Chloride ion probe calibration method based on selectivity coefficient correction

Abstract

The invention belongs to the technical field of electrochemical analysis and testing, and discloses a chloride ion probe calibration method based on selectivity coefficient correction. According to the method, main calibration is carried out under the condition that the ionic strength and temperature are consistent with those of a sample, the selectivity coefficient to Br and I is measured, interference is analyzed and corrected by utilizing the expansion potential-activity relation, and the accurate chloride ion activity / concentration is obtained. The method is suitable for complex media such as seawater and brine, and the accuracy, repeatability and traceability of measurement are remarkably improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polymer materials, and particularly relates to a chlorine ion probe calibration method based on selective coefficient correction. BACKGROUND

[0002] Chloride ion is a core index in the evaluation of ocean environment, industrial brine and reinforced concrete durability, and its concentration is directly related to the corrosion threshold, development rate and service life. Chloride ion selective electrode is generally used for in-situ or online measurement in engineering and environmental monitoring, and a stable potential difference is formed at the membrane-solution interface by relying on the selectivity of the electrode membrane to the target ion, and the potential and effective concentration are logarithmically related. Compared with traditional chemical analysis, this method has fast response, does not require complex pretreatment and is suitable for long-term continuous monitoring, and has been widely used in water supply and drainage, seawater and brine analysis, offshore engineering and concrete structure monitoring and other scenes.

[0003] Actual samples are mostly multi-ion high-salinity systems, and in addition to chloride ions, they often contain bromide ions, iodide ions and other halogens of the same valence. These components will be partially recognized by the electrode membrane and participate in the signal response, causing positive interference: as long as the content of bromine or iodine fluctuates, the electrode reading will also change when the true concentration of chloride ions remains unchanged; if the single chlorine system is still calibrated and converted, the result will often be overestimated. This phenomenon is particularly pronounced in seawater and estuary transition zones, during the tidal and seasonal alternation period and during the fluctuation stage of the chemical process composition.

[0004] In addition to interference, ion strength and temperature drift also make it difficult to transfer laboratory calibration to the field. The electrode essentially responds to the effective concentration, and the effective concentration and molar concentration are affected by the activity coefficient; the total salinity and background electrolyte of different samples will change the coefficient, and if the calibration medium and the sample differ greatly, direct substitution into the calibration straight line will produce systematic bias. On the other hand, temperature changes will change the electrode slope, and the zero point will also slowly drift in long-term operation due to membrane state, fouling, reference diffusion potential, etc.; if temperature compensation and periodic review are not performed, small errors will be amplified.

[0005] There are mainly four types of existing methods: one is single-ion calibration, which is simple but not sensitive to fluctuations in bromine and iodine; two is empirical correction, which lacks matching and tracing of ion strength, temperature and membrane batch differences, and has a high risk of extrapolation; three is to replace titration or ion chromatography, which is accurate but difficult to meet the needs of online and continuous monitoring; four is to directly use the selectivity parameters given in the literature or by the manufacturer, which are often not matched with the target medium and are sensitive to the history of the electrode. The above limitations result in insufficient consistency and traceability of readings from the same probe in different media.

[0006] Therefore, it is necessary to propose a calibration method for simultaneously determining the electrode zero point, slope and selectivity parameters of bromine and iodine under target medium conditions; in sample measurement, the equivalent contribution of interfering ions is analytically stripped, so that the reading is regressed to the true effective concentration or corresponding molar concentration of chloride ions. The method is suitable for matching temperature and ion strength compensation, calibration quality control and recalibration trigger threshold, and forming archivable certified data to ensure stable migration and consistency between laboratory and field, different batches and different time periods. SUMMARY

[0007] The purpose of the embodiments of the present application is to provide a chloride ion probe calibration method based on selectivity coefficient correction, which simultaneously determines the zero potential, slope and selectivity coefficient for bromine, iodine and other equivalent halogens under the same ion strength and temperature conditions as the sample, and performs analytical correction on the original reading based on the extended potential-activity relationship, achieving high-precision regression of chloride ion activity / concentration in complex media with interference and fluctuation; at the same time, temperature and ion strength compensation, quality control and recalibration mechanism and certification archiving are matched, so that the parameter migration between laboratory and field is more stable, traceable and reproducible, facilitating online and large-scale deployment, thereby at least one technical problem involved in the background art can be solved.

[0008] To solve the above technical problems, the present application is implemented as follows: The embodiments of the present application provide a chloride ion probe calibration method based on selectivity coefficient correction, comprising the following steps: Step S1, probe pretreatment and activation: activate the chloride ion selective electrode under the set ion strength regulator and temperature conditions until the electrode potential change rate meets the stability criterion; Step S2, matrix matching setting: make the calibration and measurement process under the same or equivalent ion strength and temperature conditions as the target sample; Step S3, pure chlorine multi-point main calibration: configure a series of chloride standard solutions under the set conditions, measure the electrode potential of each point and perform logarithmic linear regression, and determine the zero potential according to the formula Step S3, pure chlorine multi-point main calibration: configure a series of chloride standard solutions under the set conditions, measure the electrode potential of each point and perform logarithmic linear regression, and determine the zero potential according to the formula and electrode slope , wherein, is the electrode potential; is the chloride ion activity; Step S4, selectivity coefficient determination: under the same conditions as step S3, the selectivity coefficients of bromine ions and iodine ions are determined by using the matching potential method or the separate solution method and ; Step S5, unknown sample measurement: measure the electrode potential of the unknown sample under the set conditions , and obtain the bromine ion activity in the sample and iodide ion activity ; Step S6, interference correction and analytical solution: the corrected chloride ion activity , , , , , into the extended potential-activity relationship , the corrected chloride ion activity ; Step S7, activity-concentration conversion: using the activity coefficient convert the corrected chloride ion activity into the chloride ion concentration , the calculation formula is ; Step S8, output and archive: output the calibrated chloride ion activity or concentration results, and record the related calibration parameters, environmental conditions and quality control data, form a traceable certified document.

[0009] Optionally, in step S1, the ionic strength regulator is a 0.5 mol·L －1 aqueous solution of sodium nitrate or potassium nitrate; the activation is first to let the electrode stand in the regulator for 30-60 minutes, then to pre-polarize with a chloride standard solution with a concentration gradient of 10 －5 ~10 － 2 mol·L －1 for a short time of 10 seconds until the potential change rate

[0010] Optionally, in step S2, the temperature condition is 25±0.5℃; when working at other temperatures , the electrode slope needs to be temperature compensated, the compensation formula is , where takes -59.16 mV / dec.

[0011] Optionally, in step S3, the series of chloride standard solutions has no less than 5 concentration points, the concentration range covers 10 －5 ~10 －1 mol·L －1 ; the regression needs to meet the coefficient of determination and the residual standard deviation ≤1.5 mV.

[0012] Optionally, in step S4, the operation of the matching potential method includes: at a fixed chloride ion activity A trace amount of chloride is added to the reference solution to produce a predetermined change in electrode potential , and the required chloride increment is recorded ; another identical reference solution is added with bromide or iodide to produce the same change in electrode potential , and the required interfering ion increment is recorded , the selectivity coefficient , where is or .

[0013] Alternatively, in step S4, the calculation formula of the separation solution method is , where is the electrode potential at chloride ion activity , and is the electrode potential at interfering ion activity .

[0014] Alternatively, in step S5, the bromide ion activity and the iodide ion activity are obtained by ion-selective electrodes or independent chemical analysis methods, and are converted to activity values under the same ion intensity and temperature conditions as the chloride ion calibration.

[0015] Alternatively, in step S7, the activity coefficient is calculated using the Davies equation: , where the constant is 0.509, is the ion intensity of the solution.

[0016] Alternatively, the method further comprises a quality control and recalibration step: the linear regression of the primary calibration needs to meet , the residual standard deviation is ≤1.5 mV, and is verified at 10 －3 mol·L －1 and 10 －2 mol·L －1 , and the relative error of the inverse calculation concentration should be ≤2%; when the zero potential or the electrode slope drifts more than 5% relative to the previous certificate value, or the relative deviation of any selectivity coefficient exceeds 10%, the recalibration procedure is triggered.

[0017] Alternatively, in step S8, the certified document comprises the zero potential , the electrode slope and its temperature correction relationship, the selectivity coefficient and ion strength adjuster information, calibration and measurement temperature, original potential reading and stabilization time, regression quality parameter, cross-check point error, activity-concentration conversion model and parameter, uncertainty evaluation result and re-calibration trigger threshold; the correction calculation process can be completed in real time in an embedded system or upper computer software, and supports an alarm function.

[0018] Compared with the prior art, the present application has the following beneficial effects: (1) High measurement accuracy: by synchronously determining the electrode slope, zero point and selectivity coefficient of bromine and iodine ions under the same matrix conditions as the sample, and based on the extended potential-activity relationship for analytical correction, the equivalent contribution of interfering ions can be accurately stripped from the total response signal, thereby obtaining true and accurate chloride ion activity or concentration, effectively solving the problem of systematic high measurement values caused by fluctuations of interfering ions in complex media.

[0019] (2) Strong matrix adaptability and parameter transferability: the method emphasizes calibration and measurement at the target ion strength and temperature, ensuring high matching of calibration parameters (slope, zero point and selectivity coefficient) with the matrix of the sample to be measured, so that the calibration parameters can be stably transferred and reused between the laboratory and the field, different batches and different time points, ensuring the consistency and comparability of the measurement results. , ,

[0020] (3) Efficient calculation, suitable for online application: the entire correction process uses closed analytical calculation formulas, without complex iterative operations, fast calculation speed, less resource occupation, easy to embed into an embedded system or upper computer software, and can realize real-time data processing and online continuous monitoring within seconds, meeting the needs of rapid response and automation in the field.

[0021] (4) Perfect compensation mechanism, strong anti-interference ability: the method has built-in temperature compensation model of electrode slope and activity-concentration conversion model based on ion strength, effectively reducing the systematic errors caused by environmental temperature fluctuations and sample background electrolyte differences, improving the robustness and reliability of the method.

[0022] (5) Simple operation, no complex sample pretreatment: the method does not require complex pretreatment steps such as precipitation and separation of the sample, maintaining the originality of the sample, and is particularly suitable for in-situ, online and long-term continuous monitoring applications, reducing the number of operation steps and potential error sources.

[0023] ​(6) The quality control system is perfect, and the traceability is strong: the complete quality control chain from calibration, review to re-calibration is established, the quality acceptance criteria and re-calibration trigger threshold are clearly defined, and the certification document containing all key parameters is generated, so that the standardization of the measurement process and the traceability of the results are ensured, and strong support is provided for the reliability and compliance of the data. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced in the following. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings. Figure 1 The flow chart of the chlorine ion probe calibration method based on the selective coefficient correction provided by the present application; Figure 2 The pure chlorine-based master calibration curve provided by the present application; Figure 3 The master calibration residual distribution diagram provided by the present application; Figure 4 The average value diagram of the selective coefficient (matching potential method) provided by the present application; Figure 5 The average value diagram of the selective coefficient (solution separation method) provided by the present application. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings of the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without any creative effort belong to the scope of protection of the present application.

[0026] The terms "first", "second", etc. in the specification of the present application are used to distinguish similar objects, and are not used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present application can be implemented in an order other than those illustrated or described herein, and the objects distinguished by "first", "second", etc. are generally of a kind and do not limit the number of objects, for example, the first object can be one or more. In addition, "and / or" in the specification means at least one of the connected objects, and the character " / ", generally means that the objects before and after are in an "or" relationship.

[0027] Please refer to Figure 1As shown, this embodiment of the invention provides a chloride ion probe calibration method based on selectivity coefficient correction, including the following steps: Step S1, Probe pretreatment and activation: The chloride ion selective electrode is activated under the set ion strength regulator and temperature conditions until the electrode potential change rate meets the stability criterion. Step S2, Matrix matching settings: Ensure that the calibration and measurement process is performed under ionic strength and temperature conditions that are consistent with or equivalent to those of the target sample; Step S3, Pure Chlorine System Multi-Point Master Calibration: Under set conditions, prepare a series of chloride standard solutions, measure the electrode potential at each point, and perform logarithmic linear regression, according to the formula... Obtaining zero-point potential With electrode slope ,in, Electrode potential; Chloride ion activity; Step S4, Selectivity coefficient determination: Under the same conditions as in step S3, the selectivity coefficients for bromide and iodide ions are determined using the matched potential method or the solution separation method. and ; Step S5, Measurement of unknown sample: Measure the electrode potential of the unknown sample under set conditions. And obtain the bromide ion activity in the sample. and iodide ion activity ; Step S6, Interference Correction and Analytical Solution: The results obtained in steps S3, S4, and S5 are used to solve the problem. , , , , , Substituting into the extended potential-activity relationship In the middle, the corrected chloride ion activity is obtained by analytical solution. ; Step S7, Activity-Concentration Conversion: Using the activity coefficient Corrected chloride ion activity Converted to chloride ion concentration The calculation formula is: ; Step S8, Output and Archiving: Output the calibrated chloride ion activity or concentration results, and record the relevant calibration parameters, environmental conditions and quality control data to form a traceable certificate document.

[0028] In step S1, the ionic strength modifier has a concentration of 0.5 mol·L⁻¹. －1The activation process involves first placing the electrode in a conditioning agent for 30-60 minutes, followed by short-term contact with the electrode according to a concentration gradient for 10 minutes. －5 ~10 －2 mol·L －1 The chloride standard solution was pre-polarized until the rate of potential change was reached. This process lasts 30-60 seconds. The measured temperature is recorded during this time to be used as the subsequent electrode slope. Temperature compensation is based on the reference electrode; if necessary, the liquid connection status of the reference electrode, the integrity of the salt bridge, and the air bubbles attached to the electrode surface should be visually inspected and removed to avoid false signals entering the calibration process.

[0029] Step S2 aims to ensure matrix consistency and temperature consistency between the laboratory and the field. For ionic strength, it is preferable to use the same formulation and volume fraction of ionic strength modifier in both calibration and measurement to maintain a constant background electrolyte. If on-site injection of ionic strength modifier is not possible, compensation is performed based on the activity coefficient model during data processing. The preferred temperature condition is 25 ± 0.5 °C; at other temperatures... Electrode slope during operation Temperature compensation is required; the compensation formula is as follows: ,in The value is set to -59.16 mV / dec. This setting minimizes the impact of temperature drift and ion strength variations on subsequent parameter migration.

[0030] Step S3 is used to determine the zero-point potential. With electrode slope The electrode response is anchored to the chloride ion activity scale, and under target ion strength and temperature conditions, the series of chloride standard solutions has no fewer than 5 concentration points, covering a concentration range of 10. －5 ~10 －1 mol·L －1 The regression must meet the determination coefficient. And the residual standard deviation Place the electrode in each standard solution, stir thoroughly, and allow it to stabilize until the stability criterion is met before reading the potential. Acquire standard data sequentially. Establish electrode potentials. With chloride ion activity Logarithmic linear relationship: ; Zero potential is obtained by least squares linear regression. With electrode slope Record the fitting residuals, coefficient of determination, readings at each point, and temperature for future reference. If a constant and sufficiently high background ion intensity is used, the activity coefficient can be approximated as a constant, and the nominal concentration can be used instead of activity in the regression. If a strict conversion is required, the activity coefficient can be calculated in step seven. The regression fit is completed with the correction.

[0031] Step S4 is used to determine the relative response of bromine and iodine under the same ion strength and temperature conditions as the main calibration. The operation of the matching potential method includes: in a reference solution with a fixed chloride ion activity , a trace amount of chloride is first added to produce a predetermined amount of change in the electrode potential , and the required chloride ion increment is recorded; then, bromide or iodide is added to another identical reference solution to produce the same amount of change in the electrode potential , and the required interfering ion increment is recorded, and the selectivity coefficient is selected, where is or .

[0032] The calculation formula of the separate solution method is , where is the electrode potential at the chloride ion activity , and is the electrode potential at the interfering ion activity .

[0033] To reduce weighing errors and memory effects, it is appropriate to select a medium activity reference point (such as 10 －3 or 10 －2 mol·L －1 ), and repeat three sets of experiments for each selectivity coefficient to take the average, while recording the temperature and stirring conditions, and correcting the dilution effect caused by volume differences if necessary.

[0034] In step S5, the bromide ion activity and the iodide ion activity are obtained by parallel ion-selective electrodes or independent chemical analysis methods, and are converted into activity values under the same ion strength and temperature conditions as the chloride ion calibration.

[0035] Specifically, step S5 is an optional cross-validation means of the matching potential method. A standard series containing only chloride and a standard series containing only interfering halides are configured respectively, and the "main ion solution potential " and the "interfering solution potential " are measured. Under the condition of equal potential (i.e., the same electrode potential is produced by the two groups of solutions), the selectivity coefficient For monovalent halogen with the same valence as chloride ion, the index in the above equation is 1. When the results of matching potential method and separate solution method are in good agreement, the weighted average is taken as the certified selectivity coefficient of this calibration; if there is a deviation, the test configuration that is more similar to the target scenario is preferred, and the difference source and uncertainty are explicitly stated in the certificate.

[0036] Step S6 aims to resolve the stripping interference in the actual sample and regress to the chloride ion activity or concentration. The electrode is placed in the unknown sample, stirred and statically stable under the same or equivalent ion intensity and temperature conditions as the calibration to meet the stability criterion, and the unknown sample potential Es is read. The bromide ion activity and the iodide ion activity are obtained by parallel ion probes or chemical analysis methods. The zero potential , electrode slope , selectivity coefficient , .

[0037] The above equation is solved according to the "chloride ion activity ", and the corrected chloride ion activity is obtained. If it is necessary to output in the form of concentration, the conversion of chloride ion concentration is completed after introducing the activity coefficient in step seven. For scenarios where bromine and iodine content cannot be obtained in real time, historical statistics or parallel monitoring can be combined for estimation and uncertainty interval is given; when the estimation uncertainty is unacceptable, parallel ion quantification or rapid review of selectivity coefficient should be triggered.

[0038] Step S7 is used to realize consistent conversion between activity and concentration when the ion intensity fluctuates or is not fixed. For the activity coefficient, the Davies approximation suitable for dilute to medium strength electrolyte is preferred, and the activity coefficient is calculated using the Davies equation: ; where the constant is 0.509, and the ion strength of the solution. The calculated activity coefficient is used to convert the chloride ion activity to the chloride ion concentration . When the background is maintained constant and high by ion intensity regulator on site, the activity coefficient can be considered as a constant to simplify the processing; when the ion strength fluctuates significantly over time, the activity coefficient should be calculated for each sample and the model used, parameters and applicable range are explicitly stated in the certificate.

[0039] Step S8 aims to constrain the calibration quality and long-term drift and set up a recalibration trigger. The certified document contains zero potential , electrode slope , and their temperature correction relationship, selectivity coefficient and , ion strength adjuster information, calibration and measurement temperature, original potential reading and stabilization time, regression quality parameter, review point error, activity-concentration conversion model and parameter, uncertainty evaluation result, and recalibration trigger threshold; the correction calculation process can be completed in real time in an embedded system or upper computer software, and supports alarm function.

[0040] The method further comprises a quality control and recalibration step: the linear regression of the main calibration needs to meet , residual standard deviation , and the relative error of the back-calculated concentration should be ≤2% at 10 －3 mol·L －1 and 10 －2 mol·L －1 ; when the zero potential or the electrode slope drifts more than 5% relative to the previous certified value, or the relative deviation of any selectivity coefficient exceeds 10%, the recalibration program is triggered. For abnormal readings, the Dixon or Grubbs rule can be used for outlier discrimination, and the quick recovery process of “deionized water flushing-background electrolyte infiltration-midpoint re-stabilization” is implemented; if necessary, the reference salt bridge is replaced or the membrane surface is reactivated. All abnormal determinations and treatments should be recorded to meet the traceability requirements.

[0041] Step S9 is used to generate a traceable calibration certificate and support field applications. The certificate content at least includes: zero potential , electrode slope (including temperature correction relationship), selectivity coefficient and ion strength adjuster formula and batch, calibration and measurement temperature, original reading and stabilization time of each calibration point, regression and residual information, review point error, activity-concentration conversion model and parameter, uncertainty evaluation method and result, recalibration trigger threshold. After the certificate is archived, the above parameters can be automatically called and real-time correction and alarm determination can be completed when unknown samples are measured through the software interface, realizing the closed loop of laboratory-site consistency.

[0042] The calibration method for chloride ion probes based on selectivity coefficient correction provided by the present application is described in detail below with specific embodiment 1.

[0043] Embodiment 1 This example 1 provides a complete calibration procedure and is verified in a simulated seawater matrix.

[0044] 1. Instruments and reagents Main instruments: chloride ion selective electrode (solid-state membrane, composite reference electrode); temperature sensor (accuracy ±0.1 °C); thermostatic magnetic stirrer (controllable speed 200-300 rpm); high-precision pH / ion meter (or data acquisition system); class A volumetric flask, pipette.

[0045] Main reagents: sodium chloride (NaCl, analytical pure), sodium bromide (NaBr, analytical pure), sodium iodide (Nal, analytical pure), sodium nitrate (NaNO3, analytical pure); experimental water is ultrapure water (18.2 MΩ·cm). The ionic strength adjuster (ISA) is 0.5 mol·L －1 NaNO3, analytical pure); experimental water is ultrapure water (18.2 MΩ·cm). The ionic strength adjuster (ISA) is 0.5 mol·L

[0046] 2. Operation steps 2.1 Electrode pretreatment and activation Soak the chloride ion selective electrode and the reference electrode in the ISA solution of 0.5 mol·L －1 , and stand for activation for 45 minutes. Then, perform pre-polarization treatment: immerse the electrodes in sodium chloride standard solutions with concentrations of 10 －5 , 10 －4 , 10 －3 , 10 －2 mol·L －1 respectively (all in 0.5 mol·L －1 ISA as the matrix) in sequence for a short time, and stay at each concentration until the electrode potential change rate and continues to be stable for 1 minute. Record the ambient temperature (25.0 ± 0.2 °C).

[0047] 2.2 Pure chlorine multi-point primary calibration Under the conditions of constant temperature of 25.0 °C and stirring at 200 rpm, prepare sodium chloride standard solutions with concentrations of 1.0×10 －5 , 3.16×10 －5 , 1.0×10 －4 , 3.16×10 －4 , 1.0×10 －3 , 1.0×10 －2 , 1.0×10 －1 mol·L －1 in 0.5 mol·L －1 ISA as the matrix. Immerse the electrode system in each standard solution in sequence, and record the stable potential value after the potential is stable .

[0048] The potential value The negative logarithm of the chloride ion activity Linear least squares regression was performed to fit the Nernst equation The calibration results are as follows: zero point Potential, electrode slope , determination coefficient , residual standard deviation , midpoint (10 - ³mol·L - ¹) Repeatability error 0.7mV. See Table 1, Figure 2 and Figure 3 .

[0049] Table 1 Calibration results of different activity sodium chloride solutions 2.3 Selectivity coefficient determination (matching potential method) Under the conditions of 25.0°C, 0.5mol·L －1 ISA matrix, the solution with chloride ion activity of 1.0×10 －3 mol·L －1 was selected as the reference solution.

[0050] First, a small amount of high-concentration chloride standard solution was added to the reference solution to produce a predetermined change in electrode potential, and the amount of chloride ion required was recorded to convert the chloride ion activity increment .

[0051] Then, another identical reference solution was prepared, and a small amount of sodium bromide (or sodium iodide) standard solution was added to produce the same size change in electrode potential, and the amount of bromide ion (or iodide ion) required was recorded to convert the interfering ion activity increment .

[0052] The selectivity coefficient was calculated according to the formula .

[0053] Each of Br⁻ and I⁻ was repeated 3 times, and the arithmetic mean was taken to obtain: , (mean ± standard deviation). See Table 2 for detailed data, and Figure 4 .

[0054] Table 2 Determination results of different reference solutions for chloride solution in matching potential method (Alternative cross-validation: separation solution method) A series of standard solutions containing only chloride and only bromide (or iodide) respectively were prepared (all in 0.5 mol·L －1 ISA) and their potential values were measured at the same activity (e.g. 1.0×10 －3 mol·L －1 ) in the ISA. and .

[0055] The calculation was made according to the formula . The results of this example are in good agreement with the matching potential method results, and the weighted average was taken as the final certificate value. The data are shown in Table 3, and the results are shown in . . Figure 5 .

[0056] Table 3 Determination results of chloride solution by different reference solutions of the separation solution method 2.4, unknown sample measurement and interference correction A simulated seawater sample (0.5 mol·L －1 ISA was added to match the ionic strength) was measured. The sample potential was measured after the potential was stable at 25.0°C under the condition of 250 rpm stirring .

[0057] The bromide ion activity and iodide ion activity in the sample were measured by the parallel ion selective electrode method.

[0058] Substituting , , , , , into the extended Nernst equation: The corrected chloride ion activity was solved analytically: The total equivalent activity was calculated: ; The stripping interference contribution: .

[0059] 2.5 Activity-concentration conversion The activity coefficient was calculated using the Davis equation. The total ionic strength in the sample was known (mainly contributed by 0.5 M NO3- and various halides).

[0060] Therefore, .

[0061] Chloride ion concentration .

[0062] 2.6 Quality Control and Certificate Archiving The calibration quality was excellent. , The selectivity coefficient determination showed good repeatability (RSD < 8%). Verification points (10) －3 mol·L －1 The relative error of the back-calculated concentration is 1.1%, which meets the quality control requirement of ≤2%.

[0063] Generate a calibration certificate and archive all key parameters (see Table 4), including: , , , ISA information, temperature, raw data, regression parameters, activity coefficient model, checkpoint error, and recalibration threshold ( or Drift >5%, (Drift > 10%). This certificate parameter can be embedded in software for real-time correction and alarms during subsequent online measurements.

[0064] Table 4 Key Parameters of Calibration Certificate It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0065] Furthermore, it should be noted that the scope of the methods and systems in the embodiments of the present invention is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. In addition, features described with reference to certain examples may be combined in other examples.

[0066] The embodiments of the present application are described above with reference to the accompanying drawings, but the present application is not limited to the above-described specific embodiments, and the above-described specific embodiments are merely illustrative, but not restrictive, and a person of ordinary skill in the art can make many forms under the inspiration of the present application without departing from the scope of the present application, and all of them belong to the protection of the present application.

Claims

1. A method for calibrating a chloride ion probe based on selectivity coefficient correction, characterized in that, Includes the following steps: Step S1, Probe pretreatment and activation: The chloride ion selective electrode is activated under the set ion strength regulator and temperature conditions until the electrode potential change rate meets the stability criterion. Step S2, Matrix matching settings: Ensure that the calibration and measurement process is performed under ionic strength and temperature conditions that are consistent with or equivalent to those of the target sample; Step S3, Pure Chlorine System Multi-Point Master Calibration: Under set conditions, prepare a series of chloride standard solutions, measure the electrode potential at each point, and perform logarithmic linear regression, according to the formula... Obtaining zero-point potential With electrode slope ,in, Electrode potential; Chloride ion activity; Step S4, Selectivity coefficient determination: Under the same conditions as in step S3, the selectivity coefficients for bromide and iodide ions are determined using the matched potential method or the solution separation method. and ; Step S5, Measurement of unknown sample: Measure the electrode potential of the unknown sample under set conditions. And obtain the bromide ion activity in the sample. and iodide ion activity ; Step S6, Interference Correction and Analytical Solution: The results obtained in steps S3, S4, and S5 are used to solve the problem. , , , , , Substituting into the extended potential-activity relationship In the middle, the corrected chloride ion activity is obtained by analytical solution. ; Step S7, Activity-Concentration Conversion: Using the activity coefficient Corrected chloride ion activity Converted to chloride ion concentration The calculation formula is: ; Step S8, Output and Archiving: Output the calibrated chloride ion activity or concentration results, and record the relevant calibration parameters, environmental conditions and quality control data to form a traceable certificate document.

2. The method according to claim 1, characterized in that, In step S1, the ionic strength modifier has a concentration of 0.5 mol·L⁻¹. －1 The activation process involves first placing the electrode in a conditioning agent for 30-60 minutes, followed by short-term contact with the electrode according to a concentration gradient for 10 minutes. －5 ~10 －2 mol·L －1 The chloride standard solution was pre-polarized until the rate of potential change was reached. And it lasts for 30 to 60 seconds.

3. The method according to claim 1, characterized in that, In step S2, the temperature condition is 25±0.5℃; when at other temperatures... Electrode slope during operation Temperature compensation is required; the compensation formula is as follows: ,in The value is -59.16 mV / dec.

4. The method according to claim 1, characterized in that, In step S3, the series of chloride standard solutions includes no fewer than 5 concentration points, covering a concentration range of 10. －5 ~10 －1 mol·L －1 ; The regression must meet the determination coefficient. And the residual standard deviation is ≤1.5mV.

5. The method according to claim 1, characterized in that, In step S4, the operation of the matched potential method includes: fixing the chloride ion activity In the reference solution, a trace amount of chloride is first added to induce a predetermined change in electrode potential. Record the required chloride ion increment. Then, add bromide or iodide to another portion of the same reference solution to produce the same change in electrode potential. Record the required increment of interfering ions. Then the selectivity coefficient ,in for or .

6. The method according to claim 1, characterized in that, In step S4, the calculation formula for the solution separation method is: ,in Chloride ion activity The electrode potential below, To interfere with ion activity The electrode potential below.

7. The method according to claim 1, characterized in that, In step S5, the bromide ion activity and iodide ion activity The activity values ​​were obtained by parallel ion-selective electrodes or independent chemical analysis methods and converted into activity values ​​under ion strength and temperature conditions consistent with chloride ion calibration.

8. The method according to claim 1, characterized in that, In step S7, the activity coefficient Calculated using the Davis equation: , where constant Take 0.509, The ionic strength of the solution.

9. The method according to claim 1, characterized in that, The method also includes quality control and recalibration steps: the linear regression of the master calibration must meet the following requirements. The residual standard deviation is ≤1.5mV, and within 10 －3 mol·L －1 and 10 － 2 mol·L －1 The relative error of the calculated concentration should be ≤2% when the zero-point potential is checked. or electrode slope The drift relative to the previous certificate value exceeds 5%, or any selectivity coefficient When the relative deviation exceeds 10%, a recalibration procedure is triggered.

10. The method according to claim 1, characterized in that, In step S8, the certificate document includes the zero-point potential. Electrode slope Its temperature correction relationship and selectivity coefficient and Information on ionic strength modifiers, calibration and measurement temperatures, initial potential readings and stabilization time, regression mass parameters, verification point errors, activity-concentration conversion models and parameters, uncertainty assessment results, and recalibration trigger thresholds; the correction calculation process can be completed in real time in an embedded system or host computer software, and alarm functions are supported.

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