A method for detecting polypropylene content in aqueous solution based on electrochemiluminescence

Abstract

This invention belongs to the field of electrochemical sensing and detection, specifically relating to a method for detecting polypropylene (PP) content in aqueous solutions based on electrochemiluminescence (ECL). First, a novel amphiphilic perylene derivative (PDI-NH₂) ECL sensor is prepared for ultrasensitive detection and labeling of polypropylene microplastics (PP) in aqueous solutions. Due to its inherent amphiphilic structure, the positively charged PDI-NH₂ can efficiently capture trace amounts of PP in aqueous solutions, thereby enhancing the ECL signal. Notably, the ECL sensor based on the PDI-NH₂ luminescent group exhibits high stability and excellent sensitivity to PP, and demonstrates a rapid response time to PP, as low as 12 s, enabling efficient identification and detection of PP in complex environments. This method effectively identifies and quantifies PP microplastics without additional pretreatment or complex instruments, making it an ideal tool for accurately quantifying microplastics in aqueous solutions.

Description

Technical Field

[0001] This invention belongs to the field of biosensing and detection, specifically relating to a method for detecting polypropylene content in aqueous solution based on electrochemiluminescence. Background Technology

[0002] Microplastic particles, smaller than 5 mm, 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, making them an emerging global concern. As microplastics are released into the environment in large quantities, they degrade and weather, forming tiny plastic fragments that directly harm 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 ease of processing. Over the years, significant progress has been made in the development and utilization of PP, which is widely used in various industries, commonly found in many packaging products, cosmetics, and personal care products, accounting for 16-20% of the entire plastics industry. Furthermore, large amounts of PP waste cause serious environmental pollution, as it takes more than 30 years to decompose naturally. Therefore, monitoring PP's presence in soil, water, and air to assess its impact on ecosystems is particularly important. Current detection methods include visual analysis, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, high-performance liquid chromatography (HPLC) combined with mass spectrometry, and fluorescence detection. However, these methods are expensive, involve complex sample preparation steps, are time-consuming, and are susceptible to fluorescence interference. Electrochemiluminescence (ECL) analysis combines the advantages of spectroscopy and electrochemistry, offering advantages such as 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 based on ECL analysis to effectively detect and track micron-sized plastics in samples. Summary of the Invention

[0003] The present invention aims to disclose a method for detecting polypropylene content in aqueous solution based on electrochemiluminescence. This method utilizes a novel amphiphilic perylene derivative (PDI-NH2) that has a unique "signal-on" effect on polypropylene microplastics (PP) to achieve efficient identification and quantitative detection of PP microplastics in aqueous solution.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for detecting polypropylene content in aqueous solution based on electrochemiluminescence includes the following steps:

[0006] 1) Prepare a series of polypropylene standard solutions of varying concentrations;

[0007] 2) Using PDI-NH2 probe as electrochemiluminescence reagent and K2S2O8 as co-reactant, they were co-dissolved in phosphate buffer to obtain electrochemiluminescence reaction solution;

[0008] The preparation of the PDI-NH2 probe includes:

[0009] First, 3,4,9,10-perylenetetracarboxylic dianhydride and mono-BOC-ethylenediamine were co-dissolved in tetrahydrofuran and stirred continuously for 16-24 h under N2 protection at 70-90 °C. After centrifugation, the mixture was washed with sodium hydroxide solution and deionized water to obtain an intermediate product. Then, the intermediate product was dissolved in dichloromethane and trifluoroacetic acid was added dropwise. The mixture was stirred continuously at room temperature for 2-5 h, centrifuged, and washed with dichloromethane to obtain the final product PDI-NH2.

[0010] The molar ratio of the 3,4,9,10-perylenetetracarboxylic dianhydride and mono-BOC-ethylenediamine is 1:2 to 2:1; 0.5 to 1 mL of trifluoroacetic acid is required for protection of each 0.1 g intermediate.

[0011] The phosphate buffer solution has a pH of 7.0, specifically a 0.1 M phosphate buffer solution containing 0.1 M KCl.

[0012] 3) Mix the series of polypropylene standard solutions from step 1) with the electrochemiluminescence reaction solution from step 2) to obtain a series of electrolytes; then measure the electrochemiluminescence intensity of the series of electrolytes using a three-electrode system, and construct a standard curve or linear equation between the electrochemiluminescence intensity and the polypropylene concentration.

[0013] The three-electrode system uses GCE as the working electrode, a Pt column as the counter electrode, and Ag / AgCl as the reference electrode; the potential window for measuring the electrochemiluminescence intensity is 0 to -2.0 V.

[0014] 4) Mix the polypropylene-containing solution to be tested with the electrochemiluminescence reaction solution in step 2), measure the electrochemiluminescence intensity, and obtain the polypropylene concentration in the polypropylene-containing solution to be tested by using the standard curve or linear equation of electrochemiluminescence intensity versus polypropylene concentration constructed in step 3).

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] This invention utilizes a novel amphiphilic perylene derivative (PDI-NH2) with a unique "signal-on" effect on polypropylene microplastics (PP) as a luminescent group to construct an electrochemiluminescence (ECL) detection system for ultrasensitive detection and labeling of PP microplastics in aqueous solutions. Due to its inherent amphiphilic structure, the positively charged PDI-NH2 can efficiently capture trace amounts of PP in aqueous solutions, thereby enhancing the ECL signal. Notably, the ECL based on the PDI-NH2 luminescent group exhibits high stability and excellent sensitivity to PP, with an ideal linear range (5 μg·ml). -1 Up to 45 μg·ml -1 ) and low limit of detection (0.948 mg·L⁻¹) −1 Furthermore, this ECL exhibits a rapid response to PP, with a response time as low as 12 seconds, enabling efficient identification and detection of polypropylene in complex environments.

[0017] In summary, this invention provides a simple and sensitive method for detecting PP. This method can effectively identify and quantify microplastics PP without additional pretreatment or complex instruments, making it an ideal tool for accurately quantifying microplastics in aqueous solutions. Attached Figure Description

[0018] Figure 1 The image shows the infrared spectrum of PDI-NH2 synthesized in an embodiment of the present invention.

[0019] Figure 2 The image shows the 1H NMR spectrum of PDI-NH2 synthesized in this embodiment of the invention.

[0020] Figure 3 The influencing factors of the electrochemiluminescence detection system constructed in the embodiments of the present invention are: (A) concentration of co-reactant K2S2O8; (B) pH value; (C) scan rate; and (D) potential range.

[0021] Figure 4 The effect of the PDI-NH2 concentration synthesized in this embodiment of the invention on the electrochemiluminescence detection system is shown in the following: (A) optimization of PDI-NH2 concentration; (B) cycle stability tested under optimal experimental conditions.

[0022] Figure 5 The ECL intensity and PP concentration response of the electrochemiluminescence detection system constructed in this embodiment of the invention are shown in the figure, wherein: (A) ECL plots of PP at different concentrations; (B) Linear relationship between ECL intensity and PP concentration.

[0023] Figure 6 The stability of the electrochemiluminescence detection system constructed in the embodiments of the present invention.

[0024] Figure 7The selectivity of the electrochemiluminescence detection system constructed for embodiments of the present invention.

[0025] Figure 8 Mechanism investigation of the electrochemiluminescence detection system constructed for embodiments of the present invention: Changes in zeta potential before and after mixing with 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 ).

[0026] Figure 9 Mechanism investigation of the electrochemiluminescence detection system constructed for embodiments of the present invention: changes in infrared radiation before and after mixing polypropylene (PP) and probe PDI-NH2. Detailed Implementation

[0027] The present invention will be further explained and described below with reference to specific embodiments. Example

[0028] 1. Synthesis of PDI-NH2

[0029] First, 0.392 g of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and 0.32 mL of mono-BOC-ethylenediamine were added to 15 mL of tetrahydrofuran (THF). The mixture was then stirred continuously for 18 h at 80 °C under N2 protection. The mixture was centrifuged and washed three times with sodium hydroxide solution (NaOH, 1%) and deionized water to remove excess substances, yielding an intermediate product. Next, 0.2 g of the intermediate product was dissolved in 5 mL of dichloromethane (DCM), and 1 mL of trifluoroacetic acid (F3CCOOH) was added dropwise. The mixture was stirred continuously at room temperature for 3 h, and finally centrifuged. The mixture was washed multiple times with dichloromethane (DCM) to remove excess substances, yielding the final product PDI-NH2.

[0030] 2. Construction of Electrochemiluminescence (ECL) Detection System

[0031] 2.1 Preparation of Polypropylene Standard Solution

[0032] A series of polypropylene standard solutions with different concentrations were prepared by diluting a 1.0 mg / mL polypropylene solution with pH=7.4 using a 0.1 M phosphate buffer containing 0.1 M KCl. The concentration range was 5.0 μg / mL to 45.0 μg / mL.

[0033] 2.2 Preparation of PDI-NH2 solution

[0034] Prepare a 4 μM PDI-NH2 solution using ultrapure water, and then dilute it to 16 mM for later use.

[0035] 2.3 Preparation of PDI-NH2 / K2S2O8 electrochemiluminescence reaction solution

[0036] The PDI-NH2 / K2S2O8 electrochemiluminescence reaction solution containing 150 μM K2S2O8 and 0.30 μM PDI-NH2 was prepared using a 0.1 M phosphate buffer containing 0.1 M KCl at pH 7.4.

[0037] 2.4 Establishing a linear relationship between electrochemiluminescence intensity and polypropylene concentration

[0038] A three-electrode system was constructed using GCE as the working electrode, a Pt column as the counter electrode, and Ag / AgCl as the reference electrode, containing different concentrations of polypropylene (5 μg·ml). -1 Up to 45 μg·ml -1 Using PDI-NH2 / K2S2O8 electrochemiluminescence reaction solution as the electrolyte, cyclic voltammetry was performed within an electrochemical window of -2.0 to 0 V, with a photomultiplier tube voltage of 800 V, a magnification level of 4, and a scan rate of 0.15 V / s. The difference in luminescence intensity (ΔECL) before and after the addition of polypropylene was recorded, and a linear regression equation between polypropylene concentration and the difference in luminescence intensity (ΔECL) was constructed. Subsequently, the polypropylene-containing sample solution to be tested was mixed with the PDI-NH2 / K2S2O8 electrochemiluminescence reaction solution, and the electrochemiluminescence intensity was measured. The concentration of polypropylene in the polypropylene-containing sample solution to be tested can then be obtained from the linear regression equation.

[0039] Characterization of PDI-NH2 and performance evaluation of the electrochemiluminescence detection system

[0040] 1. Characterization of PDI-NH2

[0041] Figure 1 This is the infrared spectrum of PDI-NH2 synthesized in an embodiment of the present invention. Figure 1 It can be seen that the tertiary amide group in the PDI-NH2 molecule is located at 1688 cm⁻¹. −1 A sharp band indicates that an amidation reaction occurred between PTCDA and mono-BOC-ethylenediamine. Figure 2 The above is the 1H NMR spectrum of PDI-NH2 synthesized in this embodiment of the invention, with DMSO as the deuterated reagent. d 6. ( 1¹H NMR (400 MHz, DMSO-d⁶) δ 8.71 (s, 4H), 7.94 (s, 4H), 4.35 (t, J = 5.8 Hz, 4H), 3.27–3.13 (m, 4H). The above tests all confirm the successful preparation of the probe molecule.

[0042] 2. Factors affecting the electrochemiluminescence detection system

[0043] To achieve the optimal electrochemiluminescence (ECL) performance of the system, numerous experiments were conducted to investigate factors that might affect ECL performance. The results are as follows: Figure 3 and 4 As shown.

[0044] We found that the ECL strength of PDI-NH2 increased with increasing concentration of the co-reactant K2S2O8, reaching its maximum at 150 mM. Figure 3 A) indicates that K2S2O8 can serve as an effective co-reactant to amplify the ECL emission of PDI-NH2. Furthermore, pH optimization of the system revealed an optimal pH of 7.4. Figure 3 B). Furthermore, the strongest ECL signal was observed when the optimized scan rate was 0.15 V / s and the potential window range was 0 ~ -2.0 V. Figure 3 C, D). Subsequently, we explored the optimal concentration of PDI-NH2 under optimal conditions, and the ECL luminescence intensity reached its maximum when the concentration of PDI-NH2 was 0.30 μM. Figure 4 A). From Figure 4 As can be seen from B, under 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%, demonstrating good stability and reliability, laying a solid foundation for subsequent research.

[0045] 3. Performance analysis of the electrochemiluminescence detection system for microplastic detection

[0046] To evaluate the performance of the proposed sensor, ECL measurements were performed on target PP at different concentrations under optimal reaction conditions. Figure 5 As shown in A, at 5 μg•ml -1 ~45μg•ml -1 Within this range, ECL intensity increases with increasing PP concentration. For example... Figure 5 As shown in Figure B, the calibration plot shows a good linear relationship between ECL intensity and PP concentration, with a linear regression equation of I = 158.68x + 8769.57 and a detection limit of 0.948 mg•L. −1 (Signal-to-noise ratio (S / N) = 3).

[0047] Stability and selectivity are two important factors in evaluating the performance of a proposed sensor. For example... Figure 6 As shown, the ECL intensity remained relatively stable after 20 consecutive scan cycles, with a corresponding relative standard deviation (RSD) of 2.93%. The results indicate that the bonding stability between PDI-NH2 and PP is excellent due to the strong electrostatic and hydrophobic interactions. Since microplastics are generated 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, PDI-NH2 exhibits significant differences in its responsiveness to different types of micron-sized plastics. The proposed sensor only shows a high ECL response in the presence of the target PP, indicating that the ECL sensor has strong selectivity for PP measurement.

[0048] Mechanism of electrochemiluminescence detection system

[0049] When using this sensor to detect microplastic polypropylene, firstly, the luminescent group PDI-NH2 interacts with the negatively charged polypropylene surface through electrostatic attraction. According to... Figure 8 The results showed that the zeta potential of polypropylene (PP) in PBS buffer solution was -4.22 mV. During the experiment, the absolute value of the zeta potential increased to 0.536 mV after the addition of PDI-NH2. This result indicates that positively charged PDI-NH2 molecules bind to the PP surface through electrostatic interactions, leading to a significant change in potential. In contrast, the potential change was smaller when PDI-NH2 bound to other types of microplastics, with only slight fluctuations in absolute value, indicating weak or almost non-existent electrostatic interactions 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 PBS solution, and then vacuum dried. The infrared spectra before and after mixing were compared. Figure 9 The results show that after mixing PDI-NH2 with PP, stretching vibration peaks of the -CH2- and -CH3 groups of PP are clearly observed in the 2800 cm⁻¹ to 3000 cm⁻¹ range. Simultaneously, a bending vibration peak of -CH2- appears at 1453 cm⁻¹, a symmetric deformation vibration peak of -CH3 group appears at 1375 cm⁻¹, and an in-plane rocking vibration peak of -CH3 appears at 971 cm⁻¹. These characteristic peaks indicate an effective interaction between PDI-NH2 and PP. This further demonstrates that the interaction between PDI-NH2 and PP is more significant.

[0050] Practical applications of electrochemiluminescence detection systems

[0051] During daily use, plastic food packaging materials such as tea bags, lunch boxes, mineral bottles, and disposable water cups also release microplastics. Therefore, this invention selects the most commonly used disposable food packaging boxes to detect the release of soluble microplastics.

[0052] Four different brands of disposable PP food packaging boxes, labeled PP-A, PP-B, PP-C, and PP-D, were purchased from a supermarket. To simulate the preservation process of different foods, 50 mL of ultrapure water at 85°C was added to the food containers, and the containers were shaken in a water bath at the same temperature for 30 minutes. The water sample was then filtered through a 0.22µm filter, and the sample was concentrated by rotary distillation to obtain 100 μL of concentrated solution, which was stored in a clean sample bottle for later use.

[0053] Using the standard addition method, a concentration of 4 mg•L was added to each of the four sample solutions. -1 8 mg•L -1 and 12 mg•L -1 A polypropylene standard solution was used to obtain spiked samples.

[0054] The electrochemiluminescence detection system constructed in the above embodiments was used to detect all PP packaging box spiked samples. The measurement data are shown in Table 1 below. It can be seen that the 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.

[0055] Table 1. Concentration and recovery rate of microplastics released from polypropylene plastic packaging boxes of different brands.

[0056]

[0057] Note: a is the average of three measurements.

[0058] To further evaluate the performance of the constructed electrochemiluminescence detection system in detecting microplastics in water samples from complex environments, the method was applied to tap water samples.

[0059] For tap water samples, turn on the tap for 5 minutes, measure 1000 mL of tap water using a graduated cylinder, then filter it three times through a 0.22µm filter, and then store the water sample in a clean glass bottle with a glass stopper for later use.

[0060] Using the same standard addition method, a concentration of 4 mg•L was added to the tap water sample solution. -1 8 mg•L -1 and 12 mg•L -1A polypropylene standard solution was used to obtain spiked samples of tap water.

[0061] The electrochemiluminescence detection system constructed in the above embodiments was used to detect all tap water spiked samples. The measurement data are shown in Table 2 below. It can be seen that the recovery rate of PP in the spiked samples varied between 98.2% and 107.64%, indicating that PP can be effectively detected in water samples in complex environments.

[0062] Table 2. Concentration and recovery rate of microplastics in tap water.

[0063]

[0064] Note: a is the average of three measurements; b indicates values ​​outside the detection limit; ND indicates values ​​below the detection limit.

Claims

1. A method for detecting polypropylene content in aqueous solution based on electrochemiluminescence, characterized in that, Includes the following steps: 1) Prepare a series of polypropylene standard solutions of varying concentrations; 2) Using PDI-NH2 probe as electrochemiluminescence reagent and K2S2O8 as co-reactant, they were co-dissolved in phosphate buffer to obtain electrochemiluminescence reaction solution; 3) Mix the series of polypropylene standard solutions from step 1) with the electrochemiluminescence reaction solution from step 2) to obtain a series of electrolytes; then measure the electrochemiluminescence intensity of the series of electrolytes using a three-electrode system, and construct a standard curve or linear equation between the electrochemiluminescence intensity and the polypropylene concentration. 4) Mix the polypropylene sample solution to be tested with the electrochemiluminescence reaction solution in step 2), measure the electrochemiluminescence intensity, and obtain the polypropylene concentration in the polypropylene sample solution to be tested by using the standard curve or linear equation of electrochemiluminescence intensity versus polypropylene concentration constructed in step 3).

2. The method for detecting polypropylene content in aqueous solution based on electrochemiluminescence as described 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 were co-dissolved in tetrahydrofuran and stirred continuously for 16-24 h under N2 protection at 70-90 °C. After centrifugation, the mixture was washed with sodium hydroxide solution and deionized water to obtain an intermediate product. Then, the intermediate product was dissolved in dichloromethane and trifluoroacetic acid was added dropwise. The mixture was stirred continuously at room temperature for 2-5 h, centrifuged, and washed with dichloromethane to obtain the final product PDI-NH2.

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

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

4.

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

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