Photometric titration method

Abstract

The invention provides a photometric titration method, which adopts photoelectric equipment to measure a photovoltage signal after a light source penetrates through a liquid to be measured, and comprises a dynamic titration method and an equivalent titration method, in the dynamic titration method, the titration volume is added according to a volume rule, and the titration end point is judged through a primary differential method; in the equivalent titration method, the titration volume is a set volume, and a broken line method or a primary differential method is automatically selected according to judgment conditions to judge a titration end point; the broken line method is a quadratic differential method. The titration end point can be accurately judged.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of titration determination, and particularly relates to a photometric titration method. BACKGROUND

[0002] Titration is a method for determining the reaction end point and analyzing the composition of a solution by adding a standard solution to an analyzed solution in small amounts, and determining the reaction end point according to the color, precipitation or conductivity change caused by the measured component, titrant and reaction product in the titration process. According to the principle of titration end point determination, titration can be divided into photometric titration, potentiometric titration, coulometric titration and the like; and according to the reaction principle, titration can be divided into acid-base titration, oxidation-reduction titration, precipitation titration and complexometric titration.

[0003] As a titration analysis technology, photometric titration is a method for determining the reaction end point by adding a certain amount of standard solution to a measured solution, simultaneously measuring the absorbance of the measured solution system at a proper wavelength, and determining the reaction end point by plotting the absorbance against the amount of titrant (i.e., the photometric titration curve). The core principle is to determine the titration end point by monitoring the change in the absorbance of the solution. This method has high applicability in titration reaction systems involving color change, and has a very wide range of applications. Compared with other titration methods such as potentiometric titration and complexometric titration, the dependence of photometric titration on electrodes is significantly reduced, and accurate analysis can be achieved without complex electrodes.

[0004] The titration reaction in a laboratory requires high titration process, and manual operation often titrates in excess, and consumes a large amount of reagent. Now, automatic titration devices are often used to complete the titration process, but the automatic determination of the titration end point (including automatic selection of the end point determination method) and the automatic calculation of the titration result have not been fully realized in the automatic titration device of the photometric method, which limits the effective promotion and application of the photometric method automatic titration device. SUMMARY

[0005] The purpose of the present application is to provide a photometric titration method which can accurately determine the titration end point. The technical solution adopted is as follows: A photometric titration method, which measures the photovoltage signal of the light source after passing through the measured solution by using photoelectric equipment, includes dynamic titration method and equivalent titration method; In the dynamic titration method, the titration volume is added according to the volume rule, and the titration end point is determined by the first-order differential method. In the equivalent titration method, the titration volume is a set volume, and the titration end point is determined by automatically selecting the broken line method or the first-order differential method according to the determination condition; the broken line method is the second-order differential method.

[0006] Preferably, the determination condition in the equivalent titration method includes: After starting titration, the fitting linear correlation coefficient R of N groups of continuous titration data is calculated 2, the fitting linear correlation R 2 > 0.95; each group of titration data includes: photovoltage, corresponding titration volume; and the fitting linear correlation R 2 > 0.95 of the continuous N groups of titration data after the photovoltage starts to change; At this time, the end point determination selects the broken line method.

[0007] Preferably, the photovoltage change value ≥ 10mV; the photovoltage change value = photovoltage initial value - photovoltage current value.

[0008] Preferably, the determination condition in the equal amount titration method includes: ; and the fitting linear correlation coefficient R 2 satisfies: R 2 > 0.99; Wherein, - the photovoltage difference of the adjacent two groups of titration data; - the titration volume difference of the adjacent two groups of titration data; At this time, the titration end point determination selects the broken line method.

[0009] Preferably, in the photovoltage stable stage and the photovoltage end point stage, the abnormal photovoltage value is removed; Wherein, the first derivative of the continuous three groups of titration data < 30, then the photovoltage is in the stable stage; The first derivative of the continuous three groups of titration data > 30, then the photovoltage is in the photovoltage end point stage.

[0010] Preferably, before determining the titration end point, the step of performing mean value filtering on the titration data is further included.

[0011] Preferably, the volume rule in the dynamic titration method is: ; ; Wherein, - the titration volume of the next addition; - the maximum titration volume; - the minimum titration volume; - the constant; - the first derivative; - the photovoltage difference between two adjacent titration data sets; wherein one set of titration data comprises the current photovoltage and the current titration volume, and the other set of titration data comprises the photovoltage before the current photovoltage and the corresponding titration volume; - the titration volume difference between two adjacent titration data sets.

[0012] Preferably, the first-order differential method comprises the following steps: identifying a first-order differential dE jump peak meeting a determination condition, i.e., an extreme point of the first-order differential, taking the extreme point as a titration end point and calculating a titration result according to the titration end point; wherein the determination condition of the jump peak is: monitoring the first-order differential values of two adjacent titration data sets, and when two consecutive increasing first-order differential values are monitored and the maximum value of the found first-order differential is greater than a set jump threshold, the time corresponding to the maximum value is determined as the titration end point.

[0013] Preferably, the broken line method comprises the following steps: identifying a second-order differential jump peak meeting a determination condition, i.e., an extreme point of the second-order differential, taking the extreme point as a titration end point and calculating a titration result according to the titration end point; wherein the determination condition of the jump peak is: monitoring the second-order differential values of two adjacent titration data sets, and when two consecutive increasing second-order differential values are monitored and the maximum value of the found second-order differential is greater than a set jump threshold, the time corresponding to the maximum value is determined as the titration end point.

[0014] Compared with the prior art, the present application has the following advantages: 1. The dynamic titration model (photometric titration method) constructed by the present application has rich titration control parameters, which gives it excellent controllability and flexibility. In the stage near the end of titration operation, the model can accurately respond and timely "brake" to accurately control the titration process, effectively avoiding over-titration and ensuring the accuracy and reliability of the titration result.

[0015] 2. The present application uses a mean filter to smooth the titration data (including photovoltage and titration volume), and the titration curve after this processing presents a more smooth morphology. In this way, the risk of titration end point misjudgment is greatly reduced, thereby effectively ensuring the accuracy of the titration operation.

[0016] 3. By analyzing the original data curve in depth, accurately identifying and removing common abnormal data, the possibility of titration end point misjudgment can be significantly reduced.

[0017] 4. The model algorithm can analyze the data curve in depth according to the specific reaction characteristics, and then automatically select the appropriate end point determination method, thereby ensuring that the titration result has high accuracy and reliability. Attached Figure Description

[0018] Figure 1 This is a framework diagram of the photometric titration method. Detailed Implementation

[0019] The photometric titration method of the present invention will now be described in more detail with reference to the schematic diagrams, which illustrate preferred embodiments of the invention. It should be understood that those skilled in the art can modify the invention described herein while still achieving its advantageous effects. Therefore, the following description should be understood as being of general knowledge to those skilled in the art and is not intended to limit the invention.

[0020] A photometric titration method includes dynamic titration and equal volume titration.

[0021] Both methods use photoelectric equipment to measure and record the photovoltage signal after the light source passes through the liquid to be tested, and obtain the time signal curve.

[0022] In dynamic titration, the titration volume is added according to a volumetric rule. After titration is completed, the titration endpoint is determined by the first differential method. The broken-line method cannot be used in dynamic titration because it is unsuitable from a reaction principle perspective; the large volume added in dynamic titration would lead to significant errors with the broken-line method.

[0023] In the equal volume titration method, the titration volume is the set volume. After the titration is terminated, the endpoint is determined automatically by either the broken line method or the first differential method according to the judgment conditions; the broken line method is the second differential method.

[0024] The first differential method includes the following steps: Identify the first derivative dE jump peak that meets the judgment criteria, i.e. the extreme point of the first derivative, take the extreme point as the titration endpoint, and calculate the titration result based on the titration endpoint; The criteria for determining a sudden peak are as follows: Calculate the first derivative of two adjacent sets of data. If two consecutive increasing first derivative values ​​are detected and the maximum value of the first derivative is greater than the set threshold, then the time corresponding to the maximum value is determined as the titration endpoint.

[0025] The broken line method includes the following steps: Identify the second derivative jump peak that meets the judgment criteria, i.e. the extreme point of the second derivative, take the extreme point as the titration endpoint, and calculate the titration result based on the titration endpoint; The criteria for determining a sudden peak are as follows: If two consecutive increasing second derivative values ​​are detected, and the maximum value of the second derivative is greater than the set threshold, then the time corresponding to the maximum value is determined as the titration endpoint.

[0026] The present application relates to a kind of intelligent titration model (photometric titration) dedicated to photometric titration analysis (photometric titration).The model is based on the principle of photometric titration, and can be adapted to the reaction system accompanying absorbance change in titration process, especially suitable for classical titration scenarios such as precipitation titration, acid-base neutralization titration, oxidation-reduction titration and complexometric titration.As a new technical tool in the field of electrochemical analysis, the model realizes the automatic determination of titration endpoint, and breaks through the subjective limitation of traditional visual colorimetry.

[0027] In the following examples, "potential" refers to photovoltage.

[0028] Example 1 The dynamic titration addition volume is added according to a certain rule, and the equilibrium waiting time is controlled by the potential drift. The end point determination is mainly through differential extremum finding, and the dynamic titration mainly includes the following steps (step S101 to step S103).

[0029] Step S101, titration starting stage, titration volume is titrated according to the set minimum addition volume, titration times five, and equilibrium waiting time is controlled by drift.

[0030] Equilibrium waiting rule: When the real-time drift value (i.e. the amount of potential change per unit time) is lower than the set drift threshold, the equilibrium waiting stage (initial stage) ends. If the waiting time exceeds the set maximum waiting time, the system automatically uses the maximum waiting time.

[0031] Step S102, dynamic titration stage, addition volume is added according to the rule, and equilibrium waiting time is controlled by drift.

[0032] Volume addition rule is as follows: ; ; Wherein, - the titration volume of the next addition, unit milliliter mL, can be set; According to the time sequence, it is arranged in the order of current time, next time; - maximum addition volume (maximum titration volume), unit milliliter mL, can be set; - minimum addition volume, unit milliliter (mL); - constant, can be set; - one differential; - the photovoltage difference between two adjacent data sets; wherein one data set contains the current photovoltage and the current titration volume, and the other data set contains the photovoltage before the current photovoltage and the corresponding titration volume; - the titration volume difference between two adjacent data sets.

[0033] Step S103, dynamic end phase, the instrument identifies a differential dE spike (i.e. the extreme point of the differential) that meets the determination condition, and calculates the titration result accordingly.

[0034] The determination condition of the spike is as follows: The first differential value of two adjacent data sets is calculated, and when two consecutive increasing differential values are monitored, and the maximum differential value found in all the first differential data is greater than the set spike threshold, it is determined that the titration end point is valid, and the titration is stopped after adding several times.

[0035] The first differential value of two adjacent data sets refers to, for example, three data sets, the first and second sets are calculated for the first differential, and the second and third sets are calculated for the first differential.

[0036] Example 2 The equivalent titration is added by equal volume, and the equilibrium waiting time is also controlled by potential drift. The equivalent titration can automatically match the end point determination method, which mainly includes the following steps (step 1 to step 2).

[0037] Step 1, the equivalent titration mode uses a set volume for equivalent addition, and after each addition is completed, it waits for equilibrium according to drift control.

[0038] In photometric titration, when using the equivalent titration mode, if the single titration addition volume is too small, the local concentration of the solution may change suddenly, causing fluctuations in the absorbance response curve, and thus causing the risk of misjudgment of the titration end point.

[0039] Step 2, there are two end point determination methods in the equivalent titration mode: One is the first differential method, the core of which is to accurately identify the first differential peak (same as the dynamic titration end point determination); The second is the broken line method, the key of which is to accurately find the second differential peak (calculate the second differential and find the maximum value, the determination method is the same as the differential method).

[0040] The present application innovatively develops a set of end point determination system that can automatically adapt to the differential method or the broken line method. This system breaks through the limitations of traditional operation, and does not require manual selection of the end point determination method by the operator before starting the titration experiment, which significantly improves the intelligent level of the analysis process.

[0041] The method for automatically determining the end point is: The broken line method should only be used to determine the endpoint if the following conditions are met; otherwise, the differential method should be used.

[0042] The criteria for determining the polyline method (meeting any one of the following is sufficient): After the titration begins, calculate the linear correlation coefficient R of five consecutive sets of data. 2 Fitting linear correlation R 2 A linear correlation R0.95 was found in the five sets of data after the potential began to change (a potential change of more than 10 mV). 2 If it is also greater than 0.95, then the endpoint determination should be based on the broken line method.

[0043] The photovoltage at the start of titration is equal to the initial photovoltage value.

[0044] The potential changes slowly in the early stage, with the first derivative value being less than 50. As the endpoint approaches, the potential remains basically unchanged, and the titration curve becomes linear in the later stage. At this point, the endpoint is determined using the broken line method.

[0045] Furthermore, the data fitted with constant potential exhibits a linear correlation R. 2 Greater than 0.99.

[0046] In Example 2, a dynamically adaptable endpoint determination method was constructed for the first time. This system can flexibly adjust the endpoint determination strategy according to specific reaction characteristics, ensuring the accuracy and reliability of titration results.

[0047] Furthermore, in the two embodiments described above, outlier detection methods and extreme value removal mean filtering algorithms are used for the points (titration data) on the acquired time signal curves.

[0048] Outlier detection methods: Abnormal data in photometric titration are often caused by the photometric electrode potential. Abnormal data often lead to misjudgment of the endpoint. The following methods can be used to remove abnormal values.

[0049] In the stable potential phase: During this phase, the potential change is small. If the first derivative of three consecutive sets of data is less than 30, the potential can be considered to be in the stable potential phase.

[0050] Abnormal potential values ​​are removed using the Z-score method; data with a Z value greater than 1.5 are considered outliers.

[0051] ; in: Z - Calculate the standard scores for five consecutive sets of data; - The average of five consecutive data sets, in millivolts (mV). - The standard deviation of five consecutive data sets, in millivolts (mV).

[0052] Near the end point phase: the first derivative of the three consecutive groups of data is greater than 30, and the potential reaches the end point phase. The potential changes in one direction (increases or decreases) during the titration process, so the abnormal values inconsistent with the change of the potential can be removed, and the abnormal potential determination meets the following formula (remove some values with large reverse direction change, and do not process the values with small reverse direction change): ; Wherein: , , - the potential of the three consecutive groups of data, in millivolts (mV); Wherein, the "potential" is the photovoltage.

[0053] The extreme value mean filtering algorithm (for filtering the potential): First, remove the maximum and minimum values in the five data, and then calculate the arithmetic mean of the remaining three data. The filtered data is placed in the middle position of the original data, and the calculation formula is as follows.

[0054] ; Wherein: - the potential value obtained after filtering, in millivolts (mV); - the potential of the five consecutive groups of data, in millivolts (mV); - the maximum potential of the five consecutive groups of data, in millivolts (mV); - the minimum potential of the five consecutive groups of data, in millivolts (mV).

[0055] In summary, since the titration curve is not smooth, it is easy to cause end point misjudgment. In view of this, the mean filter is innovatively introduced to smooth the data, which effectively reduces the interference of curve fluctuation on end point judgment.

[0056] At the same time, for the common abnormal data that may appear in the titration process, the present application adopts the elimination strategy, so that the titration curve is more smooth and beautiful, and the risk of end point misjudgment is further reduced.

[0057] The above is only the preferred embodiment of the present application, and does not limit the present application in any way. Any person skilled in the art can make any form of equivalent replacement, modification or change to the technical solutions and technical contents disclosed in the present application without departing from the scope of the technical solutions of the present application, which still belongs to the protection scope of the present application.

Claims

1. A photometric titration method, which measures the photovoltage signal of a light source after passing through a liquid to be measured by using a photoelectric device, characterized in that, The dynamic titration method and the equivalent titration method are included. In the dynamic titration method, the titration volume is added according to a volume rule, and the titration end point is determined by a first-order differential method. In the equivalent titration method, the titration volume is a set volume, and the titration end point is determined by automatically selecting a broken line method or a first-order differential method according to a determination condition; the broken line method is a second-order differential method.

2. The photometric titration method according to claim 1, characterized in that, The determination condition in the equivalent titration method includes: After starting titration, calculate the fitting linear correlation coefficient R of N groups of continuous titration data 2 , fitting linear correlation R 2 > 0.95; each group of titration data includes: photovoltage, corresponding titration volume; and the linear correlation R of the continuous N groups of titration data after the photovoltage starts to change 2 > 0.95; At this time, the end point determination selects the broken line method.

3. The photometric titration method according to claim 2, characterized in that, The photovoltage change value is greater than or equal to 10 mV; the photovoltage change value is equal to the initial photovoltage value minus the current photovoltage value.

4. The photometric titration method according to claim 2, characterized in that, The determination condition in the equivalent titration method includes: ； and the linear correlation coefficient R of the fitting line of the continuous N groups of titration data after the photovoltaic voltage is unchanged 2 satisfies: R 2 ＞0.99； wherein, - the photovoltage difference between two adjacent titration data sets; - the difference in titration volume between two adjacent sets of titration data; At this time, the titration end point determination selects the broken line method.

5. The photometric titration method according to claim 1, characterized in that, In the photovoltage stable stage and the photovoltage end point stage, abnormal photovoltage values are removed; wherein, if the first-order differential of the three consecutive titration data is less than 30, the photovoltage is in the stable stage; if the first-order differential of the three consecutive titration data is greater than 30, the photovoltage is in the photovoltage end point stage.

6. The photometric titration method according to claim 1, characterized in that, Before determining the titration end point, a step of performing mean value filtering on the titration data is further included.

7. The photometric titration method according to claim 1, characterized in that, The volume rule in the dynamic titration method is: ； ； wherein, - the titration volume of the next addition; - maximum titration volume; - minimum titration volume; - constant; - first derivative; - a photovoltage difference between two adjacent sets of titration data; wherein one set of titration data comprises a current photovoltage and a current titration volume, and the other set of titration data comprises a photovoltage preceding the current photovoltage and a corresponding titration volume; - the difference in titration volume of two adjacent sets of titration data.

8. The photometric titration method according to claim 7, characterized in that, The first-order differential method includes the following steps: identify the first-order differential dE jump peak that meets the determination condition, that is, the extreme point of the first-order differential, take the extreme point as the titration end point, and calculate the titration result according to the titration end point; wherein, the determination condition of the jump peak is: calculate the first-order differential values of the adjacent two groups of titration data, monitor the two consecutive increasing first-order differential values, and find that the maximum value of the first-order differential is greater than the set jump threshold value, then determine the time corresponding to the maximum value as the titration end point.

9. The photometric titration method according to claim 8, characterized in that, The broken line method includes the following steps: identify the second-order differential jump peak that meets the determination condition, that is, the extreme point of the second-order differential, take the extreme point as the titration end point, and calculate the titration result according to the titration end point; wherein, the determination condition of the jump peak is: monitor the two consecutive increasing second-order differential values, and find that the maximum value of the second-order differential is greater than the set jump threshold value, then determine the time corresponding to the maximum value as the titration end point.

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