Monolithic Cadmium Ion Selective Electrode Based on Highly Dispersed MoS2 and Its Preparation Method

Abstract

This invention discloses a monolithic cadmium ion-selective electrode based on highly dispersible lipophilic molybdenum disulfide and its preparation method. The main steps include: preparing a mixture of molybdenum and sulfur sources → mixing the mixture with long-chain alkyl groups to obtain product A → adding product A to an ion-selective membrane solution → casting onto an electrode, followed by ventilation and evaporation to obtain the monolithic cadmium ion-selective electrode. By controlling the capacitance and surface wettability of molybdenum disulfide through surface / interlayer modulation, the superhydrophobic and high capacitance characteristics of the highly lipophilic molybdenum disulfide material are achieved, while exhibiting high dispersibility in the key flow components of the membrane. The highly dispersible membrane component material designed in this invention provides an alternative method for the simplified manufacturing of all-solid-state ion-selective electrodes and offers a new approach for mass production.

Description

Technical Field

[0001] This invention relates to the field of ion-selective electrodes, specifically a monolithic cadmium ion-selective electrode based on highly dispersed MoS2 and its preparation method. Background Technology

[0002] Traditional polymer membrane-based liquid contact ion-selective electrodes have been commercially used in routine detection, but their further development is limited by the need for additional maintenance of the internal filling solution, which hinders storage and miniaturization. In 1971, Cattrall et al. first proposed applying ion-selective membranes (ISMs) directly to wire-coated electrodes on Pt substrates, opening a new chapter in the use of solid contacts to replace internal reference liquids, enabling miniaturized, maintenance-free all-solid-state ion-selective electrodes.

[0003] In 2008, Bakker et al. first reported the existence of approximately [missing information - likely a number] at the interface between the transduction layer and the ion-selective membrane. Direct structural evidence of the water layer. The reverse ion flux in the interfacial water layer leads to electrode potential drift. To improve the hydrophobicity between the solid contact layer and the ISM, various hydrophobic high-capacitance solid-contact all-solid-state ion-selective electrodes have flourished. It has been reported that the essential cause of the interfacial water layer is the absorption of water by the ion-selective membrane, leading to its accumulation. Importantly, Lindfors et al., using attenuated total reflection Fourier transform infrared spectroscopy and finite difference simulations, revealed that incorporating high concentrations of lipophilic components into the membrane composition can reduce the water absorption and migration of plasticized PVC membranes, thereby suppressing the beneficial property of harmful water layers. Furthermore, Shoukry et al., using X-ray photoelectron spectroscopy and atomic force microscopy to analyze cross-sectional depth, revealed that electrode lifetime is limited by the leaching of the active component (hydrophobic ion exchanger). It seems that the introduction of lipophilic components into the ISM can reduce the leakage of key components from the ISM and inhibit water absorption. Therefore, we expect to introduce highly dispersed lipophilic high-capacitance membrane components to suppress the interfacial water layer and thus stabilize the electrode potential.

[0004] Monolithic ion-selective electrodes have become highly attractive candidates for mass production due to their ease of fabrication. Bobacka et al. pioneered the introduction of conductive polymers into membrane components, achieving near-Nernst response lithium-ion detection. However, for inorganic nanomaterials, surfactants are typically required to obtain well-dispersed suspensions. Unfortunately, the presence of these surfactants can adversely affect sensing performance. Therefore, finding a lipophilic, highly capacitive nanomaterial that can be dispersed in membrane components remains a challenge.

[0005] Molybdenum disulfide (MoS2), with a structure similar to graphite, represents a layered two-dimensional transition metal chalcogenide compound and shows broad application prospects in supercapacitors, energy, and electrocatalysis. In 2016, Qin et al. first demonstrated good potential response using 2H-phase molybdenum disulfide nanoflowers as a potassium-ion selective electrode in a solid contact. However, the 2H-phase MoS2 crystal structure, with its triangular prism coordination of metal atoms and a monolayer band gap of 1.9 eV, makes it semi-insulating, making it difficult to provide a sufficiently large interfacial capacitance to stabilize the interfacial potential. Furthermore, its strong hydrophilicity has a certain negative impact on suppressing the interfacial water layer.

[0006] Metallic 1T phase MoS2 stands out among different phases due to its unique physical properties. For example, the conductivity of 1T MoS2 is 107 times higher than that of the 2H phase, and its superior capacitance performance makes it widely used in energy storage. However, its excellent hydrophilicity is not ideal. Molybdenum disulfide exhibits tunable physicochemical properties after interlayer expansion / exfoliation or surface modification. It has been reported that interlayer modulation of MoS2 can achieve a phase transition from 2H to 1T, effectively regulating electronic properties and surface wettability. Therefore, developing a simple and efficient method for preparing monolithic selective nanocomposite film electrodes is of great significance. Summary of the Invention

[0007] The purpose of this invention is to provide a monolithic cadmium ion selective electrode based on highly dispersed MoS2 and its preparation method, so as to solve the problems mentioned in the background art. By directionally controlling the phase structure and lipophilicity of MoS2 through interlayer engineering, it provides an alternative method for developing simple and efficient monolithic selective nanocomposite membrane electrodes, and at the same time provides a new idea for mass production.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This invention discloses a method for preparing a monolithic cadmium ion selective electrode based on highly dispersed MoS2, comprising the following steps:

[0010] S1. Mix thiourea, anhydrous sodium molybdate and deionized water in a molar ratio of 18:6:(5-6) and stir magnetically at room temperature until clear to obtain the first mixed solution.

[0011] S2. Add long-chain alkyl groups to the first mixed solution, stir thoroughly and defoam, react fully at 220-280℃ and cool to room temperature to obtain a black reactant; wash, centrifuge and precipitate the black reactant and dry it to obtain product A.

[0012] S3. Add product A to the ion-selective membrane solution and sonicate to obtain a homogeneous second mixed solution.

[0013] S4. The second mixed solution is uniformly poured onto the bare electrode, and after ventilation and evaporation, a monolithic cadmium ion selective electrode based on highly dispersed MoS2 is obtained.

[0014] As a further aspect of the present invention: in step S2, the molar ratio of the long-chain alkyl group to anhydrous sodium molybdate is (1.5-2.5):6.

[0015] As a further aspect of the present invention: in step S2, the long-chain alkyl group is at least one of hexadecyltrimethylammonium bromide and octadecyltrimethylammonium bromide.

[0016] As a further aspect of the present invention: in step S3, the amount of product A added is 0.25wt%-1.25wt% of the ion-selective membrane solution.

[0017] As a further aspect of the present invention: the membrane component in the ion-selective membrane solution is Cd. 2+ K + Na + Ca 2+ Any one of them.

[0018] Another aspect of the present invention discloses a monolithic cadmium ion selective electrode based on highly dispersed MoS2, which is prepared by the preparation method described in any of the above claims.

[0019] As a further aspect of the present invention: the dynamic potential response range of the monolithic cadmium ion selective electrode is 10. -3 ~10 -8 M.

[0020] As a further aspect of the present invention: the near-Nernst response limit of the monolithic cadmium ion selective electrode is 10. -8.14 M.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] The preparation method of the monolithic ion-selective electrode based on MoS2 developed in this invention is simpler than that of all-solid-state ion-selective electrodes, requiring only a single drop casting, thus avoiding the uncertainty of interface consistency caused by multiple drop castings. By controlling the capacitance and surface wettability of molybdenum disulfide on the surface / interlayer, the superhydrophobic and high capacitance characteristics of the highly lipophilic molybdenum disulfide material are achieved, while exhibiting high dispersibility in the key flow components of the membrane.

[0023] The detection performance (10) of the monolithic cadmium ion selective electrode based on highly dispersed molybdenum disulfide provided by this invention -3 ~10 -8 M, LOD = 10 -8.14M) far exceeds that of wire-coated electrodes (10 -3 ~10 -6 M, LOD = 10 -6.59 M), which can achieve an all-solid-state cadmium ion selective electrode based on superhydrophobic molybdenum disulfide (10 -3 ~10 -8 M, LOD = 10 -8.10 Equivalent to M).

[0024] This invention utilizes a method for simultaneously modulating the capacitance and surface wettability of MoS2 using long-chain alkyl groups, which can be extended to various two-dimensional layered materials, such as MXene. It provides an alternative method for developing simple and efficient monolithic selective nanocomposite film electrodes, and also offers a new approach for mass production. Attached Figure Description

[0025] Figure 1 Scanning electron microscope (SEM) images of the products MoS2, 0.5 CTAB-MoS2, 1.0 CTAB-MoS2, 1.5 CTAB-MoS2, 2.0 CTAB-MoS2, and 2.5 CTAB-MoS2 obtained in the examples and comparative examples;

[0026] Figure 2 XRD, Raman, IR, and XPS spectra of the products MoS2, 0.5 CTAB-MoS2, 1.0 CTAB-MoS2, 1.5 CTAB-MoS2, 2.0 CTAB-MoS2, and 2.5 CTAB-MoS2 prepared for the examples and comparative examples.

[0027] Figure 3 Cyclic voltammetry curves of the products MoS2, 0.5 CTAB-MoS2, 1.0 CTAB-MoS2, 1.5 CTAB-MoS2, 2.0 CTAB-MoS2, and 2.5 CTAB-MoS2 prepared in the examples and comparative examples in 0.1 M KCl;

[0028] Figure 4 The images show the water contact angles of the products MoS2, 0.5 CTAB-MoS2, 1.0 CTAB-MoS2, 1.5 CTAB-MoS2, 2.0 CTAB-MoS2, and 2.5 CTAB-MoS2 obtained in the examples and comparative examples, as well as optical images of 2.0 CTAB-MoS2 material after ultrasonic dispersion in H2O, THF, o-NPOE, o-NPOE and PVC solutions, respectively.

[0029] Figure 5 Contact angle tests of 2.0 CTAB-MoS2 against THF and o-NPOE solutions;

[0030] Figure 6 Optical photographs of different concentrations of 2.0 CTAB-MoS2 dispersed in the membrane composition and the corresponding water contact angles of the ion-selective membranes;

[0031] Figure 7 CV curves and corresponding integrated area histograms for electrode surfaces loaded with different concentrations of 2.0 CTAB-MoS2;

[0032] Figure 8 The dynamic potential response curve and the corresponding calibration curve are shown. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] Dissolve 18 mmol of thiourea and 6 mmol of anhydrous sodium molybdate in 100 mL of deionized water and stir magnetically at room temperature until clear to obtain the first mixed solution.

[0036] 1.5 mmol of white CTAB powder was added to the first mixed solution, stirred until completely dissolved and defoamed, and then placed in a 100 mL polytetrafluoroethylene reactor. The mixture was reacted at 240 °C for 24 h and then cooled to room temperature to obtain a black reactant.

[0037] The black reactant was washed several times with distilled water and anhydrous ethanol to remove organic matter and ionic impurities, and the precipitate was collected by centrifugation. It was then dried overnight in a vacuum oven at 60°C. The resulting product was designated as 1.5CTAB-MoS2.

[0038] Example 2

[0039] Dissolve 18 mmol of thiourea and 6 mmol of anhydrous sodium molybdate in 100 mL of deionized water and stir magnetically at room temperature until clear to obtain the first mixed solution.

[0040] 2.0 mmol of white CTAB powder was added to the first mixed solution, stirred until completely dissolved and defoamed, and then placed in a 100 mL polytetrafluoroethylene reactor. The mixture was reacted at 240 °C for 24 h and then cooled to room temperature to obtain a black reactant.

[0041] The black reactant was washed several times with distilled water and anhydrous ethanol to remove organic matter and ionic impurities, and the precipitate was collected by centrifugation. It was then dried overnight in a vacuum oven at 60°C. The resulting product was designated as 2.0 CTAB-MoS2.

[0042] Example 3

[0043] Dissolve 18 mmol of thiourea and 6 mmol of anhydrous sodium molybdate in 100 mL of deionized water and stir magnetically at room temperature until clear to obtain the first mixed solution.

[0044] 2.5 mmol of white CTAB powder was added to the first mixed solution, stirred until completely dissolved and defoamed, and then placed in a 100 mL polytetrafluoroethylene reactor. The mixture was reacted at 240 °C for 24 h and then cooled to room temperature to obtain a black reactant.

[0045] The black reactant was washed several times with distilled water and anhydrous ethanol to remove organic matter and ionic impurities, and the precipitate was collected by centrifugation. It was then dried overnight in a vacuum oven at 60°C. The resulting product was designated as 2.5CTAB-MoS2.

[0046] Comparative Example 1

[0047] Dissolve 18 mmol of thiourea and 6 mmol of anhydrous sodium molybdate in 100 mL of deionized water and stir magnetically at room temperature until clear to obtain the first mixed solution.

[0048] 0.5 mmol of white CTAB powder was added to the first mixed solution, stirred until completely dissolved and defoamed, and then placed in a 100 mL polytetrafluoroethylene reactor. The mixture was reacted at 240 °C for 24 h and then cooled to room temperature to obtain a black reactant.

[0049] The black reactant was washed several times with distilled water and anhydrous ethanol to remove organic matter and ionic impurities, and the precipitate was collected by centrifugation. It was then dried overnight in a vacuum oven at 60°C. The resulting product was denoted as 0.5CTAB-MoS2.

[0050] Comparative Example 2

[0051] Dissolve 18 mmol of thiourea and 6 mmol of anhydrous sodium molybdate in 100 mL of deionized water and stir magnetically at room temperature until clear to obtain the first mixed solution.

[0052] 1.0 mmol of white CTAB powder was added to the first mixed solution, stirred until completely dissolved and defoamed, and then placed in a 100 mL polytetrafluoroethylene reactor. The mixture was reacted at 240 °C for 24 h and then cooled to room temperature to obtain a black reactant.

[0053] The black reactant was washed several times with distilled water and anhydrous ethanol to remove organic matter and ionic impurities, and the precipitate was collected by centrifugation. It was then dried overnight in a vacuum oven at 60°C. The resulting product was denoted as: 1.0 CTAB-MoS2.

[0054] Comparative Example 3

[0055] 18 mmol of thiourea and 6 mmol of anhydrous sodium molybdate were dissolved in 100 mL of deionized water and stirred magnetically at room temperature until clear, yielding a first mixed solution. This first mixed solution was placed in a 100 mL polytetrafluoroethylene liner, then placed in a reaction vessel and sealed. The reaction was carried out at 240 °C for 24 h and then cooled to room temperature. The resulting reactants were washed several times with distilled water and anhydrous ethanol to remove organic matter and ionic impurities, and the precipitate was collected by centrifugation. Subsequently, the precipitate was dried overnight in a vacuum drying oven at 60 °C. The resulting product was designated as MoS2.

[0056] Please see Figure 1-2 When the products obtained in Examples 1-3 and Comparative Examples 1-3 were observed under an electron microscope, as the amount of CTAB increased, flower-like structures with thinner lamellae gradually grew. This was attributed to the repulsion between lamellae caused by the long-chain alkyl groups adsorbed on the surface. Figure 2 The image shows that, with the modulation of CTAB, the 2H phase MoS2 gradually forms the characteristic peak of the (001) plane 1T phase with a unique superlattice structure. According to the Bragg equation (2dsinθ=nλ), the corresponding interplanar spacing increases from the original 0.625 nm (14.16°) to 1.023 nm (8.969°); indicating that the stacking of MoS2 nanosheets is significantly reduced, and CTAB is successfully inserted between the MoS2 layers, thereby preventing the stacking of nanosheets. Figure 2 b shows the vibrational modes of octahedral coordination E1g and A1g originating from the 2H phase MoS2 at 401.47 cm⁻¹. -1 and 372.05cm -1 In addition to the Raman shift at a certain point, when the CTAB content is 1.5 mmol or higher, the value is 140.44 cm⁻¹. -1 (J1), 228.67cm -1 (J2) and 333.62cm -1 The characteristic Raman peak of the 1T metallic phase MoS2 corresponding to (J3) appears. This is consistent with XRD ( Figure 2 a) The changing patterns are consistent. Furthermore, 2853cm -1 and 2916cm -1 The peaks at these locations correspond to the characteristic peaks of symmetric and asymmetric stretching vibrations of the -CH- and -CH2- bonds in the alkyl chain of CTAB, respectively, indicating the successful introduction of CTAB. Figure 2 c). Figure 2Figure d shows the full spectrum of XPS, which shows that the C content in the product increases with the increase of CTAB regulation, further illustrating the introduction of alkyl chains in the material.

[0057] A three-electrode system was constructed using a glassy carbon electrode as the working electrode, a platinum wire electrode as the counter electrode, and Ag / AgCl as the reference electrode. Cyclic voltammetry (CV) tests were performed on all products in a solution containing 0.1 M KCl at a scan rate of 0.1 V / s and a potential range of -0.5 V to +0.5 V. The capacitance of the material can be measured by the area under the integral of the CV curve. Figure 3 The CV curves of different materials with an electrode surface loading of 0.1 mg are shown. 2.0 CTAB-MoS2 showed the integral area of ​​the maximum capacitance, therefore 2.0 CTAB-MoS2 was selected for subsequent regulation.

[0058] The contact angle of surface water droplets on the products obtained in Examples 1-3 and Comparative Examples 1-3 was tested using a DSAHT17C high-temperature contact angle meter and the seated drop method. The test results are as follows: Figure 4 As shown in figure a, when the amount of CTAB was increased to 1.5 mmol, MoS2 (15.8°) underwent a hydrophilic-to-superhydrophobic transition. Figure 4 b shows the dispersibility of the material in the membrane components before and after regulation. MoS2 exhibits hydrophilic and THF dispersibility, but shows aggregation in the o-NPOE and o-NPOE / PVC mixed solutions flowing in the membrane. Furthermore, 2.0CTAB-MoS2 exhibits hydrophobic properties. Notably, 2.0CTAB-MoS2 shows excellent dispersibility in the key components of the membrane solution, THF, o-NPOE, and o-NPOE / PVC mixed solutions. In addition, Figure 5 The study demonstrated that 2.0 CTAB-MoS2 exhibited a high affinity for THF and o-NPOE solutions, with near-complete absorption within 5 seconds.

[0059] Preparation of cadmium ion selective membrane solution (Cd 2+ -ISM):

[0060] 300 mg of 1 wt% cadmium ion carrier I (ETH 1062), 1.02 wt% NaTFPB, 65.32 wt% o-NPOE and 32.66 wt% PVC were dissolved together in 3 mL THF to obtain a cadmium ion selective membrane solution. Eight identical cadmium ion selective membrane solutions were prepared for later use.

[0061] Fabrication of monolithic electrodes:

[0062] First, the electrodes were cleaned: the GCE was polished on the surface of the ibex hide with 1.0 μm, 0.3 μm, and 0.05 μm Al2O3, respectively. Then, it was ultrasonically cleaned sequentially with 50% nitric acid, ethanol, and deionized water. Finally, it was dried with nitrogen gas for later use.

[0063] Next, 0 wt%, 0.25 wt%, 0.5 wt%, 0.75 wt%, 1.0 wt%, 1.25 wt%, 1.5 wt%, and 2 wt% of 2.0 CTAB-MoS2 were added to eight membrane solutions, respectively. These eight solutions were then sonicated for 1 hour to obtain a homogeneous second mixed solution. The second mixed solution containing 100 μL of 2.0 CTAB-MoS2 at different concentrations was uniformly cast onto a bare GCE. The solvent was completely evaporated in a fume hood at room temperature, thus obtaining a monolithic electrode with different concentrations of 2.0 CTAB-MoS2 dispersed in the membrane, denoted as Xwt% 2.0 CTAB-MoS2-SPE.

[0064] Preparation of all-solid-state cadmium ion selective electrode:

[0065] 100 μL of a mixture without 2.0 CTAB-MoS2 (i.e., cadmium ion selective membrane solution (Cd)) was prepared. 2+ -ISM) was uniformly cast onto the surface of a 2.0 CTAB-MoS2 electrode to obtain Cd based on 2.0 CTAB-MoS2. 2+ -ISE, denoted as 2.0 CT AB-MoS2-Cd 2+ -ISE. To compare the detection performance of a monolithic electrode, the loading of 2.0 CTAB-MoS2 on the electrode surface was optimized to 0.1 mg as a transduction layer. Figure 7 ).

[0066] Preparation of cadmium ion-coated wire electrodes:

[0067] 100 μL of cadmium ion-selective film solution was directly drop-coated onto the surface of a GCE to prepare a wire-coated electrode (Cd). 2+ -ISM) is used for easy comparison later.

[0068] like Figure 6 As shown in Figure a, the material exhibits uniform dispersion in membrane solutions of 0.25 wt%, 0.5 wt%, 0.75 wt%, 1.0 wt%, and 1.25 wt%. With increasing concentration, some suspended matter is observed at 1.5 wt% and 2 wt%, which is due to agglomeration caused by excess material. Figure 6b shows the water contact angle of the monolithic electrode surface for different mass concentration gradients. Compared to the hydrophilic wire-coated electrode surface (75.6°), the monolithic electrode shows an initial increase followed by a slight decrease in hydrophobic properties. The slight decrease in the membrane's water contact angle may be due to excessive material aggregation and precipitation during the natural drying process, which reduces the concentration of highly hydrophobic materials in the membrane composition, thus forming a sandwich-interface quasi-all-solid-state electrode.

[0069] The open-circuit potential test method was used to test 2.0 CTAB-MoS2-SPE and Cd. 2+ -ISE and 2.0 CTAB-MoS2-Cd 2 + -ISE is used for dynamic potential response testing. For example... Figure 8 As shown, the detection limit first decreases and then increases with the increase of the proportion of 2.0 CTAB-MoS2 in the membrane. At 10... -3 -10 -10 In the dynamic potential response test of M, when the mass percentage of 2.0 CTAB-MoS2 in the controlled membrane composition was 0.75 w%, 10 -8.14 The lowest detection limit of M in the near-Nernst response is 28.52 mV / dec. This far exceeds the detection limit of the wire-coated electrode (10). -6.59 M), and even comparable to all-solid-state ion-selective electrodes based on superhydrophobic 2.0 CTAB-MoS2 (10 -8.10 M). This implies the existence of alternative manufacturing strategies for all-solid-state electrodes.

[0070] Although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0071] Therefore, the above description is only a preferred embodiment of this application and is not intended to limit the scope of this application; that is, all equivalent modifications made in accordance with the scope of the claims of this application shall be within the protection scope of the claims of this application.

Claims

1. A method for preparing a monolithic cadmium ion selective electrode based on highly dispersed MoS2, characterized in that, Includes the following steps: S1. Thiourea, anhydrous sodium molybdate and deionized water are mixed in a molar ratio of 18:6:(5-6) and magnetically stirred at room temperature until clear to obtain the first mixed solution; S2. Add long-chain alkyl groups to the first mixed solution, stir thoroughly and defoam, react fully at 220-280°C and cool to room temperature to obtain a black reactant; wash, centrifuge to precipitate, and dry the black reactant to obtain product A. S3. Add the product A to the ion-selective membrane solution and sonicate it to obtain a homogeneous second mixed solution; S4. The second mixed solution is uniformly poured onto the bare electrode. After ventilation and evaporation, a monolithic cadmium ion selective electrode based on highly dispersed MoS2 is obtained. The long-chain alkyl group is at least one of hexadecyltrimethylammonium bromide and octadecyltrimethylammonium bromide.

2. The preparation method according to claim 1, characterized in that, In step S2, the molar ratio of the long-chain alkyl group to anhydrous sodium molybdate is (1.5-2.5):

6.

3. The preparation method according to claim 1, characterized in that, In step S3, the amount of product A added is 0.25wt%-1.25wt% of the ion-selective membrane solution.

4. The preparation method according to claim 1, characterized in that, The membrane component in the ion-selective membrane solution is Cd. 2+ .

5. A monolithic cadmium ion selective electrode based on highly dispersed MoS2, which is prepared by the preparation method according to any one of claims 1-4.

6. A monolithic cadmium ion selective electrode based on highly dispersed MoS2 according to claim 5, characterized in that, The dynamic potential response range of the monolithic cadmium ion selective electrode is 10. -3 ~10 -8 M.

7. A monolithic cadmium ion selective electrode based on highly dispersed MoS2 according to claim 5, characterized in that, The near-Nernst response limit of the monolithic cadmium ion selective electrode is 10. -8.14 M.

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