Potentiometric titration method for measuring concentration of divalent silver ions

Abstract

The invention relates to a potentiometric titration method for measuring the concentration of divalent silver ions, which comprises the following steps: installing an electrode in a container, and adding sample liquid into the container to submerge the electrode; a burette is installed above the container, a titrating solution is put into the burette, and the titrating solution is cerous nitrate; dropwise adding the titration solution into the sample liquid for multiple times, determining the titration amount of each dropwise adding and the electrode potential in the corresponding titration process, waiting for a first preset time after each titration, then reading the electrode potential, waiting for a second preset time after reading the electrode potential, and then carrying out next titration; based on the titer and the electrode potential of each time, the change rate of the electrode potential along with the titer is obtained; positioning a critical point of the electrode potential based on the change rate, and determining a target titer when the electrode potential reaches the critical point; and determining the concentration of the divalent silver ions based on the target titer. The technical effects that the detection result is more accurate, the automation degree is improved, and the risk of the reagent is reduced are achieved.

Description

Technical Field

[0001] This invention relates to the field of analytical chemistry, and in particular to a potentiometric titration method for measuring the concentration of divalent silver ions. Background Technology

[0002] When analyzing the composition and content of each component in a sample solution, a redox reaction is required. The critical value of the redox reaction is recorded when changes occur, thus determining the content of each component in the sample solution.

[0003] Regarding the detection of divalent silver ions, existing technologies employ laser-induced breakdown spectroscopy (LIBS), fluorescence spectroscopy, inductively coupled plasma mass spectrometry (ICP-MS), or anodic stripping voltammetry. The redox agents used in these methods are often affected by pH or temperature, leading to inaccurate detection of divalent silver ion content in the sample solution. Furthermore, most of these methods rely on color changes in the solution to determine whether the critical value of the redox reaction has been reached. This requires continuous monitoring of the color change by the experimenter, but in some redox reactions, the color change may be subtle, making it impossible to accurately determine the critical value and resulting in inaccurate detection of divalent silver ion content in the sample solution. Additionally, most of these methods require full manual intervention, resulting in low automation.

[0004] In related experiments, the redox agents are usually reagents containing sulfate ions. Because sulfate ions are highly corrosive, their use can be dangerous and may cause safety losses to laboratory personnel.

[0005] The above problems urgently need to be addressed. Summary of the Invention

[0006] This invention discloses a potentiometric titration method for measuring the concentration of divalent silver ions, aiming to solve the technical problems existing in the prior art.

[0007] The present invention adopts the following technical solution: This invention provides a potentiometric titration method for measuring the concentration of divalent silver ions, comprising: S1: Potentiometric titrator preparation: installing electrodes in a container, adding sample liquid to the container to submerge the electrodes, wherein the electrodes include a calomel electrode and a platinum electrode, and the sample liquid contains divalent silver ions; installing a burette above the container, and adding titrant, wherein the titrant is cerium nitrate; S2: Equivalent point titration: repeatedly adding the titrant to the sample liquid, determining the titration amount added each time and the corresponding electrode potential during the titration process. In this process, after each titration, a first predetermined time is waited before the electrode potential is read. After reading the electrode potential, a second predetermined time is waited before the next titration is performed. S3: Concentration calculation: Based on the titration amount and electrode potential for each titration, the rate of change of the electrode potential with respect to the titration amount is obtained. Based on the rate of change, the critical point of the electrode potential is located, and the target titration amount when the electrode potential reaches the critical point is determined. The critical point of the electrode potential is used to indicate the critical state in which the potential changes from a positive electromotive force to a negative electromotive force. Based on the target titration amount, the concentration of divalent silver ions is determined.

[0008] Optionally, in the step of preparing the potentiometric titrator: the container is a centrifuge tube; a magnetic stir bar is placed into the centrifuge tube, wherein the magnetic stir bar is used to stir the sample liquid in the centrifuge tube.

[0009] Optionally, in the step of preparing the potentiometric titrator: before installing the burette above the container, the burette is rinsed with the titrant.

[0010] Optionally, in the equivalence point titration step, the amount of titration added each time is in the range of 0.05 ml to 0.5 ml.

[0011] Optionally, in the equivalence point titration step: the first predetermined time is between 10 and 25 seconds; the second predetermined time is 2 seconds.

[0012] Optionally, in the equivalence point titration step: before adding the titrant to the sample liquid multiple times, it is necessary to record the initial voltage value and the initial volume of the titrant.

[0013] Optionally, in the concentration calculation step: the rate of change of the titration amount is calculated as follows: in, For the rate of change, This is the electrode potential before titration. This represents the electrode potential after the titration has ended. This is the total titration volume before the current titration. This represents the total titration volume after the current titration.

[0014] Optionally, the step of locating the critical point of the electrode potential based on the rate of change and determining the target titration amount when the electrode potential reaches the critical point includes: obtaining the second derivative of the rate of change; determining the critical point of the electrode potential when the second derivative is equal to 0; determining the critical voltage value at the critical point; and calculating the total titration amount before the number of titrations based on the number of titrations corresponding to the critical voltage value to obtain the target titration amount.

[0015] Optionally, the second derivative of the rate of change is calculated as follows: in, It is the second derivative. The rate of change after the current titration has ended. The rate of change from the previous titration is given. The average of the two titration amounts used in the calculation of the rate of change of the current titration. This is the average of the two titration amounts used in the calculation of the rate of change from the previous titration.

[0016] Optionally, determining the concentration of divalent silver ions based on the target titration amount includes: determining the content of trivalent cerium ions in the cerium nitrate based on the target titration amount; determining the content of divalent silver ions in the sample liquid based on the content of trivalent cerium ions; determining the volume of the sample liquid; and determining the concentration of divalent silver ions based on the volume of the sample liquid and the content of divalent silver ions.

[0017] The technical solution adopted in this invention can achieve at least one of the following beneficial effects: In this embodiment of the invention, preparation is carried out using a potentiometric titrator: electrodes are installed in a container, and sample liquid is added to the container to submerge the electrodes, wherein the electrodes include a calomel electrode and a platinum electrode, and the sample liquid contains divalent silver ions; a burette is installed above the container, and titrant is placed into the burette, wherein the titrant is cerium nitrate; equivalence point titration: the titrant is repeatedly added to the sample liquid, and the amount of titrant added each time and the corresponding electrode potential during the titration process are determined, wherein after each titration, a first predetermined time is waited before reading the electrode potential, and after reading the electrode potential, a second predetermined time is waited before the next titration; concentration calculation: based on the amount of titrant added each time and the electrode potential, the rate of change of the electrode potential with the amount of titrant is obtained; based on the rate of change, the critical point of the electrode potential is located, and the target titrant amount when the electrode potential reaches the critical point is determined, wherein the critical point of the electrode potential is used to indicate the critical state where the potential changes from a positive electromotive force to a negative electromotive force; based on the target titrant amount, the concentration of divalent silver ions is determined. Determining the critical value of a redox reaction by detecting electrode potential is more accurate than manual observation through machine detection, thus improving the accuracy of concentration detection results. This method eliminates the need for prolonged, intensive manual observation, enabling automated detection. Furthermore, the use of cerium nitrate as the redox agent reduces the risk. These measures achieve the technical benefits of more accurate detection results, increased automation, and reduced reagent hazard. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below, forming part of the present invention. The illustrative embodiments of the present invention and their descriptions explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings: Figure 1 This is a flowchart of a potentiometric titration method for measuring the concentration of divalent silver ions in Embodiment 1 of the present invention; Figure 2 This is a graph showing the relationship between potential and trivalent cerium ion content in a potentiometric titration method for measuring the concentration of divalent silver ions in Embodiment 1 of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. In the description of this invention, it should be noted that the term "or" is generally used to include the meaning of "and / or," unless otherwise expressly indicated.

[0020] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or a magnetic connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. Furthermore, in the description of this application, the terms "first," "second," etc., are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance. In the description of this invention, "a plurality of" means at least two, such as two, three, or more, unless otherwise explicitly specified.

[0021] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0022] First, to facilitate understanding of the embodiments of the present invention, some terms or nouns involved in the present invention will be explained below: Potentiometric titration is an electrochemical analysis method that determines the titration endpoint by measuring the change in solution potential (voltage) during titration, thereby enabling quantitative analysis of the analyte. Its core concept is the "potential jump".

[0023] To address the problems existing in related technologies, this application provides a potentiometric titration method for measuring the concentration of divalent silver ions. This embodiment provides a potentiometric titration method for measuring the concentration of divalent silver ions, such as... Figure 1 As shown, Figure 1 This is a flowchart of a potentiometric titration method for measuring the concentration of divalent silver ions according to Embodiment 1 of the present invention. The method includes: Step S1, Preparation of the potentiometric titrator: Optionally, the potentiometric titrator preparation requires the installation of calomel and platinum electrodes, with the electrodes placed in a beaker and water added until the electrodes are submerged.

[0024] Optionally, when performing titration analysis using a potentiometric titrator, appropriate indicator and reference electrodes must be selected based on the reaction principle. Platinum electrodes are indicator electrodes for measuring redox potentials and can be applied to potentiometric titration analysis of redox reactions. They exhibit high sensitivity for reactions involving electron transfer. The core requirement for an indicator electrode is that its potential varies with the analyte (Ag). + The concentration of platinum (Pt) changes depending on the concentration of the reaction products. Platinum is an inert metal, and in silver ion titration systems (such as those using Ce), the concentration of the reaction products changes. 3+Titration of Ag 2+ ,use Titration (Generates silver nitrate), will not react with Titrant (such as Ce) 3+ , ) undergoes a chemical reaction, acting only as an "electron transport carrier" to ensure the main reaction (Ag) + The reaction with the titrant is not affected by the electrode material. The titration of silver ions often involves redox reactions (such as Ag...). 2+ + Ce 3+ → Ag + + Ce 4+ Platinum electrodes can sense the oxidation state (e.g., Ag) in solution through surface electron exchange. 2+ Ce 4+ ) and reduced state (such as Ag) + Ce 3+ The change in the concentration ratio of a substance is directly reflected by the Nernst equation, and its potential strictly follows the Nernst equation. + Real-time changes in concentration. Near the titration endpoint, Ag... + The concentration can change abruptly (e.g., from a high concentration to an extremely low concentration). At this time, the concentration ratio of oxidized and reduced substances in the solution changes drastically, resulting in a significant "jump" in the platinum electrode potential (e.g., the potential rises rapidly from 0.3V to 0.7V). This jump signal is clear and quantifiable, far superior to the color change of an indicator, and avoids visual interference.

[0025] Optionally, a calomel electrode is used as the reference electrode to provide a stable potential reference. Specifically, the core requirements for the reference electrode are a constant potential, unaffected by the solution composition (e.g., Ag). + The concentration and titrant affect the potentiometric titration of silver ions, which is usually performed under neutral or weakly acidic conditions (to avoid Ag). + (Hydrolysis), while the calomel electrode has good stability within this pH range, requires no special adjustment, and has a simple structure and is easy to maintain.

[0026] Step S11: Install electrodes in a container and add sample liquid to the container to submerge the electrodes. The electrodes include calomel electrodes and platinum electrodes, and the sample liquid contains divalent silver ions. Optionally, submerging the electrodes in the sample liquid is a core operation to ensure stable and accurate measurement of potential signals in potentiometric titration. Essentially, it meets the "contact requirement" and "system consistency requirement" for normal electrode operation. The electrodes in potentiometric titration (indicator and reference electrodes) must be in contact with the solution to function; failure to submerge them will directly lead to electrode "failure." If the sample liquid does not submerge the electrodes, the electrodes are only in contact with a "localized small amount of solution," not the entire sample system, causing the measurement results to deviate from the true value.

[0027] Optionally, during titration, the added titrant must be thoroughly mixed with the sample solution through stirring to form a "uniform concentration system." If the electrode is not submerged and only contacts a poorly stirred localized area of ​​the solution (such as the liquid surface or an unmixed area around the electrode), the measured potential reflects the "local concentration," not the true concentration of the entire sample (e.g., excessive titrant in a localized area may cause a sudden potential jump, but the overall system has not yet reached the endpoint), leading to incorrect endpoint determination. If the electrode is partially exposed to air, the exposed electrode surface may react with the air (e.g., oxidation of the platinum electrode or evaporation of electrolytes from the reference electrode), altering the electrode surface state and further interfering with the accuracy of the potential signal.

[0028] Optionally, submerging the electrode can isolate it from air, prevent electrode contamination, and ensure the repeatability and reliability of the experiment. This also protects against certain ions (such as Ce). 3+ Fe 2+ Platinum electrodes are easily oxidized by oxygen in the air. If the electrode is not submerged, oxidation will occur in the area where the liquid surface contacts the air, leading to changes in local ion concentration. Simultaneously, air entering the solution may generate bubbles that adhere to the electrode surface, hindering ion contact and causing potential readings to "jump." Exposed portions of the unsubmerged electrode may come into contact with impurities from the container walls or dust from the experimental environment, contaminating the electrode surface (e.g., impurities on the platinum electrode surface reduce electron exchange efficiency), resulting in decreased potential response sensitivity and making subsequent experiments difficult to replicate.

[0029] In some preferred embodiments, the steps of preparing the potentiometric titrator include: using centrifuge tubes as the container; placing a magnetic stir bar into the centrifuge tube, wherein the magnetic stir bar is used to agitate the sample liquid inside the centrifuge tube.

[0030] Optional, take 10mLAg 2+ The solution was placed in a 50 mL centrifuge tube, a magnetic stir bar was added, and the electrode was inserted into the centrifuge tube. The stirring system of the potentiometric titrator consists of an external magnetic drive and an internal magnetic stir bar. The external magnetic drive generates a rotating magnetic field, which drives the magnetic stir bar (a small magnetic rotor) placed in the solution to rotate synchronously, thereby agitating the liquid and achieving homogenization of the solution.

[0031] Optionally, use rigid centrifuge tubes (with or without graduations) (such as those made of PTFE or glass). The volume should match the sample liquid volume (the sample liquid should occupy 1 / 3 to 2 / 3 of the centrifuge tube's volume to prevent overflow during stirring). The tube walls should be transparent for easy observation of the electrode insertion status. Place a suitably sized magnetic stir bar (e.g., a cylindrical stir bar 5-10 mm in length, smaller than the centrifuge tube's inner diameter) at the bottom of the centrifuge tube, then add the sample liquid (ensuring the liquid submerges the stir bar to prevent it from spinning dry and damaging the tube wall). Place the centrifuge tube containing the sample liquid and magnetic stir bar into the sample holder of the potentiometric titrator (it must be stable and not suspended). Slowly insert the indicator electrode and reference electrode, ensuring the electrode tips are completely submerged in the sample liquid. The electrodes should not contact the centrifuge tube wall or the magnetic stir bar (to prevent electrode impact during stirring, which could cause signal fluctuations). Turn on the stirring function of the potentiometric titrator and adjust the stirring speed (starting from low speed and gradually adjusting it until the liquid forms a stable vortex but does not splash) to ensure that the titrant is quickly mixed after being added, avoiding local concentration deviations.

[0032] Step S12: Install a burette above the container and put titrant into the burette, wherein the titrant is cerium nitrate; Optional, the reaction principle is Ce 3+ + Ag 2+ → Ag + + Ce 4+ Based on this reaction principle, Ag in solution can be directly analyzed and measured. 2+ Compared to indirect titration, this method reduces the use of hazardous reagents such as sulfuric acid and increases Ag concentration. 2+ The ease of use of concentration analysis methods.

[0033] In some preferred embodiments, the step of preparing the potentiometric titrator includes rinsing the burette with titrant before attaching it above the container.

[0034] Optionally, install a burette and titrant (Ce(NO3)3 solution), and clean the burette with the titrant to effectively ensure that there is no distilled water residue or impurities in the burette, so that the concentration of the titrant added later is completely consistent with the standard concentration, avoiding errors in the calculation of the content of the analyte due to concentration deviation.

[0035] After cleaning (e.g., rinsing with tap water and then distilled water), a very thin layer of distilled water will adhere to the inner wall of the burette. If the titrant is added directly: This distilled water will be mixed with the titrant, diluting the actual concentration of the titrant. During subsequent titrations, because the titrant concentration is lower, a larger volume of water will be needed to reach the endpoint, resulting in a lower calculated concentration of the analyte (e.g., Ag). 2+The concentration might be too high, leading to inaccurate analytical results. It also helps remove impurities from the inner wall, preventing contamination of the titrant, such as residual reagents from the previous experiment (for example, if hydrochloric acid was used for titration, Cl- might remain in the tube). - If AgNO3 is used for titration this time, Cl - Will with Ag + The reaction produces AgCl precipitate, which contaminates the titrant and clogs the nozzle.

[0036] Step S2, equivalence point titration: Optionally, a potentiometric titrator can automate the titration process. After setting the initial parameters, it can automatically measure the electrode potential and titration volume, directly outputting the data. This effectively improves the level of automation and reduces the workload of laboratory personnel. The specific titration parameter settings are shown in the table below:

[0037] Step S21: The titrant is added to the sample liquid multiple times to determine the amount of titrant added each time and the corresponding electrode potential during the titration process. After each titration, wait for a first predetermined time before reading the electrode potential. After reading the electrode potential, wait for a second predetermined time before performing the next titration. Optionally, the specific experimental procedure shall be carried out according to the steps above, taking 7.55g Ag 2+ The solution was titrated with a Ce(NO3)3 concentration of 0.3005 mmol / g. The following data were obtained from the potentiometric titrator. A total of 17 titrations were performed, with the amount of titrant added decreasing gradually. A sudden jump in the solution potential occurred during the 10th titration, at which point 0.45 mL of titrant was consumed. The density of the Ce(NO3)3 solution was taken as 1 g / mL. The Ag was calculated based on the chemical equation. 2+ The solution concentration is 0.0179 mmol / g.

[0038] Optionally, based on the above experimental data, a graph showing the relationship between potential and the content of trivalent cerium ions can be obtained, such as... Figure 2 As shown.

[0039] In some preferred embodiments, during the equivalence point titration step, the amount of titration added each time ranges from 0.05 ml to 0.5 ml.

[0040] Optionally, in equivalence point titration, the amount of titrant added each time is controlled between 0.05 and 0.5 mL. In order to balance "titration accuracy" and "experimental efficiency", it is necessary to avoid missing the endpoint due to excessive titration and causing errors, and to avoid prolonging the experimental time and increasing operational errors due to insufficient titration. This is the optimal range that adapts to the "jump characteristics" of the equivalence point and the accuracy of the burette.

[0041] Optionally, this range is not fixed but should be adjusted flexibly according to the "titration stage." The closer to the endpoint, the smaller the amount added, as detailed below: In the initial stage of titration (far from the endpoint): add the titrant at the upper limit of 0.5 mL. At this point, the analyte concentration is high, and the concentration change in the system is gradual after the addition of the titrant (no significant fluctuation in potential). The 0.5 mL volume will not approach the abrupt jump point, allowing for rapid experimental progression without introducing large errors (e.g., using 0.1 mol / L Ce). 3+ Titration of Ag 2+ (For the first 15 mL, add 0.5 mL each time).

[0042] Near the endpoint (potential begins to fluctuate): Reduce the addition to 0.1 to 0.05 mL. When a small change in potential occurs (e.g., the potential rises from 0.3V to 0.35V with each 0.5 mL addition), it indicates that the abrupt change point is approaching. The addition volume should be reduced to 0.1 mL each time, observing the potential change. If the potential change accelerates (e.g., the potential rises by 0.1V with each 0.1 mL addition), reduce the volume to 0.05 mL to ensure that each drop is accurately recorded and to avoid skipping the abrupt change point.

[0043] Near the point of sudden change (drastic change in potential): stop adding drops and wait for the potential to stabilize before adding another 0.05 mL until the "potential jump peak" (such as the point of maximum first derivative) is recorded, ensuring that there is no excess at the endpoint.

[0044] In some preferred embodiments, in the equivalence point titration step: the first predetermined time is between 10 and 25 seconds; the second predetermined time is 2 seconds.

[0045] Optionally, after one titration, a period of 10 to 25 seconds is required to ensure that the electrode potential is stable before proceeding to the next titration. After reading the electrode potential, wait 2 seconds before proceeding to the next titration. It is necessary to wait for the titrant and sample liquid to be completely mixed and the stirring rhythm to be synchronized, i.e., to form a stable vortex, before proceeding to the next titration.

[0046] In some preferred embodiments, during the equivalence point titration step, the initial voltage value and the initial volume of the titrant need to be recorded before the titrant is added to the sample liquid multiple times.

[0047] Step S3, Concentration Calculation: Step S31: Based on the titration amount and electrode potential each time, obtain the rate of change of electrode potential with titration amount; In some preferred embodiments, the concentration calculation step involves calculating the rate of change of the titration amount as follows: in, For the rate of change, This is the electrode potential before titration. This represents the electrode potential after the titration has ended. This is the total titration volume before the current titration. This represents the total titration volume after the current titration.

[0048] Optional, derivative It is a concept of limits (such as) To reduce error, the volume interval (V2-V1) between the two points should be as small as possible, and they should be adjacent points of continuous titration (e.g., E is measured once when only 0.1 mL or 0.05 mL of titrant is added each time).

[0049] Step S32: Based on the rate of change, locate the critical point of the electrode potential and determine the target titration amount when the electrode potential reaches the critical point. The critical point of the electrode potential is used to indicate the critical state when the potential changes from positive electromotive force to negative electromotive force. In some preferred embodiments, based on the rate of change, the critical point of the electrode potential is located, and the target titration amount when the electrode potential reaches the critical point is determined, including: obtaining the second derivative of the rate of change; determining the critical point of the electrode potential when the second derivative is equal to 0; determining the critical voltage value at the critical point; and calculating the total titration amount before the number of titrations based on the number of titrations corresponding to the critical voltage value to obtain the target titration amount.

[0050] In some preferred embodiments, the second derivative of the rate of change is calculated as follows: in, It is the second derivative. The rate of change after the current titration has ended. The rate of change from the previous titration is given. The average of the two titration amounts used in the calculation of the rate of change of the current titration. This is the average of the two titration amounts used in the calculation of the rate of change from the previous titration.

[0051] Optionally, observe the second derivative data, find the volume range when it changes from positive to negative (or from negative to positive), and then calculate the precise endpoint volume using interpolation (more accurate than the "maximum point" of the first derivative).

[0052] Step S33: Determine the concentration of divalent silver ions based on the target titration amount.

[0053] In some preferred embodiments, determining the concentration of divalent silver ions based on the target titration amount includes: determining the content of trivalent cerium ions in cerium nitrate based on the target titration amount; determining the content of divalent silver ions in the sample liquid based on the content of trivalent cerium ions; determining the volume of the sample liquid; and determining the concentration of divalent silver ions based on the volume of the sample liquid and the content of divalent silver ions.

[0054] Optionally, first clarify the core reaction: Ce 3+ With Ag 2+ Measurement relationship: Ag 2+ It is a strong oxidizing agent, Ce 3+ (The effective ions in cerium nitrate) act as reducing agents. Under acidic conditions, the two undergo a 1:1 redox reaction, with electron transfer conserved. The reaction equation is as follows: Ag 2+ + Ce 3+ → Ag + + Ce 4+ From the reaction equation, we can see that the stoichiometric ratio of substances is 1:1, that is: n(Ag) / n(g) = 1 / 10. 2+ ) = n( Ce 3+ (n represents the amount of substance, unit: mol) Another crucial calculation: from cerium nitrate "content" to Ag 2+ concentration: In titration analysis, the "cerium nitrate content" refers to the concentration (c) of the titrant and the volume (V) consumed in the titration, which needs to be derived according to the following steps: 1. Calculate the Ce consumed. 3+ Amount of substance: The concentration of cerium nitrate, Ce 3+ The concentration (1:1 ionization, Ce(NO3)3=Ce) 3+ + 3NO3 - The formula is: n(Ce) 3 + ) = c(Ce 3+ ) × V(Ce 3+ ) Wherein, c (Ce 3+ V(Ce) represents the concentration of the cerium nitrate standard solution (unit: mol / L, must be pre-standardized or known, such as 0.1000 mol / L); 3+ ): Volume of cerium nitrate consumed in titration (unit: L; the burette reading in mL needs to be converted to L, e.g., 20.00 mL = 0.02000 L).

[0055] 2. Determine Ag based on the stoichiometric ratio 2+ Amount of substance: From the 1:1 stoichiometric ratio, we can directly obtain: n(Ag) 2+ ) = n(Ag 2+ ) 3. Calculate Ag 2+ Concentration: Ag 2+ Concentration = Ag 2+ Amount of substance ÷ analyte Ag 2+ The volume of a solution is given by the formula: c(Ag) 2+ ) = n(Ag 2+ ) ÷V(Ag 2+ ) Among them, V (Ag) 2+ ) is the Ag to be tested 2+ The volume of the solution (unit: L, must be accurately measured in advance, e.g., 25.00 mL = 0.02500 L); c (Ag) 2+ ): The final Ag value sought 2+ Concentration (unit: mol / L, retain 4 significant figures, in accordance with the accuracy of titration analysis).

[0056] Through steps S1 to S3 above, the established potentiometric titration method determines the titration endpoint by measuring changes in electrode potential, based on the redox reaction Ag. 2+ + Ce 3+ → Ag + + Ce 4+ By adding Ce 3+ The amount of Ag is determined 2+ In titration, as the titrant is added, the chemical reactions in the solution undergo continuous processes, changing the solution's composition and consequently altering the electrode potential. When the stoichiometric point (i.e., the titration endpoint) is reached, a sudden jump in electrode potential occurs. By detecting this potential jump, the titration endpoint can be determined. This approach achieves the advantages of simple principle, high automation, and low cost.

[0057] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A potentiometric titration method for the measurement of divalent silver ion concentration, characterized by, The method comprises the following steps: S1: a potential titrator is prepared: an electrode is installed in a container, a sample liquid containing divalent silver ions is added into the container to submerge the electrode, the electrode comprises a calomel electrode and a platinum electrode; a burette is installed above the container, a titrant is put into the burette, the titrant is cerous nitrate; S2: equivalence point titration: the titrant is dropped into the sample liquid for multiple times, the titration amount of each time and the electrode potential in the corresponding titration process are determined, after each titration, a first predetermined time is waited, then the electrode potential is read, after the electrode potential is read, a second predetermined time is waited, then the next titration is performed; S3: concentration calculation: based on the titration amount and the electrode potential of each time, a change rate of the electrode potential with respect to the titration amount is obtained; based on the change rate, a critical point of the electrode potential is located, a target titration amount when the electrode potential reaches the critical point is determined, the critical point of the electrode potential is used to indicate a critical state that the potential changes from positive electromotive force to negative electromotive force; based on the target titration amount, the concentration of the divalent silver ions is determined.

2. A potentiometric titration method for the measurement of divalent silver ion concentration according to claim 1, characterized in that, In the step of preparing the potential titrator: the container is a centrifuge tube; a magnetic stirring bar is put into the centrifuge tube, the magnetic stirring bar is used to stir the sample liquid in the centrifuge tube.

3. A potentiometric titration method for the measurement of divalent silver ion concentration according to claim 1, characterized in that, In the step of preparing the potential titrator: before the burette is installed above the container, the burette is flushed with the titrant.

4. A potentiometric titration method for the measurement of divalent silver ion concentration according to claim 1, characterized in that, In the step of the equivalence point titration: the range of the titration amount of each time is between 0.05 milliliter and 0.5 milliliter.

5. A potentiometric titration method for measurement of divalent silver ion concentration according to claim 1, wherein, In the step of the equivalence point titration: the first predetermined time is between 10 seconds and 25 seconds; the second predetermined time is 2 seconds.

6. A potentiometric titration method for measurement of divalent silver ion concentration according to claim 1, wherein, In the step of the equivalence point titration: before the titrant is dropped into the sample liquid for multiple times, an initial voltage value and an initial capacity of the titrant are recorded.

7. A potentiometric titration method for the measurement of divalent silver ion concentration according to claim 1, characterized in that, In the step of the concentration calculation: the change rate of the titration amount is calculated as follows: wherein, is the rate of change, is the electrode potential before the current titration, is the electrode potential after the current titration, is the total amount of titration before the current titration, is the total amount of titration after the current titration.

8. A potentiometric titration method for the measurement of divalent silver ion concentration according to claim 7, characterized in that, based on the change rate, the critical point of the electrode potential is located, the target titration amount when the electrode potential reaches the critical point is determined, which comprises: a second derivative of the change rate is obtained; when the second derivative is equal to 0, the critical point of the electrode potential is determined; a critical voltage value at the critical point is determined; based on the titration number corresponding to the critical voltage value, a total of the titration amount before the titration number is calculated to obtain the target titration amount.

9. The method according to claim 8, wherein the second derivative of the change rate is calculated as follows: wherein, is the second derivative, is the rate of change after the current titration, is the rate of change before the current titration, is the average of the two titration amounts used in the rate of change calculation for the current titration, is the average of the two titration amounts used in the rate of change calculation for the previous titration.

10. A potentiometric titration method for the measurement of divalent silver ion concentration according to claim 9, wherein, based on the target titration amount, the concentration of the divalent silver ions is determined, which comprises: based on the target titration amount, the content of trivalent cerium ions in the cerous nitrate is determined; based on the content of the trivalent cerium ions, the content of the divalent silver ions in the sample liquid is determined; the volume of the sample liquid is determined, based on the volume of the sample liquid and the content of the divalent silver ions, the concentration of the divalent silver ions is determined.

Images