenience to modern life, the large-scale use of plastic products has brought about safety issues that cannot be ignored. In 2004, Plymouth University scientist Thompson first proposed the concept of "microplastics" in the journal *Science*, defining them as plastic fragments and particles with a diameter of less than 5 millimeters. The environmental pollution caused by microplastics has attracted the attention of researchers worldwide.

[0003] The distribution, migration, toxicology, and ecological effects of microplastics in aquatic environments are important aspects of microplastic research. Establishing accurate and efficient microplastic detection techniques and analytical methods provides crucial tools and methodological support for this research. Currently, commonly used methods for identifying microplastics include visual inspection, microscopy, scanning electron microscopy, infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis with differential scanning calorimetry (TGA), pyrolysis gas chromatography-mass spectrometry (GC-MS), and thermal extraction-desorption GC-MS. However, these methods all require large instruments and specialized training for operators, making rapid, immediate, and low-cost detection difficult. Furthermore, these methods necessitate time-consuming and complex sample pretreatment, further complicating microplastic detection.

[0004] The applicant previously proposed an electrochemical sensing method for detecting microplastics, which involves modifying the working electrode and then using electrochemical sensing for detection. This significantly reduces the difficulty of detection, enabling rapid and real-time detection, and exhibiting good accuracy and stability. However, it still has limitations, such as requiring the use of multiple container devices and a lengthy electrode preparation process. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide another microplastic detection method based on cyclic voltammetry electro-incubation, which eliminates the need for modification of the working electrode, further simplifies the detection process, improves the detection rate, is simple to operate, low in cost, and maintains good sensitivity.

[0006] To achieve the above objectives, this invention provides a method for detecting microplastics based on cyclic voltammetry and electro-incubation. The method is characterized by using a glassy carbon electrode as the working electrode, a platinum wire electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, and potassium ferricyanide / potassium ferrocyanide probe molecules as electrochemical signal molecules. The three-electrode system is placed in a KCl electrolyte solution containing microplastics and the potassium ferricyanide / potassium ferrocyanide probe, and connected to an electrochemical workstation. Cyclic voltammetry is then used to electro-incubate the solution system. After incubation, differential pulse voltammetry is used to detect the concentration of microplastics.

[0007] In the above scheme: the potential range of the cyclic voltammetry is 0 to 0.5V for positive scanning, the number of cycles is 1 to 9, and the scanning speed is 20 to 100mV / s.

[0008] In the above scheme, the pH of the KCl electrolyte solution is 5-9.

[0009] In the above scheme: the pH of the KCl electrolyte solution is 7, the number of circulation cycles is 5, and the scan rate is 60 mV / s.

[0010] In the above scheme: the parameters of the differential pulse voltammetry method are: positive scan with a potential range of 0 to 0.5V, potential increment of 0.004V, potential amplitude of 0.025V, pulse width of 0.025s, and pulse period of 0.075s.

[0011] In the above scheme, the concentration of potassium ferricyanide / potassium ferrocyanide is 0.5-10 mM.

[0012] In the above scheme, the concentration of KCl in the KCl electrolyte solution is 0.05-0.3M.

[0013] This invention innovatively proposes an electrochemical technique for microplastic detection. Utilizing the characteristic that microplastics readily adsorb onto the surface of a glassy carbon electrode, this invention employs an electro-incubation method to enhance adsorption and reduce the response of signal molecules, thereby establishing a simple and low-cost electrochemical sensing detection method. This method offers advantages such as speed, simplicity, and low cost, and can effectively detect microplastics over a wide range while maintaining good sensitivity, demonstrating broad application prospects.

[0014] This invention uses a glassy carbon electrode as the working electrode and employs charged external probe molecules (potassium ferricyanide / potassium ferrocyanide) as electrochemical signal molecules to reflect the current status of the circuit. When microplastics are absent in the water sample, the working electrode adsorbs charged external probe molecules, which indirectly indicate the current status of the circuit through redox reactions, generating an electrochemical signal. When microplastics are present in the water sample, cyclic voltammetry is used to enhance the adsorption of microplastics on the surface of the working electrode. The shielding effect of the microplastics affects the redox reaction of the charged external probe molecules. The adsorption of microplastics on the working electrode surface after electro-incubation affects the conductivity of the circuit and thus the electrochemical signal. Finally, by recording the changes in the electrochemical signal of the external probe molecules, the electrochemical detection of trace microplastics in water is achieved. The higher the concentration of microplastics, the lower the circuit current and the weaker the generated electrochemical signal. Based on this, a correlation between microplastic concentration and electrochemical signal intensity is established, yielding a corresponding linear regression equation. The detection method of this invention provides a rapid detection of microplastics in water, which is safe, accurate, effective and simple. The linear detection range of this method for microplastics is 25 μg / L to 1000 μg / L, the detection limit is 4.84 μg / L, the linear detection range is wide, the sensitivity is high and the reliability is good. Attached Figure Description

[0015] Figure 1 To illustrate this invention, the current response values ​​of 100 μg / L microplastics were measured under different operating conditions (pH, number of electric incubation cycles, incubation rate).

[0016] Figure 2 Images are obtained by differential pulse voltammetry detection of microplastic solutions of different concentrations under the conditions of solution pH 7, 5 cycles, and scanning speed of 60 mV / s.

[0017] Figure 3 This is a standard curve of electrochemical signal versus microplastic concentration under the above conditions. Detailed Implementation

[0018] The present invention will be further described below with reference to the embodiments and accompanying drawings:

[0019] Example 1

[0020] Using a glassy carbon electrode as the working electrode, a platinum wire electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, and potassium ferricyanide / potassium ferrocyanide probe molecules as electrochemical signal molecules, the three-electrode system was placed in a KCl electrolyte solution containing microplastics and potassium ferricyanide / potassium ferrocyanide probe molecules, and connected to an electrochemical workstation. Subsequently, the solution system was electro-incubated using cyclic voltammetry. After incubation, the concentration of microplastics was detected using differential pulse voltammetry.

[0021] The cyclic voltammetry method uses a potential range of 0–0.5 V for positive scan, with 1–9 cycles and a scan rate of 20–100 mV / s. The pH of the KCl electrolyte solution is 5–9. The concentration of potassium ferricyanide / potassium ferrocyanide is 0.5–10 mM. The concentration of KCl in the KCl electrolyte solution is 0.05–0.3 M. The differential pulse voltammetry method uses a potential range of 0–0.5 V for positive scan, a potential increment of 0.004 V, a potential amplitude of 0.025 V, a pulse width of 0.025 s, and a pulse period of 0.075 s.

[0022] Figure 1 The small graph on the left shows the current response values ​​of 100 μg / L microplastics with pH values ​​of 5, 6, 7, 8, and 9, 5 cyclic voltammetry scans, a scan rate of 60 mV / s, a potassium ferricyanide / potassium ferrocyanide concentration of 1 mM, and a KCl concentration of 0.1 M in the KCl electrolyte solution. As can be seen from the graph, the response value is the highest when the pH is 7.

[0023] Figure 1 The small graph in the middle represents pH 7. The number of cyclic voltammetry scans were 1, 3, 5, 7, and 9, respectively. The scan rate was 60 mV / s, the potassium ferrocyanide / potassium ferrocyanide concentration was 1 mM, the KCl concentration in the KCl electrolyte solution was 0.1 M, and the current response value of 100 μg / L microplastics was also shown in the graph. It can be seen from the graph that the response value was the highest when there were 5 cycles.

[0024] Figure 1 The small graph on the right shows the current response values ​​of 100 μg / L microplastics at pH 7, 5 cycles, scan rates of 20, 40, 60, 80, and 100 mV / s, potassium ferricyanide / potassium ferrocyanide concentration of 1 mM, and KCl concentration of 0.1 M in the KCl electrolyte solution. As can be seen from the graph, the response value is the highest when the scan rate is 60 mV / s.

[0025] Figure 2 Images are obtained by differential pulse voltammetry detection of microplastic solutions with different concentrations (0, 25, 50, 100, 250, 500, 750, 1000 μg / L) under the following conditions: solution pH 7, 5 cycles, scan rate 60 mV / s, potassium ferricyanide / potassium ferrocyanide concentration 1 mM, and KCl concentration in the KCl electrolyte solution 0.1 M. Figure 3 This is a standard curve showing the electrochemical signal and microplastic concentration under these conditions. A linear relationship was established between the peak current value y and the logarithm of the concentration x, yielding the corresponding regression equation y = 100.8 - 28.9x, R0. 2=0.996, P<0.0001. The residuals conform to a normal distribution. According to the limit of detection formula LOD = 3ω' / s, where ω' is the standard deviation of the blank sample signal and s is the slope of the calibration curve, the limit of detection is calculated to be 4.84 μg / L within the linear detection range of 25 μg / L to 1000 μg / L. At least 9 parallel experiments were performed for each experimental point, and the relative standard deviation (RSD) was ≤2.48%.

[0026] This invention is not limited to the above embodiments. Those skilled in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this invention. The scope of this invention is defined by the claims and their equivalents.

Claims

1. A method for detecting microplastics based on cyclic voltammetry electroincubation, characterized in that: Using a glassy carbon electrode as the working electrode, a platinum wire electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, and potassium ferricyanide / potassium ferrocyanide probe molecules as electrochemical signal molecules, the three-electrode system was placed in a KCl electrolyte solution containing microplastics and potassium ferricyanide / potassium ferrocyanide probe molecules, and connected to an electrochemical workstation. Subsequently, the solution system was electro-incubated using cyclic voltammetry. After incubation, the concentration of microplastics was detected using differential pulse voltammetry.

2. The microplastic detection method based on cyclic voltammetry electroincubation according to claim 1, characterized in that: The potential range of cyclic voltammetry is 0 to 0.5 V for positive scanning, with 1 to 9 cycles and a scanning speed of 20 to 100 mV / s.

3. The microplastic detection method based on cyclic voltammetry electroincubation according to claim 2, characterized in that: The pH of KCl electrolyte solution is 5–9.

4. The microplastic detection method based on cyclic voltammetry electroincubation according to claim 3, characterized in that: The KCl electrolyte solution had a pH of 7, 5 circulation cycles, and a scan rate of 60 mV / s.

5. The microplastic detection method based on cyclic voltammetry electroincubation according to claim 4, characterized in that: The parameters for the differential pulse voltammetry method are: positive scan with a potential range of 0 to 0.5V, a potential increment of 0.004V, a potential amplitude of 0.025V, a pulse width of 0.025s, and a pulse period of 0.075s.

6. The microplastic detection method based on cyclic voltammetry electroincubation according to claim 5, characterized in that: The concentration of potassium ferricyanide / potassium ferrocyanide is 0.5-10 mM.

7. The microplastic detection method based on cyclic voltammetry electroincubation according to claim 5, characterized in that: The concentration of KCl in the KCl electrolyte solution is 0.05-0.3M.

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