A method for detecting chloride ions in high concentration samples for the salt making industry

Abstract

This invention belongs to the field of detection technology, specifically disclosing a method and system for detecting chloride ions in high-concentration samples used in the salt-making industry. The detection method includes the following steps: (1) cyclically taking samples from the process pipeline to ensure real-time sample availability; (2) diluting the sample to ensure that the concentration of the sample falls within the optimal detection range; (3) inputting the diluted sample into the titration system, performing titration using potentiometric titration, outputting the first derivative DE / DV in real time, and using a nonlinear normalization function to normalize the original DE / DV sequence to obtain S. norm Value, according to S norm Adjust the speed of the titration pump, S norm The point corresponding to the maximum value is the titration endpoint. The titration volume V2 of the silver nitrate standard solution at this point is recorded, and the chloride ion concentration in the pipeline sample is calculated. This invention stably maps the wide-range fluctuating DE / DV signal to a fixed interval, solving the core problem of inaccurate endpoint determination and ensuring the accuracy and reliability of the detection results.

Description

Technical Field

[0001] This invention belongs to the field of detection technology and relates to the detection of chloride ion concentration, particularly to a method for detecting chloride ions in high-concentration samples used in the salt production industry. Background Technology

[0002] In the salt-making industry, the rapid and accurate determination of chloride ion content in raw brine, intermediate products, and final products is a crucial aspect of quality control and process optimization. Currently, the commonly used method in this field is automated potentiometric titration using silver nitrate as the standard titration solution. However, when applying this standard method to test high-concentration chloride ion samples (such as salt field brine, evaporation concentrate, and refined salt mother liquor), existing technologies reveal a series of core problems that urgently need to be addressed. (1) Failure of endpoint judgment mechanism at extreme concentrations The core of automated potentiometric titration lies in the accurate determination of the titration endpoint. Currently available commercial instruments generally use the peak value of the first derivative of the potential (dE / dV, or DE / DV) as the endpoint indication signal. However, this results in an excessively wide dynamic range: when titrating high-concentration samples, the extremely high ionic strength in the reaction system causes the DE / DV signal value to fluctuate drastically throughout the titration process, ranging from hundreds to thousands of values. This ultra-wide dynamic range renders fixed, preset endpoint determination thresholds inapplicable. Setting the threshold too high will lead to premature endpoint misjudgment; setting it too low will result in failure to identify the endpoint or a significant delay.

[0003] (2) Incompatibility between high-concentration samples and titration systems High-concentration samples require a larger volume of titrant to reach the endpoint. This causes the titration curve to be horizontally "stretched," with the potential jump near the endpoint becoming gentler and wider. The inherent minimum addition volume (resolution) of existing titrators is insufficient in this case to accurately pinpoint the inflection point of the jump.

[0004] (3) The reagents are uneconomical: a large amount of silver nitrate standard solution is consumed, which increases the cost of a single test.

[0005] To address the aforementioned concentration mismatch issue, the only currently effective approach is to manually pre-dilute the original sample. However, this manual dilution disrupts the fully automated process from sampling to analysis, making true "online detection" difficult and resulting in significant data delays. The dilution process involves multiple pipetting and volume adjustments, and its accuracy heavily relies on the operator's skill level; errors in the dilution factor are directly transmitted and amplified in the final result.

[0006] In summary, existing technologies face three major bottlenecks in high-concentration chloride ion titration scenarios: inaccurate endpoint determination, poor system matching, and reliance on manual pretreatment. These problems severely hinder the progress of comprehensive online quality monitoring and intelligent production in the salt industry. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a method and system for detecting chloride ions in high-concentration samples in the salt-making industry. This invention achieves intelligent and precise pretreatment of samples with a wide concentration range by constructing a programmable two-stage automatic dilution process. By introducing a dynamic signal normalization (DRC) model, the wide-range fluctuations in DE / DV signals are stably mapped to a fixed interval, establishing a universal and stable endpoint criterion. This fundamentally solves the core problem of inaccurate endpoint determination, ensuring the accuracy and reliability of the results. Another objective of this invention is to provide a detection system for implementing this detection method.

[0008] This invention is achieved through the following technical solution: A method for detecting chloride ions in high-concentration samples used in the salt production industry includes the following steps: (1) Samples are taken from the process pipeline in a cyclical manner to ensure the real-time nature of the samples; (2) The sample was diluted twice to ensure that the concentration of the sample fell within the optimal detection range; (3) Input the diluted sample into the titration system and perform titration using potentiometric titration. Output the first derivative DE / DV in real time. Use a nonlinear normalization function to normalize the original DE / DV sequence. The nonlinear normalization function is shown below:

[0009] S norm The normalized output signal has a value that is stabilized in the range [0, A]. A is the normalized amplitude, which defines the upper limit of the output signal and eliminates the influence of the absolute amplitude of the original signal. Its value is 60. The steepness of the curve from 0 to A, controlled by constants K and n, directly affects the sensitivity of identifying the endpoint jump. K is set to 100 and n to 1. (4) Real-time judgment of S norm The relationship with A is used to adjust the speed of the titration pump. Specifically: when S... norm When ≤20%A, set the single drop volume of the syringe pump to 100μL; when 20%A < S norm When S ≤ 80%A, set the single drop volume of the syringe pump to 10-50 μL; when S norm When the concentration of A is >80%, set the single drop volume of the syringe pump to 5-10 μL; (5)Snorm The point corresponding to the maximum value is the titration endpoint. Record the titration volume V2 of the silver nitrate standard solution at this point and calculate the chloride ion concentration in the sample from the pipeline. C1 = C2V2*x / V1 C2 represents the concentration of the silver nitrate standard solution, in g / L. V2 is the volume of silver nitrate standard solution consumed, in mL; x is the first dilution factor; V1 is the sample volume after the first dilution, in mL.

[0010] A further improvement to the present invention is as follows: The high-concentration sample is salt field brine, evaporation concentrate, or refined salt mother liquor.

[0011] Furthermore, the chloride ion concentration in the high-concentration sample is 50 g / L to 300 g / L.

[0012] Furthermore, the two dilution processes are as follows: the sample obtained from the process pipeline is diluted 40-60 times, and an appropriate amount of the diluted sample is further diluted 10-30 times.

[0013] A further improvement of the present invention is as follows: An online detection system for the above method includes: A sampling module, which is used to quantitatively sample from the process pipeline and filter the sample, includes a sampling injection pump and a filter element; The potential analysis module includes a dilution unit, a titration and sensing unit, a first multi-channel valve, and a second multi-channel valve. The dilution unit is used to perform the first dilution of the sample and includes a first syringe pump, a dilution cup, a first magnetic stirrer, and a sampling pump. The titration and sensing unit is used to perform the second dilution and chloride ion titration and includes a second syringe pump, a titration cup, a second magnetic stirrer, and a silver ion selective electrode. Human-computer interaction module, which is used to set method parameters and view detection results; A reagent storage module, comprising multiple reagent bottles, a pure water tank, and a liquid level sensor; The cleaning and waste discharge module is used to discharge the waste liquid from pipeline cleaning and rinsing, sampling and titration in dilution cups and titration cups, and cleaning to the waste liquid tank.

[0014] Furthermore, the filter element is made of polypropylene with a pore size of 20μm; Furthermore, the first multi-channel valve is a six-channel valve used for switching between sample and pure water; the second multi-channel valve is a ten-channel valve used for switching between silver nitrate standard solution and pure water.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) By introducing a dynamic signal (DRC) normalization model, this invention stably maps the wide-amplitude fluctuating DE / DV signal to a fixed interval, establishes a universal and stable endpoint criterion, fundamentally solves the core problem of inaccurate endpoint judgment, and ensures the accuracy and reliability of the results.

[0016] (2) This invention achieves intelligent and precise pretreatment of samples with a wide concentration range (especially high-concentration brine) by constructing a programmable automatic dilution process. It automatically dilutes the sample to the optimal detection range, completely replacing manual dilution, and significantly improving analytical efficiency and reducing reagent costs while ensuring accuracy.

[0017] (3) This invention maps unstable DE / DV signals to a stable [0, A] interval using a dynamic signal normalization model, and combines this with a dynamic titration algorithm to adjust the titration speed in real time. In the early stage of titration, the titration speed is increased, and in the later stage (S... norm When the titration rate is >80% (the volume of a single drop decreases), the titration speed is reduced, thus improving accuracy.

[0018] (4) The automatic dilution technology of the present invention adapts ultra-high concentration samples (such as concentrated brine) to the optimal detection range, enabling the system to cover the full range of detection from ordinary salt products to extremely high concentration brine; it avoids the large volume consumption of direct titration and significantly reduces the consumption of reagents (silver nitrate).

[0019] (5) This invention creatively provides a fully automated online titration system that integrates intelligent sample pretreatment, adaptive signal analysis, and high-precision endpoint determination. It overcomes the challenges posed by high-concentration samples and achieves full-process automation, precision, and intelligence from "sample import" to "result output," providing solid technical support for the upgrading of the salt industry. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the detection method of the present invention; Figure 2 This is a schematic diagram of the detection system of the present invention; Among them, 11-sampling pump, 12-filter element, 21-first injection pump, 22-dilution cup, 23-first magnetic stirring device, 24-sampling pump, 25-first waste discharge pump, 31-second injection pump, 32-tipping cup, 33-second magnetic stirring device, 34-silver ion selective electrode, 35-second waste discharge pump, 4-first multi-channel valve, 5-second multi-channel valve, 6-pure water tank, 7-standard sample tank, 8-waste liquid tank, 9-human-machine interaction module; Figure 3 This is a graph of the data collected in Example 1; Figure 4 This is a graph of the data collected for Comparative Example 1. Detailed Implementation

[0021] In the description of this invention, it should be noted that unless specific conditions are specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0022] The present invention will now be described in detail with reference to specific embodiments.

[0023] like Figure 1 As shown in the figure, a specific embodiment of the present invention provides a method for detecting chloride ions in high-concentration samples used in the salt production industry, comprising the following steps: (1) Samples are taken from the process pipeline in a cyclical manner to ensure the real-time nature of the samples; (2) The sample was diluted twice to ensure that the concentration of the sample fell within the optimal detection range; (3) Input the diluted sample into the titration system and perform titration using potentiometric titration. Output the first derivative DE / DV in real time. Use a nonlinear normalization function to normalize the original DE / DV sequence. The nonlinear normalization function is shown below:

[0024] S norm The normalized output signal has a value that is stabilized in the range [0, A]. A is the normalized amplitude, which defines the upper limit of the output signal and eliminates the influence of the absolute amplitude of the original signal. Its value is 60. The steepness of the curve from 0 to A, controlled by constants K and n, directly affects the sensitivity of identifying the endpoint jump. K is set to 100 and n to 1. (4) Real-time judgment of S norm The relationship with A is used to adjust the speed of the titration pump. Specifically: when S... norm When ≤20%A, set the single drop volume of the syringe pump to 100μL; when 20%A < S norm When S ≤ 80%A, set the single drop volume of the syringe pump to 10-50 μL; when S norm When the concentration of A is >80%, set the single drop volume of the syringe pump to 5-10 μL; (5)S norm The point corresponding to the maximum value is the titration endpoint. Record the titration volume V2 of the silver nitrate standard solution at this point and calculate the chloride ion concentration in the sample from the pipeline. C1 = C2V2*x / V1 C2 represents the concentration of the silver nitrate standard solution, in g / L; V2 is the volume of silver nitrate standard solution consumed, in mL; x is the first dilution factor; V1 is the sample volume after the first dilution, in mL.

[0025] In a specific embodiment, the high-concentration sample is brine from a salt field, concentrated evaporation liquid, or mother liquor of refined salt, etc., and the chloride ion concentration in the high-concentration sample is 50g / L~300g / L.

[0026] A specific embodiment of the present invention also provides an online detection system for implementing the above-described detection method, such as... Figure 2 As shown, it includes a sampling module, a potential analysis module, a human-computer interaction module, a reagent storage module, and a cleaning and waste disposal module; The sampling module is used to quantitatively sample from the process pipeline and filter the sample, including a sampling injection pump and a filter element; the filter element is made of polypropylene and has a pore size of 20μm. The potentiometric analysis module includes a dilution unit, a titration and sensing unit, a first multi-channel valve, and a second multi-channel valve. The dilution unit performs the first dilution of the sample and includes a first syringe pump, a dilution cup, a first magnetic stirrer, and a sampling pump. The titration and sensing unit performs the second dilution and chloride ion titration and includes a second syringe pump, a titration cup, a second magnetic stirrer, and a silver ion selective electrode. The first multi-channel valve is a six-channel valve used for switching between sample and pure water. The second multi-channel valve is a ten-channel valve used for switching between silver nitrate standard solution and pure water. Human-computer interaction module, which is used to set method parameters and view detection results; A reagent storage module, comprising multiple reagent bottles, a pure water tank, and a liquid level sensor; The cleaning and waste discharge module is used to discharge the waste liquid from pipeline cleaning and rinsing, sampling and titration in dilution cups and titration cups, and cleaning to the waste liquid tank. The above modules are connected by necessary pipes or lines.

[0027] Example 1 Sample preparation: Accurately weigh 90.87 g of analytical grade sodium chloride using a balance, dissolve it in ultrapure water and bring the volume to 500 mL, with a concentration of 181.74 g / L.

[0028] The testing process is as follows Figure 1 As shown.

[0029] (1) A 1 ml sample is accurately and quantitatively taken by a sampling injection pump, filtered through a filter cartridge, and then sent to a dilution cup; (2) The first multi-channel valve is switched to the pure water channel. 49 ml of pure water is drawn from the pure water tank and injected into the dilution cup using the first syringe pump. The first magnetic stirrer is turned on to mix the sample and diluent evenly, completing the first dilution. 2 ml of the diluted sample is taken by the sampling pump and sent to the titration cup. The second multi-channel valve is switched to the pure water channel. 38 ml of pure water is drawn from the pure water tank and injected into the titration cup using the second syringe pump. The second magnetic stirrer is turned on to stir evenly. (3) The second multi-channel valve is switched to the silver nitrate standard solution channel, and the silver nitrate standard solution (5.00 g / L) is titrated by the second injection pump. At the same time, the potential signal is collected by the silver ion selective electrode and sent to the system. The system outputs the first derivative DE / DV in real time. The original DE / DV sequence is normalized by a nonlinear normalization function, which is shown below:

[0030] S norm The normalized output signal has a value that is stabilized in the range [0, A]. A is the normalized amplitude, which defines the upper limit of the output signal and eliminates the influence of the absolute amplitude of the original signal. Its value is 60. The steepness of the curve from 0 to A, controlled by constants K and n, directly affects the sensitivity of identifying the endpoint jump. K is set to 100 and n to 1. (4) Real-time judgment of S norm The relationship with A is used to adjust the speed of the titration pump. Specifically: when S... norm When ≤20%A, set the single drop volume of the syringe pump to 100μL; when 20%A < S norm When S ≤ 80%A, set the single drop volume of the syringe pump to 10-50 μL; when S norm When the concentration of A is >80%, set the single drop volume of the syringe pump to 5-10 μL; (5)S norm The point corresponding to the maximum value is the titration endpoint. Record the titration volume V2 of the silver nitrate standard solution at this point and calculate the chloride ion concentration in the sample from the pipeline. C1 = C2V2*x / V1 C2 represents the concentration of the silver nitrate standard solution, in g / L; V2 is the volume of silver nitrate standard solution consumed, in mL; x represents the first dilution factor, which is 50 in this embodiment; V1 is the sample volume after the first dilution, which is 2 ml in this example.

[0031] The statistics are shown in the table below: 1 0 0 2 0.1 2 3 0.2 1 4 0.3 1 5 0.4 2 6 0.5 2 7 0.6 3 8 0.7 3 9 0.8 4 10 0.9 7 11 1 11 12 1.025 13 13 1.05 15 14 1.075 16 15 1.1 22 16 1.125 25 17 1.15 30 18 1.175 35 19 1.2 37 20 1.225 40 21 1.25 42 22 1.275 43 23 1.3 43 24 1.325 44 26 1.335 45 27 1.345 46 28 1.355 48 29 1.365 50 30 1.375 51 31 1.385 52 32 1.395 53 33 1.405 54 34 1.415 54 35 1.425 55 36 1.435 56 37 1.445 56 38 1.455 57 39 1.465 58 40 1.475 58 41 1.485 57 42 1.495 56 43 1.505 53 44 1.515 51 The endpoint of the dynamic titration was determined to be 1.465 mL. Substituting this into the formula: C1 = C2V2*x / V1 = 183.125 g / L.

[0032] After the test is completed, both the first and second multi-channel valves are switched to the pure water channel to draw pure water and rinse the pipes, dilution cups and titration cups. The waste liquid is discharged to the waste liquid tank through the drain valve.

[0033] Comparative Example 1 The comparative dilution titration procedure is largely the same as in Example 1. The first derivatives (DE / DV) obtained are not normalized. The data collection is shown in the table below: 1 0 0 2 0.05 8 3 0.1 4 4 0.15 3 5 0.2 2 6 0.25 2 7 0.3 2 8 0.35 3 9 0.4 3 10 0.45 3 11 0.5 4 12 0.55 4 13 0.6 4 14 0.65 5 15 0.7 5 16 0.75 7 17 0.8 8 18 0.85 10 19 0.9 13 20 0.95 16 21 1 22 22 1.05 33 23 1.1 57 24 1.15 103 25 1.2 162 26 1.25 228 27 1.3 330 28 1.35 583 29 1.4 1062 30 1.45 1568 31 1.5 3204 32 1.55 1644 33 1.6 740 34 1.65 638 35 1.7 345 36 1.75 297 37 1.8 237 Determine the titration endpoint volume as 1.50 mL, and substitute it into the formula: C1 = C2V2*x / V1 = 187.5 g / L.

[0034] Comparing the data from the examples and the comparative examples, it can be seen that (1) detection accuracy (titration resolution): the titration speed is adjusted in real time. In the early stage of titration, the titration speed is increased, and in the later stage of titration (S norm When >80%A), the titration speed slows down (the volume of a single drop decreases), and the detection accuracy is improved by 5 times (from 50μL / drop to 10μL / drop); (2) Accuracy: The prepared concentration is 181.74g / L; the normalized dynamic titration concentration is 183.125g / L, the absolute error is 1.385g / L, and the accuracy is 100.8%; the first derivative is used as the basis for titration concentration of 187.5g / L, the absolute error is 5.8g / L, and the accuracy is 103.2%.

[0035] The above description of the embodiments is only for illustrating the technical concept and features of the present invention. Its purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. Those skilled in the art can obviously easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative effort. Therefore, the above embodiments should not be used to limit the scope of protection of the present invention. All improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for detecting chloride ions in high-concentration samples used in the salt-making industry, characterized in that, Includes the following steps: (1) Samples are taken from the process pipeline in a cyclical manner to ensure the real-time nature of the samples; (2) The sample was diluted twice to ensure that the concentration of the sample fell within the optimal detection range; (3) Input the diluted sample into the titration system and perform titration using potentiometric titration. Output the first derivative DE / DV in real time. Use a nonlinear normalization function to normalize the original DE / DV sequence. The nonlinear normalization function is shown below: ; S norm The normalized output signal has a value that is stabilized in the range [0, A]. A is the normalized amplitude, which defines the upper limit of the output signal and eliminates the influence of the absolute amplitude of the original signal. Its value is 60. The steepness of the curve from 0 to A, controlled by constants K and n, directly affects the sensitivity of identifying the endpoint jump. K is set to 100 and n to 1. (4) Real-time judgment of S norm The relationship with A is used to adjust the speed of the titration pump to achieve dynamic titration. Specifically: when S... norm When ≤20%A, set the single drop volume of the syringe pump to 100μL; when 20%A < S norm When S ≤ 80%A, set the single drop volume of the syringe pump to 10-50 μL; when S norm When A > 80%, set the single drop volume of the syringe pump to 5-10 μL; (5)S norm The point corresponding to the maximum value is the titration endpoint. Record the titration volume V2 of the silver nitrate standard solution at this point and calculate the chloride ion concentration in the sample from the pipeline: C1 = C2Vx / V1 C2 represents the concentration of the silver nitrate standard solution, in g / L; V2 is the volume of silver nitrate standard solution consumed, in mL; x is the first dilution factor; V1 is the sample volume after the first dilution, in mL.

2. The method for detecting chloride ions in high-concentration samples used in the salt-making industry according to claim 1, characterized in that: The high-concentration sample is salt field brine, evaporation concentrate, or refined salt mother liquor.

3. The method for detecting chloride ions in high-concentration samples used in the salt-making industry according to claim 2, characterized in that: The chloride ion concentration in the high-concentration sample was 50 g / L to 300 g / L.

4. The method for detecting chloride ions in high-concentration samples used in the salt-making industry according to claim 1, characterized in that: The two dilution processes are as follows: the sample obtained from the process pipeline is diluted 40-60 times, and an appropriate amount of the diluted sample is further diluted 10-30 times.

5. An online detection system for the method described in any one of Examples 1 to 4, characterized in that, include: A sampling module, which is used to sample from the process pipeline and filter the sample, includes a sampling injection pump and a filter element; The potential analysis module includes a dilution unit, a titration and sensing unit, a first multi-channel valve, and a second multi-channel valve. The dilution unit is used to perform the first dilution of the sample and includes a first syringe pump, a dilution cup, a first magnetic stirrer, and a sampling pump. The titration and sensing unit is used to perform the second dilution and chloride ion titration and includes a second syringe pump, a titration cup, a second magnetic stirrer, and a silver ion selective electrode. Human-computer interaction module, which is used to set method parameters and view detection results; A reagent storage module, comprising multiple reagent bottles, a pure water tank, and a liquid level sensor; The cleaning and waste discharge module is used to discharge the waste liquid from pipeline cleaning and rinsing, sampling and titration in dilution cups and titration cups, and cleaning to the waste liquid tank.

6. The online detection system according to claim 5, characterized in that: The filter element is a polypropylene filter element with a pore size of 20μm.

7. The online detection system according to claim 5, characterized in that: The first multi-channel valve is a six-channel valve used for switching between sample and pure water; the second multi-channel valve is a ten-channel valve used for switching between silver nitrate standard solution and pure water.

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