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CN-121656480-B - Cyanide titration detection method and system based on thymolphthalein-TBPE double indicator

CN121656480BCN 121656480 BCN121656480 BCN 121656480BCN-121656480-B

Abstract

The invention relates to the technical field of environmental analysis chemistry, and discloses a cyanide titration detection method and system based on thymolphthalein-TBPE double indicators, wherein the cyanide titration detection method comprises the steps of adjusting a water sample to be detected to an alkaline pH range to construct a detection matrix; A double indicator system consisting of thymolphthalein and tetrabromophenolphthalein ethyl ester according to a specific proportion is introduced into a detection matrix, a spectrum background for masking sulfide yellow interference is constructed by utilizing the blue color development characteristic of thymolphthalein, a silver nitrate standard solution is dripped into a mixed system to carry out a complex reaction, the chromaticity response of the system in a specific wave band is monitored in real time, when a chromaticity mutation signal from green to blue-violet is captured, a titration endpoint is judged, and cyanide concentration is calculated.

Inventors

  • LI YAQI
  • MA XINFENG
  • ZHANG QINGYUN

Assignees

  • 潍坊弘润石化科技有限公司

Dates

Publication Date
20260512
Application Date
20260205

Claims (8)

  1. 1. The cyanide titration detection method based on the thymolphthalein-TBPE double indicator is characterized by comprising the following steps of: Step S101, adding sodium hydroxide solution into a water sample to be detected, and regulating the pH value of the water sample to be detected to be stable between 11.0 and 12.0 so as to construct an alkaline detection matrix for inhibiting cyanide volatilization; Step S102, introducing a double-indicator system into an alkaline detection matrix, wherein the double-indicator system is formed by mixing thymolphthalein and tetrabromophenolphthalein ethyl ester TBPE according to a preset mass ratio, constructing a spectral background for masking sulfide yellow interference chromaticity by utilizing the blue chromaticity characteristic of thymolphthalein in the alkaline detection matrix, and enabling the mixed system to be in a green initial state, wherein the mass ratio of thymolphthalein to tetrabromophenolphthalein ethyl ester is 1:4; step S103, dropwise adding a silver nitrate standard solution into the mixed system at a preset rate to carry out a complexing reaction on silver ions and cyanide ions; Step S104, monitoring absorbance change or chromaticity coordinate drift of a mixed system in a 600 nm-650 nm wave band in real time in a titration process, wherein the blue chromaticity characteristic of thymolphthalein is kept stable in the process so as to filter turbidity interference signals generated by sulfides; Step S105, when the comprehensive chromaticity of the mixed system is monitored to be changed from green to blue-violet, and the change rate exceeds a preset threshold, determining that the titration reaches the end point, and calculating the cyanide concentration according to the volume of the consumed silver nitrate standard solution; and, in step S102, the mass ratio of 1:4 is based on the chroma separation degree evaluation function The evaluation function is used for representing the identifiable degree of the titration endpoint color change relative to the interference background, and the calculation formula is as follows: , wherein, Is a separation index; color difference modulus of a mixed system before and after a titration end point in a CIE-Lab chromaticity space; The projection included angle of the chromaticity change vector of the titration end point and the chromaticity change vector generated by sulfide interference on an a * -b * chromaticity plane is formed; the mass ratio of 1:4 is that The real-time monitoring operation in the step S104 specifically comprises the steps of using a narrow-band light source with the center wavelength of 620nm to irradiate a mixed system, collecting a transmitted light intensity signal, converting the transmitted light intensity signal into an absorbance value, and physically isolating absorbance fluctuation which is caused by sulfide and is mainly distributed in a wave band from 400nm to 500nm from a total signal by using the strong absorption characteristic of thymolphthalein at 620nm as a reference background.
  2. 2. The cyanide titration detection method based on thymolphthalein-TBPE double indicator according to claim 1, wherein the operation of adjusting the pH value in step S101 comprises the steps of detecting the potential value of a water sample to be detected in real time by utilizing a pH online electrode, and adjusting the dosing pump frequency of the sodium hydroxide solution by a PID control algorithm based on the difference between the potential value and a potential interval corresponding to a target pH value of 11.0-12.0.
  3. 3. The cyanide titration detection method based on thymolphthalein-TBPE double indicator according to claim 1, wherein the specific preparation step of the double indicator system in step S102 comprises the steps of preparing a thymolphthalein ethanol solution with the concentration of 0.5g/L to 1.5g/L, preparing a tetrabromophenolphthalein ethyl ester ethanol solution with the concentration of 2.0g/L to 6.0g/L, and mixing the thymolphthalein ethyl ester ethanol solution and the tetrabromophenolphthalein ethyl ester ethanol solution according to the volume ratio to maintain the mass ratio of solutes in the mixed solution to be 1:4.
  4. 4. The cyanide titration detection method based on thymolphthalein-TBPE double indicator according to claim 1, wherein the step S103 is characterized in that the operation of dropwise adding the silver nitrate standard solution at a preset speed comprises the steps of adding the silver nitrate standard solution at a first constant flow rate in the initial titration stage, calculating the first derivative of absorbance of a mixed system in real time, triggering a variable frequency control logic when the first derivative is larger than a preset critical slope, and switching the dropwise adding flow rate to a second flow rate which is smaller than 10% of the first constant flow rate until the titration is judged to reach the end point.
  5. 5. The cyanide titration detection method based on thymolphthalein-TBPE double indicator according to claim 1, further comprising a pre-distillation step performed before step S101, wherein tartaric acid solution and zinc nitrate solution are added into the original water sample, the original water sample is heated in a closed distillation device to release cyanide in the form of hydrogen cyanide, the hydrogen cyanide gas is captured by an absorption bottle filled with sodium hydroxide solution, and the captured absorption liquid is used as the water sample to be tested in step S101.
  6. 6. The cyanide titration detection method based on thymolphthalein-TBPE double indicator according to claim 1, wherein the specific basis for determining that the titration reaches the end point in step S105 is that a * value and a b * value of a mixed system in CIE-Lab chromaticity space are calculated, and when a * value is detected to jump from a negative value to a positive value in a zero crossing manner and the dropping rate of the b * value exceeds a preset threshold value, an end point determination instruction is generated.
  7. 7. The cyanide titration detection method based on the thymolphthalein-TBPE double indicator, which is disclosed in claim 1, is characterized in that the method is applied to a high-sulfur high-turbidity industrial wastewater environment, and the specific effect of constructing a spectral background in step S102 is that the yellow degree deviation introduced by sulfide interference is limited in the human eye insensitivity range of delta E <2.0, so that the blue-violet mutation signal of a titration end point is still identified.
  8. 8. A thymolphthalein-TBPE double indicator-based cyanide titration detection system for implementing a thymolphthalein-TBPE double indicator-based cyanide titration detection method as recited in claim 1, comprising: the substrate regulation and control unit is used for quantitatively conveying sodium hydroxide solution into the acquired water sample to be detected, and locking the pH value of the water sample to be detected at a preset interval of 11.0-12.0 according to a potential signal fed back in real time so as to construct an alkaline detection substrate; the spectrum background construction unit is used for injecting a thymolphthalein and tetrabromophenolphthalein ethyl ester dual-indicator system prepared according to a preset mass ratio into the alkaline detection matrix, and establishing a spectrum background shielding field for shielding sulfide interference by utilizing the color development characteristic of the thymolphthalein; A fine titration execution unit for controlling the delivery rate of the silver nitrate standard solution, and executing complexation titration into the mixed solution containing the dual indicator system; the photoelectric sensing monitoring unit is provided with a brightness sensor with a response wave band covering 600nm to 650nm, and is used for collecting optical signals of the mixed solution in the titration process in real time and capturing the chromaticity mutation characteristic from green to blue-violet; The analysis control unit is respectively and electrically connected with the matrix regulation and control unit, the spectral background construction unit, the precise titration execution unit and the photoelectric sensing monitoring unit, and is used for receiving optical signals, judging a titration endpoint according to the chromaticity mutation characteristics, and calculating cyanide concentration according to the volume of the silver nitrate standard solution consumed by the precise titration execution unit.

Description

Cyanide titration detection method and system based on thymolphthalein-TBPE double indicator Technical Field The invention belongs to the technical field of environmental analytical chemistry, and particularly relates to a cyanide titration detection method and system based on thymolphthalein-TBPE double indicators. Background In the current environment monitoring and industrial wastewater control system, quantitative detection for cyanide mainly depends on a classical silver nitrate titration method, by means of standardization of an operation flow and economy of equipment cost, standard test means commonly adopted in the industry are formed, in the conventional operation flow, technicians titrate a pretreated water sample by using a silver nitrate standard solution and judge a stoichiometric end point through color change of a silver ion indicator, the method can provide relatively accurate concentration data when treating surface water or domestic sewage with a relatively single substrate, and forms a basic defense line for current water quality safety monitoring, however, when the general detection method is placed in complex wastewater scenes discharged by industries such as petrochemical industry, electroplating or coking, the boundary of technical applicability begins to appear, the industrial wastewater contains sulfide, thiocyanate and various organic reducing substances with high concentration, the coexisting components are not always inert backgrounds in a titration reaction system, but are active interference sources, in the actual operation level, sulfide ions with high concentration can preferentially compete with silver ions to generate a relatively high-level competitive interference color, the silver ions are in a dark state, the contrast is a sharp contrast is converted into a dark state, the dark state is a contrast is converted from a sharp contrast to a dark state, the dark state is a sharp, the contrast is converted into a sharp contrast is converted into a contrast of a dark state, and a contrast is a contrast of a suspension system is converted into a dark state, and a dark state is a contrast of a contrast is a low in a traditional contrast state, the operator is difficult to capture the exact abrupt change moment in a sharp way, so that the reading of the titration volume is often delayed from the real chemical equivalent point, and a non-negligible systematic positive error is introduced. Aiming at the common dilemma, the conventional improvement thought in the industry is usually concentrated on adding a physical separation step of sample pretreatment or adding an excessive chemical masking agent before titration to precipitate interfering ions, and although the absolute concentration of the interfering substances can be reduced to a certain extent by the means, the physical separation step is added to prolong a single detection period and reduce timeliness of coping with sudden pollution events, the adding of the excessive chemical precipitant often causes coprecipitation loss of micro cyanide due to the introduction of new ionic strength change or adsorption effect, thereby causing negative deviation in a low concentration detection region, the prior art replaces manual operation by simple instrument automation to reduce errors, but hardware upgrading is difficult to solve fundamental problems, for example, the patent of the utility model of the authority publication number CN209606450U discloses a full-automatic cyanide analysis system which realizes automatic control of distillation, absorption and titration through cooperation of a plurality of task sites, but the detection principle of the device still belongs to the traditional standard method, and the core detection logic is established on a single indicator or a conventional standard indicator, the high sulfur content automatic substrate is opposite to the high, the color and the color of the high-quality industrial substrate is difficult to be detected, and the color-down is difficult to be detected by the system is difficult to capture the color-down, and the color-down-mix-state signal is difficult to capture the background signal, and the color-down-mix-state is difficult to be detected. Therefore, how to construct a detection scheme for effectively decoupling a target signal and a noise signal under a strong interference background only by optimizing the spectral response characteristics in a reaction system without depending on expensive instruments and complex physical separation becomes a technical problem to be solved by the invention. Disclosure of Invention The invention provides a cyanide titration detection method based on thymolphthalein-TBPE double indicators, which comprises the following steps: Step S101, adding sodium hydroxide solution into a water sample to be detected, and regulating the pH value of the water sample to be detected to be stable between 11.0 and 12.0 so as to construct an alkaline dete