Highly sensitive ammonium ion electrochemical sensor and application thereof

Abstract

The application discloses a high-sensitivity ammonium ion electrochemical sensor and application thereof, and belongs to the technical field of electrochemical sensors.The electrochemical sensor comprises a full-solid-state ammonium ion selective electrode, the electrode comprises an electrically conductive base, a solid-state contact layer and an ammonium ion sensitive film arranged in sequence, the electrically conductive base is a silk screen printed carbon electrode with copper nanoparticles on the surface; the solid-state contact layer is composed of a polyaniline and reduced graphene oxide composite; and the composition of the ammonium ion sensitive film comprises polydopamine and an ammonium ion carrier.The characteristics of the above-mentioned modified materials expand the linear detection range of the sensor to ammonium ions, improve the sensitivity, and can sensitively detect 10 ‑7 ~ 10 ‑1 M ammonium ion concentrations, and have good application prospects in the fields of on-site rapid detection of low-concentration ammonium ions in environmental water, aquaculture water and seawater.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemical sensors, in particular to a high-sensitivity ammonium ion electrochemical sensor and application thereof. BACKGROUND

[0002] Ammonia nitrogen is derived from the discharge of domestic sewage, agricultural sewage and industrial sewage, etc. Ammonia nitrogen in water is an important nutrient salt indicator of water, and its content occupies an important position in water nitrogen cycle. Ammonia nitrogen pollution in water will have toxic and side effects on aquatic plants and animals, leading to poor water quality, causing water eutrophication, and seriously damaging the balance of aquatic ecosystems and human life quality. Therefore, the content of ammonia nitrogen is an important indicator for judging the pollution condition of water body, an important indicator for water quality monitoring in China, and one of the indicators for total pollutant emission control, occupying an important position in the environmental quality monitoring system.

[0003] Ammonia nitrogen exists in two ways in the water environment, namely free ammonia (NH3) in gaseous form and ammonium ion (NH4 + ) in ionic form. The proportion of these two forms of ammonia is related to the pH value of the water environment. The non-ionic ammonia concentration in aquaculture water should not exceed 0.02 mg / L according to the GB11607-89 Fishery Water Quality Standard, so the maximum ammonium ion concentration in aquaculture water is about 1 x 10 -6 M. The total ammonia nitrogen concentration in type I groundwater should not exceed 0.02 mg / L according to the GB / T14848-2017 Groundwater Quality Standard, so the maximum ammonium ion concentration in type I groundwater is also not more than 1 x 10 -6 M.

[0004] At present, the methods for detecting ammonia nitrogen mainly include ion chromatography, titration, turbidimetry, spectrophotometry, inductively coupled plasma emission spectrometry, etc., but these methods have the disadvantages of complex sample pretreatment, tedious operation, expensive instruments, high technical requirements for operators, etc.

[0005] The ammonium ion selective electrode method is more suitable for water quality samples with low ammonia nitrogen concentration, and can measure the ammonium ion concentration in water and then calculate the ammonia nitrogen concentration in water according to the percentage of ionic ammonia in aqueous solution.

[0006] Ammonium ion sensors based on ammonium ion selective electrodes have attracted more and more attention due to their advantages of simple instrument, low cost, portability, good selectivity, low detection limit, fast response, etc. For example, Ding et al. added polythiophene (POT) as a solid contact layer on the surface of a polished glassy carbon electrode, dried it, and then deposited an ion-sensitive membrane on the solid contact layer by drop coating to prepare an ammonium ion selective electrode for rapid detection of ammonia nitrogen content in seawater. The linear range of ammonium ion detection is 10 -6-10 -3 M, with a sensitivity of 59.5 mV / dec (Ding, L.; Ding, J.; Ding, B.; Qin, W., Solid-contact Potentiometric Sensor for the Determination of Total Ammonia Nitrogen in Seawater. International Journal of Electrochemical Science 2017, 12, 3296-3308.). Colozza et al. dropped multi-walled carbon nanotubes (f-MWCNTs) on the surface of a polished glassy carbon electrode as a solid-state contact layer, and after drying, an ion-sensitive film was modified on the solid-state contact layer by drop coating to prepare an ammonium ion selective electrode. The linear range of ammonium ion detection was 10 -5 -10 -2 M, with a sensitivity of 60 mV / dec (Colozza, N.; Casanova, A.; Fernandez-Perez, B. M.; Crespo, G. A.; Flores, G. A.; Kavallieratos, K.; de Gracia, J.; Ahlquist, M.; Cuartero, M., Insights into Tripodal Tris(pyrazolyl) Compounds as Ionophores for Potentiometric Ammonium Ion Sensing. ChemElectroChem 2022, 9, e202200716.).

[0007] There are also some research reports on this field in China. For example, Li Xianbing et al. used indium tin oxide glass as a conductive matrix material, then plated a polyaniline film, and finally coated an ammonium ion selective solution to prepare an ammonium ion selective electrode. The linear range was 10 -4 M to 10 -1 M, with a sensitivity of 43.8 mV / dec (Li Xianbing, Liu Keke, Zhu Likang, et al. A new type of solid-state ammonium ion selective electrode based on indium tin oxide as conductive matrix material and its application [J]. Anhui Agricultural Science, 2016 (12): 15-17.).

[0008] The above sensors have good sensitivity to ammonium ions, but the detection lower limit is high, the detection range is small, and they cannot directly detect ammonium ions with a concentration lower than 10 -6 M rapidly. SUMMARY

[0009] The present application aims to provide a high-sensitivity full-solid-state electrochemical sensor capable of being applied to low-concentration ammonium ion detection, so as to solve the problem that the existing electrochemical sensor cannot cover the range below 10 -6 M of the present application.

[0010] To achieve the above object, the present application adopts the following technical solutions:

[0011] The present application provides a high-sensitivity ammonium ion electrochemical sensor, comprising a full-solid-state ammonium ion selective electrode, wherein the full-solid-state ammonium ion selective electrode comprises an electrically conductive substrate, a solid-state contact layer and an ammonium ion sensitive film arranged in sequence, the electrically conductive substrate is a screen-printed carbon electrode with copper nanoparticles on the surface; the solid-state contact layer is composed of a polyaniline and reduced graphene oxide composite; and the composition of the ammonium ion sensitive film comprises polydopamine (PDA) and an ammonium ion carrier.

[0012] The ammonium ion electrochemical sensor provided by the present application takes the full-solid-state ammonium ion selective electrode as a working electrode, and its working principle is as follows: the ammonium ion selective electrode can convert the activity (input) of ammonium ions in a sample solution to be measured into a potential signal (output), the change of the potential signal can be obtained by measuring the open-circuit voltage of the electrode in the sample to be measured, which is proportional to the ammonium ion concentration in the solution to be measured, and then the ammonium ion content is calculated.

[0013] The ammonium ion selective electrode provided by the present application is prepared by sequentially depositing copper nanoparticles, depositing a polyaniline and reduced graphene oxide composite as a solid-state contact layer and modifying an ammonium ion sensitive film on the surface of a screen-printed carbon electrode. Among them, the modification of copper nanoparticles can improve the specific surface area of the electrode and significantly improve the conductivity of the electrode, thereby greatly improving the sensitivity of the sensor and reducing the lower detection limit; the double-layer capacitance effect of reduced graphene oxide and the oxidation-reduction capacitance effect of polyaniline produce a synergistic effect, which improves the "ion-electron" transduction capacity, and the three-dimensional structure improves the electron transfer rate, shortens the transfer distance of electrons between the solid-state contact layer and the ion sensitive film, which all helps to increase the potential response capacity of the sensor; the ammonium ion sensitive film selects polydopamine (PDA) and polyvinyl chloride (PVC) as the sensitive film matrix material, polydopamine has good thermal stability, excellent adhesion and excellent film forming ability, which can prevent the leakage of the ammonium ion carrier and the falling off of the ammonium ion sensitive film, thereby improving the linear detection range and stability of the sensor to ammonium ions. The present application has the advantages of low detection lower limit, high sensitivity, good stability and the like.

[0014] The present application is suitable for on-site rapid detection of low-concentration ammonium ions in environmental water, aquaculture water and seawater.

[0015] The electrochemical sensor is composed of an electrochemical three-electrode system, including a working electrode, an auxiliary electrode and a reference electrode, the auxiliary electrode is a carbon electrode, and the reference electrode is a silver / silver chloride (Ag / AgCl) electrode. Specifically, the electrochemical three-electrode system can be prepared by printing the materials of the three electrodes onto the surface of a substrate by a screen printing process. The substrate material can be polyethylene terephthalate (PET) or polyvinyl chloride (PVC) or ceramic. The screen-printed electrode is batch-produced and low-cost, which helps to promote the product.

[0016] The screen-printed carbon electrode is prepared by printing conductive carbon paste onto the surface of the working electrode region of the substrate material by a screen printing process.

[0017] The copper nanoparticles are generated by electrodeposition of an electrolyte copper solution on the surface of the screen-printed carbon electrode. Reduced graphene oxide and polyaniline are co-deposited on the surface of the screen-printed carbon electrode modified with copper nanoparticles. The ammonium ion sensitive film is prepared by modifying the ion sensitive film mixture onto the solid contact layer by one of the methods of drop coating, spin coating and inkjet printing.

[0018] Preferably, the particle size of the copper nanoparticles is 50-200 nm.

[0019] Preferably, the solid contact layer is co-deposited by electrochemical deposition of graphene oxide and aniline monomers, the mass concentration of graphene oxide in the electroplating solution is 0.5-2 mg / L, and the molar concentration of aniline monomers is 0.1-1 M.

[0020] Preferably, the ammonium ion sensitive film comprises, in mass percentage: polydopamine 2-10%, polyvinyl chloride (PVC) 20-50%, potassium tetrakis(3,5-di(trifluoromethyl)phenyl)borate (KTFPB) 0.5-2%, o-nitrophenyl octyl ether (o-NPOE) 30-70%, and ammonium ion carrier 1-10%.

[0021] More preferably, the ammonium ion sensitive film comprises, in mass percentage: polydopamine 5-10%, polyvinyl chloride 35-50%, potassium tetrakis(3,5-di(trifluoromethyl)phenyl)borate 0.5-1.5%, o-nitrophenyl octyl ether 35-50%, and ammonium ion carrier 1-3.5%.

[0022] Further, the preparation method of the all-solid-state ammonium ion selective electrode comprises:

[0023] (1) dropping an electrolyte copper solution on the surface of the screen-printed carbon electrode, and forming copper nanoparticles on the surface of the screen-printed carbon electrode by electrochemical deposition to prepare a conductive substrate;

[0024] (2) dispersing graphene oxide in a sulfuric acid solution, adding aniline monomer to form a mixed solution, dropping the mixed solution on the surface of the conductive substrate, and using electrochemical co-deposition to form a polyaniline and reduced graphene oxide composite deposited on the surface of the conductive substrate to form a solid-state contact layer;

[0025] (3) using one of a drop coating method, a spin coating method, and an inkjet printing method to modify an ammonium ion-sensitive membrane solution containing dopamine and an ammonium ion carrier to the surface of the solid-state contact layer, and forming an ammonium ion-sensitive membrane after self-polymerization.

[0026] In step (1), the parameters (applied potential, deposition time, etc.) of the electrochemical deposition method and the concentration of the electrolyte copper solution affect the diameter and dispersion uniformity of the copper nanoparticles. Too long deposition time or too high electrolyte copper solution concentration can cause the copper nanoparticles to agglomerate and be unevenly dispersed. Selecting appropriate electrochemical methods and parameters (applied potential, deposition time, etc.) and appropriate electrolyte copper solution concentration can make the copper nanoparticles uniformly dispersed on the electrode surface, with a particle diameter range of 50-200 nm, which helps to improve the conductive performance of the screen-printed carbon electrode. This method is simple and quantitatively controllable.

[0027] Preferably, the electrolyte copper solution has a concentration of 1-10 mM, and the constant potential method is scanned for 3-100 s with an applied potential value in the range of -1.5 V to -0.5 V. The electrolyte copper solution can be a copper acetate solution or a copper sulfate solution.

[0028] More preferably, the electrolyte copper solution has a concentration of 2-10 mM, and the constant potential method is deposited for 60-100 s with an applied potential of -1.2 V to -1.0 V.

[0029] In step (2), the polyaniline and reduced graphene oxide composite is modified on the surface of the conductive substrate to form a solid-state contact layer using electrochemical co-deposition. Appropriate electrochemical deposition parameters, mixed solution dosage, and concentration are selected to control the thickness of the solid-state contact layer to be 50-200 μm. The solid-state contact layer modified by electrochemical co-deposition is stable and not easy to fall off, and the thickness is controllable.

[0030] Preferably, the preparation method of the mixed solution comprises: dispersing graphene oxide dispersion in a 0.1-1 M sulfuric acid solution with a concentration of 0.5-2 mg / L, and adding aniline after ultrasonic dispersion, wherein the aniline concentration is 0.1-1 M.

[0031] 50-100 μL of the mixed solution is dropped on the surface of the working electrode, and cyclic voltammetry is scanned for 2-30 cycles with a scanning potential range of -1.5-1.5 V.

[0032] More preferably, the graphene oxide dispersion solution is dissolved in a 0.1-0.5M sulfuric acid solution with a concentration of 0.5-1mg / L, after ultrasonic stirring, aniline is added for mixing, wherein the concentration of aniline is 0.5-1M; the mixed solution is dropped on the surface of the working electrode, and cyclic voltammetry is used for scanning 15-20 times, and the scanning potential range falls in the range of-1.5-1.5V.

[0033] In step (3), one of drop coating, spin coating and inkjet printing is used to coat the ammonium ion sensitive film solution onto the solid contact layer, and then the electrode is immersed in an alkaline solution, the ammonium ion sensitive film solution contains dopamine, and the self-polymerization forms polydopamine. The thickness of the ammonium ion sensitive film is controlled to be 10-100μm.

[0034] Preferably, the preparation method of the ammonium ion sensitive film comprises the following steps: firstly, dopamine hydrochloride, polyvinyl chloride (PVC), potassium tetra(3,5-di(trifluoromethyl)phenyl)borate (KTFPB, anion additive), o-nitrophenyl octyl ether (o-NPOE, plasticizer) and an ammonium ion carrier are dissolved in tetrahydrofuran according to a mass ratio of 5-10:35-50:0.5-1.5:35-50:1-3.5, and ultrasonic stirring is applied to prepare an ammonium ion sensitive film solution; and then the ammonium ion sensitive film solution is modified to the surface of the solid contact layer and then immersed in an alkaline solution for self-polymerization to form the ammonium ion sensitive film.

[0035] The ammonium ion carrier can be, but is not limited to, ammonium ion carrier I.

[0036] Specifically, 5-10wt% of dopamine hydrochloride, 35-50wt% of polyvinyl chloride, 0.5-1.5wt% of potassium tetra(3,5-di(trifluoromethyl)phenyl)borate, 35-50wt% of o-nitrophenyl octyl ether and 1-3.5wt% of ammonium ion carrier I are dissolved in 1.0-5.0mL of tetrahydrofuran solution, and ultrasonic stirring is applied for 1-3h to prepare a mixed solution.

[0037] The mixed solution after ultrasonic treatment is deposited on the solid contact layer by drop coating, spin coating, inkjet printing and the like, and then the electrode is immersed in a Tris solution (10mM, pH=8.5) for self-polymerization for 3min to form a stable ammonium ion sensitive film.

[0038] The application also provides application of the above-mentioned electrochemical sensor in detection of ammonium ions, wherein the electrochemical sensor takes a full-solid-state ammonium ion selective electrode as a working electrode, a carbon electrode as an auxiliary electrode and a silver / silver chloride (Ag / AgCl) electrode as a reference electrode; and the concentration range of the detected ammonium ions is 10 -7 ~10 -1 M.

[0039] The application includes:

[0040] (1) Preparation of standard solution: Prepare the ammonium ion standard solution, dilute to constant volume to obtain a series of different concentrations of the standard solution to be measured;

[0041] (2) Standard curve drawing: Drop different concentrations of ammonium ion standard solution on the surface of the working electrode ammonium ion sensitive membrane, measure the open circuit voltage, record the stable potential response value, and draw the calibration linear curve between the potential response value and the ammonium ion concentration;

[0042] (3) Actual sample test: Take the sample to be measured and drop it on the surface of the working electrode ammonium ion sensitive membrane, measure the open circuit voltage by the method of step (2), and convert the ammonium ion content in the sample to be measured by entering the stable potential response value into the above corresponding calibration linear curve equation.

[0043] The actual sample can be, but is not limited to, environmental water, aquaculture water and seawater. The actual sample is obtained by centrifugal filtration to obtain the sample to be measured.

[0044] In step (2), 20-100 μL of ammonium ion standard solution is dropped on the surface of the working electrode for open circuit voltage test.

[0045] The present application has the following beneficial effects:

[0046] (1) The high-sensitivity full-solid-state ammonium ion selective electrode provided by the present application uses a screen-printed carbon electrode as a substrate, and the copper nanoparticles modified on the surface thereof have a large specific surface area and excellent electrical conductivity, which can improve the sensitivity of the sensor; the reduced graphene oxide and polyaniline compound of the solid-state contact layer have a three-dimensional structure, which improves the electron transfer rate and shortens the transfer distance of electrons between the solid-state contact layer and the ion selective membrane; the redox capacitance of polyaniline and the double-layer capacitance of reduced graphene oxide produce a synergistic effect, which improves the "ion-electron" transduction capacity and helps to enhance the potential response of the sensor; the substrate material of the ammonium ion sensitive membrane, polydopamine, has good thermal stability, excellent adhesion and excellent film forming ability, which can prevent the leakage of ammonium ion carriers and the peeling of the sensitive membrane, thereby improving the linear detection range and stability of the sensor. The sensor of the present application can detect ammonium ions in the concentration range of 10 -7 ~ 10 -1 M, and the lower limit of detection is as low as 5.8 x 10 -8 M.

[0047] (2) The electrochemical sensor provided by the present application is small and portable, low in cost, high in sensitivity, fast in response, and can quickly detect ammonium ions in environmental water, aquaculture water and seawater on site, and has good market prospects. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1The following are electron microscope (EM) images of the working electrodes modified with different materials: (a) an EEM image of copper nanoparticles modified on a screen-printed electrode; (b) an EEM image of a solid contact layer composed of reduced graphene oxide and polyaniline modified on the surface of copper nanoparticles; and (c) an EEM image of an ammonium ion sensitive membrane modified on the solid contact layer.

[0049] Figure 2 Examples 1 show the real-time test curves of open-circuit voltage on the working electrode for ammonium ion standard solutions of different concentrations (A) and the linear calibration curves (B) between open-circuit voltage and corresponding ammonium ion concentrations. The ammonium ion concentration is 10. -7 Up to 10 -1 M.

[0050] Figure 3 Example 2 shows the real-time test curves of open-circuit voltage on the working electrode for ammonium ion standard solutions of different concentrations (A) and the linear calibration curves (B) between open-circuit voltage and corresponding ammonium ion concentrations. The ammonium ion concentration is 10. -7 Up to 10 -1 M.

[0051] Figure 4 Example 3 shows the linear calibration curves of the open-circuit voltage on the working electrode and the corresponding ammonium ion concentration for ammonium ion standard solutions of different concentrations. The ammonium ion concentration is 10. -7 Up to 10 -1 M.

[0052] Figure 5 To illustrate the linear calibration curves of open-circuit voltage versus corresponding ammonium ion concentrations at the working electrode for ammonium ion standard solutions of different concentrations in Comparative Example 1, the ammonium ion concentration was 10. -6 Up to 10 -1 M.

[0053] Figure 6 To illustrate the linear calibration curves of open-circuit voltage versus corresponding ammonium ion concentrations at the working electrode for different concentrations of ammonium ion standard solutions in Comparative Example 2, the ammonium ion concentration was 10. -5 Up to 10 -1 M. Detailed Implementation

[0054] The present invention will be further described below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Any modifications or substitutions made to the methods, steps, or conditions of the present invention without departing from the spirit and essence of the invention are within the scope of the invention.

[0055] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0056] The screen-printed carbon electrode was purchased from Weipu Technology (Weihai) Co., Ltd.; the graphene oxide dispersion was purchased from Nanjing Xianfeng Nanometer Material Technology Co., Ltd.; the polyvinyl chloride (PVC) (CAS No.: 9002-86-2) and aniline monomer were purchased from Shanghai Aladdin Bio-Chem Technology Co., Ltd.; dopamine hydrochloride (CAS No.: 62-31-7), potassium tetra(3,5-di(trifluoromethyl)phenyl)borate (KTFPB), o-nitrophenyl octyl ether (o-NPOE) and ammonium ion carrier I (CAS No.: 6833-84-7) were purchased from Sigma-Aldrich.

[0057] Example 1

[0058] I. Preparation of the working electrode

[0059] 1. 100 μL of 10 mM copper acetate solution was dropped onto the surface of the screen-printed carbon electrode, and copper nanoparticles were formed by constant potential electrodeposition at -1.2 V for 60 s (the auxiliary electrode was a screen-printed carbon electrode, and the reference electrode was a screen-printed silver / silver chloride electrode). The scanning electron microscope (SEM) image of the working electrode surface after the formation of copper nanoparticles is shown in Fig. (a). Figure 1

[0060] 2. The graphene oxide dispersion was dissolved in 0.1 M sulfuric acid to form a solution with a concentration of 1 mg / L. After ultrasonic dispersion (400 W, 1 h), aniline was added to form a mixed solution, in which the concentration of aniline was 0.5 M.

[0061] 100 μL of the mixed solution was dropped onto the surface of the working electrode, and 20 cycles of cyclic voltammetry (CV) were performed (the auxiliary electrode was a screen-printed carbon electrode, and the reference electrode was a screen-printed silver / silver chloride electrode). The scanning potential range was -1.5-1.5 V, and a solid-state contact layer was formed. The SEM image is shown in Fig. (b). Figure 1

[0062] 3. The ammonium ion sensitive film was modified onto the above-mentioned solid-state contact layer by drop coating. The components of the ammonium ion sensitive film solution were as follows: 5 wt% dopamine hydrochloride, 35 wt% polyvinyl chloride, 1 wt% potassium tetra(3,5-di(trifluoromethyl)phenyl)borate (KTFPB), 58 wt% o-nitrophenyl octyl ether (o-NPOE) and 1 wt% ammonium ion carrier I. The above-mentioned components were mixed and dissolved in 1.0 mL of tetrahydrofuran, and the required sensitive film solution was prepared after ultrasonic stirring (400 W, 2 h). Ultrasonic treatment can mix the sensitive film solution and prevent the self-polymerization of dopamine.

[0063] ​​Take 20 μL of the sensitive film solution and drop coat it on the surface of the solid contact layer, then immerse the electrode into Tris solution (10 mM, pH = 8.5) for self-polymerization for 3 minutes to form a stable ion-sensitive film, in which dopamine hydrochloride is polymerized into polydopamine spontaneously. The electron microscope image is as shown in Figure 1 (c) shown.

[0064] II. Drawing of standard curve

[0065] The electrochemical three-electrode system is composed of the working electrode prepared in step one, an auxiliary electrode and a reference electrode. The auxiliary electrode is a carbon electrode, and the reference electrode is a silver / silver chloride (Ag / AgCl) electrode.

[0066] Dissolve NH4Cl in deionized water to prepare a standard ammonium ion solution with 7 concentration gradients, including 10 -1 , 10 -2 , 10 -3 , 10 -4 , 10 -5 , 10 -6 , and 10 -7 M.

[0067] Take 80 μL of the above-mentioned standard ammonium ion solution with the above-mentioned concentration and drop it on the surface area of the working electrode, and use the electrochemical workstation (Gamry, reference 3000) to detect the open circuit voltage. Record the open circuit voltage when different concentrations of standard ammonium ion solution are added, and draw the calibration linear curve between the open circuit voltage and the ammonium ion concentration.

[0068] After calibration, the linear relationship between the open circuit voltage response of the ammonium ion electrochemical sensor of the present embodiment and different concentrations of ammonium ions is obtained, as shown in Figure 2 . The linear range is 10 -1 -10 -7 M, the lower limit of detection is 6.4 x 10 -8 M, and the sensitivity is as high as 43.35 mV / dec.

[0069] III. Determination of the sample to be measured

[0070] Take 100 mL of a certain fishpond water sample, centrifuge and filter it at high speed, then add 1 μM and 10 μM of NH4Cl respectively, and then use the ammonium ion electrochemical sensor of the present embodiment to detect it.

[0071] Measure according to the electrochemical method in the foregoing (ii), and convert the open circuit voltage value into the ammonium ion content in the sample to be measured by using the calibration linear curve equation, and record it in Table 1.

[0072] Measure the same sample solution to be measured by the national standard method (Nessler's reagent spectrophotometry) to obtain the ammonium ion concentration value, and record it in Table 1.

[0073] Table 1. The results of the sensor of Example 1 for detecting the content of ammonium ions in various samples

[0074]

[0075] Table 1 shows that the results of the electrochemical sensor of the application for detecting ammonium ions are basically consistent with the results of the national standard method, indicating that the performance of the application is reliable.

[0076] Example 2

[0077] I. Preparation of the working electrode

[0078] 100 μL of 5 mM electrolyte copper solution was dropped onto the surface of the screen-printed carbon electrode, and copper nanoparticles were formed by constant potential electrodeposition at -1.0 V for 100 s;

[0079] The graphene oxide dispersion solution was dissolved in 0.5 M sulfuric acid to a concentration of 0.5 mg / L, and after ultrasonic stirring, aniline was added to form a mixed solution, wherein the concentration of aniline was 1 M; 80 μL of the mixed solution was dropped onto the surface of the working electrode, and cyclic voltammetry (CV) was used to scan 15 times (the auxiliary electrode was a screen-printed carbon electrode, and the reference electrode was a screen-printed Ag / AgCl electrode), and the scanning potential range was -1.5-1.0 V.

[0080] The ammonium ion sensitive film was modified onto the above-mentioned solid contact layer by spin coating. The components of the ammonium ion sensitive film solution were: 8 wt% of dopamine hydrochloride, 40 wt% of PVC, 0.5 wt% of KTFPB, 50 wt% of o-NPOE, and 1.5 wt% of ammonium ion carrier I. The above components were mixed and dissolved in 1.0 mL of tetrahydrofuran, and after ultrasonic stirring (350 W, 1.5 h), the required sensitive film solution was obtained. 30 μL of the sensitive film solution was spin-coated on the surface of the solid contact layer, and then the electrode was immersed in a Tris solution (10 mM, pH = 8.5) for self-polymerization for 3 minutes to form a stable ion-sensitive film.

[0081] II. Drawing of the standard curve

[0082] NH4Cl was dissolved in deionized water to prepare a standard ammonium ion solution with 7 concentration gradients, including 10 -1 , 10 -2 , 10 -3 , 10 -4 , 10 -5 , 10 -6 , 10 -7 M.

[0083] Take 100 μL of the above concentration of standard ammonium ion solution, drop to the surface area of the working electrode, detect the open circuit voltage, record the open circuit voltage when different concentrations of standard ammonium ion solution are added, and draw the calibration linear curve between the open circuit voltage and the concentration of ammonium ion.

[0084] After calibration, the linear relationship between the open circuit voltage response of the ammonium ion electrochemical sensor of the embodiment and different concentrations of ammonium ion is obtained, as shown in the following figure. Figure 3 -1 -10 -7 M, the lower limit of detection is 5.8 x 10 -8 M, and the sensitivity is 43.92 mV / dec.

[0085] III. Determination of the sample to be tested

[0086] Take 100 mL of a certain river water sample, centrifuge and filter it at high speed, then add 1 μM and 5 μM of NH4Cl respectively, and then detect it using the ammonium ion electrochemical sensor of the embodiment.

[0087] According to the electrochemical method in the foregoing (ii), the open circuit voltage value is brought into the calibration linear curve equation, and the content of ammonium ion in the sample to be tested is converted and recorded in Table 2.

[0088] The same sample solution to be tested is measured by the national standard method (Nash reagent spectrophotometry), and the ammonium ion concentration value is obtained and recorded in Table 2.

[0089] Table 2. Detection results of the ammonium ion content in various samples by the sensor of Example 2

[0090]

[0091]

[0092] Table 2 shows that the detection results of the electrochemical sensor of the application applied to ammonium ion are basically consistent with the detection results of the national standard method, which shows that the performance of the application is reliable.

[0093] Example 3

[0094] I. Preparation of the working electrode

[0095] 100 μL of 2 mM electrolyte copper solution is dropped onto the surface of the screen-printed carbon electrode, and copper nanoparticles are formed by constant potential electrodeposition at -1.2 V for 60 s;

[0096] ​The graphene oxide dispersion solution was dissolved in 0.2M sulfuric acid with a concentration of 1mg / L, and after ultrasonic dispersion, aniline was added to form a mixed solution, wherein the concentration of aniline was 0.5M; 100μL of the mixed solution was dropped on the surface of the working electrode, and cyclic voltammetry (CV) was used for scanning 20 times (the auxiliary electrode was a silk screen printed carbon electrode, and the reference electrode was a silk screen printed Ag / AgCl electrode), and the scanning potential range was-1.5-1.0V;

[0097] The ammonium ion sensitive film was modified on the above solid contact layer by drop coating. The components of the ammonium ion sensitive film solution were: 10wt% of dopamine hydrochloride, 50wt% of polyvinyl chloride, 1.5wt% of potassium tetrakis(3,5-di(trifluoromethyl)phenyl)borate (KTFPB), 35wt% of o-nitrophenyl octyl ether (o-NPOE), and 3.5wt% of ammonium ion carrier I. The above components were mixed and dissolved in 1.0mL of tetrahydrofuran, and after ultrasonic stirring (450W, 1h), the required sensitive film solution was prepared. 40μL of the sensitive film solution was drop coated on the surface of the solid contact layer, and then the electrode was immersed in a Tris solution (10mM, pH=8.5) for self-polymerization for 3 minutes to form a stable ion sensitive film.

[0098] II. Drawing of standard curve

[0099] The NH4Cl was dissolved in deionized water to prepare a standard ammonium ion solution with 7 concentration gradients, including 10 -1 , 10 -2 , 10 -3 , 10 -4 , 10 -5 , 10 -6 , and 10 -7 M.

[0100] 50μL of the above concentration standard ammonium ion solution was taken and dropped on the surface area of the working electrode, and the open circuit voltage was detected. The open circuit voltage when different concentrations of standard ammonium ion solution were added was recorded, and a calibration linear curve between the open circuit voltage and the ammonium ion concentration was drawn.

[0101] After calibration, the linear relationship between the open circuit voltage response of the ammonium ion electrochemical sensor of the embodiment and different concentrations of ammonium ions was obtained, as shown in Figure 4 . The linear range was 10 -1 -10 -7 M, the lower limit of detection was 7.3×10 -8 M, and the sensitivity was 42.3mV / dec.

[0102] III. Determination of the sample to be tested

[0103] Take 100 mL of a certain sea area of seawater sample, after high-speed centrifugal filtration, add 1 μM, 10 μM of NH4Cl respectively, and then detect by the ammonium ion electrochemical sensor of the embodiment.

[0104] According to the electrochemical method in the foregoing (ii), the open circuit voltage value is brought into the calibration linear curve equation, and the ammonium ion content in the sample to be measured is converted and recorded in Table 3.

[0105] The same sample solution to be measured is measured by the national standard method (Nash reagent spectrophotometry), and the ammonium ion concentration value is obtained and recorded in Table 3.

[0106] Table 3. The detection results of the sensor of Example 3 on the ammonium ion content in various samples

[0107]

[0108] Table 3 shows that the detection results of the electrochemical sensor of the application on ammonium ion are basically consistent with the detection results of the national standard method, indicating that the performance of the application is reliable.

[0109] Comparative Example 1

[0110] I. Preparation of working electrode

[0111] The bare screen-printed carbon electrode with unmodified copper nanoparticles is selected as the electrode matrix;

[0112] The graphene oxide dispersion solution is dissolved in 0.5M sulfuric acid with a concentration of 1mg / L. After ultrasonic dispersion, 80μL of the graphene oxide dispersion solution is dropped on the surface of the working electrode. The cyclic voltammetry (CV) scanning is performed for 20 cycles, and the scanning potential range is-1.5-1.0V.

[0113] The ammonium ion sensitive film is modified on the above-mentioned solid contact layer by drop coating method. The composition of the ammonium ion sensitive film solution is: 10wt% of dopamine hydrochloride, 50wt% of polyvinyl chloride (PVC), 1.5wt% of potassium tetrakis (3,5-di (trifluoromethyl) phenyl) borate (KTFPB), 35wt% of o-nitrophenyl octyl ether (o-NPOE) and 3.5wt% of ammonium ion carrier I. The above components are mixed and dissolved in 1.0mL of tetrahydrofuran, and then ultrasonic stirring (450W, 1h) is performed to obtain the required sensitive film solution. 80μL of the sensitive film solution is drop coated on the surface of the solid contact layer, and then the electrode is immersed in the Tris solution (10mM, pH=8.5) for self-polymerization for 3 minutes to form a stable ion sensitive film.

[0114] II. Drawing of standard curve

[0115] Take NH4Cl dissolved in deionized water to prepare a standard ammonium ion solution, a total of 7 concentration gradients, including 10 -1 , 10 -2 , 10 -3 , 10 -4 , 10 -5 , 10 -6 , 10 -7 M.

[0116] Take 80 μL of the above concentration standard ammonium ion solution, drop it on the surface area of the working electrode, detect the open circuit voltage, record the open circuit voltage when different concentrations of standard ammonium ion solution are added, and draw a calibration linear curve between the open circuit voltage and the concentration of ammonium ion.

[0117] After calibration, the linear relationship between the open circuit voltage response of the ammonium ion electrochemical sensor of the embodiment and the different concentrations of ammonium ion is obtained, as shown in Figure 5 . The linear range is 10 -1 -10 -6 M, the lower limit of detection is 8.5 x 10 -7 M, and the sensitivity is 24.57 mV / dec.

[0118] As can be seen from Comparative Example 1, the bare screen-printed carbon electrode without modified copper nanoparticles is selected as the electrode matrix, and the graphene alone is selected as the solid contact layer, and the ammonium ion sensor prepared has obvious disadvantages in the detection linear range and sensitivity, which shows that the large specific surface area, excellent conductivity and other properties of copper nanoparticles, the redox capacitance of polyaniline and the synergistic effect of the double-layer capacitance of reduced graphene oxide, and the "ion-electron" transduction ability, all of which are helpful to improve the sensitivity of the sensor and expand the linear detection range.

[0119] Comparative Example 2

[0120] I. Preparation of working electrode

[0121] The bare screen-printed carbon electrode without modified copper nanoparticles is selected as the electrode matrix;

[0122] The graphene oxide dispersion solution is dissolved in 0.5 M sulfuric acid with a concentration of 1 mg / L, and after ultrasonic dispersion, aniline is added for mixing to form a mixed solution, wherein the concentration of aniline is 0.5 M; 100 μL of the mixed solution is dropped on the surface of the working electrode, and the cyclic voltammetry (CV) is scanned for 20 times (the auxiliary electrode is a screen-printed carbon electrode, and the reference electrode is a screen-printed Ag / AgCl electrode), and the scanning potential range falls within the interval of -1.5-1.0 V;

[0123] An ammonium ion-sensitive membrane was modified onto the aforementioned solid contact layer using a drop-coating method. The ammonium ion-sensitive membrane solution consisted of: 60 wt% polyvinyl chloride (PVC), 1 wt% potassium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate (KTFPB), 38 wt% o-nitrophenyl octyl ether (o-NPOE), and 1 wt% ammonium ion support I. The above components were mixed and dissolved in 1.0 mL of tetrahydrofuran, and the mixture was ultrasonically stirred (400 W, 3 h) to obtain the desired sensitive membrane solution. 40 μL of the sensitive membrane solution was dropped onto the surface of the solid contact layer and allowed to air dry at room temperature for 30 min to form the ammonium ion-sensitive membrane.

[0124] II. Drawing the Standard Curve

[0125] Dissolve NH4Cl in deionized water to prepare standard ammonium ion solutions with seven concentration gradients, including 10... -1 10 -2 10 -3 10 -4 10 -5 10 -6 10 -7 M.

[0126] Take 100 μL of the above-mentioned standard ammonium ion solution and drop it onto the surface area of ​​the working electrode. Detect the open-circuit voltage and record the open-circuit voltage when adding standard ammonium ion solutions of different concentrations. Plot the calibration linear curve between the open-circuit voltage and the ammonium ion concentration.

[0127] After calibration, the linear relationship between the open-circuit voltage response of the ammonium ion electrochemical sensor in this embodiment and different concentrations of ammonium ions was obtained, such as... Figure 6 As shown. The linear range is 10. -1 -10 -5 M, detection limit is 9.3×10 -6 M, with a sensitivity of 24.04 mV / dec.

[0128] As shown in Comparative Example 2, the ammonium ion sensor made with an ammonium ion sensitive membrane without added polydopamine (PDA) showed a significant deterioration in the detection linear range. This indicates that the excellent adhesion and film-forming ability of polydopamine (PDA) can prevent leakage of the ammonium ion carrier and detachment of the sensitive membrane, thereby improving the linear detection range and stability of the sensor.

[0129] The foregoing example embodiments have been described in order to explain the application and its performance. These descriptions are not intended to limit the application to the form disclosed, but want to make modifications within the scope of the application, which is subject to the conditions, parameters and sample processing. The description of the example embodiments is intended to explain the principles of the application and to exemplify its practical application, so that other skilled persons in the art can implement and modify the application. The scope of the application is defined by the claims and their equivalents.

Claims

1. A high-sensitivity ammonium ion electrochemical sensor comprising a solid-state ammonium ion selective electrode, the solid-state ammonium ion selective electrode comprising an electrically conductive substrate, a solid-state contact layer, and an ammonium ion sensitive membrane disposed in that order, characterized in that, The conductive base is a silk screen printed carbon electrode with copper nanoparticles on the surface; the solid contact layer is composed of a polyaniline and reduced graphene oxide composite; the composition of the ammonium ion sensitive film includes polydopamine and an ammonium ion carrier; The particle size of the copper nanoparticles is 50-200 nm. The solid contact layer is formed by electrochemical co-deposition of graphene oxide and aniline monomers, the mass concentration of graphene oxide in the electroplating solution is 0.5-2 mg / L, and the molar concentration of aniline monomers is 0.1-1 M. The composition of the ammonium ion sensitive film includes, in mass percentage, polydopamine 2-10%, polyvinyl chloride 20-50%, potassium tetra(3,5-di(trifluoromethyl)phenyl)borate 0.5-2%, o-nitrophenyl octyl ether 30-70%, and an ammonium ion carrier 1-10%.

2. The high sensitivity ammonium ion electrochemical sensor of claim 1, wherein, The composition of the ammonium ion sensitive film includes, in mass percentage, polydopamine 5-10%, polyvinyl chloride 35-50%, potassium tetra(3,5-di(trifluoromethyl)phenyl)borate 0.5-1.5%, o-nitrophenyl octyl ether 35-50%, and an ammonium ion carrier 1-3.5%.

3. The high sensitive ammonium ion electrochemical sensor of claim 1, wherein, The preparation method of the all-solid-state ammonium ion selective electrode comprises: (1) dropping an electrolyte copper solution on the surface of a silk screen printed carbon electrode to form copper nanoparticles on the surface of the silk screen printed carbon electrode by electrochemical deposition to obtain a conductive base; (2) dispersing graphene oxide in a sulfuric acid solution, adding aniline monomers to form a mixed solution, and dropping the mixed solution on the surface of the conductive base to form a polyaniline and reduced graphene oxide composite on the surface of the conductive base by electrochemical co-deposition to obtain a solid contact layer; (3) modifying an ammonium ion sensitive film solution containing dopamine and an ammonium ion carrier to the surface of the solid contact layer by one of drop coating, spin coating, and inkjet printing, and self-polymerizing to form an ammonium ion sensitive film.

4. The high sensitivity ammonium ion electrochemical sensor of claim 3, wherein, In step (1), the concentration of the electrolyte copper solution is 2-10 mM; the constant potential method is used for deposition for 60-100 s, and the applied potential is-1.2 V to-1.0 V.

5. The high sensitive ammonium ion electrochemical sensor of claim 3, wherein, In step (2), the preparation method of the mixed solution comprises: dissolving graphene oxide dispersion in a 0.1-0.5 M sulfuric acid solution with a concentration of 0.5-1 mg / L, ultrasonic dispersion, and then adding aniline with a concentration of 0.5-1 M; the electrochemical co-deposition method is cyclic voltammetry scanning for 15-20 cycles with a scanning potential range of-1.5-1.5 V.

6. The high sensitivity ammonium ion electrochemical sensor of claim 3, wherein, In step (3), the preparation method of the ammonium ion sensitive film comprises: first dissolving dopamine hydrochloride, polyvinyl chloride, potassium tetra(3,5-di(trifluoromethyl)phenyl)borate, o-nitrophenyl octyl ether, and an ammonium ion carrier I in tetrahydrofuran according to a mass ratio of 5-10:35-50:0.5-1.5:35-50:1-3.5, and applying ultrasonic stirring to obtain an ammonium ion sensitive film solution; then modifying the ammonium ion sensitive film solution to the surface of the solid contact layer and immersing it in an alkaline solution for self-polymerization to form an ammonium ion sensitive film.

7. Use of an electrochemical sensor according to any one of claims 1 to 6 for the detection of ammonium ions, characterized in that, The electrochemical sensor takes a full solid-state ammonium ion selective electrode as a working electrode, and the concentration range of the detected ammonium ion is 10 -7 ~10 -1 M.

8. Use according to claim 7, wherein the compound is ###0002### The application comprises the following steps: (1) Preparation of standard solution: The ammonium ion standard solution was prepared, and a series of different concentrations of the standard solution to be measured were obtained by dilution and constant volume; (2) Standard curve drawing: The ammonium ion standard solution of different concentrations was added dropwise on the surface of the working electrode ammonium ion sensitive membrane, the open circuit voltage was measured, the stable potential response value was recorded, and the calibration linear curve between the potential response value and the ammonium ion concentration was drawn; (3) Actual sample test: The sample to be measured was added dropwise on the surface of the working electrode ammonium ion sensitive membrane, the open circuit voltage was measured by the method of step (2), and the stable potential response value was brought into the above corresponding calibration linear curve equation to obtain the ammonium ion content in the sample to be measured.

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