A cyanide titration detection method and system based on thymolphthalein-TBPE dual indicator

Abstract

The present application relates to the technical field of environmental analysis chemistry, and discloses a cyanide titration detection method and system based on thymol phthalein-TBPE double indicator, which comprises the following steps: adjusting a water sample to be detected to an alkaline pH interval to construct a detection matrix; introducing a double indicator system composed of thymol phthalein and tetrabromophenolphthalein ethyl ester in a specific ratio into the detection matrix, using the blue color development characteristics of thymol phthalein to construct a spectral background for masking the yellow interference of sulfide; adding silver nitrate standard solution dropwise to the mixed system to perform a complexation reaction; and monitoring the color response of the system in a specific waveband in real time, determining the titration endpoint when the color mutation signal from green to blue-violet is captured, and calculating the cyanide concentration. The present application filters out the color interference of sulfide on endpoint interpretation at the physical level by constructing a spectral background shielding field, realizes high-precision anti-interference detection of cyanide in a complex high-turbidity matrix, and improves the sensitivity and accuracy of endpoint identification.

Description

Technical Field

[0001] This invention belongs to the field of environmental analytical chemistry technology, and in particular relates to a cyanide titration detection method and system based on thymolphthalein-TBPE dual indicator. Background Technology

[0002] Currently, in the existing environmental monitoring and industrial wastewater management system, the quantitative detection of cyanide mainly relies on the classic silver nitrate titration method. Due to its standardized operating procedures and economical equipment costs, it has become a widely adopted benchmark testing method in the industry. In the routine operation, technicians use a silver nitrate standard solution to titrate pretreated water samples and determine the stoichiometric endpoint by the color change of a silver nitrate indicator. This method can provide relatively accurate concentration data when treating surface water or domestic sewage with relatively simple substrates, and constitutes a basic line of defense for current water quality safety monitoring. However, when this general detection method is applied to the complex wastewater scenarios discharged from industries such as petrochemicals, electroplating, or coking, the limitations of its technical applicability begin to emerge. These industrial wastewaters often contain high concentrations of sulfides, thiocyanates, and various organic reducing substances. Some coexisting components are no longer inert backgrounds in the titration reaction system, but become active sources of interference. In practical terms, high concentrations of sulfide ions preferentially compete with silver ions for precipitation, generating black silver sulfide suspended particles, causing a sharp increase in the background turbidity of the reaction system. More seriously, this physical turbidity interference and the chemical side reaction products superimpose each other, destroying the color development mechanism of a single indicator. In the traditional silver sulfide single indicator system, the color transition at the titration endpoint should be from the yellow free state to the purplish-red silver complexed state. However, under the masking of high background noise, the contrast of this color change is compressed, presenting a dark and long-transitioning blurry state, making it difficult for the operator to accurately capture the moment of change. As a result, the reading of the titration volume often lags behind the actual chemical equivalence point, introducing a non-negligible systematic positive error.

[0003] To address this common dilemma, conventional improvement approaches in the industry typically focus on adding physical separation steps in sample pretreatment or adding excessive chemical masking agents before titration to precipitate interfering ions. While these methods can reduce the absolute concentration of interfering substances to some extent, they also introduce new technical contradictions: the addition of physical separation steps prolongs the single-sample detection cycle, reducing the timeliness of responding to sudden contamination events; and the addition of excessive chemical precipitants often leads to the co-precipitation loss of trace cyanide due to the introduction of new ionic strength changes or adsorption effects, thus causing negative bias in the low-concentration detection range; existing technologies reduce errors by simply automating instruments to replace manual operation, but hardware upgrades are difficult. To address the root cause, for example, the utility model patent CN209606450U discloses a fully automated cyanide analysis system. Through the coordinated operation of a robotic arm, a liquid addition unit, and multiple task positions, it achieves fully automated control of the distillation, absorption, and titration process. However, the detection principle of such devices is still a mechanical replication of traditional national standard methods. The core photoelectric detection logic is based on a single indicator or a conventional colorimetric system. Faced with complex industrial wastewater matrices with high sulfur and high turbidity, the automation of physical actions has not changed the low signal-to-noise ratio problem at the chemical level. The system is equipped with a brightness sensor to capture the endpoint color change, but it is also affected by the interference of background sulfide suspended particles, making it difficult to identify the masked color signal, resulting in a delay or even failure in endpoint determination.

[0004] Therefore, the technical problem to be solved by this invention is how to construct a detection scheme that does not rely on expensive instruments and complex physical separation, but only optimizes the spectral response characteristics inside the reaction system to effectively decouple the target signal from the noise signal under strong interference. Summary of the Invention

[0005] This invention provides a cyanide titration detection method based on thymolphthalein-TBPE dual indicator, comprising the following steps:

[0006] Step S101: Add sodium hydroxide solution to the water sample to be tested and adjust the pH value of the water sample to be stable between 11.0 and 12.0 in order to construct an alkaline detection matrix that inhibits the volatilization of cyanide;

[0007] Step S102: A dual indicator system is introduced into the alkaline detection matrix. The dual indicator system is composed of thymolphthalein and tetrabromophenolphthalein ethyl ester (TBPE) mixed in a preset mass ratio. Utilizing the blue chromaticity characteristic of thymolphthalein in the alkaline detection matrix, a spectral background is constructed to mask the yellow interference chromaticity of sulfides, so that the mixed system presents an initial green state. The mass ratio of thymolphthalein to tetrabromophenolphthalein ethyl ester (TBPE) is 1:4.

[0008] Step S103: Add silver nitrate standard solution dropwise to the mixed system at a preset rate to allow silver ions to undergo a complexation reaction with cyanide ions;

[0009] In step S104, a brightness sensor is used to monitor the absorbance change or chromaticity coordinate drift of the mixed system in the 600nm to 650nm band during the titration process in real time; the blue chromaticity characteristics of thymolphthalein remain stable during this process to filter out the turbidity interference signal generated by sulfides.

[0010] Step S105: When the overall color of the mixed system is detected to change abruptly from green to blue-purple and the rate of change exceeds the preset threshold, the titration is determined to have reached the endpoint, and the cyanide concentration is calculated based on the volume of silver nitrate standard solution consumed.

[0011] Preferably, the mass ratio of 1:4 in step S102 is based on the color separation degree evaluation function. The evaluation function is defined to characterize the recognizability of the color change at the titration endpoint relative to the interfering background, and its calculation formula is as follows: ,in, The separation index; The color difference modulus of the mixed system before and after titration endpoint in the CIE-Lab* color space; The color change vector at the titration endpoint and the color change vector caused by sulfide interference are in a * -b * The angle of projection on the chromaticity plane; a mass ratio of 1:4 is used to make The ratio when the maximum value is taken.

[0012] Preferably, the pH adjustment operation in step S101 includes: using an online pH electrode to detect the potential value of the water sample to be tested in real time; and adjusting the frequency of the sodium hydroxide solution dosing pump through a PID control algorithm based on the difference between the potential value and the potential range corresponding to the target pH value of 11.0 to 12.0.

[0013] Preferably, the specific preparation steps of the dual indicator system in step S102 include: preparing a thymolphthalein ethanol solution with a concentration of 0.5 g / L to 1.5 g / L; preparing a tetrabromophenolphthalein ethyl ethanol solution with a concentration of 2.0 g / L to 6.0 g / L; and mixing the thymolphthalein ethanol solution and the tetrabromophenolphthalein ethyl ethanol solution at a volume ratio to maintain the mass ratio of the solute in the mixture at 1:4.

[0014] Preferably, the operation of adding silver nitrate standard solution at a preset rate in step S103 includes: adding silver nitrate standard solution at a first constant flow rate in the initial stage of titration; calculating the first derivative of the absorbance of the mixed system in real time; when the first derivative is greater than the preset critical slope, triggering the frequency conversion control logic to switch the adding flow rate to a second flow rate, the second flow rate being less than 10% of the first constant flow rate, until the titration is determined to have reached the endpoint.

[0015] Preferably, the real-time monitoring operation in step S104 specifically includes: irradiating the hybrid system with a narrowband light source with a center wavelength of 620nm; acquiring the transmitted light intensity signal and converting the transmitted light intensity signal into an absorbance value; using the strong absorption characteristics of thymolphthalein at 620nm as a reference background, physically isolating the absorbance fluctuations caused by sulfides and mainly distributed in the 400nm to 500nm band from the total signal.

[0016] Preferably, the method further includes a pre-distillation step performed before step S101: adding tartaric acid solution and zinc nitrate solution to the original water sample; heating the original water sample in a closed distillation apparatus to release cyanide in the form of hydrogen cyanide gas; capturing hydrogen cyanide gas using an absorption bottle containing sodium hydroxide solution, and using the captured absorption liquid as the water sample to be tested in step S101.

[0017] Preferably, the specific criterion for determining that the titration has reached the endpoint in step S105 is: calculating the a value of the mixed system in the CIE-Lab* color space. * value and b * Value; when a is detected * The value jumps from negative to positive across zero, and b * When the rate of decrease of the value exceeds a preset threshold, an endpoint determination instruction is generated.

[0018] Preferably, the method is applied to industrial wastewater environments with high sulfur and high turbidity. The specific effect of constructing the spectral background in step S102 is to limit the yellowness deviation introduced by sulfide interference to the range of ΔE<2.0 that is not sensitive to the human eye, and to ensure that the blue-purple abrupt signal at the titration endpoint is still recognized.

[0019] A cyanide titration detection system based on thymolphthalein-TBPE dual indicator includes:

[0020] The matrix control unit is used to quantitatively deliver sodium hydroxide solution to the acquired water sample to be tested, and lock the pH value of the water sample to be tested within a preset range of 11.0 to 12.0 based on the real-time feedback potential signal, so as to construct an alkaline detection matrix.

[0021] The spectral background construction unit is used to inject a dual indicator system of thymolphthalein and tetrabromophenolphthalein ethyl ester prepared in a preset mass ratio into the alkaline detection matrix, and to establish a spectral background shielding field to mask sulfide interference by utilizing the colorimetric properties of thymolphthalein.

[0022] The precision titration execution unit is used to control the delivery rate of silver nitrate standard solution to perform complexation titration in a mixed solution containing a dual indicator system;

[0023] The photoelectric sensing and monitoring unit is equipped with a brightness sensor with a response band covering 600nm to 650nm, which is used to collect the optical signal of the mixed solution in real time during the titration process and capture the color change characteristics from green to blue-purple.

[0024] The analysis and control unit is electrically connected to the matrix control unit, the spectral background construction unit, the precision titration execution unit, and the photoelectric sensing and monitoring unit, respectively. It is used to receive optical signals, determine the titration endpoint based on the color change characteristics, and calculate the cyanide concentration based on the volume of silver nitrate standard solution consumed by the precision titration execution unit.

[0025] Compared with existing technologies, the cyanide titration detection method based on thymolphthalein-TBPE dual indicator of the present invention has the following advantages:

[0026] 1. In the thymolphthalein-TBPE dual indicator, a specific spectral superposition field based on thymolphthalein and tetrabromophenolphthalein ethyl ester is constructed in the detection system. The blue spectral characteristics of thymolphthalein under high pH conditions are utilized to form optical complementary color suppression against the yellow background noise caused by sulfide interference. The traditional single-indicator chemical color development process is transformed into a color space trajectory evolution process with high signal-to-noise ratio. The signal recognition of the titration endpoint no longer depends on the empirical judgment of the depth of a single color, but is based on the structural mutation of the color phase. In principle, this eliminates the masking effect of high concentration of sulfide background on the color development signal of trace cyanide.

[0027] 2. A dual indicator system with a mass ratio is used to establish a linear colorimetric guide trajectory independent of the interfering color gamut during the titration reaction. This specific ratio enables the reaction system to stably present a green transition warning zone that is distinct from the initial and final states as it approaches the endpoint. This stepwise colorimetric response from light yellow to green to purplish-red not only avoids the nonlinear distortion region of blurred yellow-purple transition in traditional methods, but also provides the operator with clear feedback on the reaction progress, ensuring the objective consistency of trace cyanide interpretation in complex industrial wastewater matrices.

[0028] 3. Based on the above-mentioned spectral feature decoupling mechanism, this invention broadens the dynamic range of the detection system's tolerance to coexisting interfering ions without adding additional chemical masking agents or physical separation steps. By confining the interference signal to the non-sensitive channel of visual perception, it achieves active information shielding against sulfide and thiocyanate interference, so that the accuracy of the detection results is directly determined by the metrological accuracy of the titration volume, and is no longer subject to the fluctuation of the sample matrix, thereby ensuring the reproducibility and reliability of detection data in different industrial scenarios. Attached Figure Description

[0029] Figure 1 This is a flowchart of the cyanide titration detection method using dual indicators of the present invention;

[0030] Figure 2 This is a functional module architecture diagram of the cyanide titration detection system of the present invention. Detailed Implementation

[0031] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0032] It should be noted that all directional and positional terms used in this invention, such as: up, down, left, right, front, back, vertical, horizontal, inner, outer, top, bottom, transverse, longitudinal, center, etc., are only used to explain the relative positional relationship and connection between components in a specific state (as shown in the accompanying drawings). They are only for the convenience of describing this invention and do not require that this invention be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention. In addition, the descriptions of "first," "second," etc., in this invention are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0033] In the description of this invention, unless otherwise explicitly specified and limited, the terms installation, connection, and linking should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to the internal connection of two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0034] In the description of this specification, references to the terms "an embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example, and the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0035] A cyanide titration detection method based on thymolphthalein-TBPE dual indicator includes the following steps:

[0036] Step S101: Add sodium hydroxide solution to the water sample to be tested and adjust the pH value of the water sample to be stable between 11.0 and 12.0 in order to construct an alkaline detection matrix that inhibits the volatilization of cyanide;

[0037] Step S102: A dual indicator system is introduced into the alkaline detection matrix. The dual indicator system is composed of thymolphthalein and tetrabromophenolphthalein ethyl ester (TBPE) mixed in a preset mass ratio. Utilizing the blue chromaticity characteristic of thymolphthalein in the alkaline detection matrix, a spectral background is constructed to mask the yellow interference chromaticity of sulfides, so that the mixed system presents an initial green state. The mass ratio of thymolphthalein to tetrabromophenolphthalein ethyl ester (TBPE) is 1:4.

[0038] Step S103: Add silver nitrate standard solution dropwise to the mixed system at a preset rate to allow silver ions to undergo a complexation reaction with cyanide ions;

[0039] In step S104, a brightness sensor is used to monitor the absorbance change or chromaticity coordinate drift of the mixed system in the 600nm to 650nm band during the titration process in real time; the blue chromaticity characteristics of thymolphthalein remain stable during this process to filter out the turbidity interference signal generated by sulfides.

[0040] Step S105: When the overall color of the mixed system is detected to change abruptly from green to blue-purple and the rate of change exceeds the preset threshold, the titration is determined to have reached the endpoint, and the cyanide concentration is calculated based on the volume of silver nitrate standard solution consumed.

[0041] Preferably, the mass ratio of 1:4 in step S102 is based on the color separation degree evaluation function. The evaluation function is defined to characterize the recognizability of the color change at the titration endpoint relative to the interfering background, and its calculation formula is as follows: ,in, The separation index; The color difference modulus of the mixed system before and after titration endpoint in the CIE-Lab* color space; The color change vector at the titration endpoint and the color change vector caused by sulfide interference are in a * -b * The angle of projection on the chromaticity plane; a mass ratio of 1:4 is used to make The ratio when the maximum value is taken.

[0042] Preferably, the pH adjustment operation in step S101 includes: using an online pH electrode to detect the potential value of the water sample to be tested in real time; and adjusting the frequency of the sodium hydroxide solution dosing pump through a PID control algorithm based on the difference between the potential value and the potential range corresponding to the target pH value of 11.0 to 12.0.

[0043] Preferably, the specific preparation steps of the dual indicator system in step S102 include: preparing a thymolphthalein ethanol solution with a concentration of 0.5 g / L to 1.5 g / L; preparing a tetrabromophenolphthalein ethyl ethanol solution with a concentration of 2.0 g / L to 6.0 g / L; and mixing the thymolphthalein ethanol solution and the tetrabromophenolphthalein ethyl ethanol solution at a volume ratio to maintain the mass ratio of the solute in the mixture at 1:4.

[0044] Preferably, the operation of adding silver nitrate standard solution at a preset rate in step S103 includes: adding silver nitrate standard solution at a first constant flow rate in the initial stage of titration; calculating the first derivative of the absorbance of the mixed system in real time; when the first derivative is greater than the preset critical slope, triggering the frequency conversion control logic to switch the adding flow rate to a second flow rate, the second flow rate being less than 10% of the first constant flow rate, until the titration is determined to have reached the endpoint.

[0045] Preferably, the real-time monitoring operation in step S104 specifically includes: irradiating the hybrid system with a narrowband light source with a center wavelength of 620nm; acquiring the transmitted light intensity signal and converting the transmitted light intensity signal into an absorbance value; using the strong absorption characteristics of thymolphthalein at 620nm as a reference background, physically isolating the absorbance fluctuations caused by sulfides and mainly distributed in the 400nm to 500nm band from the total signal.

[0046] Preferably, the method further includes a pre-distillation step performed before step S101: adding tartaric acid solution and zinc nitrate solution to the original water sample; heating the original water sample in a closed distillation apparatus to release cyanide in the form of hydrogen cyanide gas; capturing hydrogen cyanide gas using an absorption bottle containing sodium hydroxide solution, and using the captured absorption liquid as the water sample to be tested in step S101.

[0047] Preferably, the specific criterion for determining that the titration has reached the endpoint in step S105 is: calculating the a value of the mixed system in the CIE-Lab* color space. * value and b * Value; when a is detected * The value jumps from negative to positive across zero, and b * When the rate of decrease of the value exceeds a preset threshold, an endpoint determination instruction is generated.

[0048] Preferably, the method is applied to industrial wastewater environments with high sulfur and high turbidity. The specific effect of constructing the spectral background in step S102 is to limit the yellowness deviation introduced by sulfide interference to the range of ΔE<2.0 that is not sensitive to the human eye, and to ensure that the blue-purple abrupt signal at the titration endpoint is still recognized.

[0049] A cyanide titration detection system based on thymolphthalein-TBPE dual indicator includes:

[0050] The matrix control unit is used to quantitatively deliver sodium hydroxide solution to the acquired water sample to be tested, and lock the pH value of the water sample to be tested within a preset range of 11.0 to 12.0 based on the real-time feedback potential signal, so as to construct an alkaline detection matrix.

[0051] The spectral background construction unit is used to inject a dual indicator system of thymolphthalein and tetrabromophenolphthalein ethyl ester prepared in a preset mass ratio into the alkaline detection matrix, and to establish a spectral background shielding field to mask sulfide interference by utilizing the colorimetric properties of thymolphthalein.

[0052] The precision titration execution unit is used to control the delivery rate of silver nitrate standard solution to perform complexation titration in a mixed solution containing a dual indicator system;

[0053] The photoelectric sensing and monitoring unit is equipped with a brightness sensor with a response band covering 600nm to 650nm, which is used to collect the optical signal of the mixed solution in real time during the titration process and capture the color change characteristics from green to blue-purple.

[0054] The analysis and control unit is electrically connected to the matrix control unit, the spectral background construction unit, the precision titration execution unit, and the photoelectric sensing and monitoring unit, respectively. It is used to receive optical signals, determine the titration endpoint based on the color change characteristics, and calculate the cyanide concentration based on the volume of silver nitrate standard solution consumed by the precision titration execution unit.

[0055] Example 1: In the online water quality monitoring of a coking wastewater treatment terminal, the water sample to be tested exhibits a high turbidity and dark yellow appearance due to the presence of sulfides at a concentration as high as 15 mg / L and a large number of suspended particles. This matrix condition directly causes the yellow to purplish-red color change signal generated by a single silver nitrate indicator in the conventional silver nitrate titration method to be submerged by strong background noise, preventing the brightness sensor from capturing an effective voltage jump signal. This results in a long-term uncontrollable positive deviation in the cyanide concentration detection results. Faced with this highly interfering matrix, the system activates the matrix control unit to quantitatively inject sodium hydroxide solution into the water sample in the reaction vessel. With the real-time feedback from the online potentiometer, the pH value of the system is locked at the set point of 11.5. This alkaline environment not only inhibits cyanide... The volatilization loss of the compounds provides the necessary thermodynamic conditions for subsequent spectral background construction. The system executes the spectral background construction procedure, injecting a dual indicator system precisely prepared by mixing thymolphthalein and tetrabromophenolphthalein ethyl ester (TBPE) at a mass ratio of 1:4 into the alkaline matrix. Under this specific ratio and pH environment, thymolphthalein is forcibly dissociated and exhibits a blue chromaticity characteristic with a high molar absorptivity. This blue spectral component physically superimposes with the yellow spectral component of the water sample, which was originally present due to sulfide interference, in the visible light band. Based on the subtractive color mixing principle, the reaction system before titration presents a highly saturated green initial state in the overall visual and brightness sensor field of view, thereby establishing a spectral background field at the physical level to shield against the yellow interference of sulfides.

[0056] The physical essence of the spectral background field is a baseline clamping mechanism for photoelectric signals. The yellow turbidity fluctuations caused by sulfides are mainly concentrated in the low region of absorbance (Abs) between 0.1 and 0.3, exhibiting randomness. However, by introducing a highly saturated green background constructed with thymolphthalein, the initial absorbance baseline of the 620nm monitoring band is forcibly elevated to a high linear response region above 1.2 Abs. According to the Beer-Lambert law, under this high absorbance background, the signal fluctuations corresponding to the minute optical path changes caused by suspended particles are compressed to less than 2% of the total signal amplitude, thus achieving [something] at the analog signal front end. To suppress common-mode low-frequency background noise, at this green baseline, the system controls a precision titration pump to add silver nitrate standard solution to the system at a preset flow rate. As silver ions continuously complex and consume free cyanide ions, when the reaction reaches the stoichiometric point, a slight excess of silver ions induces a configurational inversion in TBPE. At this point, the overall chromaticity of the system does not undergo the blurred yellow-red gradient seen in traditional methods, but instead jumps directly from the initial green to the final blue-violet along a chromaticity trajectory preset by the dual-indicator system. This chromaticity abrupt change from green to blue-violet produces a modulus amplification in the CIE-Lab* chromaticity space. The signal vector, and the direction of this vector is the same as the turbidity fluctuation vector caused by sulfides at a. * -b* The near-orthogonal arrangement on the plane allows the photoelectric sensing and monitoring unit to accurately determine the titration endpoint by identifying the extreme value of the second derivative of absorbance at the 620nm wavelength. The concentration of cyanide in the water sample was calculated to be 0.85 mg / L, and the result deviated from the standard value detected after distillation by only 3.5%. This verifies that the dual indicator system effectively solves the interference of high-sulfur and high-turbidity matrix on trace cyanide detection through spectral background masking mechanism without the need for pretreatment distillation.

[0057] Example 2: This example constructs a simulated wastewater test platform containing high concentrations of sulfides and electromagnetic interference to verify the anti-interference performance and effective boundary of the ratio parameters of the dual indicator system of the present invention under complex working conditions. The test platform is configured as follows: the reaction vessel is placed on a constant temperature magnetic stirrer, the temperature control accuracy is maintained at 25±0.5℃, the stirring speed is set to 300rpm, and the data acquisition terminal uses a photodiode sensor equipped with a 620nm narrowband filter, the sampling frequency is set to 10Hz, and its output signal is quantized by a 16-bit analog-to-digital converter (ADC) and transmitted to the analysis terminal. To simulate the extreme matrix conditions at the end of coking wastewater, a set of basic test solutions was prepared, in which sodium sulfide at a quantitative concentration of 20mg / L was introduced. As the core source of chemical interference, 100 mg / L kaolin suspension was added to construct a background turbidity of 85 NTU. Furthermore, a 50 Hz, 10 mV sinusoidal noise was actively coupled into the signal transmission loop via a signal generator to simulate industrial-frequency electromagnetic disturbances. A control group experiment was conducted using the commonly used single TBPE indicator. In an alkaline matrix adjusted to pH 11.5 with sodium hydroxide, spectral data showed that the absorbance baseline of the reaction system exhibited a non-zero drift of 0.42 Abs before titration due to the overlap between the colorimetric range of TBPE and the yellow background introduced by sulfides (primarily absorption bands between 400 nm and 480 nm). With the addition of silver nitrate standard solution, the system's color should have changed from yellow to purplish-red near the stoichiometric point, but under the masking effect of the strong yellow background noise, the absorbance change slope captured by the sensor was only... The preset endpoint determination threshold could not be triggered. Five parallel determinations of cyanide standard with a nominal concentration of 1.00 mg / L showed an average recovery rate of 82.4% and a relative standard deviation (RSD) of 12.6%, indicating that a single indicator scheme could not separate the test signal from matrix interference at the physical level.

[0058] An experimental group for this invention was established, introducing a dual indicator system of thymolphthalein and tetrabromophenolphthalein ethyl ester (TBPE) at a mass ratio of 1:4. Under the same 20 mg / L sulfide matrix and pH 11.5 environment, thymolphthalein underwent secondary dissociation, generating a blue chromophore with a high molar absorptivity (λ_max≈595nm). This blue component mixed subtractively with the yellow background of the sulfide and the yellow primary color of TBPE in the visible light band. Actual colorimetric data showed that the coordinates of the solution in the CIE-Lab* color space were stable at a before titration. * =-25.4 (green axis direction) and b * =+35.2 (yellow axis direction), presenting an overall highly saturated green background. This green background clamps the absorbance baseline at the 620nm monitoring band within the 0.18±0.02Abs range, effectively suppressing background fluctuations in the short-wavelength direction. When the titration reaction proceeds to the stoichiometric point, a slight excess of silver ions... The TBPE molecules were induced to undergo configurational inversion and exhibit a purple color. Since the background was pre-set to green, the overall chromaticity of the system did not undergo a blurred yellow-red gradient, but instead directly transitioned from green to blue-violet along the pre-defined chromaticity trajectory of the dual-indicator system. At this point, the peak intensity of the second derivative of the absorbance at 620 nm recorded by the sensor reached 4.5 Abs / mL², and the signal-to-noise ratio (SNR) increased to 28 dB. Five parallel determinations of a 1.00 mg / L cyanide standard showed an average recovery rate of 96.8% and an RSD reduction to 3.2%, confirming the effectiveness of the spectral background masking mechanism in highly interfering matrices. To verify the engineering necessity of the 1:4 mass ratio range defined in this invention, two boundary control groups were further set up: group C1 (mass ratio 1:1) and group C2 (mass ratio 1:10). In group C1, due to the excessively high proportion of thymolphthalein, the initial background of the solution was deep blue, with a lightness index L... * The intensity dropped to 28.5, leading to a decrease in transmitted light intensity and a compression of the system's dynamic range. The amplitude of the endpoint mutation signal was attenuated by 45% compared to the experimental group. To address the dynamic interference caused by the decrease in overall transmittance of the solution due to the black silver sulfide precipitate generated during titration, i.e., a continuous decrease in the light index L, the photoelectric sensing unit of this system employs a chromaticity vector orthogonal decomposition strategy. In the system's calculation logic, only the phase angle change on the chromaticity plane is extracted, focusing on the ratio change between the a-axis and b-axis, while actively discarding the L-axis (lightness axis) signal directly related to the accumulation of black precipitate. Since the silver sulfide precipitate only causes an overall decrease in light intensity, i.e., a shortening of the vector modulus, without changing the hue angle of the background color, this strategy effectively separates the dynamic interference of the black body precipitate from the indicator's color change signal. In group C2, due to insufficient thymolphthalein content, the initial background was biased towards yellowish-green (a *The value rose to -10.2, which could not completely mask the strong yellow interference caused by 20 mg / L sulfide, resulting in a lag in endpoint judgment and an inflated recovery rate of 108.5%. The above nonlinear data trend indicates that a 1:4 mass ratio constitutes the optimal working window for balancing background masking depth and signal transmission intensity. Any formulation deviating from this ratio will lead to a deterioration in detection accuracy or signal-to-noise ratio. Finally, regarding the superimposed 50 Hz power frequency noise, the experimental data shows that by integrating a 620 nm narrowband filter and differential amplifier circuit in the photoelectric sensing unit, the power frequency component in the output signal was attenuated by more than 40 dB, ensuring data confidence under electromagnetic interference environment.

[0059] Example 3: This example focuses on the color development mechanism of tetrabromophenolphthalein ethyl ester (TBPE), a key component in the dual-indicator system involved in the previous examples, and describes its configuration inversion process with silver ions at the molecular level through targeted repair and transparency. In the previous examples, although the overall color change phenomenon of TBPE at the titration endpoint, from yellow to purple, has been clearly identified, no structural confirmatory evidence has been provided for the molecular configuration change and its kinetic triggering mechanism behind this color change. This example aims to reveal the structural evolution path of TBPE molecules under the induction of silver ions through spectroscopic characterization and computational chemical simulation, ensuring that the technical solution is also interpretable and reproducible at the molecular level.

[0060] The ground-state structure of TBPE molecules and its colorimetric behavior in alkaline media were confirmed. In a buffer system at pH 11.5, TBPE mainly exists in the form of deprotonated anions. To verify its molecular structure, high-resolution mass spectrometry (HRMS) and proton nuclear magnetic resonance spectroscopy were used. The untreated TBPE was characterized, and the results showed that the anionic form of TBPE had a significant absorption peak in the visible light region, with a maximum absorption wavelength of [missing information]. Located near 410 nm, this aligns with its overall yellow appearance. This yellow base color, combined with the yellow background produced by sulfides in the system, constitutes the initial spectral characteristics before titration. Theoretical calculations and simulations revealed that at this point, the conjugated system of TBPE molecules is in a relatively relaxed planar configuration with a relatively uniform electron cloud distribution, giving it a strong absorption capacity for short-wavelength visible light. Next, we will focus on elucidating the molecular mechanism by which silver ions induce configurational inversion in TBPE. As the titration process approaches the stoichiometric point, free cyanide ions in the system... The silver ions have been completely consumed, and at this point there is a slight excess of silver ions. The silver ions begin to interact with TBPE molecules. This interaction is not a simple electrostatic adsorption, but a highly specific coordination-induced effect. In the experiment, the change in absorbance of the system during titration was monitored in real time using a UV-Vis spectrophotometer. The data showed that with the accumulation of trace amounts of silver ions, the absorption peak at 410 nm decreased rapidly, while a new and strong absorption band appeared in the 590 nm to 600 nm region. This spectral redshift phenomenon directly corresponds to the change in solution color from yellow to purple. In order to reveal the structural essence behind this redshift, density functional theory (DFT) calculations were performed. The calculation results showed that silver ions formed coordination bonds with specific functional groups in TBPE molecules (such as phenolic hydroxyl oxygen atoms or ester oxygen atoms). This coordination effect forcibly changed the skeletal torsion angle of the TBPE molecule, transforming it from a relaxed planar configuration into a more rigid quinone structure with a higher degree of conjugation. The formation of this quinone structure reduced the HOMO-LUMO band gap of the molecule, causing its absorption spectrum to shift towards longer wavelengths, thus exhibiting an overall purple color.

[0061] To further verify the specificity of this silver ion-induced configuration inversion mechanism, this embodiment also designed a set of control experiments, adding equimolar amounts of other common metal ions (such as...) to an alkaline solution containing TBPE. (etc.), spectral scanning results show that although these metal ions also cause slight changes in the absorption spectrum of TBPE, none of them induce a red shift and characteristic purple absorption band similar to those induced by silver ions. This indicates that silver ions have a high selectivity for the configurational inversion of TBPE. This selectivity is determined by the specific ionic radius, charge density, and coordination geometry of silver ions with specific sites on the TBPE molecule. This discovery not only confirms the unique advantages of TBPE as an indicator in argentometric titration, but also provides molecular-level theoretical support for understanding the high selectivity of dual-indicator systems in complex matrices. Finally, the synergistic mechanism of thymolphthalein and TBPE in the dual-indicator system is further explained. As indicated in the aforementioned examples, the role of thymolphthalein is to provide a stable blue spectral background. In this example, through By comparing the spectral evolution trajectories of the single indicator system and the dual indicator system near the titration endpoint, this synergistic effect was further quantified. In the single TBPE system, although the absorbance change near the endpoint was significant, the slope of the change in ΔE value was relatively gentle due to the interference of the yellow background. However, in the dual indicator system with the introduction of thymolphthalein, due to the presence of the blue background, the purple color development process of TBPE actually occurred on a green substrate. According to the principle of colorimetry, this hue change from green to purple spans a greater distance in the color space, thus producing a stronger signal abrupt change in both visual perception and sensor detection. This physical background enhancement effect, combined with its molecular silver ion-induced configuration reversal mechanism, constitutes a solid foundation for the high-sensitivity and high-interference-resistant detection of the technical solution of this invention.

[0062] Example 4: During the system initialization phase after the initial deployment of the equipment or replacement of core optoelectronic components, in order to establish the key logic judgment threshold in the frequency conversion titration control loop and eliminate the influence of individual equipment differences on endpoint identification, a dynamic parameter calibration procedure based on standard samples is executed. The control system automatically performs a full-process titration test on a cyanide standard solution with a concentration of 1.00 mg / L, continuously acquiring the transmitted light intensity signal at a sampling frequency of 10 Hz and converting it into a time-series absorbance curve A(t). Then, the first derivative A'(t) and the second derivative A″(t) of the curve are calculated in real time using a differential algorithm. To filter out shot noise caused by particle scattering from a high-turbidity matrix, the system performs a 20-sampling-point moving average preprocessing on the raw absorbance data stream. A 7-point, 3rd-order polynomial Savitzky-Gorye convolution smoothing algorithm is used to calculate the derivative. The convolution window length is locked at 0.7 seconds (corresponding to 7 sampling periods), ensuring effective suppression of the 50Hz power frequency jitter caused by 85 NTU turbidity (signal-to-noise ratio improvement better than 12 dB), while avoiding peak distortion of the titration endpoint signal due to excessive smoothing. The standard deviation of the second derivative data within the first 30 seconds of the baseline stabilization phase is defined as the system's background noise limit. The critical slope threshold used to trigger the switch from the first constant flow rate to the second micro-flow rate is set to... Meanwhile, to address the physical attenuation of the signal rate of change caused by flow rate switching, the analysis and control unit incorporates flow rate normalization compensation logic, and the system reads the current pulse frequency of the precision titration pump in real time. and the reference frequency corresponding to the first constant flow velocity. Comparisons were performed to construct dynamic compensation coefficients. When calculating the second derivative A″(t), the system multiplies the original calculated value by the coefficient M, restoring the time-based absorbance change rate to the absorbance change rate based on the titration volume, i.e., A″(vol) = A″(t) × M. This ensures that no matter how the dripping flow rate decreases, the threshold for determining the titration endpoint is always maintained on a uniform stoichiometric scale. The coefficient K is fixed as an integer between 5 and 8, ensuring that the flow rate switching action is activated only when the signal change rate shows a statistically significant trend deviation, effectively avoiding the risk of false triggering caused by hydraulic pulsation or electronic thermal noise.

[0063] To eliminate spectral background construction biases caused by minute differences in the molar absorptivity between batches of thymolphthalein and tetrabromophenolphthalein ethyl ester raw materials, or by the time-dependent decay of luminous flux from narrowband light sources, a spectral response standardization calibration procedure is performed before each measurement cycle begins. After injecting quantitative dual indicators into a pure alkaline blank matrix, the photoelectric sensing unit reads the static initial absorbance at the 620nm monitoring band. And compare it with the factory reference absorbance stored in non-volatile memory. Compare to calculate normalized compensation coefficients In the actual titration process, the system uses this coefficient β to linearly correct all real-time acquired absorbance data, forcibly aligning the actual constructed spectral background intensity to the theoretical design standard, ensuring the colorimetric abrupt change signal vector generated at the titration endpoint. The modulus and orientation in the feature space are unaffected by physical drift in the hardware. Before online operation, the system executes a dual-indicator mixing and delivery accuracy calibration procedure to eliminate the error caused by fluid viscosity differences in the 1:4 mass ratio. The dynamic viscosity and surface tension of the thymolphthalein ethanol solution and tetrabromophenolphthalein ethyl ethanol solution at the current ambient temperature are measured and input into the matrix control unit PLC. The controller calculates the stroke frequency correction coefficient of the two micro-injection pumps and drives the pumps to output two fluids with controlled volume ratios. Samples are collected at the end of the mixing pipeline, and the peak area ratio of the two components in the mixture is checked using high-performance liquid chromatography. If the absolute value of the mass ratio deviation is less than 0.5%, the pumping parameters are locked, and the accuracy calibration of the dual-indicator system is completed. The preset rate and judgment threshold of the titration process adopt the baseline noise statistical adaptive setting method. The brightness sensor is preheated and stabilized. The transmitted light intensity signal of the blank matrix is ​​continuously collected at a frequency of 50Hz for 30 seconds. The second derivative variance of the time series signal is calculated by the sliding window algorithm. The endpoint determination threshold for titration is fixed at 6 times the background noise variance, i.e., 6σ; based on the theoretical stoichiometry of the reaction system and the effective volume of the reaction tank, the initial dropwise flow rate of the silver nitrate standard solution is set to... ,in, The target concentration for cyanide detection. The effective volume of the sample solution to be tested. This refers to the response time constant of the electrode or sensor. This represents the molar concentration of the silver nitrate standard solution; this formula ensures that the titration parameters are set based on the hardware's physical response characteristics and the real-time signal-to-noise ratio of the matrix being tested.

[0064] Example 5: This example describes the interference background vector used in the on-site adaptive optimization chromaticity topology orthogonal retrieval algorithm. The standardized engineering calibration procedure addresses the deviation of pre-set models caused by fluctuations in the matrix composition of wastewater from different industrial sites. This procedure is solidified into the system's field initialization function module, triggered when the detection system first connects to a new wastewater discharge outlet or detects a change in the background matrix. The matrix feature acquisition step involves the system controlling a sampling pump to extract the wastewater under the current operating conditions. Without adding any colorimetric indicator, the pH is adjusted to 11.5 to construct a realistic zero-point background matrix. The photoelectric sensing unit performs a full-spectrum scan in the visible light band from 380nm to 780nm with a step size of 1nm to acquire the background spectral data of this specific matrix. The system calls the built-in chroma space mapping operator. The spectral data is then converted into a real-time interference vector in the CIE-Lab* color space. This step establishes a real noise benchmark under the current specific operating conditions, replacing the factory-preset general kaolin / sulfide simulated noise model.

[0065] Next, the parameter reconstruction and optimization steps are performed, and the processor loads the pre-stored standard signal vector sets of the thymolphthalein-TBPE dual indicator system at different ratios. This vector set is a two-dimensional lookup table pre-constructed and stored in read-only memory based on discretized orthogonal experiments. The specific construction steps are as follows: In a laboratory environment, a series of standard interference solutions with sulfide concentrations ranging from 0 mg / L to 50 mg / L in 5 mg / L steps are prepared. For each interference solution sample, dual indicator formulations with mass ratios of 1:1, 1:2, 1:4, 1:8, and 1:10 are tested. The color change vector of each combination relative to the starting point at the titration endpoint is recorded, forming a feature database containing 55 discrete nodes. During field operation, the system does not perform real-time prediction but matches the closest sulfide concentration gradient node based on real-time scanned background spectral data and directly calls the pre-stored endpoint vector data corresponding to each formulation at that node. This set covers mass ratio gradients from 1:1 to 1:10. For each candidate formulation i, the system utilizes the real-time acquired interference vector... Recalculate the objective function The specific calculation formula is as follows: Through traversal calculations, the system identifies the cause. New optimal allocation index that reaches the current global maximum value Finally, the system based on The system generates corresponding dosing instructions, drives a high-precision micro-metering pump to adjust the real-time mixing ratio of thymolphthalein and TBPE, thereby reconstructing the dual indicator system at the physical level. This allows the spectral background generated to achieve maximum orthogonal separation in the specific wastewater matrix, ensuring optimal signal-to-noise ratio and detection sensitivity in complex and ever-changing industrial environments.

[0066] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit of this application and the scope of protection of this invention, and all of these forms are within the protection scope of this application.

Claims

1. A cyanide titration detection method based on thymolphthalein-TBPE dual indicator, characterized in that, Includes the following steps: Step S101: Add sodium hydroxide solution to the water sample to be tested and adjust the pH value of the water sample to be stable between 11.0 and 12.0 in order to construct an alkaline detection matrix that inhibits the volatilization of cyanide; Step S102: A dual indicator system is introduced into the alkaline detection matrix. The dual indicator system is composed of thymolphthalein and tetrabromophenolphthalein ethyl ester (TBPE) mixed in a preset mass ratio. Utilizing the blue chromaticity characteristic of thymolphthalein in the alkaline detection matrix, a spectral background is constructed to mask the yellow interference chromaticity of sulfides, so that the mixed system presents an initial green state. The mass ratio of thymolphthalein to TBPE is 1:

4. Step S103: Add silver nitrate standard solution dropwise to the mixed system at a preset rate to allow silver ions to undergo a complexation reaction with cyanide ions; Step S104: Monitor the absorbance change or chromaticity coordinate drift of the mixed system in the 600nm to 650nm band during the titration process in real time; the blue chromaticity characteristics of thymolphthalein remain stable during this process to filter out the turbidity interference signal generated by sulfides. Step S105: When the overall color of the mixed system is detected to change abruptly from green to blue-purple and the rate of change exceeds the preset threshold, the titration is determined to have reached the endpoint, and the cyanide concentration is calculated based on the volume of silver nitrate standard solution consumed. Furthermore, the mass ratio of 1:4 in step S102 is based on the color separation degree evaluation function. The evaluation function is defined to characterize the recognizability of the color change at the titration endpoint relative to the interfering background, and its calculation formula is as follows: ,in, The separation index; The color difference modulus of the mixed system before and after titration endpoint in the CIE-Lab* color space; The color change vector at the titration endpoint and the color change vector caused by sulfide interference are in a * -b * The angle of projection on the chromaticity plane; a mass ratio of 1:4 is used to make The ratio at which the maximum value is taken; the real-time monitoring operation in step S104 specifically includes: irradiating the mixing system with a narrow-band light source with a center wavelength of 620nm; collecting the transmitted light intensity signal and converting the transmitted light intensity signal into an absorbance value; using the strong absorption characteristics of thymolphthalein at 620nm as a reference background, physically isolating the absorbance fluctuations caused by sulfides and mainly distributed in the 400nm to 500nm band from the total signal.

2. The cyanide titration detection method based on thymolphthalein-TBPE dual indicator according to claim 1, characterized in that, The pH adjustment operation in step S101 includes: using an online pH electrode to detect the potential value of the water sample to be tested in real time; and adjusting the frequency of the sodium hydroxide solution dosing pump based on the difference between the potential value and the potential range corresponding to the target pH value of 11.0 to 12.0 through a PID control algorithm.

3. The cyanide titration detection method based on thymolphthalein-TBPE dual indicator according to claim 1, characterized in that, The specific preparation steps of the dual indicator system in step S102 include: preparing a thymolphthalein ethanol solution with a concentration of 0.5 g / L to 1.5 g / L; preparing a tetrabromophenolphthalein ethyl ethanol solution with a concentration of 2.0 g / L to 6.0 g / L; and mixing the thymolphthalein ethanol solution and the tetrabromophenolphthalein ethyl ethanol solution at a volume ratio to maintain the mass ratio of the solute in the mixture at 1:

4.

4. The cyanide titration detection method based on thymolphthalein-TBPE dual indicator according to claim 1, characterized in that, The operation of adding silver nitrate standard solution at a preset rate in step S103 includes: adding silver nitrate standard solution at a first constant flow rate in the initial stage of titration; calculating the first derivative of the absorbance of the mixed system in real time; when the first derivative is greater than the preset critical slope, triggering the frequency conversion control logic to switch the adding flow rate to a second flow rate, the second flow rate being less than 10% of the first constant flow rate, until the titration is determined to have reached the endpoint.

5. The cyanide titration detection method based on thymolphthalein-TBPE dual indicator according to claim 1, characterized in that, The method also includes a pre-distillation step performed before step S101: adding tartaric acid solution and zinc nitrate solution to the original water sample; heating the original water sample in a closed distillation apparatus to release cyanide in the form of hydrogen cyanide gas; capturing hydrogen cyanide gas using an absorption bottle containing sodium hydroxide solution, and using the captured absorption liquid as the water sample to be tested in step S101.

6. The cyanide titration detection method based on thymolphthalein-TBPE dual indicator according to claim 1, characterized in that, The specific basis for determining the titration endpoint in step S105 is: calculating the a value of the mixed system in the CIE-Lab* color space. * value and b * Value; when a is detected * The value jumps from negative to positive across zero, and b * When the rate of decrease of the value exceeds a preset threshold, an endpoint determination instruction is generated.

7. The cyanide titration detection method based on thymolphthalein-TBPE dual indicator according to claim 1, characterized in that, The method is applied to industrial wastewater environments with high sulfur and high turbidity. The specific effect of constructing the spectral background in step S102 is to limit the yellowness deviation introduced by sulfide interference to the range of ΔE<2.0 that is not sensitive to the human eye, and to ensure that the blue-purple abrupt signal at the titration endpoint is still recognized.

8. A cyanide titration detection system based on thymolphthalein-TBPE dual indicators, used to implement the cyanide titration detection method based on thymolphthalein-TBPE dual indicators as described in claim 1, characterized in that, include: The matrix control unit is used to quantitatively deliver sodium hydroxide solution to the acquired water sample to be tested, and lock the pH value of the water sample to be tested within a preset range of 11.0 to 12.0 based on the real-time feedback potential signal, so as to construct an alkaline detection matrix. The spectral background construction unit is used to inject a dual indicator system of thymolphthalein and tetrabromophenolphthalein ethyl ester prepared in a preset mass ratio into the alkaline detection matrix, and to establish a spectral background shielding field to mask sulfide interference by utilizing the colorimetric properties of thymolphthalein. The precision titration execution unit is used to control the delivery rate of silver nitrate standard solution to perform complexation titration in a mixed solution containing a dual indicator system; The photoelectric sensing and monitoring unit is equipped with a brightness sensor with a response band covering 600nm to 650nm, which is used to collect the optical signal of the mixed solution in real time during the titration process and capture the color change characteristics from green to blue-purple. The analysis and control unit is electrically connected to the matrix control unit, the spectral background construction unit, the precision titration execution unit, and the photoelectric sensing and monitoring unit, respectively. It is used to receive optical signals, determine the titration endpoint based on the color change characteristics, and calculate the cyanide concentration based on the volume of silver nitrate standard solution consumed by the precision titration execution unit.

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