A method for calibrating a chloride ion probe based on selective coefficient correction

Abstract

The application belongs to the technical field of electrochemical analysis and test, and discloses a chlorine ion probe calibration method based on selective coefficient correction. The method calibrates the main standard under the same ion intensity and temperature conditions as the sample, measures the selective coefficient of Br⁻ and I⁻, uses the extended potential-activity relationship to analyze and correct the interference, and obtains the accurate chlorine ion activity / concentration. The application is suitable for seawater, brine and other complex media, and significantly improves the accuracy, repeatability and traceability of measurement.

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, thereby achieving high-precision regression of chloride ion activity / concentration in complex media with interference and fluctuation; meanwhile, 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, which is convenient for 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:

[0009] The embodiments of the present application provide a chloride ion probe calibration method based on selectivity coefficient correction, comprising the following steps:

[0010] 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;

[0011] Step S2, matrix matching setting: the calibration and measurement processes are carried out under the same or equivalent ion strength and temperature conditions as the target sample;

[0012] Step S3, pure chlorine multi-point main calibration: under the set conditions, a series of chloride standard solutions are configured, the electrode potential of each point is measured and logarithmic linear regression is performed, and the zero potential is obtained according to the formula wherein, is the electrode slope; , wherein, is the electrode potential; is the chloride ion activity;

[0013] 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 ;

[0014] Step S5, unknown sample measurement: measure the electrode potential of unknown sample under the set conditions , and obtain the bromide ion activity and iodide ion activity in the sample

[0015] Step S6, interference correction and analytical solution: substitute the , , , , , obtained in step S3, step S4, step S5 into the extended potential-activity relationship , and analytically solve to obtain the corrected chloride ion activity

[0016] Step S7, activity-concentration conversion: use the activity coefficient to convert the corrected chloride ion activity to the chloride ion concentration , and the calculation formula is

[0017] Step S8, output and archiving: output the corrected chloride ion activity or concentration result, and record the related calibration parameters, environmental conditions and quality control data to form a traceable certified document.

[0018] 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 to first immerse the electrode in the regulator for 30-60 minutes, and then pre-polarize it by short-time contact with a 10 －5 ~10 － 2 mol·L －1 chloride standard solution in a concentration gradient, until the potential change rate and lasts for 30-60 seconds.

[0019] Optionally, in step S2, the temperature condition is 25±0.5℃; when working at other temperatures , the electrode slope needs to be temperature-compensated, and the compensation formula is , where takes -59.16 mV / dec.

[0020] Optionally, in step S3, the series of chloride standard solutions has no less than 5 concentration points, and the concentration range covers 10 －5 ~10 －1 mol·L －1 ​​; regression needs to meet the determination coefficient and the residual standard deviation is ≤1.5 mV.

[0021] Optionally, in step S4, 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 cause a predetermined amount of change in the electrode potential , and the required chloride ion increment is recorded; then, in another identical reference solution, bromide or iodide is added to cause the same amount of change in the electrode potential , and the required interference ion increment is recorded, and the selectivity coefficient is selected, wherein is or .

[0022] Optionally, in step S4, the calculation formula of the separate solution method is , wherein is the electrode potential at the chloride ion activity , and is the electrode potential at the interference ion activity .

[0023] Optionally, 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 into activity values under the same ion intensity and temperature conditions as the chloride ion calibration.

[0024] Optionally, in step S7, the activity coefficient is calculated using the Davies equation: , wherein the constant is 0.509, is the ion intensity of the solution.

[0025] Optionally, 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%, a recalibration procedure is triggered.

[0026] Optionally, in step S8, the certified document contains the zero potential , electrode slope , and its temperature correction relationship, selectivity coefficient , and , ion strength regulator 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.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] (1) High measurement accuracy: by simultaneously 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 the true and accurate chloride ion activity or concentration, effectively solving the problem of systematic high measurement values caused by fluctuation of interfering ions in complex media.

[0029] (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 (a, b, c) 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. , ,

[0030] (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 embedded systems 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.

[0031] (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 differences in sample background electrolyte, improving the robustness and reliability of the method.

[0032] (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.

[0033] ​(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

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. 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 creative labor on the basis of these drawings.

[0035] Figure 1 The flow chart of the chlorine ion probe calibration method based on selective coefficient correction provided by the present application;

[0036] Figure 2 The pure chlorine-based master calibration curve provided by the present application;

[0037] Figure 3 The master calibration residual distribution diagram provided by the present application;

[0038] Figure 4 The average value diagram of the selective coefficient (matching potential method) provided by the present application;

[0039] Figure 5 The average value diagram of the selective coefficient (solution separation method) provided by the present application. DETAILED DESCRIPTION

[0040] 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 some of the 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 creative labor fall within the scope of protection of the present application.

[0041] 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.

[0042] Referring to Figure 1 The embodiment of the present application provides a chlorine ion probe calibration method based on selective coefficient correction, comprising the following steps:

[0043] Step S1, probe pretreatment and activation: the chlorine ion selective electrode is activated under the set ion intensity regulator and temperature conditions until the electrode potential change rate meets the stability criterion;

[0044] Step S2, matrix matching setting: the calibration and measurement processes are carried out under the ion intensity and temperature conditions consistent with or equivalent to the target sample;

[0045] Step S3, pure chlorine multi-point main calibration: under the set conditions, a series of chloride standard solutions are configured, the electrode potential of each point is measured and logarithmic linear regression is performed, and the zero point potential is obtained according to the formula wherein, is the electrode potential; is the chlorine ion activity; is the electrode slope; is the electrode potential;

[0046] Step S4, selective coefficient determination: under the same conditions as step S3, the selective coefficients of bromide ions and iodide ions are determined by using the matching potential method or the separate solution method and ;

[0047] Step S5, unknown sample measurement: under the set conditions, the electrode potential of the unknown sample is measured , and the bromide ion activity in the sample is obtained and the iodide ion activity ;

[0048] Step S6, interference correction and analytical solution: the , , , , , obtained from step S3, step S4 and step S5 are substituted into the extended potential-activity relationship formula , and the corrected chlorine ion activity is obtained by analytical solution;

[0049] Step S7, activity-concentration conversion: the corrected chlorine ion activity is converted into the chlorine ion concentration using the activity coefficient , and the calculation formula is ;

[0050] Step S8, output and archive: output the corrected chloride ion activity or concentration results, and record the relevant calibration parameters, environmental conditions and quality control data to form traceable certified documents.

[0051] In step S1, the ionic strength adjuster is an aqueous solution of sodium nitrate or potassium nitrate with a concentration of 0.5 mol·L －1 ; the activation is to first place the electrode in the adjuster for 30-60 minutes, and then pre-polarize by short-time contact with a chloride standard solution with a concentration gradient of 10 －5 ~10 －2 mol·L －1 , until the potential change rate and duration of 30-60 seconds. The measurement temperature is recorded during this process as the basis for temperature compensation of the subsequent electrode slope ; if necessary, the reference electrode liquid interface state, salt bridge integrity and electrode surface attached bubbles are visually inspected and removed to avoid false signals entering the calibration link.

[0052] In step S2, the aim is to ensure matrix consistency and temperature consistency between the laboratory and the field. For ionic strength, it is preferred to use the same formula and volume fraction of ionic strength adjuster in calibration and measurement to keep the background electrolyte constant; if the ionic strength adjuster cannot be injected in the field, compensation is made based on the activity coefficient model in the data processing stage. The temperature condition is preferably 25±0.5℃; when working at other temperatures , the electrode slope needs to be temperature compensated, and the compensation formula is , where is taken as -59.16 mV / dec. Through this setting, the influence of temperature drift and ionic strength change on subsequent parameter migration can be minimized.

[0053] Step S3 is used to determine the zero point potential and the electrode slope , and to anchor the electrode response to the chloride ion activity scale. Under the target ionic strength and temperature conditions, the series of chloride standard solutions has no less than 5 concentration points, and 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 . The electrode is placed in each standard solution, stirred well and allowed to stabilize until the stability criterion is met, and then the potential is read to obtain the standard data in sequence. The logarithmic linear relationship between the electrode potential and the chloride ion activity is established:

[0054] ;

[0055] Obtaining zero potential by least square linear regression With electrode slope , and record the fitting residual, the coefficient of determination, each point reading and temperature information for traceability. If a constant and high enough background ion strength is used, the activity coefficient can be approximately constant, and the nominal concentration can be used instead of activity to participate in regression; if strict conversion is required, the activity coefficient calculation can be introduced in step seven to correct , and complete the regression fitting.

[0056] 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 the reference solution with a fixed chloride ion activity , first add a small amount of chloride to make the electrode potential produce a predetermined change , and record the required chloride ion increment ; then add bromide or iodide to another identical reference solution to produce the same change , and record the required interfering ion increment , then the selectivity coefficient , where is or .

[0057] The calculation formula of the separation solution method is , where is the electrode potential under the chloride ion activity , and is the electrode potential under the interfering ion activity .

[0058] 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 difference if necessary.

[0059] 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.

[0060] 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 halide are configured respectively, and the "main ion solution potential " and the "interfering solution potential ”. Under the condition of equal potential (i.e. two groups of solutions produce the same electrode potential), the selectivity coefficient is derived from the extended potential-activity relationship . For monovalent halogen of the same valence as chloride ion, the index of the above formula is 1. When the matching potential method and the separate solution method are in good agreement, their weighted average is taken as the certificate selectivity coefficient of this calibration; if there is a deviation, the test configuration that is more similar to the target scene is preferred, and the difference source and uncertainty are explicitly stated in the certificate.

[0061] 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 stabilized under the same 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 means. The zero potential , the electrode slope , the selectivity coefficient , are substituted into the extended potential-activity relationship formula:

[0062] .

[0063] The above formula is solved according to “chloride ion activity ” to obtain the corrected chloride ion activity . 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 scenes where the bromine and iodine contents cannot be obtained in real time, historical statistics or parallel monitoring can be combined for estimation and the uncertainty interval is given; when the estimation uncertainty is unacceptable, parallel ion quantification or rapid review of the selectivity coefficient should be triggered.

[0064] 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 electrolytes is preferably used, and the activity coefficient is calculated using the Davies equation:

[0065] ;

[0066] 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 kept constant and high by ion strength adjuster in situ, the activity coefficient can be treated as a constant to simplify the process; when the ion strength fluctuates significantly over time, the activity coefficient should be calculated sample by sample and the model used, parameters and applicable range should be explicitly shown in the certificate.

[0067] Step S8 aims to constrain the calibration quality and long-term drift and set up the recalibration trigger. The certified document contains the 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 parameters, review point error, activity-concentration conversion model and parameters, uncertainty evaluation results, and recalibration trigger threshold; the correction calculation process can be completed in real time in the embedded system or upper computer software, and supports alarm function.

[0068] The method also includes quality control and recalibration steps: 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 "deionized water flushing-background electrolyte infiltration-midpoint re-stabilization" rapid recovery process is implemented; if necessary, replace the reference salt bridge or perform membrane surface reactivation. All abnormal determinations and treatments should be recorded to meet the traceability requirements.

[0069] Step S9 is used to generate traceable calibration certificates and support field applications. The certificate content includes at least: 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 parameters used, uncertainty evaluation method and results, 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 consistency of laboratory-site.

[0070] The calibration method of the chlorine ion probe based on the selective coefficient correction provided by the present application is described in detail below with specific example 1.

[0071] Example 1

[0072] Example 1 provides a complete calibration process, which is verified in a simulated seawater matrix.

[0073] 1. Instruments and reagents

[0074] Main instruments: chloride ion selective electrode (solid-state membrane, composite reference electrode); temperature sensor (accuracy ±0.1°C); constant-temperature magnetic stirrer (controllable speed 200-300 rpm); high-precision pH / ion meter (or data acquisition system); Class A volumetric flask, pipette.

[0075] Main reagents: sodium chloride (NaCl, analytical pure), sodium bromide (NaBr, analytical pure), sodium iodide (NaI, 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 sodium nitrate aqueous solution.

[0076] 2. Operation steps

[0077] 2.1 Electrode pretreatment and activation

[0078] Soak the chloride ion selective electrode and the reference electrode in the 0.5 mol·L －1 ISA solution 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 , and 10 －2 mol·L －1 (0.5 mol·L －1 ISA as the matrix) in sequence for a short time, 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).

[0079] 2.2 Pure chlorine multi-point primary calibration

[0080] Under the conditions of constant temperature at 25.0°C and 200 rpm stirring, prepare sodium chloride standard solutions with concentrations of 1.0×10 －1 , 3.16×10 －5 , 1.0×10 －5 , and 1.0×10 －4, 3.16×10 －4 , 1.0×10 －3 , 1.0×10 －2 , 1.0×10 －1 mol·L －1 of sodium chloride standard solution series. The electrode system was immersed in each standard solution in turn, and when the potential was stable (after 300 s) , the stable potential value was recorded.

[0081] The negative logarithm of the chloride ion activity was linearly least square regressed with the potential value , and the Nernst equation was fitted . The results of this calibration were: zero point potential, electrode slope, determination coefficient, and residual standard deviation , , , , respectively. The midpoint (10 - ³mol·L - ¹) retest deviation was 0.7 mV. See Table 1, Figure 2 and Figure 3 .

[0082] Table 1 Calibration results of different activity sodium chloride solutions

[0083]

[0084] 2.3 Selectivity coefficient determination (matching potential method)

[0085] At 25.0 °C, 0.5 mol·L －1 of ISA matrix, the solution with a chloride ion activity of 1.0×10 －3 mol·L －1 was selected as the reference solution.

[0086] First, a trace amount of high-concentration chloride standard solution was added to the reference solution to produce a predetermined change in the electrode potential, and the amount of chloride ion required to be added was recorded to convert the chloride ion activity increment .

[0087] Then, another portion of the same reference solution was taken, and a trace amount of sodium bromide (or sodium iodide) standard solution was added instead to produce the same size change in the electrode potential, and the amount of bromide ion (or iodide ion) required to be added was recorded to convert the interfering ion activity increment .

[0088] The selectivity coefficient was calculated according to the formula .

[0089] Each of Br⁻ and I⁻ was repeated 3 times, and the arithmetic mean value was obtained: , (mean ± standard deviation). Detailed data are shown in Table 2, and the results are shown in Figure 4 .

[0090] Table 2 Determination results of different reference solutions in matching potential method

[0091]

[0092] (Alternative cross-validation: separate solution method)

[0093] The standard solution series containing only chloride and only bromide (or iodide) (all in 0.5 mol·L －1 ISA) were prepared, and their potential values at the same activity (such as 1.0×10 －3 mol·L －1 ) were measured and .

[0094] According to the formula , the calculation was performed. In this embodiment, the measured , , which was in good agreement with the results of the matching potential method. The weighted average value was taken as the final certificate value. The data are shown in Table 3, and the results are shown in Figure 5 .

[0095] Table 3 Determination results of different reference solutions in separate solution method

[0096]

[0097] 2.4, Measurement of unknown samples and correction of interference

[0098] A simulated seawater sample (0.5 mol·L －1 ISA was added to match the ionic strength) was measured. At 25.0°C, under the condition of 250 rpm stirring, the sample potential was measured after the potential was stable.

[0099] The bromide ion activity and the iodide ion activity in the sample were measured by the parallel ion selective electrode method.

[0100] Substituting , , , , , into the extended Nernst equation: Analytical solution for corrected chloride activity :

[0101] Calculation of total equivalent activity: ;

[0102] Peeling off interference contributions: .

[0103] 2.5 Activity-concentration conversion

[0104] Activity coefficient calculation using Davis equation . Total ionic strength in the sample is known (main contributions from 0.5 M NO3- and various halides).

[0105]

[0106] Therefore, .

[0107] Chloride concentration .

[0108] 2.6 Quality control and certification archive

[0109] The quality of this calibration is excellent ( , ), with good repeatability of the selectivity coefficient determination (RSD < 8%). The check point (10 －3 mol·L －1 ) has a relative error of 1.1% on the back-calculated concentration, which meets the quality control requirement of ≤ 2%.

[0110] A calibration certificate is generated, archiving all key parameters (see Table 4), including: , , , , ISA information, temperature, raw data, regression parameters, activity coefficient model, check point error, and recalibration threshold ( or drift > 5%, drift > 10%). The certificate parameters can be embedded in the software for real-time correction and alarm of subsequent online measurements.

[0111] Table 4 Calibration certificate key parameters

[0112]

[0113] It has to be understood that, in the present document, the terms "comprising", "including", or any other variant thereof, are intended to cover a non-exclusive inclusion, such that processes, methods, articles, or apparatuses that comprise a list of elements are not limited to those elements, but can include other elements not expressly listed or inherent to such processes, methods, articles, or apparatuses. Without further limitation, an element preceded by "comprises a" does not, without more constraints, foreclose the existence of additional identical elements in the process, method, article, or apparatus that comprises the recited element.

[0114] Furthermore, it is indicated that the scope of the methods and systems of the embodiments of the present application is not limited to performing functions in the order discussed or illustrated, and can include performing functions in a substantially simultaneous manner or in reverse order, for example, the described methods can be performed in other than the order described, and additional, fewer, or different steps can be added, omitted, or combined. Also, features described with respect to certain examples can be combined in other examples.

[0115] The embodiments of the present application described above are only illustrative, and the present application is not limited to the above-described specific embodiments, which 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.

Claims

1. A method for calibrating a chloride ion probe based on selective coefficient correction, characterized by, The method comprises the following steps: Step S1, probe pretreatment and activation: the chloride ion selective electrode is activated under the set ion intensity adjuster and temperature condition until the electrode potential change rate meets the stability criterion; Step S2, matrix matching setting: the calibration and measurement processes are performed under the ion intensity and temperature conditions consistent with or equivalent to the target sample; Step S3, pure chlorine multi-point primary calibration: configure series of chloride standard solutions under set conditions, measure electrode potential of each point and perform logarithmic linear regression, and obtain electrode potential of zero point and electrode slope according to formula obtaining the zero point potential and the 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 for bromide and iodide ions are determined using the matched potential method or the separate solution method and ; Step S5, unknown sample measurement: measuring the electrode potential of the unknown sample under the set conditions and obtaining the bromide ion activity and the iodide ion activity in the sample; Step S6, interference correction and analytical solution: the interference corrected chloride ion activity , , , , , Substitute the extended potential-activity relationship formula In the formula, the analytical solution obtains the corrected chloride ion activity ; Step S7, activity-concentration conversion: using the activity coefficient The corrected chloride ion activity is converted into the chloride ion concentration , and the calculation formula is ; Step S8, output and archiving: the corrected chloride ion activity or concentration result is output, and the related calibration parameters, environmental conditions and quality control data are recorded to form a traceable certified document.

2. The method of claim 1, wherein, In step S1, the ionic strength adjuster is an aqueous solution of sodium nitrate or potassium nitrate with a concentration of 0.5 mol·L －1 ; the activation is to first let the electrode stand in the adjuster for 30-60 minutes, and then to perform pre-polarization by short-time contact with a chloride standard solution with a concentration gradient of 10 －5 ~10 －2 0 mol·L －1 , until the potential change rate and the duration are 30-60 seconds.

3. The method of claim 1, wherein, In step S2, the temperature condition is 25±0.5℃; when at other temperatures Under the working condition, the electrode slope Temperature compensation is needed, and the compensation formula is Wherein -59.16 mV / dec is taken.

4. The method of claim 1, wherein, In step S3, the series of chloride standard solutions is not less than 5 concentration points, and the concentration range covers 10 －5 ~10 －1 mol·L －1 ; Regression must meet a coefficient of determination and a residual standard deviation of <1.5 mV.

5. The method of claim 1, wherein, In step S4, the operation of the matching potential method includes: in a reference solution with fixed chloride ion activity , adding a trace amount of chloride to make the electrode potential produce a predetermined change , and recording the required chloride ion increment ; then adding bromide or iodide to another identical reference solution to make the electrode potential produce the same change , and recording the required interfering ion increment , then the selectivity coefficient , where , or , or .

6. The method of claim 1, wherein, In step S4, the calculation formula for the separation solution method is wherein is the electrode potential at the chloride ion activity is the electrode potential at the interfering ion activity is the electrode potential at the interfering ion activity is the electrode potential at the interfering ion activity 7. The method of claim 1, wherein, In step S5, the bromide ion activity and iodide ion activity are obtained by means of ion-selective electrodes arranged in parallel or independent chemical analysis methods and converted into activity values under the same conditions of ionic strength and temperature as for the calibration with chloride ions.

8. The method of claim 1, wherein, In step S7, the activity coefficient The Davies equation was used to calculate: where the constant Taking 0.509, is the ionic strength of the solution.

9. The method of claim 1, wherein, The method also contains quality control and recalibration steps: the linear regression of the primary calibration needs to satisfy , the residual standard deviation ≤1.5mV, and the relative error of the inverse calculation 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 certificate value, or the relative deviation of any selectivity coefficient exceeds 10%, the recalibration procedure is triggered.

10. The method of claim 1, wherein, In step S8, the certified document contains the zero-point potential , electrode slope , and its temperature correction relationship, selectivity coefficient , and , ion strength adjuster information, calibration and measurement temperature, original potential reading and stabilization time, regression quality parameters, review point error, activity-concentration conversion model and parameters, uncertainty evaluation results, and recalibration trigger threshold; the correction calculation process can be completed in real time in the embedded system or the host computer software, and supports alarm function.

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