Method for on-line detection of available chlorine concentration by thin-layer channel electrochemical sensor

Abstract

This invention provides an online detection method for effective chlorine concentration using a thin-layer channel electrochemical sensor. The method includes: measuring the charge transfer resistance of the sensor's working electrode using electrochemical impedance spectroscopy; intelligently determining the electrode's contamination state and triggering closed-loop adaptive cleaning; after cleaning, measuring the high-frequency impedance of the solution to obtain real-time conductivity parameters; applying a detection sequence containing at least three different potential steps, simultaneously acquiring the steady-state current, pH value, and temperature of the solution at each potential; correcting the current for conductivity based on the solution impedance; and calculating the molecular hypochlorous acid concentration in real time based on the dissociation equilibrium formula of hypochlorous acid, combined with pH value and temperature. This invention achieves intelligent maintenance of the electrode state and dynamic compensation for solution matrix interference, enabling high-precision and high-stability online detection of the molecular hypochlorous acid concentration, which plays a crucial role in disinfection efficacy.

Description

Technical Field

[0001] This invention relates to the field of electrochemical analysis and detection technology, and in particular to an online detection method for effective chlorine concentration using a thin-layer channel electrochemical sensor. Background Technology

[0002] Hypochlorous acid disinfectant has gained widespread attention and application in fields such as medical and health care, food processing, planting and breeding, and epidemic prevention and control due to its advantages such as strong disinfection ability, rapid speed, broad bactericidal spectrum, and good safety. Rapid, accurate, and stable online monitoring of its effective chlorine concentration, especially the concentration of molecular hypochlorous acid (HClO) that truly plays the main bactericidal role, is crucial to ensuring disinfection effectiveness and process control.

[0003] Traditional electrochemical detection methods, such as indirect measurement based on redox potential (ORP), are significantly affected by fluctuations in solution pH, leading to high uncertainty and an inability to accurately reflect HClO concentration. When using a conventional three-electrode system for amperometric detection, the sensor is typically immersed in the bulk solution, making it susceptible to convection and turbulence, resulting in high signal noise. Furthermore, the electrode surface is easily contaminated by the sample matrix, leading to performance degradation.

[0004] To overcome the aforementioned problems, thin-layer channel electrochemical sensor technology has emerged. This technology constructs a flat flow channel with a height of only tens to hundreds of micrometers, allowing the test solution to flow at high speed through a miniaturized working electrode surface in a laminar flow manner. It possesses potential advantages such as high mass transfer rate, fast response, and small sample volume requirement. Existing technologies include thin-layer channel sensor designs for the detection of available chlorine. For example, Chinese patent application CN119355088A discloses a thin-layer channel electrochemical sensor for online detection of available chlorine concentration. By setting independent acid and alkali mechanical cleaning components, it can chemically clean the working electrode and flow channel without disassembling the sensor, aiming to solve the problems of electrode contamination and the need for frequent electrolyte addition during continuous detection. However, the triggering and stopping of the cleaning action in this scheme depends on a preset time or number of detections, which is an open-loop control and cannot adaptively adjust according to the actual contamination state of the electrode surface, potentially leading to insufficient or excessive cleaning. Furthermore, this scheme fails to address the dynamic interference of changes in matrix parameters such as solution conductivity, temperature, and pH on the detection current signal, and it also fails to distinguish between the concentration of total available chlorine and molecular hypochlorous acid (HClO).

[0005] Another related Chinese patent application, CN119355087A, discloses an electro-cleaning method and its application for maintaining the stable electrochemical activity of the working electrode surface. This method induces an electrolytic reaction of water on the working electrode surface under a specific potential sequence, generating an acidic or alkaline environment in situ to clean different types of contaminants, thus achieving online electrochemical cleaning. However, this method also lacks a real-time evaluation and feedback mechanism for the cleaning effect; the cleaning procedure, including the potential and duration, remains fixed. More importantly, this technical solution focuses on electrode maintenance and does not address how to overcome the influence of solution matrix fluctuations on the detection signal, nor does it mention how to utilize parameters such as pH to achieve accurate decoupled calculation of HClO concentration.

[0006] In summary, while existing technologies have made beneficial explorations in the construction of thin-layer channel structures or online cleaning, there are still technical problems that urgently need to be solved. These include the fact that the cleaning of thin-layer channel sensors is mostly open-loop control, lacking real-time assessment and adaptive adjustment of the degree of contamination; at the same time, it is difficult to overcome the interference of matrix fluctuations such as solution conductivity and pH, and usually only the total available chlorine can be detected, which cannot accurately reflect the concentration of molecular hypochlorous acid, which plays the main bactericidal role. Summary of the Invention

[0007] To address the technical problems existing in the prior art, this invention proposes an online detection method for effective chlorine concentration using a thin-layer channel electrochemical sensor.

[0008] The present invention specifically provides the following technical solution:

[0009] A method for online detection of effective chlorine concentration using a thin-layer channel electrochemical sensor, the method comprising the following steps:

[0010] S1. The hypochlorous acid disinfectant solution to be tested is pumped into the thin-layer channel of the thin-layer channel electrochemical sensor at a constant flow rate; before the detection begins, an electrochemical impedance spectroscopy scan containing a small amplitude AC signal is applied to the working electrode of the sensor to obtain the charge transfer resistance R of the working electrode in the test solution. ct ;

[0011] S2. The charge transfer resistor R ct It is compared with a preset cleaning status threshold R0; if R ct If R > 0, electrode contamination is determined, and a closed-loop cleaning procedure is initiated. The closed-loop cleaning procedure includes: applying a cleaning potential or injecting cleaning fluid, and re-performing step S1's electrode status diagnosis after the cleaning operation, until R > 0. ct ≤R0; if R ct If ≤R0, proceed directly to the next step;

[0012] S3. Under the condition that the solution flow is stable within the thin-layer channel, a high-frequency AC signal is applied to the working electrode to measure the equivalent impedance Z of the solution under test within the thin-layer channel. s The equivalent impedance Z s Used to characterize the conductivity of the current solution matrix;

[0013] S4. After completing step S3, a detection sequence containing at least three different DC potential steps is applied to the working electrode, and the steady-state current response I1, I2, I3 under each potential step is recorded simultaneously. At the same time, the real-time pH value and temperature T of the solution are collected simultaneously by the pH sensor and temperature sensor integrated in the thin-layer channel.

[0014] S5. Using the solution equivalent impedance Z measured in step S3 s The steady-state current responses I1, I2, and I3 obtained in step S4 are corrected for conductivity to obtain the corrected current I. 1corr I 2corr I 3corr Based on the correction current I 2corr Based on the synchronously collected pH value and temperature T, the concentration of molecular hypochlorous acid in the test solution is calculated in real time according to the dissociation equilibrium formula of hypochlorous acid in water.

[0015] Further, in S1, the electrochemical impedance spectroscopy scan is performed at a single characteristic frequency in the range of 50 Hz to 200 Hz; by measuring the impedance phase angle obtained at this characteristic frequency and comparing it with a reference phase angle pre-stored in the system corresponding to a clean electrode state, the degree of electrode contamination is quickly assessed based on the difference between the two, and the charge transfer resistance R is obtained. ct The estimated value.

[0016] Furthermore, in S2, the specific execution method of the closed-loop cleaning procedure is based on the charge transfer resistor R. ct The difference between the cleaning status threshold R0 and the value is dynamically adjusted; the closed-loop cleaning procedure includes the following steps:

[0017] S2.1. Calculate the difference ΔR, ΔR = R ct -R0;

[0018] S2.2. Based on the value of ΔR, select one of the at least two pre-stored cleaning modes to perform the initial cleaning operation, wherein a larger ΔR value corresponds to selecting a cleaning mode with higher intensity or longer duration;

[0019] S2.3. After performing the initial cleaning operation, repeat step S1 to obtain a new charge transfer resistance R. ct' ;

[0020] S2.4. Determine R ct' Does R satisfy? ct' ≤R0;

[0021] If the conditions are met, the cleaning process ends and proceeds to step S3; if not, a new difference ΔR'=R is calculated. ct' -R0, then adjust the cleaning parameters according to ΔR', and perform the cleaning operation again based on the adjusted cleaning parameters, and then return to step S2.3.

[0022] Further, in S3, the high-frequency AC signal is a single-frequency sine wave signal with a fixed frequency in the range of 10kHz to 50kHz; the equivalent impedance Z s The real part of the impedance measured at this frequency is used directly as the solution resistance Rs for subsequent correction calculations.

[0023] In S4, the at least three different DC potential steps are the first detection potential E1, the second detection potential E2, and the third detection potential E3, respectively.

[0024] Specifically, the first detection potential E1 is set within the range of +0.6V to +0.8V relative to the Ag / AgCl reference electrode to drive the oxidation reaction between hypochlorite ions and molecular hypochlorous acid in the solution; the second detection potential E2 is set within the range of +0.3V to +0.5V relative to the Ag / AgCl reference electrode to selectively drive the oxidation reaction of the molecular hypochlorous acid while inhibiting the oxidation reaction of the hypochlorite ions; and the third detection potential E3 is set within the range of 0V to +0.1V relative to the Ag / AgCl reference electrode to collect the background current response.

[0025] The steady-state current responses I1, I2, and I3 are the current values ​​collected after the current response reaches a steady state under the first detection potential E1, the second detection potential E2, and the third detection potential E3, respectively.

[0026] The acquisition times of the pH value and temperature T are synchronized with the acquisition times of the steady-state current responses. Further, in S5, the correction calculation method related to conductivity is specifically as follows:

[0027] I corr =I×(R S0 / R S );

[0028] Where I is the original steady-state current response I1, I2, or I3 acquired in step S4, I corr The corresponding corrected current I 1corr I 2corrOr I 3corr R S R is the solution resistance measured in step S3. S0 The resistance of the reference solution obtained by pre-calibration in a standard conductivity solution;

[0029] The concentration of hypochlorous acid in molecular state C HClO The following formula is used to calculate:

[0030] ;

[0031] Wherein, S is the sensitivity coefficient of the sensor to the oxidation reaction of molecular hypochlorous acid at the second detection potential E2, which is obtained by standard solution calibration; pKa(T) is the negative logarithm of the dissociation constant of hypochlorous acid at temperature T, and its value is a function of temperature.

[0032] The present invention also provides a thin-layer channel electrochemical sensor, comprising:

[0033] The sensor chip body has a thin-layer channel inside.

[0034] The working electrode, counter electrode, and reference electrode have their active surfaces coplanarly disposed on the same sidewall of the thin-film channel and exposed inside the channel.

[0035] A solid pH sensing element, wherein the sensing part of the solid pH sensing element is disposed in the thin-film channel and is located downstream of the working electrode along the solution flow direction and adjacent to the working electrode;

[0036] A temperature sensing element, which is integrated on the sensor chip body and thermally coupled to the thin-layer channel wall;

[0037] The working electrode has a metal oxide nanomaterial layer that is catalytically selective for the oxidation of molecular hypochlorous acid on its surface; the thin-layer channel has a flow channel widening and turbulence structure in the upstream section of the region corresponding to the working electrode.

[0038] Furthermore, the metal oxide nanomaterial layer is a Pt-IrO2 composite nanomaterial layer;

[0039] The solid-state pH sensing element is IrO. x A metal oxide thin film electrode is integrated with the working electrode on the same substrate plane through microfabrication technology, and the distance between the sensing part of the solid pH sensing element and the edge of the active surface of the working electrode along the solution flow direction is no more than 5 mm.

[0040] The flow channel widening and turbulence structure is a zigzag or sawtooth channel set in the upstream section of the thin-layer channel.

[0041] The present invention also provides an online detection system for molecular hypochlorous acid, comprising: the aforementioned thin-layer channel electrochemical sensor;

[0042] The fluid control module is connected to the thin-layer channel inlet of the thin-layer channel electrochemical sensor and is used to pump the hypochlorous acid disinfectant and cleaning solution to be tested at a constant flow rate.

[0043] The multi-channel signal excitation and acquisition module is electrically connected to the thin-layer channel electrochemical sensor and is used to apply electrochemical impedance spectroscopy scanning signals, high-frequency AC signals, DC detection potential sequences and cleaning potentials to the working electrode of the sensor, and to acquire the current response and impedance signals of the working electrode, while also acquiring the signals of the solid pH sensing element and the temperature sensing element.

[0044] The data processing and control module is communicatively connected to both the fluid control module and the multi-channel signal excitation and acquisition module. Internally, it stores a preset cleanliness state threshold R0 and a reference solution resistance R. s0 The sensitivity coefficient S and pKa(T) function are configured to perform the steps of the method and output the molecular state hypochlorous acid concentration value.

[0045] Furthermore, the data processing and control module also includes a self-optimization unit, which is used to record the charge transfer resistance, solution equivalent impedance and corresponding detection results of each diagnosis, and dynamically adjust the preset threshold and correction parameters in the concentration calculation based on historical data.

[0046] This invention offers the following beneficial technical effects: It provides an online detection method for effective chlorine concentration using a thin-layer channel electrochemical sensor. This method involves real-time diagnosis of charge transfer resistance and dynamic adjustment of cleaning accordingly, simultaneous measurement of solution resistance, pH, and temperature, and dynamic correction of the detection current. Furthermore, by employing multi-potential step detection combined with a dissociation equilibrium model, it ensures electrode activity while avoiding insufficient or excessive cleaning. It also effectively overcomes the interference of solution matrix fluctuations on measurement results and achieves direct and accurate measurement of molecular hypochlorous acid concentration, which plays a crucial role in disinfection efficacy. Attached Figure Description

[0047] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a schematic longitudinal cross-sectional view of the sensor along the length of the thin-layer channel provided in an embodiment of the present invention.

[0049] Figure 2 A flowchart illustrating the online detection method for effective chlorine concentration using a thin-layer channel electrochemical sensor provided in this embodiment of the invention.

[0050] Figure 3 This is a timing diagram of the multipotential detection signal provided in an embodiment of the present invention.

[0051] Figure 4 The concentration-current calibration curve is provided for an embodiment of the present invention.

[0052] Figure 5 Cyclic voltammetry curves of a thin-layer channel electrochemical sensor provided in an embodiment of the present invention in hypochlorous acid disinfectant.

[0053] Figure 6 The electrochemical cleaning potential waveform diagram provided for an embodiment of the present invention.

[0054] In the figure: 1. Sensor chip substrate; 2. Working electrode; 3. Pt-IrO2 composite nanomaterial catalytic layer; 4. Counter electrode; 5. Reference electrode; 6. Solid pH sensing element; 7. Thin-layer channel. Detailed Implementation

[0055] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0056] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0057] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and the structure and / or function of any markings described herein are merely illustrative. Based on this application, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number and aspects set forth herein can be used to implement the apparatus and / or practical methods.

[0058] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this application.

[0059] Additionally, specific details are provided in the following description to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that practice can be carried out without these marked details.

[0060] The purpose of this invention is to provide an online detection method for effective chlorine concentration using a thin-layer channel electrochemical sensor to achieve intelligent and accurate online detection of molecular-state hypochlorous acid concentration.

[0061] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0062] All formula calculations involved in this invention are presented after parameter normalization and dimension removal.

[0063] Example 1

[0064] First, such as Figure 1 The diagram illustrates the fabrication of a thin-layer channel electrochemical sensor. Silicon or glass is selected as the sensor chip substrate material. Using standard microfabrication processes, including but not limited to photolithography and etching, a thin-layer channel with a depth of 50 μm, a width of 2 mm, and a length of 20 mm is fabricated on its surface. Approximately 5 mm upstream of the thin-layer channel inlet, a zigzag channel is fabricated as a flow channel widening and turbulence-inducing structure to ensure thorough mixing of the incoming solution and stabilize the flow state.

[0065] A coplanar working electrode, counter electrode, and reference electrode were fabricated on the same side of the bottom surface of a thin-film channel using magnetron sputtering and exfoliation processes. The working electrode is a strip-shaped gold electrode with a width consistent with the channel width (2 mm) and a length of 3 mm. A Pt-IrO2 composite nanomaterial catalytic layer was deposited on its surface using electrodeposition, which enhances and selectivity for the oxidation of molecular hypochlorous acid. The counter electrode is a Pt electrode, and the reference electrode is an Ag / AgCl electrode. Using thin-film technology, an IrO2 electrode was integrated on the same substrate plane as the working electrode, 3 mm downstream of the working electrode along the solution flow direction. x The thin film serves as a solid-state pH sensing element. Simultaneously, a thin-film Pt resistance temperature sensor is integrated on the back side of the chip substrate near the thin-film channel, ensuring good thermal coupling with the channel wall. Figure 1 In the image, the channel depth is 50 μm, and the vertical scale is magnified. The area within the dashed box is the Pt-IrO2 composite nanocatalytic layer, which is only on the surface of the working electrode. The arrows indicate the direction of solution flow.

[0066] The aforementioned online detection system was constructed. The sensor chip prepared above was encapsulated in a flow path substrate to form a complete thin-layer channel electrochemical sensor. The hypochlorous acid disinfectant solution to be tested was pumped into the thin-layer channel of the sensor at a constant flow rate of 50 μL / min using a micro-injection pump, which serves as the fluid control module. A multi-channel electrochemical workstation, acting as a multi-channel signal excitation and acquisition module, was connected to the sensor. This workstation could generate various excitation signals such as AC impedance and DC potential sequences, and simultaneously acquire current, voltage, impedance, and signals from the pH sensing element and temperature sensor. An embedded industrial computer, serving as the data processing and control module, controlled the electrochemical workstation and injection pump through a communication interface and ran built-in detection control, data processing, and self-optimization algorithms. The system pre-stored a cleanliness threshold R0, corresponding to a charge transfer resistance of 5000Ω and a reference solution resistance R measured in a 0.01M KCl standard solution. s0 A table showing the sensitivity coefficient S and the functional relationship between pKa(T) and temperature T obtained by calibration with HClO standard solution.

[0067] like Figure 2 A flowchart of the online detection method according to an embodiment of the present invention is shown. After the system is powered on, the following cyclic detection process is automatically executed:

[0068] S1. Electrode status diagnosis.

[0069] At the start of the detection cycle, after the test solution has filled the thin-layer channel and the flow state is stable, the data processing and control module instructs the electrochemical workstation to apply a single-frequency sinusoidal AC signal with a frequency of 100 Hz and an amplitude of 10 mV to the working electrode for electrochemical impedance spectroscopy measurement. The system measures the impedance phase angle θ at this frequency. measAnd compared with the reference phase angle θ of the sensor in pure water after fresh preparation or deep cleaning in the pre-stored system. ref Compare at -80°. Calculate the difference Δθ = |θ meas -θ ref |. Through the pre-calibrated relationship Δθ=k*ΔR ct The phase angle difference is converted into a charge transfer resistance R. ct The estimated value is given. Here, k is a proportionality coefficient, obtained through experimental calibration. This step rapidly assesses the degree of contamination on the electrode surface at millisecond speeds.

[0070] S2. Adaptive closed-loop cleaning decision and execution.

[0071] The data processing and control module will process the R obtained in step S1 ct The estimated value is compared with the preset cleanliness threshold R0=5000Ω.

[0072] If R ct If R0 ≤ R0, the electrode is determined to be clean, and the process proceeds directly to the next step S3.

[0073] If R ct >R0, electrode contamination detected, closed-loop cleaning procedure initiated. Calculate the difference ΔR = R ct -R0.

[0074] The system has two pre-stored cleaning modes: Mode A is a weak cleaning mode, which applies a cleaning potential of -0.8 V (vs. Ag / AgCl) for 10 seconds; Mode B is a strong cleaning mode, which applies a cleaning potential of -1.2 V for 20 seconds.

[0075] Select the mode based on the magnitude of ΔR: if ΔR < 2000Ω, select mode A; if ΔR ≥ 2000Ω, select mode B. Perform the selected initial cleaning operation.

[0076] After the cleaning operation is completed, immediately re-execute the electrode status diagnosis in step S to obtain new R. ct’ .

[0077] Determine R ct’ Check if ≤R0 is true. If true, end the cleaning process and proceed to step S3; if false, calculate the new difference ΔR' = R. ct’ -R0, based on ΔR', enhances the cleaning parameters, for example, extending the cleaning time by 10 seconds based on mode B, then cleans again and diagnoses until the cleaning conditions are met. This process achieves closed-loop adaptive control of the cleaning process.

[0078] S3. Solution impedance measurement.

[0079] After confirming electrode cleanliness, the system controls the electrochemical workstation to apply a 20 kHz single-frequency sinusoidal high-frequency AC signal to the working electrode. The real part of the impedance at this high frequency is measured, and this value is directly used as the solution resistance R of the solution to be tested. s This step is used to sense changes in the conductivity of the solution in real time.

[0080] S4. Multi-parameter synchronous detection.

[0081] Following step S3, the system applies a DC potential detection sequence containing three steps to the working electrode: E1 (+0.7 V vs. Ag / AgCl): applied for 3 seconds, driving the co-oxidation of HClO and ClO⁻, and collecting the steady-state current I1. E2 (+0.4 V vs. Ag / AgCl): applied for 5 seconds, at which potential the oxidation of ClO⁻ is significantly suppressed, mainly oxidizing HClO, and collecting the steady-state current I2. E3 (0 V vs. Ag / AgCl): applied for 2 seconds, used to collect the background current, and collecting the steady-state current I3. Figure 3 The timing diagram of the multi-potential detection signal is shown. In the figure, E1, E2, and E3 are DC potential step sequences, the shaded area is the current acquisition period, and the vertical dashed line is the pH / temperature synchronous acquisition time.

[0082] S5. Signal correction and concentration calculation.

[0083] First, conductivity correction is performed. This is done using the real-time solution resistance R measured in step S3. s and the pre-stored reference solution resistance R s0 According to formula I corr =I×(R S0 / R S The original currents I1, I2, and I3 are corrected to obtain the corrected current I. 1corr I 2corr I 3corr This eliminates the variation in current amplitude caused by differences in solution conductivity.

[0084] Then, the concentration of molecular hypochlorous acid is calculated. Using the corrected current, combined with the simultaneously measured pH and temperature T, the calculation is performed as follows:

[0085] Calculate the net response current of HClO at potential E2: ΔI HClO =I 2corr -I 3corr .

[0086] Based on the synchronously measured temperature T, the dissociation constant pKa(T) of hypochlorous acid at that temperature can be obtained by referring to a table or calculation. For example, pKa is approximately 7.53 at 25°C and 7.40 at 30°C. ΔI HClOSubstituting the sensitivity coefficient S, measured pH value, and pKa(T) into the formula:

[0087] ;

[0088] The concentration of molecular hypochlorous acid (HClO) in the test solution can be calculated in real time. The total available chlorine concentration can be determined by (I... 1corr -I 3corr ) / S total Calculate, where S total This represents the overall sensitivity coefficient at potential E1. During initial system use or periodic calibration, a molecularly stable hypochlorous acid standard solution of known concentration (pH adjusted to ensure HClO content >99%) is pumped into the sensor at the same flow rate. The current response is measured at the second detection potential E2, and the sensitivity coefficient S is determined by the slope of the concentration-current curve. For example... Figure 4 The concentration-current calibration curve shown was measured under the following conditions: flow rate 50 μL / min, pH < 5 (HClO content > 99%), temperature 25°C, thin-layer channel thickness 25 μm, and working electrode was a strip gold electrode with a Pt-IrO2 catalyst layer modified on its surface. The steady-state response current of different concentrations of molecular hypochlorous acid standard solutions at the second detection potential E2 = +0.4V (vs. Ag / AgCl) is linearly fitted, and the slope is the sensitivity coefficient S (μA·L / mg).

[0089] At the moment of acquiring each steady-state current I1, I2, I3, the system synchronously reads the potential value output by the solid-state pH sensor integrated in the flow channel (which is then converted into a pH value) and the resistance value of the temperature sensor (which is then converted into a temperature T) through a multi-channel acquisition card. This ensures strict time synchronization.

[0090] S6. The self-optimizing unit in the data processing and control module will continuously record the diagnostic data R in each detection cycle. ct Matrix parameters include R s pH, T, and the final calculation results. Through statistical analysis of long-term historical data, this unit can dynamically fine-tune the cleaning state threshold R0 to better adapt to the long-term aging trend of the sensor; it can also perform rolling calibration of the sensitivity coefficient S based on a large amount of measured data, thereby maintaining the accuracy and robustness of the entire system in long-term operation.

[0091] By employing the method, sensor, and system described in this embodiment, the online stable operation cycle of the sensor can be significantly extended through real-time closed-loop management of the working electrode state. Through simultaneous measurement and dynamic compensation of multiple parameters such as solution resistance, pH, and temperature, the online detection error of molecular hypochlorous acid concentration can be controlled within ±5%, which is significantly more accurate than the traditional ORP method. At the same time, the system's self-optimization function can adapt to the slow aging of the sensor and the long-term drift of the solution matrix.

[0092] Example 2

[0093] To verify the response characteristics of the thin-layer channel electrochemical sensor prepared in this invention to available chlorine, the electrochemical behavior of the sensor in hypochlorous acid disinfectant was first characterized using cyclic voltammetry. The experimental conditions were as follows: the working electrode was used as the working electrode, the counter electrode as the counter electrode, and the Ag / AgCl electrode as the reference electrode; the test solution was hypochlorous acid disinfectant with an available chlorine concentration of 100 mg / L, pH 5.6, without any added supporting electrolyte; the potential scan range was -600 mV to +800 mV vs. Ag / AgCl, with scan rates of 10 mV / s, 20 mV / s, 30 mV / s, 40 mV / s, 50 mV / s, 100 mV / s, 200 mV / s, 300 mV / s, 400 mV / s, and 500 mV / s, respectively. Figure 5 The scanning speed of the curves increases progressively from top to bottom, with the top curve having the slowest scanning speed and the bottom curve having the fastest scanning speed. For example... Figure 5 As shown, the cyclic voltammetry curve exhibits a distinct irreversible reduction peak in the range of -200±50 mV vs. Ag / AgCl. This peak corresponds to the reduction reaction of hypochlorous acid (HClO) on the working electrode surface. The identification of this characteristic peak lays the electrochemical foundation for subsequent quantitative detection of effective chlorine concentration using chronoamperometry or square-wave potentiometry. The horizontal axis represents potential (mV vs. Ag / AgCl), and the vertical axis represents current response (μA).

[0094] In this embodiment, the online detection system of the present invention can be configured to execute a pre-stored, fixed-program electrochemical cleaning method as one or more cleaning modes selectable in the closed-loop cleaning program.

[0095] This method achieves online cleaning by applying a specific square-wave potential sequence to the working electrode of the thin-layer channel electrochemical sensor. This sequence, as a complete cleaning cycle unit, can be repeatedly executed under the control of the data processing and control module. A typical cleaning cycle includes the following sequentially executed potential steps:

[0096] The first cleaning step involves applying a high positive potential, such as +1.3V (vs. Ag / AgCl), to the working electrode and maintaining it for 2.0 seconds. Under this strong positive potential, the surface of the working electrode primarily undergoes an oxidation reaction of water, producing hydrogen ions and creating a strongly acidic local microenvironment at the electrode-solution interface. This step aims to dissolve or remove inorganic scale and certain negatively charged contaminants adhering to the electrode surface through an "acid washing" effect.

[0097] First interval step: Switch the potential applied to the working electrode to an intermediate potential close to the open circuit potential, such as 0.0V (vs. Ag / AgCl), and maintain it for 2.0 seconds. The purpose of this step is to allow gases such as oxygen and chemical products generated in the previous step to be carried away from the electrode surface by the solution flow within the thin-layer channel, avoiding interference with subsequent cleaning steps.

[0098] The second cleaning step involves switching the working electrode potential to a higher negative potential, such as -0.9V (vs. Ag / AgCl), and maintaining this position for 2.0 seconds. At this strong negative potential, a water reduction reaction primarily occurs on the working electrode surface, generating hydroxide ions and creating a strongly alkaline local microenvironment at the electrode-solution interface. This step aims to remove organic contaminants and certain metal ions adhering to the electrode surface through an "alkaline wash."

[0099] The second interval step: The working electrode potential is restored to the intermediate potential of 0.0V again and maintained for a sufficient time of 3.0 seconds. This step aims to remove reaction products such as hydrogen gas generated by the "alkali washing" step, ensuring that the electrode surface is restored to a clean and stable chemical state at the end of the cleaning cycle.

[0100] like Figure 6 The above electrochemical cleaning potential waveform diagram is shown, specifically illustrating the cleaning process from acid washing to interval washing to alkali washing to interval washing, achieving in-situ cleaning of the electrode surface.

[0101] The aforementioned fixed square wave potential cleaning procedure can be pre-stored as a basic "standard cleaning mode". When the data processing and control module determines that cleaning is required based on the charge transfer resistance diagnostic results and calculates the difference ΔR, it can invoke this procedure according to a preset strategy. For example, this procedure can be set to a cleaning mode suitable for moderate contamination levels, i.e., ΔR within a specific range. The cleaning effect will be verified by a subsequent, immediately executed electrode state diagnostic step—namely, re-measuring the charge transfer resistance—and based on this, a decision will be made whether to end the cleaning process or trigger a more powerful cleaning mode.

[0102] The different embodiments described above can be combined, substituted, or used in combination with each other.

[0103] The above are exemplary embodiments disclosed in this invention. However, it should be noted that various changes and modifications can be made without departing from the scope of the embodiments of this invention as defined by the claims. The functions, steps, and / or actions of the methods according to the disclosed embodiments described herein do not need to be performed in any marked order. Furthermore, although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular.

[0104] In this specification, the same or similar parts between the various embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the descriptions of the embodiments described later are relatively simple, and relevant parts can be referred to the descriptions of the foregoing embodiments.

[0105] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for online detection of effective chlorine concentration using a thin-layer channel electrochemical sensor, characterized in that, The method includes the following steps: S1. Pumping the test hypochlorous acid disinfectant solution into the thin layer channel of the thin layer channel electrochemical sensor at a constant flow rate; before the start of the test, applying an electrochemical impedance spectroscopy scan comprising a small amplitude alternating current signal to the working electrode of the sensor to obtain the charge transfer resistance R of the working electrode in the test solution ct ; S2. The charge transfer resistor R ct It is compared with a preset cleaning status threshold R0; if R ct If R0 > 0, electrode contamination is determined, and a closed-loop cleaning procedure is initiated. The closed-loop cleaning procedure includes: applying a cleaning potential or injecting cleaning fluid, and re-performing step S1's electrode status diagnosis after the cleaning operation, until R > 0. ct ≤R0; if R ct If ≤R0, proceed directly to the next step; S3. Under the condition that the solution flow is stable within the thin-layer channel, a high-frequency AC signal is applied to the working electrode to measure the equivalent impedance Z of the solution under test within the thin-layer channel. s The equivalent impedance Z s Used to characterize the conductivity of the current solution matrix; S4. After completing step S3, a detection sequence containing at least three different DC potential steps is applied to the working electrode, and the steady-state current response I1, I2, I3 under each potential step is recorded simultaneously. At the same time, the real-time pH value and temperature T of the solution are collected simultaneously by the pH sensor and temperature sensor integrated in the thin-layer channel. S5. Using the solution equivalent impedance Z measured in step S3 s The steady-state current responses I1, I2, and I3 obtained in step S4 are corrected for conductivity to obtain the corrected current I. 1corr I 2corr I 3corr Based on the correction current I 2corr Based on the synchronously collected pH value and temperature T, the concentration of molecular hypochlorous acid in the test solution is calculated in real time according to the dissociation equilibrium formula of hypochlorous acid in water.

2. The method for online detection of effective chlorine concentration using a thin-layer channel electrochemical sensor according to claim 1, characterized in that, In S1, the electrochemical impedance spectroscopy scan is performed at a single characteristic frequency in the range of 50 Hz to 200 Hz; by measuring the impedance phase angle obtained at this characteristic frequency and comparing it with a reference phase angle pre-stored in the system corresponding to a clean electrode state, the degree of electrode contamination is rapidly assessed based on the difference between the two, and the charge transfer resistance R is obtained. ct The estimated value.

3. The method for online detection of effective chlorine concentration using a thin-layer channel electrochemical sensor according to claim 2, characterized in that, In S2, the specific execution method of the closed-loop cleaning procedure is based on the charge transfer resistor R. ct The difference between the cleaning status threshold R0 and the value is dynamically adjusted; the closed-loop cleaning procedure includes the following steps: S2.

1. Calculate the difference ΔR, ΔR = R ct -R0; S2.

2. Based on the value of ΔR, select one of the at least two pre-stored cleaning modes to perform the initial cleaning operation, wherein a larger ΔR value corresponds to selecting a cleaning mode with higher intensity or longer duration; S2.

3. After performing the initial cleaning operation, repeat step S1 to obtain a new charge transfer resistance R. ct' ; S2.

4. Determine R ct' Does R satisfy? ct' ≤R0; If the conditions are met, the cleaning process ends and proceeds to step S3; if not, a new difference ΔR'=R is calculated. ct' -R0, then adjust the cleaning parameters according to ΔR', and perform the cleaning operation again based on the adjusted cleaning parameters, and then return to step S2.

3.

4. A method for online detection of effective chlorine concentration using a thin-layer channel electrochemical sensor according to any one of claims 1-3, characterized in that, In S3, the high-frequency AC signal is a single-frequency sine wave signal with a fixed frequency in the range of 10kHz to 50kHz; the equivalent impedance Z s The real part of the impedance measured at this frequency is used directly as the solution resistance Rs for subsequent correction calculations.

5. The method for online detection of effective chlorine concentration using a thin-layer channel electrochemical sensor according to claim 1, characterized in that, In S4, the at least three different DC potential steps are the first detection potential E1, the second detection potential E2, and the third detection potential E3, respectively. Specifically, the first detection potential E1 is set within the range of +0.6V to +0.8V relative to the Ag / AgCl reference electrode to drive the oxidation reaction between hypochlorite ions and molecular hypochlorous acid in the solution; the second detection potential E2 is set within the range of +0.3V to +0.5V relative to the Ag / AgCl reference electrode to selectively drive the oxidation reaction of the molecular hypochlorous acid while inhibiting the oxidation reaction of the hypochlorite ions; and the third detection potential E3 is set within the range of 0V to +0.1V relative to the Ag / AgCl reference electrode to collect the background current response. The steady-state current responses I1, I2, and I3 are the current values ​​collected after the current response reaches a steady state under the first detection potential E1, the second detection potential E2, and the third detection potential E3, respectively. The acquisition times of the pH value and temperature T are synchronized with the acquisition times of each steady-state current response.

6. The method for online detection of effective chlorine concentration using a thin-layer channel electrochemical sensor according to claim 1, characterized in that, In S5, the correction calculation method related to conductivity is specifically as follows: I corr =I×(R S0 / R S ); Where I is the original steady-state current response I1, I2, or I3 acquired in step S4, I corr The corresponding corrected current I 1corr I 2corr or I 3corr R S R is the solution resistance measured in step S3. S0 The resistance of the reference solution obtained by pre-calibration in a standard conductivity solution; The concentration of hypochlorous acid in molecular state C HClO The following formula is used to calculate: ； Wherein, S is the sensitivity coefficient of the sensor to the oxidation reaction of molecular hypochlorous acid at the second detection potential E2, which is obtained by standard solution calibration; pKa(T) is the negative logarithm of the dissociation constant of hypochlorous acid at temperature T, and its value is a function of temperature.

7. A thin-layer channel electrochemical sensor for implementing the method according to any one of claims 1-6, characterized in that, include: The sensor chip body has a thin-layer channel inside. The working electrode, counter electrode, and reference electrode have their active surfaces coplanarly disposed on the same sidewall of the thin-film channel and exposed inside the channel. A solid pH sensing element, wherein the sensing part of the solid pH sensing element is disposed in the thin-film channel and is located downstream of the working electrode along the solution flow direction and adjacent to the working electrode; A temperature sensing element, which is integrated on the sensor chip body and thermally coupled to the thin-layer channel wall; The working electrode has a metal oxide nanomaterial layer that is catalytically selective for the oxidation of molecular hypochlorous acid on its surface; the thin-layer channel has a flow channel widening and turbulence structure in the upstream section of the region corresponding to the working electrode.

8. The thin-layer channel electrochemical sensor according to claim 7, characterized in that, The metal oxide nanomaterial layer is a Pt-IrO2 composite nanomaterial layer; The solid pH sensing element is IrO. x A metal oxide thin film electrode is integrated with the working electrode on the same substrate plane through microfabrication technology, and the distance between the sensing part of the solid pH sensing element and the edge of the active surface of the working electrode along the solution flow direction is no more than 5 mm. The flow channel widening and turbulence structure is a zigzag or sawtooth channel set in the upstream section of the thin-layer channel.

9. An online detection system for molecular hypochlorous acid, characterized in that, include: The thin-layer channel electrochemical sensor as described in claim 7 or 8; The fluid control module is connected to the thin-layer channel inlet of the thin-layer channel electrochemical sensor and is used to pump the hypochlorous acid disinfectant and cleaning solution to be tested at a constant flow rate. The multi-channel signal excitation and acquisition module is electrically connected to the thin-layer channel electrochemical sensor. It is used to apply electrochemical impedance spectroscopy scanning signals, high-frequency AC signals, DC detection potential sequences and cleaning potentials to the working electrode of the sensor, and to acquire the current response and impedance signals of the working electrode, while also acquiring signals from the solid pH sensing element and the temperature sensing element. The data processing and control module is communicatively connected to both the fluid control module and the multi-channel signal excitation and acquisition module. Internally, it stores a preset cleanliness state threshold R0 and a reference solution resistance R. s0 The sensitivity coefficient S and pKa(T) function are configured to perform the steps of the method as described in any one of claims 1 to 6, and output the molecular state hypochlorous acid concentration value.

10. The online detection system for molecular hypochlorous acid according to claim 9, characterized in that, The data processing and control module also includes a self-optimization unit, which is used to record the charge transfer resistance, solution equivalent impedance and corresponding detection results of each diagnosis, and dynamically adjust the preset threshold and correction parameters in the concentration calculation based on historical data.

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