Electrochemical detection of monochloramine and / or ammonia

Abstract

An apparatus and method for determining the presence or amount of monochloramine and / or ammonia. The devices and methods utilize an electrochemical sensor that includes a working electrode, a reference electrode, and a counter electrode. The working electrode is coated with a formulation specifically for the analysis of monochloramine and / or ammonia comprising reagents associated with the Berthelot reaction to produce an indophenol product for electrochemical detection by voltammetry, in particular differential pulse voltammetry.

Description

Technical Field

[0001] This invention relates to an electrochemical method and apparatus for analyzing target analytes in liquid samples, and more particularly (but not limited to) an electrochemical analysis system for determining the presence or amount of monochloramine and / or ammonia in aqueous samples. Background Technology

[0002] Monochloramine is increasingly used as a secondary disinfectant for drinking water because it is more effective than using only free chlorine (Cl2 / HOCl / OCl). - Compared to other disinfection methods, monochloramine has several unique advantages. These advantages include durability / stability and a lower tendency to form harmful disinfection byproducts. Monochloramine is formed by the reaction between free chlorine and ammonia, both of which are intentionally added to drinking water systems in strictly controlled doses. Ammonia is also present in natural waters and is toxic to aquatic life. Ammonia can also exist as aqueous NH3 or as the conjugate acid form NH4. + Found in water 。 The latter can be considered a weak acid with a pKa value of 9.25. As mentioned above, ammonia can be intentionally added to drinking water, but it can also be present in natural water bodies. Besides industrial wastewater discharge, ammonia can also enter natural water bodies through pathways such as the decomposition of organic waste and animal excrement.

[0003] Chloramine is composed of free chlorine substances (Cl2 / HOCl / OCl) - ) and ammonia substances (NH3 / NH4) + Chloramines are formed through a reaction between nitrogen and nitrogen. The three inorganic chloramines formed are monochloramine, dichloramine, and trichloramine, where the prefix indicates the number of chlorine atoms bonded to nitrogen. Dichloramine and trichloramine have significantly lower taste and odor thresholds in water, making their presence undesirable. Furthermore, the latter two chloramines may pose a health threat. The distribution of these chloramines depends on factors such as the chlorine / ammonia ratio, temperature, and pH. The general equilibrium equation for chloramine formation is as follows: Figure 1 As shown.

[0004]

[0005] There is a need for a method to monitor the levels of monochloramine and ammonia in water bodies that can be easily detected without interference from free chlorine, dichloramine, or trichloramine. Several methods have been developed, as detailed below.

[0006] Ampere titration (standard method 4500-CI D) is a method that typically requires a higher level of operator skill compared to other methods. The sample is buffered to a pH between 6.5 and 7.5, and then titrated with benzoarsene oxide (PAO) until the current change on the microammeter stops. Extreme care must be taken near the endpoint, and the final titration increment may need to be subtracted to avoid over-titering. The free chlorine concentration is determined by the amount of PAO titrated. After determining the free chlorine, the amount of monochloramine is determined by adding a small amount of potassium iodide solution and continuing titration with PAO. The endpoint is determined in the same manner as described above.

[0007] The DPD colorimetric method (standard method 4500-Cl D) employs a similar approach to free chlorine detection, determining monochloramine concentration by adding N,N-diethyl-p-phenylenediamine (DPD). Under suitable pH conditions, DPD reacts with the target analyte to produce a colorimetric reaction; at a wavelength of 515 nm, the color intensity is directly proportional to the free chlorine concentration in the sample. Subsequently, a small amount of potassium iodide crystals (approximately 0.1 mg) is added, and the color is immediately interpreted again. The amount of potassium iodide added and the reading interval may affect the degree of interference from dichloramine.

[0008] The phenolate method (standard method 4500-NH3F) is a method based on indophenol, which utilizes the Berthelot reaction to generate a highly stained compound that can be detected colorimetrically. Due to the high molar absorptivity of indophenol, this method is highly sensitive and selective for monochloramines. However, the process is slow. Therefore, catalysts are usually employed to accelerate color development.

[0009] The Berthelot reaction proceeds in a series of steps, described here as follows: 1. Ammonia / ammonium substances react with hypochlorite / hypochlorous acid to produce monochloramine.

[0010] 2. Monochloramine reacts with phenol to form an imine compound.

[0011] 3. Imine reacts with excess phenol to eventually produce indophenol.

[0012] The following is the general reaction scheme; for clarity, intermediate steps have been omitted.

[0013] .

[0014] However, there is still a need for improved devices and methods to identify and / or quantify the concentrations of monochloramine and / or ammonia in liquid samples. Summary of the Invention

[0015] The objective is to provide an electrochemical-based apparatus and method for determining the presence and / or amount of monochloramine and / or ammonia in liquid samples, particularly aqueous samples. Another specific objective is to provide an apparatus and method that utilizes an electrochemical potentiostat capable of voltammetric analysis to efficiently, conveniently, and reliably detect monochloramine and / or ammonia in liquid samples. A further specific objective is to provide a portable apparatus and method that is convenient to use as needed in a variety of locations and environments.

[0016] Therefore, the inventors provide an electrochemical device, method, and system based on an electrochemical sensor having a working electrode, a reference electrode, and a counter electrode, wherein the working electrode comprises a formulation specifically adapted for detecting monochloramine and / or ammonia in liquid samples. In particular, this concept focuses on the high-accuracy electrochemical determination of monochloramine and / or ammonia over a wide range of analyte concentrations. Specifically, this concept provides a highly sensitive electrochemical analysis system that offers greater accuracy in determining the concentration of the target analyte compared to existing technologies.

[0017] This apparatus and method utilize the Berthelot chemical reaction and its reaction pathway described herein. In particular, this concept provides a quantitative, rather than batch, Berthelot chemical analysis system. Specifically, and according to several aspects of this concept, the electrochemical sensor is quantitatively loaded with a formulation containing the components required for the Berthelot reaction and the components required for the sensor's quantitative loading.

[0018] According to a first aspect of this concept, an electrochemical sensor is provided for determining the presence or amount of monochloramine and / or ammonia in a liquid sample, comprising: a substrate; a working electrode, a reference electrode, and a counter electrode disposed on the substrate; and a coating disposed on the working electrode, the coating comprising a formulation comprising: phenol or a phenol derivative; and a coupling agent or coupling agent precursor compound comprising a transition metal-based complex.

[0019] Optionally, the electrochemical sensor includes a first working electrode and a second working electrode. The first electrode can be configured to be in an operating state, while the second electrode can be configured to be in a non-operating state. Optionally, both the first electrode and the second electrode can be configured to be in an operating state.

[0020] Preferably, the formulation further comprises any one or a combination of the following: a wetting agent; a complexing agent for retaining phenol at the coating; an adhesion promoter for promoting adhesion of the coating to the substrate; a pH buffer; and a coating stabilizer.

[0021] Preferably, the wetting agent comprises an alcohol, propan-2-ol, methanol, or ethanol.

[0022] Preferably, the complexing agent comprises any or a combination of α-cyclodextrin, β-cyclodextrin, or γ-cyclodextrin or their derivatives. Optionally, the complexing agent may comprise a β-cyclodextrin polymer or 2-hydroxypropyl-β-cyclodextrin. Optionally, the complexing agent may comprise any or a combination of the following: polysaccharides, starch or starch derivatives, cyclodextrin, cellulose or cellulose derivatives, gelatin, plant exudates, pectin, gums, gum arabic, carrageenan, tragacanth gum, mesona gum, marine extracts, alginate, carrageenan, chitosan, proteins, and lipids.

[0023] Preferably, the adhesion promoter comprises any or a combination of carboxymethyl cellulose or cellulose-based polymers.

[0024] Preferably, the pH buffer may comprise boric acid, phosphoric acid, and phosphate compounds. Optionally, the stabilizer may comprise D-glucol.

[0025] Preferably, the transition metal-based complex comprises any or a combination of the following: Mn, Cr, or Fe-based complexes; nitroprusside or sodium nitroprusside; nitrosopentamerite and / or hydrated pentacyanoferite.

[0026] Preferably, the formulation comprises a coupling agent precursor; and wherein the coupling agent is generated in situ from a transition metal-based complex by using a preconditioning potential applied to the sensor.

[0027] Preferably, the substrate is an elongated body having a first longitudinal end and a second longitudinal end.

[0028] Preferably, the working electrode, reference electrode, and counter electrode include conductive traces that extend axially between a first end and a second end of the substrate and are spaced apart from each other in the width direction of the substrate. Preferably, the reference electrode includes silver traces, and both the working electrode and the counter electrode include carbon traces.

[0029] Preferably, a first dielectric layer is formed on the region between the first and second ends of the substrate of the working electrode, the reference electrode, and the counter electrode, such that the longitudinal end regions of each of the working electrode, the reference electrode, and the counter electrode are exposed without being covered by the dielectric layer. Optionally, a second dielectric layer is formed on the working electrode near the second end of the substrate, such that only a defined region of the working electrode is exposed to the solution.

[0030] Preferably, the conductive traces of the working electrode, the reference electrode, and the counter electrode extend substantially parallel to each other at the substrate.

[0031] According to another aspect of this concept, an electrochemical sensing kit for determining the presence or amount of monochloramine is provided, comprising: an electrochemical sensor as claimed in claim 1; and a first sample conditioning component comprising: an electrolyte salt; and a chlorine scavenger.

[0032] Preferably, the electrolyte salt comprises any one or a combination of the following: KNO3, KCl, or Na2SO4; and / or the chlorine scavenger comprises an alkali metal nitrite or sodium nitrite.

[0033] Preferably, the pH buffer comprises a weak acid buffer, citric acid, or boric acid. Optionally, the pH control agent comprises any or a combination of a weak base, a hydroxide, or lithium hydroxide. Optionally, the dissolving agent comprises any or a combination of an ion exchange resin, a quaternary ammonium salt resin, or 3-[(3-chlorophenyl)sulfonamide]benzoic acid (e.g., Amberlite (RTM)). Optionally, the first sample conditioning component comprises potassium carbonate, cellulose material, cellulose derivative, or microcrystalline cellulose (e.g., Avicel (RTM)) and an ion exchange resin or a quaternary ammonium resin.

[0034] Sample preparation components can be provided as tablets (compressed solid powder) or liquids / solutions. Specific sample preparation components can be selected based on the analyte to be detected (e.g., ammonia or monochloramine). For example, ammonia detection can use a liquid reagent as the first sample preparation component, while monochloramine detection can be configured to use a tablet-form preparation component. Furthermore, the sensing kit can also contain different forms of sample preparation components, including tablets and liquids or solutions, each containing the stated pH control compound (e.g., electrolyte salts, chlorine scavengers, pH buffers, pH controllers, dissolving agents).

[0035] Preferably, the sample conditioning component (e.g., tablet or liquid) further comprises: a pH buffer; a pH control agent. Optionally, when the sample conditioning component is a tablet, the component may also contain a dissolving agent.

[0036] Preferably, for determining the presence or amount of ammonia, the kit includes a second sample conditioning component comprising an electrolyte salt and a chlorine source. Similar to the first sample conditioning component, the second sample conditioning component may be provided as a tablet or liquid / solution and contains the same or similar ingredients as the first sample conditioning component.

[0037] Preferably, the electrolyte salt comprises any one or a combination of the following: KNO3, KCl or Na2SO4; and / or the chlorine source may be hypochlorite, typically calcium hypochlorite.

[0038] Preferably, the second sample conditioning component further comprises: a pH control agent; and a dissolving agent (if in tablet form). Preferably, the pH control agent comprises any or a combination of a weak base, a hydroxide, or lithium hydroxide. Optionally, the dissolving agent comprises any or a combination of an ion exchange resin, a quaternary ammonium resin, or 3-[(3-chlorophenyl)sulfonamide]benzoic acid (e.g., Amberlite (RTM)). Optionally, the second sample conditioning tablet / liquid comprises potassium carbonate, a cellulose material, a cellulose derivative, or microcrystalline cellulose (e.g., Avicel (RTM)).

[0039] According to another aspect of this concept, an electrochemical method is provided for determining the presence or amount of monochloramine and / or ammonia in a liquid sample, comprising: providing an electrochemical sensor having a working electrode, a reference electrode, and a counter electrode on a substrate, the working electrode comprising a coating containing an agent comprising: phenol or a phenol derivative; and a coupling agent or a coupling agent precursor compound comprising a transition metal-based complex; immersing the electrochemical sensor at least partially in the liquid sample; and analyzing the liquid sample by applying an electrochemical voltammetry method.

[0040] Preferably, the electrochemical voltammetry is differential pulse voltammetry.

[0041] Preferably, the transition metal-based complex comprises a nitroprusside or sodium nitroprusside.

[0042] Preferably, a preconditioning potential is applied to the electrochemical sensor before applying the electrochemical voltammetry; and nitrosopentamerite and / or hydrated nitrosopentamerite are generated from nitroprusside or sodium nitroprusside by means of the preconditioning potential applied to the electrochemical sensor.

[0043] Depending on the specific implementation method, the chemical reaction pathway on the sensor can proceed in three different stages: 1. In-situ electrochemical generation of hydrated pentacyanoferrate [Fe(CN)5H2O]³ - ; 2. The Berthelot reaction is carried out to generate indophenol compounds; 3. Electrochemical analysis of indophenol was performed using voltammetry and, optionally, differential pulse voltammetry (DPV).

[0044] Advantageously, the sensor coating on the working electrode contains a coupling agent precursor compound in the form of a nitroprusside salt. By generating an active coupling agent (i.e., nitrosopentamenoferrate and / or hydrated nitrosopentamenoferrate), this device and method provide a convenient and efficient electrochemical analysis system.

[0045] Optionally, when this concept is used for the detection of ammonia, it can provide two formulations specifically for two different concentration ranges. Optionally, the concentration ranges can be 0.2-2 ppm and 0.5-15 ppm. Preferably, all formulations for the analyte concentration ranges contain the same or similar components at their respective concentrations and operate in the same manner. Optionally, when this concept includes a phosphate buffer, the formulations are configured differently and are suitable for lower pH values. Optionally, the sensor can be configured to use, for example, boric acid or phosphoric acid to buffer pH values ​​between 7 and 9.15.

[0046] Brief description of the attached figures Specific embodiments of the present invention will now be described by way of example only, in conjunction with the accompanying drawings, wherein: Figure 1 This is a top view of an electrochemical sensor including a working electrode, a reference electrode, and a counter electrode according to a specific embodiment.

[0047] Figure 2 This is a predicted concentration-pH graph showing the speciation of nitroprusside, nitrosopentamenoferrate, and hydrated nitrosopentamenoferrate given an initial concentration of nitroprusside.

[0048] Figure 3 This is a differential pulse voltammetry curve of a sample containing monochloramine (NH2Cl).

[0049] Figure 4 shows the differential pulse voltammetry curves of the sample containing an increased concentration of monochloramine (NH2Cl); Figure 5 shows the calibration curve of monochloramine (NH2Cl).

[0050] Figure 6 shows the differential pulse voltammetry curves of the sample containing an increased concentration of ammonium chloride (NH4Cl).

[0051] Figure 7 shows the calibration curve for ammonium chloride (NH4Cl).

[0052] Figure 8 is a flowchart of a specific implementation of this concept for detecting monochloramine and ammonia in a liquid sample. Detailed Implementation

[0053] Reference Figure 1The sensor 10 includes an electrically inert plastic substrate 14 with an approximate thickness of about 500 μm. The sensor 10 also includes a carbon electrical contact 15 disposed toward a first end 19 of the generally elongated sensor to provide an electrical connection to a potentiostat (not shown). An insulating layer 16a covers conductive traces 17 to allow the sensor 10 to be immersed in a liquid sample; another insulating layer 16b defines a carbon electrode exposed to the solution. The traces 17 comprise silver or a silver-based material to provide a low-resistance current path connecting the electrical contact 15 to an array of electrodes disposed at a second end 18 of the sensor 10. In particular, the sensor 10 includes a carbon counter electrode 13 to allow current to flow between itself and the working electrode 11a, and to ensure that almost no current flows into the reference electrode 12. According to a specific embodiment, a second working electrode 11b is provided. However, this working electrode 11b can be configured to be in a non-operating state. The reference electrode 12 comprises silver or a silver-based material to provide a stable potential from which other potentials are applied. The working electrode 11a comprises carbon coated with or coated with a formulation detailed in Table 1 below. In particular, the formulation is loaded onto the carbon working electrode 11a and is specially configured to promote the Berthelot reaction and also possesses suitable physical properties such as wettability. Table 1 details the constituent components, concentrations, and technical effects.

[0054]

[0055] The formulation detailed above is dripped onto the screen-printed carbon electrode 11, subsequently dried in an oven, and sealed in an airtight package. Cyclodextrin is known to have an affinity for phenol molecules and helps prevent phenol loss during use. Furthermore, this stabilizer effectively retains moisture and prevents cracking of the loaded layer during drying. The working electrode 11 provides a working / functional electrode where the target analyte undergoes reduction and / or oxidation to generate an electrochemical current. This current is measured and analyzed to determine the concentration of the target substance in the liquid sample. Based on this system and concept, it can be understood that indophenol is oxidized, thus producing a peak. This electrochemical reaction pathway may involve a first reduction stage (reduction from the initial oxidized state of indophenol), or indophenol may already be in its reduced state.

[0056] This concept is specifically applied to the determination and analysis of monochloramine, and also to the determination and analysis of ammonia. Each analyte is analyzed by pretreating liquid samples using specially formulated pre-electrochemical analysis tablets. Tables 2 and 3 below, listing the constituent compounds, mass fractions, and related technical effects, respectively confirm the two formulations of the tablets.

[0057]

[0058]

[0059] The tablets prepared according to Tables 2 and 3 are sealed in airtight packaging for later use.

[0060] The method described herein utilizes Berthelot chemical reactions, but employs a quantitative rather than a batch approach. Sensor 10 (specifically, working electrode 11) quantitatively loads the formulations listed in Table 1. The reaction proceeds in three distinct phases, detailed below: .

[0061] Sodium nitroprusside (Na2[Fe(CN)5NO]) The addition of [Fe(CN)5H2O] as a catalyst in the Berthelot reaction allows for faster color development. However, the actual catalyst present in the reaction is considered to be hydrated pentacyanoferrate ([Fe(CN)5H2O]). 3- Hereinafter referred to as AqF. This conclusion is drawn from the observation that the stoichiometric ratio of the reaction between AqF and NH2Cl is 1:1. Because AqF is consumed in the reaction... ， Therefore, this article refers to it as a "coupling agent" rather than a catalyst.

[0062] In the reaction, an equilibrium exists between nitroprusside, nitrosopentamenoferrate, and AqF in alkaline solution, as shown below: .

[0063] the following Figure 2 The distribution of these substances as a function of pH is shown, calculated using the aforementioned equilibrium constant. It can be seen that a significant proportion of AqF is only observed at sufficiently high pH values ​​(>10). The oxygen reduction reaction (ORR), a common reaction in electrochemistry, is used here to promote the formation of AqF from NP by increasing the pH of the region surrounding the electrode surface. During the ORR process, hydroxide ions are generated on the working electrode surface. This process, combined with the electrochemical reduction of NP from Fe(III) to Fe(II), is considered to promote AqF formation without excessively high solution pH values, which may be detrimental to the electrochemical detection of indophenol. Therefore, the result of this process is that AqF can be generated in situ from NP by controlling the working electrode potential to a defined time period. After the in-situ formation of the coupling agent AqF, the Berthelot reaction proceeds, whereby the reaction between the phenol derivative and monochloramine leads to the formation of indophenol. The overall reaction is shown below.

[0064] .

[0065] The rate of this reaction is strongly dependent on pH and any substituents on the phenol molecule. A pH is typically chosen to deprotonate the phenol, and this distribution is controlled by the pKa of the phenol of interest. Functional groups at the ortho positions of the benzene ring in phenol can increase or decrease the reaction rate by donating or absorbing electrons into the aromatic system, respectively.

[0066] As the Berthelot reaction proceeds, indophenol forms in a quantitative loading layer on the surface of the working electrode. This substance is detected by electrochemical methods (particularly voltammetry) and, according to a preferred embodiment, by differential pulse voltammetry (DPV). This has been observed to provide a method with high sensitivity for the target analyte.

[0067] When the quantitative loading sensor 10 was tested using DPV in a sample solution containing monochloramine, two peaks were observed. The first peak, located at approximately -0.05 V, is attributed to the product of the Berthelot reaction and is proportional to the monochloramine concentration. The second peak, located at approximately 0.45 V, is due to the oxidation of phenol quantitatively loaded onto the sensor 10. The quantitative loading formulation typically contains excess phenol, which cannot be completely depleted during the reaction, resulting in the second peak. Figure 3 The voltammetry plot of the process is shown, in which the two peaks can be clearly observed.

[0068] A calibration curve can be generated by testing a sample containing a known amount of monochloramine. Figure 4 The typical voltammetric plot used for monochloramine calibration is shown, while Figure 5 The relevant calibration curve data is displayed. For clarity, Figure 4 The voltammogram in the image focuses only on the first peak because the second peak is not proportional to the concentration of monochloramine.

[0069] Ammonia can also be detected using the same method, but a chemical reaction to produce monochloramine must be performed first. Figure 6 The voltammogram used for typical ammonia calibration is shown, while Figure 7 The relevant calibration curve data is displayed.

[0070] According to this embodiment, a sample conditioning component in tablet form is used. However, according to other embodiments, the sample conditioning component can be a liquid, a solution, or a combination of these different forms / phases. Furthermore, the form / phase of the sample conditioning component may depend on the analyte test being performed. For example, a tablet can be used for the testing of monochloramine, while a liquid sample conditioning component can be used for the testing of ammonia. The measurement of monochloramine is performed as follows: Tablet A (or liquid) (see Table 2) mainly containing electrolytes and buffers is added to the sample and dissolved. The sensor 10 is then immersed in the sample, and an initial potential is applied to generate AqF in situ. Subsequently, a different potential is applied for a longer period of time, allowing the Berthelot reaction to proceed. After a predetermined time period, a DPV is performed, yielding a peak of approximately 0.05 V relative to Ag, which is proportional to the concentration of monochloramine in the sample. The amplitude of this peak is measured after baseline subtraction, and it is correlated with the monochloramine concentration using a calibration curve.

[0071] The determination of total ammonia is performed in the same manner as described above, but with two important differences. Tablet B (or liquid) (see Table 3) contains a source of free chlorine and a strong base, which, upon addition, creates a higher pH value in the sample. This facilitates the first stage of the Berthelot reaction described herein. The sample solution is then reacted for approximately two minutes, and the remaining steps are performed as described above for the determination of monochloramine, except that here the total ammonia (NH₂Cl + NH₃ / NH₄) is measured. + Free ammonia (NH3 / NH4) + The concentration of ) can be determined by subtracting monochloramine from the total ammonia. The entire process is schematically shown in the diagram. Figure 8 middle.

[0072] refer to Figure 8 According to Tables 2 and 3: In the initial stage 30, tablet A (or liquid) is crushed (or dispensed) into the liquid sample to ensure complete dissolution / mixing. In stage 31, the sensor is immersed in the sample, and a potential is applied to the working electrode for the specified time. In stage 32, a potential is applied to the working electrode for the specified time, and the chemical reaction is allowed to proceed. In stage 33, DPV is performed to generate an electrochemical signal. In stage 34, the NH2Cl concentration is calculated from the baseline-corrected peak amplitude using a calibration curve. In the initial stage 35, tablet / liquid B is crushed / mixed into the liquid sample to ensure complete dissolution / mixing. In stage 36, the initial reaction is allowed to proceed for approximately two minutes. In stage 37, the sensor is immersed in the sample, and a potential is applied to the working electrode for the specified time. part38. Apply a potential to the working electrode for the specified time and allow the chemical reaction to proceed. In stage 39, perform DPV to generate an electrochemical signal. In stage 40, calculate the total ammonia concentration from the baseline-corrected peak amplitude using a calibration curve. In stage 41, calculate the free ammonia concentration as the difference between monochloramine and total ammonia.

Claims

1. An electrochemical sensor for determining the presence or amount of monochloramine and / or ammonia in a liquid sample, comprising: Base; A working electrode, a reference electrode, and a counter electrode are disposed on the substrate; A coating disposed on the working electrode, the coating comprising a formulation comprising: • Phenol or phenol derivatives; and • Coupling agents or coupling agent precursor compounds containing transition metal-based complexes.

2. The sensor of claim 1, wherein the formulation further comprises any one or a combination of the following: • Wetting agent; • A complexing agent used to retain phenol at the coating; • An adhesion promoter that facilitates adhesion of the coating to the substrate; • pH buffer; • Coating stabilizer.

3. The sensor of claim 2, wherein the wetting agent comprises alcohol, methanol, propanol, or ethanol.

4. The sensor of claim 2, wherein the complexing agent comprises any or a combination of the following: α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, or a β-cyclodextrin polymer, or 2-hydroxypropyl-β-cyclodextrin or a derivative thereof.

5. The sensor of claim 2, wherein the adhesion promoter comprises any or a combination of carboxymethyl cellulose or cellulose-based polymers.

6. The sensor of claim 2, wherein the pH buffer comprises boric acid and / or the stabilizer comprises D-glucol.

7. The sensor as claimed in any of the preceding claims, wherein the transition metal-based complex comprises any one or a combination of the following: •Mn, Gr, or Fe-based complexes; • Nitroprusside or sodium nitroprusside; • Nitrospentocyanoferrate; and / or • Hydrated pentacyanoferrate.

8. The sensor as claimed in any of the preceding claims, wherein: • The formulation comprises the coupling agent precursor; •The coupling agent is generated in situ from the transition metal-based complex by using a preconditioning potential applied to the sensor.

9. The sensor as claimed in any of the preceding claims, wherein, The substrate is an elongated body having a first longitudinal end and a second longitudinal end.

10. The sensor as claimed in claim 9, wherein, The working electrode, reference electrode, and counter electrode include conductive traces that extend axially between the first and second ends of the substrate and are spaced apart from each other in the width direction of the substrate.

11. The sensor as claimed in claim 10, wherein, The reference electrode includes silver traces, and the working electrode and the counter electrode each include carbon traces.

12. The sensor of claim 10 or 11 further includes a dielectric layer disposed on the working electrode, the reference electrode, and the counter electrode in a region between a first end and a second end of the substrate, such that the longitudinal end regions of each of the working electrode, the reference electrode, and the counter electrode are not covered by the dielectric layer but are exposed.

13. The sensor of any one of claims 10 to 12, wherein the conductive traces of the working electrode, the reference electrode, and the counter electrode extend substantially parallel to each other on the substrate.

14. The sensor as described in any of the preceding claims, wherein, The working electrode includes at least a first working electrode and a second working electrode.

15. An electrochemical kit for determining the presence or amount of monochloramine, comprising: The electrochemical sensor as described in any of the preceding claims; as well as The first sample conditioning component comprises: • Electrolyte salts; as well as • Chlorine scavenger.

16. The kit of claim 15, wherein: • The electrolyte salt comprises any one or a combination of the following: KNO3, KCl, or Na2SO4; and / or • The chlorine scavenger contains alkali metal nitrites or sodium nitrites.

17. The kit of claim 15 or 16, wherein the first sample conditioning component further comprises: • pH buffer; • pH control agents; and • Dissolving agent.

18. The kit of claim 17, wherein: • The pH buffer contains a weak acid buffer, citric acid, or boric acid; • The pH control agent comprises any or a combination of a weak base, a hydroxide, or lithium hydroxide; and / or • The dissolving agent comprises any or a combination of ion exchange resin, quaternary ammonium resin, or 3-[(3-chlorophenyl)sulfonamide]benzoic acid.

19. The kit according to claims 15 to 18, further comprising: The second sample conditioning component comprises: • Electrolyte salts; as well as • Chlorine source.

20. The kit of claim 19, wherein: • The electrolyte salt comprises any one or a combination of the following: KNO3, KCl, or Na2SO4; and / or • The chlorine source contains hypochlorite or calcium hypochlorite.

21. The kit of claim 19 or 20, wherein the second sample conditioning component further comprises: • pH control agents; and • Dissolving agent.

22. The kit of claim 21, wherein: • The pH control agent comprises any or a combination of a weak base, a hydroxide, or lithium hydroxide; and / or • The dissolving agent comprises any or a combination of ion exchange resin, quaternary ammonium resin, or 3-[(3-chlorophenyl)sulfonamide]benzoic acid.

23. The kit according to any one of claims 15 to 22, wherein the sample conditioning component is provided in tablet or liquid form.

24. An electrochemical method for determining the presence or amount of monochloramine and / or ammonia in a liquid sample, comprising: An electrochemical sensor is provided having a working electrode, a reference electrode, and a counter electrode on a substrate, wherein the working electrode includes a coating, the coating comprising a formulation comprising: • Phenol or phenol derivatives; and • Coupling agents or coupling agent precursor compounds containing transition metal-based complexes; The electrochemical sensor is at least partially immersed in the liquid sample; as well as The liquid sample was analyzed using electrochemical voltammetry.

25. The method of claim 24, wherein the electrochemical voltammetry is differential pulse voltammetry.

26. The method of claim 24 or 25, wherein the transition metal-based complex comprises a nitroprusside or sodium nitroprusside.

27. The method of claim 26, further comprising: • A preconditioning potential is applied to the electrochemical sensor before applying the electrochemical voltammetry. as well as • By applying the preconditioning potential to the electrochemical sensor, nitrosopyrocyanoferrate and / or hydrated nitrosopyroferrate are generated from the nitroprusside or sodium nitroprusside.

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