Method for detecting content of polypropylene in aqueous solution based on electrochemical luminescence

Abstract

The invention belongs to the field of electrochemical sensing detection, and particularly relates to a method for detecting the content of polypropylene in an aqueous solution based on electrochemiluminescence. According to the invention, a novel amphiphilic perylene derivative (PDI-NH2) electrochemical luminescence (ECL) sensor is firstly prepared and is used for ultra-sensitive detection and marking of polypropylene (PP) in an aqueous solution; pDI-NHH with positive charges can efficiently capture a trace amount of PP in an aqueous solution due to an inherent amphiphilic structure, so that ECL signal enhancement is realized. It is worthy of noting that the ECL sensor based on the PDI-NH2 luminophore has high stability and excellent sensitivity to polypropylene PP, the sensor has rapid response capacity to PP, the response time is as low as 12 s, and polypropylene can be efficiently recognized and detected in a complex environment. According to the method, the micro-plastic PP can be effectively identified and quantified without additional pretreatment and complex instruments, so that the method becomes an ideal tool for accurately quantifying the micro-plastic in the aqueous solution.

Description

Technical Field

[0001] The invention belongs to the field of biosensor detection, and in particular relates to a method for detecting the content of polypropylene in an aqueous solution based on electrochemiluminescence. Background Art

[0002] Microplastic particles are only less than 5mm and originate from the degradation of plastic manufacturing (primary source) and plastic waste (secondary source). Their persistence in the environment is estimated to be hundreds or even thousands of years, and has become an emerging global concern. With the large-scale release of microplastics into the environment, tiny plastic fragments appear through degradation and weathering, which directly endanger environmental systems and human health. Polypropylene (PP) has become one of the most widely used plastic polymers due to its excellent performance, cost-effectiveness and easy processing. Over the years, the development and utilization of PP has made significant progress and is widely used in various industries. It is often used in many packaging products, cosmetics and personal care products, accounting for 16-20% of the entire plastic industry. In addition, a large amount of polypropylene waste will cause serious pollution to the environment. It takes more than 30 years for it to decompose naturally. Therefore, it is particularly important to monitor its presence in soil, water and air by detecting PP and assessing its impact on the ecosystem. The existing detection methods include visual analysis, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, high performance liquid chromatography (HPLC) combined with mass spectrometry, fluorescence detection and other technologies, but these methods are expensive, the sample processing steps are complicated, time-consuming and susceptible to interference from fluorescence. Electrochemiluminescence (ECL) analysis technology combines the advantages of spectroscopy and electrochemistry and has the characteristics of low background, simple operation, wide dynamic range, high sensitivity and good stability. Therefore, it is necessary to develop a simple and highly sensitive detection method in combination with ECL analysis technology to effectively detect and track microplastics in samples. Summary of the invention

[0003] The purpose of the present invention is to disclose a method for detecting the content of polypropylene in an aqueous solution based on electrochemiluminescence. The method utilizes a new amphiphilic perylene derivative (PDI-NH2) with a unique "signal-on" effect on polypropylene microplastics (PP) to achieve efficient identification and quantitative detection of microplastics PP in aqueous solution.

[0004] To achieve the above object, the present invention adopts the following technical solution: A method for detecting polypropylene content in an aqueous solution based on electrochemiluminescence comprises the following steps: 1) Prepare a series of polypropylene standard solutions; 2) PDI-NH2 probe is used as an electrochemiluminescent reagent and K2S2O8 is used as a co-reactant, which are co-dissolved in phosphate buffer to obtain an electrochemiluminescent reaction solution; The preparation of the PDI-NH2 probe includes: First, 3,4,9,10-perylenetetracarboxylic dianhydride and mono-BOC-ethylenediamine are co-dissolved in tetrahydrofuran, stirred continuously for 16-24 hours at 70-90°C under N2 protection, centrifuged, and washed with sodium hydroxide solution and deionized water to obtain an intermediate product; then, the intermediate product is dissolved in dichloromethane, trifluoroacetic acid is added dropwise, stirred continuously for 2-5 hours at room temperature, centrifuged, and washed with dichloromethane to obtain the final product PDI-NH2; The molar ratio of 3,4,9,10-perylenetetracarboxylic dianhydride to mono-BOC-ethylenediamine is 1:2-2:1; 0.5-1 mL of trifluoroacetic acid is required for each 0.1 g of the intermediate product for deprotection; The pH of the phosphate buffer is 7.0, specifically 0.1 M phosphate buffer containing 0.1 M KCl; 3) The series of polypropylene standard solutions in step 1) are mixed with the electrochemiluminescence reaction solution in step 2) to obtain a series of electrolytes; the electrochemiluminescence intensity of the series of electrolytes is measured using a three-electrode system to construct a standard curve or linear equation between the electrochemiluminescence intensity and the polypropylene concentration; The three-electrode system uses GCE as the working electrode, Pt column as the counter electrode, and Ag / AgCl as the reference electrode; the potential window for measuring the electrochemical luminescence intensity is 0~-2.0V; 4) The polypropylene solution to be tested is mixed with the electrochemiluminescence reaction solution in step 2), and the electrochemiluminescence intensity is measured. The polypropylene concentration in the polypropylene solution to be tested can be obtained by the standard curve or linear equation of electrochemiluminescence intensity and polypropylene concentration constructed in step 3).

[0005] Compared with the prior art, the present invention has the following beneficial effects: The present invention develops a new amphiphilic perylene derivative (PDI-NH2) with a unique "signal-on" effect on polypropylene microplastics (PP) as a luminophore to construct an electrochemiluminescence (ECL) detection system for ultra-sensitive detection and labeling of polypropylene microplastics (PP) in aqueous solution. The positively charged PDI-NH2 can efficiently capture trace amounts of PP in aqueous solution due to its inherent amphiphilic structure, thereby achieving ECL signal enhancement. It is worth noting that the ECL based on the PDI-NH2 luminophore has high stability and excellent sensitivity to polypropylene PP, with an ideal linear range (5μg·ml -1 Up to 45 μg ml -1 ) and a low detection limit (0.948 mg·L −1 ). Moreover, the ECL has a fast response capability to PP, with a response time as low as 12 s, and can efficiently identify and detect polypropylene in complex environments.

[0006] In summary, the present invention provides a simple and sensitive method for detecting PP, which can effectively identify and quantify microplastic PP without additional pretreatment and complex instrumentation, making it an ideal tool for accurately quantifying microplastics in aqueous solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 This is the infrared spectrum of PDI-NH2 synthesized in the embodiment of the present invention.

[0008] Figure 2 This is the H-NMR spectrum of PDI-NH2 synthesized in the embodiment of the present invention.

[0009] Figure 3 The influencing factors of the electrochemiluminescence detection system constructed for the embodiment of the present invention include: (A) the concentration of the coreactant K2S2O8; (B) the pH value; (C) the scanning rate; and (D) the potential range.

[0010] Figure 4 The effect of the concentration of PDI-NH2 synthesized in the embodiment of the present invention on the electrochemiluminescence detection system, including: (A) optimization of PDI-NH2 concentration; (B) cyclic stability tested under optimal experimental conditions.

[0011] Figure 5 The response relationship between the ECL intensity and PP concentration of the electrochemiluminescence detection system constructed for the embodiment of the present invention, including: (A) ECL graph of PP with different concentrations; (B) linear relationship graph between ECL intensity and PP concentration.

[0012] Figure 6 The stability of the electrochemiluminescence detection system constructed in the embodiment of the present invention.

[0013] Figure 7 The selectivity of the electrochemiluminescence detection system constructed in the embodiment of the present invention.

[0014] Figure 8 Mechanism exploration of the electrochemiluminescence detection system constructed for the embodiment of the present invention: Changes in Zeta potential before and after mixing with the probe PDI-NH2. Polypropylene (PP, 40 mg•L −1 ), polymethyl methacrylate (PMMA, 7 ml•L −1 ), polylactic acid (PLA, 40 mg•L −1 ), polyethylene (PE, 40 mg•L −1 ) and polystyrene (PS, 40 mg•L −1 ).

[0015] Fig. 9Mechanism exploration of the electrochemiluminescence detection system constructed for the embodiment of the present invention: changes in infrared before and after mixing polypropylene PP and probe PDI-NH2. DETAILED DESCRIPTION

[0016] The present invention is further explained below with reference to specific embodiments. Example

[0017] 1. Synthesis of PDI-NH2 First, 0.392 g of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and 0.32 mL of monoBOC-ethylenediamine were added to 15 mL of tetrahydrofuran (THF). Then, the mixture was stirred continuously for 18 h at 80 ° C under N2 protection, and the mixture was centrifuged and washed 3 times with sodium hydroxide solution (NaOH, 1%) and deionized water to remove excess substances to obtain an intermediate product. Then, 0.2 g of the intermediate product was dissolved in dichloromethane (5 mL, DCM) and 1 mL of trifluoroacetic acid (F3CCOOH) was added dropwise, stirred continuously at room temperature for 3 h, and finally centrifuged and washed several times with dichloromethane (DCM) to remove excess substances to obtain the final product PDI-NH2.

[0018] 2. Construction of electrochemiluminescence (ECL) detection system 2.1 Preparation of polypropylene standard solution A series of polypropylene standard solutions with different concentrations were prepared by diluting a 1.0 mg / ml polypropylene solution with a 0.1 M phosphate buffer containing 0.1 M KCl at pH 7.4, ranging from 5.0 μg / mL to 45.0 μg / mL.

[0019] 2.2 Preparation of PDI-NH2 solution Use ultrapure water to prepare a 4 μM PDI-NH2 solution, and then dilute it to 16 mM for later use.

[0020] 2.3 Preparation of PDI-NH2 / K2S2O8 electrochemiluminescence reaction solution A PDI-NH2 / K2S2O8 electrochemiluminescence reaction solution containing 150 mM K2S2O8 and 0.30 μM PDI-NH2 was prepared using 0.1 M phosphate buffer containing 0.1 M KCl at pH = 7.4.

[0021] 2.4 Establishing a linear relationship between electrochemiluminescence intensity and polypropylene concentration The three-electrode system was composed of GCE as the working electrode, Pt column as the counter electrode, and Ag / AgCl as the reference electrode. -1 Up to 45 μg ml -1) was used as an electrolyte, and cyclic voltammetry was performed in the electrochemical window range of -2.0~0 V with a photomultiplier tube high voltage of 800 V, an amplification order of 4, and a scan rate of 0.15 V / s. The luminescence intensity difference (ΔECL) before and after the addition of polypropylene was recorded, and a linear regression equation between the polypropylene concentration and the luminescence intensity difference (ΔECL) was constructed. Subsequently, a polypropylene-containing sample solution to be tested was mixed with the PDI-NH2 / K2S2O8 electrochemiluminescence reaction solution, and the electrochemiluminescence intensity was measured, and the polypropylene concentration in the polypropylene-containing sample solution to be tested was obtained according to the linear regression equation.

[0022] Characterization of PDI-NH2 and performance evaluation of electrochemiluminescence detection system 1. Characterization of PDI-NH2 Figure 1 The infrared spectrum of PDI-NH2 synthesized in the embodiment of the present invention is shown in FIG. Figure 1 It can be seen that the tertiary amide group in the PDI-NH2 molecule is at 1688 cm −1 There is a sharp band at , indicating the amidation reaction between PTCDA and mono-BOC-ethylenediamine. Figure 2 This is the nuclear magnetic hydrogen spectrum of PDI-NH2 synthesized in the embodiment of the present invention, the deuterated reagent is DMSO- d 6. ( 1 H NMR (400 MHz, DMSO-d6) δ8.71 (s, 4H), 7.94 (s, 4H), 4.35 (t, J = 5.8 Hz, 4H), 3.27-3.13 (m, 4H).) The above tests all proved that the probe molecule was successfully prepared.

[0023] 2. Factors affecting the electrochemiluminescence detection system In order to achieve the best electrochemiluminescence (ECL) performance of the electrochemiluminescence (ECL) system, a large number of experiments were conducted to explore the factors that may affect the ECL performance. Figure 3 and 4 shown.

[0024] We found that as the concentration of the coreactant K2S2O8 increased, the ECL intensity of PDI-NH2 also increased, reaching a maximum at 150 mM ( Figure 3 A), indicating that K2S2O8 can be used as an effective co-reactant to amplify the ECL emission of PDI-NH2. In addition, the pH value of the system was optimized and screened, and the optimal pH value was found to be 7.4 ( Figure 3 B). And when the optimized scan rate is 0.15 V / s and the potential window range is 0 ~ -2.0 V, the strongest ECL signal is observed ( Figure 3 C, D). Subsequently, we explored the optimal concentration of PDI-NH2 under the optimal conditions. When the concentration of PDI-NH2 was 0.30 μM, the ECL luminescence intensity reached the maximum ( Figure 4 A). From Figure 4 B It can be seen that under the optimal conditions, after 22 cycles of scanning, the ECL intensity of PDI-NH2 did not fluctuate significantly, and the relative standard deviation (RSD) was 1.89%, which had good stability and reliability, laying a good foundation for subsequent research.

[0025] 3. Performance analysis of electrochemiluminescence detection system for microplastic detection To evaluate the performance of the proposed sensor, ECL measurements were performed on target PPs at different concentrations under the optimal reaction conditions. Figure 5 As shown in A, at 5 μg•ml -1 ~45μg•ml -1 Within the range, as the PP concentration increases, the ECL intensity increases. Figure 5 As shown in B, the calibration graph shows that the ECL intensity has a good linear relationship with the PP concentration. The linear regression equation is I = 158.68x + 8769.57, and the detection limit is 0.948 mg•L −1 (Signal-to-noise ratio (S / N) = 3).

[0026] Stability and selectivity are two important factors to judge the performance of the proposed sensor. Figure 6 As shown, it can be observed that after 20 consecutive scans, the ECL intensity remained almost stable, with a corresponding relative standard deviation (RSD) of 2.93%. The results indicate that the binding stability between PDI-NH2 and PP is very good due to the strong electrostatic and hydrophobic interactions between them. Since microplastics are produced by different natural forces under different environmental conditions, they exhibit different morphologies and surface electrical properties. Subsequently, we tested the responsiveness of PDI-NH2 to different types of microplastics, such as PE, PVC, PLA, PMMA, and PS. Figure 7 As shown, there are significant differences in the responsiveness of PDI-NH2 to different types of microplastics, and the proposed sensor exhibits a higher ECL response only in the presence of the target PP, which indicates that the ECL sensor has a strong selectivity for the determination of PP.

[0027] Mechanism study of electrochemiluminescence detection system When the sensor is used to detect microplastic polypropylene, first, the luminophore PDI-NH2 interacts with the negatively charged polypropylene surface through electrostatic interaction. Figure 8According to the results, in PBS buffer solution, the zeta potential of polypropylene (PP) was -4.22 mV. During the experiment, the absolute value of the zeta potential of the system increased to 0.536 mV after the addition of PDI-NH2. This result indicates that the positively charged PDI-NH2 molecules bind to the PP surface through electrostatic interactions, resulting in a significant change in potential. In comparison, when PDI-NH2 binds to other types of microplastics, the change in potential is smaller, and the absolute value fluctuates only slightly, indicating that the electrostatic interaction force is weak or almost non-existent in these cases. Subsequently, we performed Fourier transform infrared spectroscopy (FTIR) analysis (see Figure 5 D). PDI-NH2 was mixed with different types of microplastics in a PBS solution and then vacuum dried. The infrared spectra before and after mixing were compared. Fig. 9 It shows that after PDI-NH2 is mixed with PP, the stretching vibration peaks of -CH2- and -CH3 groups of PP appear clearly in the range of 2800 cm⁻¹ to 3000 cm⁻¹, while the bending vibration peak of -CH2- appears at 1453 cm⁻¹, the symmetric deformation vibration peak of -CH3 group appears at 1375 cm⁻¹, and the in-plane rocking vibration peak of -CH3 appears at 971 cm⁻¹. These characteristic peaks indicate that there is an effective interaction between PDI-NH2 and PP. It further proves that the interaction between PDI-NH2 and PP is more significant.

[0028] Practical Application of Electrochemiluminescence Detection System In daily use, plastic food packaging materials such as tea bags, lunch boxes, mineral bottles and disposable cups also release microplastics. Therefore, the present invention selects the most commonly used disposable food packaging boxes to detect the release of soluble microplastics.

[0029] Four different brands of PP disposable food packaging boxes were purchased from the supermarket, labeled as PP-A, PP-B, PP-C, and PP-D. In order to simulate the process of preserving different foods, 50 mL of ultrapure water at 85°C was added to the food container and shaken in a water bath at the same temperature for 30 minutes. The water sample was then filtered through a 0.22µm filter and concentrated by rotary distillation to obtain a 100μL concentrated solution, which was stored in a clean sample bottle for use.

[0030] Using the standard addition method, 4 mg•L -1 , 8 mg•L -1 and 12 mg•L -1 The polypropylene standard solution was prepared to obtain the spiked sample.

[0031] All PP packaging box spiked samples were tested using the electrochemiluminescence detection system constructed in the above embodiment. The measurement data are shown in Table 1 below. It can be seen that the sample recovery rate of PP in the spiked samples is between 92.71% and 104.94%, indicating that PP can be effectively detected in actual samples.

[0032] Table 1 Concentration and recovery rate of microplastics released from polypropylene plastic packaging boxes of different brands Note: a is the average value of three measurements.

[0033] In order to further evaluate the performance of the constructed electrochemiluminescence detection system in detecting microplastics in complex environmental water samples, this method was applied to tap water samples.

[0034] For tap water samples, the tap was turned on for 5 min, 1000 mL of tap water was measured with a graduated cylinder, and then filtered through a 0.22 µm filter three times, and the water samples were then stored in clean glass bottles with glass stoppers for later use.

[0035] The standard addition method was also used to add 4 mg•L -1 , 8 mg•L -1 and 12mg•L -1 The tap water spiked samples were obtained by mixing the polypropylene standard solution.

[0036] All tap water spiked samples were tested using the electrochemiluminescence detection system constructed in the above embodiment. The measurement data are shown in Table 2 below. It can be seen that the recovery rate of PP in the samples varies between 98.2% and 107.64%, indicating that PP can be effectively detected in complex environmental water samples.

[0037] Table 2 Concentration and recovery rate of microplastics in tap water Note: a is the average of three measurements; b is not within the detection limit; ND: below the detection limit.

Claims

1. A method for detecting polypropylene content in an aqueous solution based on electrochemiluminescence, characterized in that: The following steps are involved: 1) Prepare a series of polypropylene standard solutions; 2) PDI-NH2 probe is used as an electrochemiluminescent reagent and K2S2O8 is used as a co-reactant, which are co-dissolved in phosphate buffer to obtain an electrochemiluminescent reaction solution; 3) The series of polypropylene standard solutions in step 1) are mixed with the electrochemiluminescence reaction solution in step 2) to obtain a series of electrolytes; the electrochemiluminescence intensity of the series of electrolytes is measured using a three-electrode system to construct a standard curve or linear equation between the electrochemiluminescence intensity and the polypropylene concentration; 4) Mixing the polypropylene sample solution to be tested with the electrochemiluminescence reaction solution in step 2), measuring the electrochemiluminescence intensity, and obtaining the polypropylene concentration in the polypropylene sample solution to be tested by the standard curve or linear equation of electrochemiluminescence intensity and polypropylene concentration constructed in step 3).

2. A method for detecting polypropylene content in an aqueous solution based on electrochemiluminescence as claimed in claim 1, characterized in that: The preparation of the PDI-NH2 probe includes: First, 3,4,9,10-perylenetetracarboxylic dianhydride and mono-BOC-ethylenediamine are co-dissolved in tetrahydrofuran, stirred continuously for 16-24 hours at 70-90°C under N2 protection, centrifuged, and washed with sodium hydroxide solution and deionized water to obtain an intermediate product; then, the intermediate product is dissolved in dichloromethane and trifluoroacetic acid is added dropwise, stirred continuously at room temperature for 2-5 hours, centrifuged, and washed with dichloromethane to obtain the final product PDI-NH2.

3. A method for detecting polypropylene content in an aqueous solution based on electrochemiluminescence as claimed in claim 2, characterized in that: The molar ratio of the 3,4,9,10-perylenetetracarboxylic dianhydride to mono-BOC-ethylenediamine is 1:2-2:1; and 0.5-1 mL of trifluoroacetic acid is required for each 0.1 g of the intermediate product for deprotection.

4. A method for detecting polypropylene content in an aqueous solution based on electrochemiluminescence as claimed in claim 1, characterized in that: The pH of the phosphate buffer is 7.

4.

5. A method for detecting polypropylene content in an aqueous solution based on electrochemiluminescence as claimed in claim 1, characterized in that: The three-electrode system uses GCE as the working electrode, Pt column as the counter electrode, and Ag / AgCl as the reference electrode; the potential window for measuring the electrochemical luminescence intensity is 0~-2.0V.

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