Preparation and application of molecularly imprinted sensitive membrane modified electrode for perfluorooctane sulfonic acid detection

Abstract

The invention belongs to the field of electroanalytical chemistry / electrochemical sensors, and discloses preparation and application of a molecularly imprinted sensitive membrane modified electrode for perfluorooctane sulfonic acid detection. According to the method, aniline and o-fluoroaniline are selected as bifunctional monomers, PFOS is taken as a template molecule, in-situ electropolymerization is carried out through cyclic voltammetry, and the molecularly imprinted sensitive membrane capable of specifically recognizing PFOS is obtained. According to the invention, o-fluoroaniline is introduced and is combined with a fluorocarbon chain of PFOS through F-F interaction, and due to the existence of fluorine atoms, non-specific combination can be reduced, so that the anti-interference capability of the molecularly imprinted sensitive membrane is stronger, and the selective limitation on a perfluorinated compound composed of a sulfonic acid group and the fluorocarbon chain is reduced; according to the invention, aniline is used as another functional monomer, so that the conductivity can be improved, and the aniline and o-fluoroaniline can be doped and electrically polymerized to form fluorinated polyaniline. And the chemical property of the fluorinated polyaniline is relatively stable, so that the stability of the eluted molecularly imprinted cavity is relatively high.

Description

Technical Field

[0001] The invention belongs to the technical field of electroanalytical chemistry / electrochemical sensors and relates to the preparation and application of a molecular imprinting sensitive membrane modified electrode for perfluorooctane sulfonic acid detection. Background Art

[0002] Perfluorooctane sulfonic acid (PFOS) is a persistent organic pollutant. Because it contains many CFs with extremely high bond energies, PFOS has strong hydrophobicity, lipophobicity, chemical and thermal stability. It has been widely used in various industrial and consumer products in the past few decades. The other end of PFOS is a polar sulfonic acid group, which has a certain degree of hydrophilicity and solubility in water. It is also considered to be the main transmission route of PFOS in the environment. PFOS is regarded as a new pollutant under control in China, so the detection of PFOS in water is particularly important.

[0003] Currently, many technologies have been developed for the detection of PFOS. Instrumental detection methods such as liquid chromatography-tandem mass spectrometry (LC-MS / MS) and gas chromatography-mass spectrometry (GC-MS) are widely used for PFOS detection. However, these methods have drawbacks such as complex operation, high cost, and difficulty in on-site detection. Therefore, a rapid, sensitive, and simple detection method is needed. Electrochemical sensors have the advantages of low cost, ease of miniaturization, simplicity of operation, and high sensitivity. They are convenient for on-site detection and have a high cost-effectiveness ratio, and have been applied to the detection of PFOS.

[0004] However, there are many perfluorinated compounds similar to PFOS, such as PFOA, PFNA, PFH X S all have long carbon-fluorine chains, so they are easily affected by nonspecific adsorption during detection using electrochemical sensors, resulting in insufficient specificity and difficulty in tracing the source of PFOS pollution and monitoring its spread in the environment. Molecular imprinting not only has high affinity and selectivity for the target, but is also low-cost and easy to make. However, most of the molecular imprinting sensitive membranes currently used for identifying PFOS use o-phenylenediamine as the molecular imprinting functional monomer, which has the advantages of simple preparation and low cost. However, the binding of o-phenylenediamine to PFOS is achieved through the use of sulfonyl and amino groups, without utilizing the structure of the carbon-fluorine chain of PFOS, which has certain limitations on the selectivity for perfluorinated compounds that are also composed of sulfonic acid groups and carbon-fluorine chains (Mattia P, S, Adrian O, et al., Engineering boron and nitrogen codoped carbon nanoarchitectures to tailor molecularly imprinted polymers for PFOS determination [J], Journal of Hazardous Materials, 2023, 458, 131873.). Furthermore, using only o-phenylenediamine as a single monomer is chemically unstable, resulting in low stability of the molecularly imprinted cavity after removal. Therefore, they attempted to use a fluorine-containing functional monomer combined with o-fluoroaniline monomer to prepare a stable molecularly imprinted sensitive membrane. This, combined with an electrochemical sensor, enabled the specific recognition and detection of PFOS through FF interactions in addition to hydrogen bonding. Summary of the Invention

[0005] To address the above problems, the present invention provides a method for preparing a molecularly imprinted sensitive membrane modified electrode for perfluorooctane sulfonic acid (PFOS) detection and its electrochemical sensing application, addressing the problems of limited detection performance and poor specificity due to the single functional monomer in PFOS detection. Because aniline molecules have the advantages of high conductivity and ease of electrochemical synthesis, aniline is selected as the functional monomer of the molecular imprinting, allowing it to interact with PFOS through hydrogen bonds. At the same time, in order to improve the specific recognition ability of PFOS, a new fluorine-containing functional monomer, o-fluoroaniline, is introduced. This further allows PFOS to interact with the functional monomer through FF and can be electrically doped with aniline to form a more stable fluorinated polyaniline. Finally, aniline and o-fluoroaniline are selected as bifunctional monomers for synthesizing a molecularly imprinted sensitive membrane for detecting PFOS.

[0006] The technical solution of the present invention:

[0007] A method for preparing a molecularly imprinted sensitive membrane modified electrode for perfluorooctane sulfonic acid detection comprises the following steps:

[0008] Step S1, using acetate buffer solution as solvent, PFOS as template molecule, aniline and o-fluoroaniline as bifunctional monomers to obtain an electropolymerization solution;

[0009] Step S2, pre-treating the glassy carbon electrode by polishing and cleaning the glassy carbon electrode with aluminum oxide powder;

[0010] Step S3, placing the pretreated glassy carbon electrode in an electropolymerization solution, using a platinum wire as a counter electrode, Ag / AgCl as a reference electrode, and the pretreated glassy carbon electrode as a working electrode, polymerizing in the solution by cyclic voltammetry to obtain a molecularly imprinted membrane modified electrode;

[0011] Step S4: immersing the obtained molecularly imprinted membrane modified electrode in a mixed solution of methanol and water to elute the template molecules, thereby obtaining a molecularly imprinted sensitive membrane modified electrode (MIP / GCE) for PFOS detection.

[0012] Preferably, in step S1, the pH of the acetate buffer solution is 3-7, the concentration of PFOS in the acetate buffer solution is 0.5-5 mmol / L, the molar concentration ratio of aniline to o-fluoroaniline is 1:1-7:1, and the concentration of aniline in the acetate buffer solution is 10-50 mmol / L.

[0013] Preferably, in step S2, the glassy carbon electrode is polished on suede with 1.0 μm, 0.3 μm, and 0.05 μm Al2O3 powders in sequence, and then ultrasonically cleaned with deionized water and ethanol for 1 min respectively, and rinsed with deionized water after each ultrasonication to obtain a pretreated glassy carbon electrode;

[0014] Preferably, in step S3, the scan rate of the polymerization by cyclic voltammetry is 30 to 100 mV / s, and the number of polymerization cycles is 5 to 30 cycles;

[0015] Preferably, in step S4, the volume ratio of methanol to water is 3:1 to 10:1, and the elution time is 5 to 30 minutes.

[0016] An application of the molecularly imprinted sensitive membrane obtained by the above preparation method is to obtain a molecularly imprinted sensitive membrane modified electrode for PFOS detection in step S4, which can detect PFOS in water. The application steps are as follows:

[0017] (1) Using 0.1M acetate buffer solution as solvent, prepare a PFOS solution with a concentration of 1000-0.1nmol / L; immerse the MIP / GCE prepared in step S4 in the above solution for incubation, and use the incubated MIP / GCE modified electrode as the working electrode, platinum wire as the counter electrode, and Ag / AgCl electrode as the reference electrode to form a three-electrode system. Place the system in a mixture of 5m mol / L K3[Fe(CN)6] and 0.1mol / L KCl for cyclic voltammetry scanning (electrochemical parameters are set as: scanning potential range -0.2-0.6V, scanning rate 100mV / s). Detect the current values ​​of MIP / GCE before and after incubation in different incubation solutions, and draw a standard curve with the peak current difference as the vertical axis and the concentration as the horizontal axis;

[0018] (2) PFOS and some possible coexisting interfering substances were detected using MIP / GCE modified electrodes, including structurally similar PFASs such as PFOA, PFBA, PFBS, and PFHxA.

[0019] Beneficial effects of the present invention:

[0020] 1. The present invention introduces o-fluoroaniline, which binds to the carbon fluoride chain of PFOS through FF interaction. Due to the presence of fluorine atoms, nonspecific binding can be reduced, making the anti-interference ability of the molecular imprinting sensitive membrane stronger, and reducing the selectivity restriction for perfluorinated compounds composed of sulfonic acid groups and carbon fluoride chains;

[0021] 2. The present invention uses aniline as another functional monomer, which not only improves conductivity but also allows for doping and electropolymerization with o-fluoroaniline to form fluorinated polyaniline. The chemical stability of fluorinated polyaniline also enhances the stability of the molecularly imprinted cavity after elution. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The figure is a flow chart for preparing the molecularly imprinted sensitive membrane for perfluorooctane sulfonic acid according to the present invention.

[0023] Figure 2 The cyclic voltammograms of the NIP / GCE electrode of the present invention before and after elution in a mixed solution of 5 mmol / L K3[Fe(CN)6] and 0.1 mol / L KCl.

[0024] Figure 3 The cyclic voltammograms of the MIP / GCE electrode of the present invention before and after elution and after incubation in a mixed solution of 5 mmol / L K3[Fe(CN)6] and 0.1 mol / L KCl.

[0025] Figure 4 This is the standard curve obtained by the electrochemical response of the MIP / GCE electrode of the present invention to different concentrations of PFOS.

[0026] Figure 5 This is a comparison diagram of the response of the MIP / GCE electrode of the present invention to PFOS analogue interferors.

[0027] Figure 6 This is a comparison diagram of the response of the MIP / GCE electrode prepared using aniline as the functional monomer of the present invention to PFOS analogue interference. DETAILED DESCRIPTION

[0028] The following further illustrates the specific implementation of the present invention in conjunction with the accompanying drawings and technical solutions.

[0029] The present invention provides a method for preparing a molecular imprinted sensitive membrane for PFOS detection. The preparation flow chart is as follows: Figure 1 As shown, and includes the following specific steps

[0030] Example 1:

[0031] Step S1, using a 0.1 mol / L acetate buffer solution with a pH of 5 as a solvent, PFOS as a template molecule, controlling its concentration in the acetate buffer solution to be 1 mmol / L, aniline and o-fluoroaniline as bifunctional monomers, controlling the concentration of aniline in the acetate buffer solution to be 36.5 mmol / L, and the concentration of o-fluoroaniline in the acetate buffer solution to be 11 mmol / L, to obtain an electropolymerization solution;

[0032] In step S2, the glassy carbon electrode is pretreated by polishing it on suede with 1.0 μm, 0.3 μm, and 0.05 μm Al2O3 powders, and then ultrasonically cleaning it with deionized water and ethanol for 1 minute respectively. After each ultrasonic cleaning, it is rinsed with deionized water to obtain a pretreated glassy carbon electrode.

[0033] Step S3, placing the pretreated glassy carbon electrode in the electropolymerization solution, using a platinum wire as a counter electrode, Ag / AgCl as a reference electrode, and the pretreated glassy carbon electrode as a working electrode, polymerizing for 10 cycles at a scan rate of 50 mV / s in a voltage range of -0.2 to 1.3 V by cyclic voltammetry to obtain a molecularly imprinted membrane modified electrode;

[0034] Step S4: After polymerization, the obtained molecularly imprinted membrane modified electrode is immersed in a methanol / water mixed solution with a volume ratio of methanol to water of 6:1. The solution is gently stirred at 60 rpm and immersed for 10 minutes to elute the template molecules, thereby obtaining a molecularly imprinted sensitive membrane for PFO S.

[0035] The cyclic voltammetry curves of non-molecularly imprinted sensitive membrane modified electrode (NIP / GCE) and MIP / GCE before and after elution and after incubation were detected by cyclic voltammetry in a mixture of 5 mmol / L K3[Fe(CN)6] as a probe and 0.1 mol / L KCl as a supporting electrolyte. Figure 2 and Figure 3 As shown, NIP / GCE showed no obvious redox peaks before and after elution. However, before elution, MIP / GCE exhibited no obvious redox peaks due to the presence of a non-conductive film on the electrode surface, preventing the probe from reaching the electrode surface. After elution, a distinct redox peak was observed, indicating that the template molecule PFOS was successfully removed, releasing a cavity that allowed the probe to reach the electrode surface. After incubation in 100 nmol / L PFOS, the redox peak significantly decreased again due to the reoccupancy of the cavity by PFOS, confirming the successful preparation of MIP / GCE.

[0036] Electrochemical sensing applications of this embodiment:

[0037] The molecularly imprinted sensitive membrane obtained in step S4 was used for the determination of PFOS:

[0038] (1) Using 0.1M acetate buffer solution as solvent, a PFOS solution of a certain concentration was prepared. The concentration range of the PFOS solution was 1000~0.1nmol / L. A three-electrode system was formed with a MIP / GCE modified electrode as the working electrode, a platinum wire as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The system was placed in a PFOS solution within the above concentration range for cyclic voltammetry scanning. The electrochemical parameters were set as follows: scanning potential range -0.2~0.6V, scanning rate 100mV / s. Figure 4 It can be seen that within the concentration range of 0.1 to 1000 nmol / L, the current changes show regularity and a good linear relationship. As the concentration increases, the amount of PFOS adsorbed in the cavity gradually increases, hindering the probe from reaching the electrode surface, resulting in a gradual decrease in the redox peak. This shows that the MIP / GCE modified electrode in this example has a wide linear detection range and a low detection limit, and has good detection performance for PFOS.

[0039] (2) MIP / GCE was used to detect PFOS and some possible coexisting interfering substances, including PFASs with similar structures such as PFOA, PFBA, PFBS, PFHxA, etc. Figure 5 As known, it can be obtained that the cyclic voltammetric current response of MIP / GCE to PFOS is significantly greater than the cyclic voltammetric current response to other interfering substances. This is because the cavity on the MIP / GCE does not match other interfering substances. It can be seen from this that the molecularly imprinted sensitive membrane of the present invention has strong specificity and can selectively identify PFOS molecules. In addition, after PFOS is mixed with other interfering substances, cyclic voltammetric detection of PFOS using MIP / GCE is performed. Even if it coexists with interfering substances, the sensor can still effectively detect the content of PFOS, which shows that the invented sensor has strong anti-interference ability. The results show that the MIP / GCE electrochemical sensor prepared by the present invention has the advantage of strong anti-interference ability.

[0040] Comparative Example 1:

[0041] Step S1, using a 0.1 mol / L acetate buffer solution with a pH of 5 as a solvent, PFOS as a template molecule, controlling its concentration in the acetate buffer solution to be 1 mmol / L, and aniline as a functional monomer, controlling the concentration of aniline in the acetate buffer solution to be 36.5 mmol / L, to obtain an electropolymerization solution;

[0042] In step S2, the glassy carbon electrode is pretreated by polishing it on suede with 1.0 μm, 0.3 μm, and 0.05 μm Al2O3 powders, and then ultrasonically cleaning it with deionized water and ethanol for 1 minute respectively. After each ultrasonic cleaning, it is rinsed with deionized water to obtain a pretreated glassy carbon electrode.

[0043] Step S3, placing the pretreated glassy carbon electrode in the electropolymerization solution, using a platinum wire as a counter electrode, Ag / AgCl as a reference electrode, and the pretreated glassy carbon electrode as a working electrode, polymerizing for 10 cycles at a scan rate of 50 mV / s in a voltage range of -0.2 to 1.3 V by cyclic voltammetry to obtain a molecularly imprinted membrane modified electrode;

[0044] In step S4, after polymerization, the obtained molecularly imprinted membrane modified electrode is immersed in a methanol / water mixed solution (volume ratio of 6:1), gently stirred at 60 rpm, and immersed for 10 minutes to elute the template molecules to obtain a molecularly imprinted sensitive membrane for PFOS.

[0045] Electrochemical sensing application of this comparative example:

[0046] The molecularly imprinted sensitive membrane obtained in step S4 was used for the determination of PFOS:

[0047] MIP / GCE was used to detect PFOS and some possible coexisting interfering substances, including PFASs with similar structures such as PFOA, PFBA, PFBS, PFHxA, etc. Figure 6 It can be seen that although the cyclic voltammetric current response of MIP / GCE to PFOS is greater than that to other interferents due to the mismatch between the cavity on MIP / GCE and other interferents, Figure 5 A comparison revealed that compared to the molecularly imprinted membrane prepared using aniline and o-fluoroaniline as dual monomers, not only was the current response to PFOS reduced, but the current response to the interfering compound was also greater, indicating that the selectivity for perfluorinated compounds composed of sulfonic acid groups and carbon fluoride chains was limited. This suggests that the molecularly imprinted membrane prepared using dual monomers has stronger specificity and can more accurately and selectively recognize PFOS molecules.

[0048] Example 2:

[0049] On the basis of Example 1, the concentration of aniline in the acetate buffer solution was changed from 36.5 mmol / L to 10 mmol / L, and the concentration of o-fluoroaniline in the acetate buffer solution was changed from 11 mmol / L to 10 mmol / L.

[0050] Example 3:

[0051] On the basis of Example 1, the concentration of aniline in the acetate buffer solution was controlled to be replaced from 36.5 mmol / L to 50 mmol / L, and the concentration of o-fluoroaniline in the acetate buffer solution was replaced from 11 mmol / L to 7 mmol / L.

[0052] Example 4:

[0053] On the basis of Example 1, the pH of the acetate buffer solution was changed from pH 5 to pH 3, and PFOS was used as a template molecule to control its concentration in the acetate buffer solution from 1 mmol / L to 2 mmol / L.

[0054] Example 5:

[0055] On the basis of Example 1, the pH of the acetate buffer solution was changed from pH 5 to pH 7, and PFOS was used as a template molecule to control its concentration in the acetate buffer solution from 1 mmol / L to 5 mmol / L.

[0056] Example 6:

[0057] On the basis of Example 1, the scan rate of polymerization performed by cyclic voltammetry was changed from 50 mV / s to 30 mV / s, and the number of polymerization cycles was changed from 10 to 30.

[0058] Example 7:

[0059] On the basis of Example 1, the scan rate of polymerization performed by cyclic voltammetry was changed from 50 mV / s to 100 mV / s, and the number of polymerization cycles was changed from 10 to 5.

[0060] Example 8:

[0061] Based on Example 1, the volume ratio of methanol to water was changed from 6:1 to 3:1, and the soaking time was changed from 10 min to 30 min.

[0062] Example 9:

[0063] Based on Example 1, the volume ratio of methanol to water was changed from 6:1 to 10:1, and the soaking time was changed from 10 min to 5 min.

[0064] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a molecularly imprinted sensitive membrane modified electrode for perfluorooctane sulfonic acid detection, characterized in that: The steps include: Step S1, using acetate buffer solution as solvent, PFOS as template molecule, aniline and o-fluoroaniline as bifunctional monomers to obtain an electropolymerization solution; Step S2, pre-treating the glassy carbon electrode by polishing and cleaning the glassy carbon electrode with aluminum oxide powder; Step S3, placing the pretreated glassy carbon electrode in an electropolymerization solution, using a platinum wire as a counter electrode, Ag / AgCl as a reference electrode, and the pretreated glassy carbon electrode as a working electrode, polymerizing in the solution by cyclic voltammetry to obtain a molecularly imprinted membrane modified electrode; Step S4: immersing the molecularly imprinted membrane modified electrode in a mixed solution of methanol and water to elute the template molecules, thereby obtaining a molecularly imprinted sensitive membrane modified electrode MIP / GCE for PFOS detection.

2. The method for preparing a molecularly imprinted sensitive membrane modified electrode for perfluorooctane sulfonic acid detection according to claim 1, characterized in that: In step S1, the pH of the acetate buffer solution is 3-7, the concentration of PFOS in the acetate buffer solution is 0.5-5 mmol / L, the molar concentration ratio of aniline to o-fluoroaniline is 1:1-7:1, and the concentration of aniline in the acetate buffer solution is 10-50 mmol / L.

3. The method for preparing a molecularly imprinted sensitive membrane modified electrode for perfluorooctane sulfonic acid detection according to claim 1, characterized in that: In step S2, the glassy carbon electrode is polished on suede with 1.0 μm, 0.3 μm, and 0.05 μm Al2O3 powders in sequence, and then ultrasonically cleaned with deionized water and ethanol for 1 min respectively. After each ultrasonic cleaning, it is rinsed with deionized water to obtain a pretreated glassy carbon electrode.

4. The method for preparing a molecularly imprinted sensitive membrane modified electrode for perfluorooctane sulfonic acid detection according to claim 1, characterized in that: In step S3, the scan rate of polymerization by cyclic voltammetry is 30 to 100 mV / s, and the number of polymerization cycles is 5 to 30 cycles.

5. The method for preparing a molecularly imprinted sensitive membrane modified electrode for perfluorooctane sulfonic acid detection according to claim 1, characterized in that: In step S4, the volume ratio of methanol to water is 3:1 to 10:1, and the elution time is 5 to 30 minutes.

6. A molecularly imprinted sensitive membrane modified electrode obtained by the preparation method of the molecularly imprinted sensitive membrane modified electrode according to any one of claims 1 to 5, for detecting PFOS in water.

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