Ammonium fluoride detection method and application

Abstract

The invention belongs to the technical field of detection, and particularly relates to an ammonium fluoride detection method and application. The method comprises the following steps: detecting the content of free acid in an ammonium fluoride aqueous solution and / or the content of ammonium fluoride by adopting a potentiometric titration method, recording a potential jump point in the detection process, measuring the consumption of a titration solution, and calculating to obtain the concentration of free acid (hydrofluoric acid) and / or the concentration of ammonium fluoride. The detection method disclosed by the invention overcomes the defects of environmental pollution and influence on body health caused by the fact that formaldehyde needs to be added to promote H < + > release in a traditional acid-base titration method; and meanwhile, the problem of inaccurate detection result of incompletely ionized weak acid and weak base salt by potentiometric titration is solved. According to the technical scheme, detection is accurate and efficient, the obtained concentration content result is more accurate compared with manual titration, and the method is particularly suitable for in-plant and out-plant detection of electronic-grade ammonium fluoride.

Description

Technical Field

[0001] The invention belongs to the field of detection technology, and particularly relates to a method for detecting the concentration of free acid and ammonium fluoride in ammonium fluoride by using a potentiometric titration method and an application thereof. Background Art

[0002] Ammonium fluoride (NH4F) is an important compound with a wide range of applications in corrosion protection, disinfection, and chemical engineering. With the rapid development of the semiconductor industry, ammonium fluoride is playing an increasingly important role. For example, ammonium fluoride is used as an etchant to selectively remove the oxide layer on silicon wafers. It can also be used as a cleaning agent to remove residues and contaminants generated during the semiconductor device manufacturing process. It is also used in chemical mechanical polishing as an additive in polishing fluids to adjust the polishing rate and improve polishing quality.

[0003] In the semiconductor industry, there are strict requirements on the purity, granularity, moisture content and acidity of ammonium fluoride, and it is necessary to reach electronic grade to ensure its validity and reliability in semiconductor manufacturing process. The production of existing electronic grade ammonium fluoride is usually obtained by utilizing ammonia (NH3) and hydrogen fluoride (HF) reaction. For example, publication number is the Chinese patent of CN102557076A, which is to heat technical grade liquid ammonia to produce ammonia, then obtain high-purity ammonia through activated carbon adsorption and impurity removal, adsorption deoxidation, and absorb the electronic grade ammonium fluoride aqueous solution with high-purity hydrofluoric acid. For another example, publication number is the Chinese patent of CN117165961A, which is to react hydrogen fluoride solution with ammoniacal liquor or ammonia, supplement hydrogen fluoride in the reaction process to control pH≤5.0 to obtain crude product liquid, then carry out ion exchange purification and ethanol dripping and molten purification to obtain electronic grade ammonium fluoride.

[0004] However, even if the raw materials and crude products are purified as described in the aforementioned patent application, the resulting product may still contain free acid. This free acid can affect etching effectiveness, corrode equipment, and impact the environment, thus requiring strict control. Furthermore, the concentration of ammonium fluoride itself is a key factor in its quality, determining its applicable range.

[0005] At the same time, ammonium fluoride is a salt formed by a weak acid and a weak base. It is difficult to completely ionize in water, and the degree of ionization will be affected by hydrolysis.

[0006] Ionization refers to the dissociation of ammonium fluoride, a weak acid and weak base salt, in water to form cationic ammonium ions (NH4 + ) and anionic fluoride ion (F - ) process. Since ammonium fluoride is a weak acid and weak base salt, it cannot be completely ionized. While ionizing, hydrolysis will occur in the ammonium fluoride aqueous solution system. Hydrolysis is the dissociation of ammonium fluoride to produce cation NH4 + and anion F -The process of reacting with water to generate the corresponding weak acid (HF) and weak base (NH3·H2O). Therefore, in the ammonium fluoride aqueous solution system, there are both ionization equilibrium and hydrolysis equilibrium, which influence each other and eventually reach a dynamic equilibrium. At equilibrium, the amount of ammonium ions in the ammonium fluoride solution is less than the total amount of ammonium in the ammonium fluoride, and the amount of fluoride ions in the ammonium fluoride solution is less than the total amount of fluorine in the ammonium fluoride. Therefore, in the process of ammonium fluoride concentration detection, achieving a balance between efficiency and accuracy is a technical challenge.

[0007] Existing tests for ammonium fluoride content and its free acid content typically utilize acid-base titration. For example, free acid in ammonium fluoride is detected using chemical titration with sodium hydroxide as the titrant and bromocresol purple as the indicator. The titration endpoint is reached when the solution turns purple. Ammonium fluoride content is detected by adding formaldehyde solution to an ammonium fluoride solution and titrating with sodium hydroxide using phenolphthalein as the indicator. The titration endpoint is reached when the solution turns pink. The amount of ammonium fluoride is determined by subtracting the amount of base consumed by the free acid from the total amount of base consumed.

[0008] However, the use of acid-base indicators to confirm the titration endpoint in the above detection method often leads to large errors due to subjective color judgment errors of humans and objective pH color change range of the indicator. This situation may be serious or even fatal for the use of electronic-grade ammonium fluoride in industry. Secondly, as mentioned above, the ionization of ammonium fluoride is not complete. In order to improve the accuracy of ammonium fluoride concentration detection, it is necessary to shake and wait after adding each drop of titration solution, resulting in low detection efficiency and long detection time. At the same time, formaldehyde needs to be added to promote H + The release of formaldehyde is a substance that is harmful to the human body and the environment. Long-term use will affect human health. The waste liquid also needs further treatment before it can be discharged, which increases the cost of the enterprise.

[0009] Therefore, developing a detection method suitable for ammonium fluoride containing free acid is of great significance for improving detection accuracy and efficiency, protecting the safety of experimenters and the social environment.

[0010] The method adopting potentiometric titration to detect free acid concentration is disclosed in the prior art.For example, publication number is the Chinese patent of CN102680555A, and the free acid in the cold-rolled sheet pickling solution is detected, and with reference to the scheme, potentiometric titration is used for the detection of ammonium fluoride, the applicant finds that there is larger difference in the concentration of the free acid obtained and the parallel test result of the concentration of ammonium fluoride, and also has larger deviation from the result of manual chemical titration in accordance with the degree of conformity, is difficult to be actually applied to the quality inspection of the ammonium fluoride product, especially is even more inappropriate for electronic-grade ammonium fluoride.The main reason causing this situation is just to, relate to strong acid and the strong acid and strong base salt formed thereby in conventional detection method, there is not the incomplete situation of ionization, and this difference with the this weak acid and weak base salt of ammonium fluoride is very large (with reference to Chinese patent CN102680555A), so only apply existing potentiometric titration method mechanically, can not reach detection requirement. Summary of the Invention

[0011] The purpose of the present invention is to overcome the problems of large error in ammonium fluoride detection results, low efficiency, large deviation in parallel detection results, and use of harmful substances in the prior art, and to provide a detection method and application of ammonium fluoride.

[0012] In order to achieve the above object, the present invention adopts the following technical solutions:

[0013] A method for detecting ammonium fluoride, comprising: detecting the content of free acid and / or the content of ammonium fluoride in an aqueous ammonium fluoride solution by potentiometric titration, recording the potential jump point during the detection process, measuring the consumption of the titration solution, and calculating the concentration of the free acid (hydrofluoric acid) and / or the concentration of ammonium fluoride;

[0014] The specific steps include:

[0015] The ammonium fluoride aqueous solution is placed in a potentiometric titrator, and titration solution is added for titration. When a potential jump point is detected, the free acid (hydrofluoric acid) concentration and / or the ammonium fluoride concentration is calculated based on the titration solution consumption and concentration.

[0016] Furthermore, the potentiometric titration method of the present invention uses a change in potential to indicate the endpoint. When the titration reaches the endpoint, the acid-base reaction is completely complete, and the free ion content in the titration system is at its lowest, resulting in a potential jump. This is the equivalence point of the titration. The concentration of the analyte can be calculated based on the volume of the analyte at this point, the titration solution dosage, and its concentration.

[0017] The method disclosed in the present invention uses potentiometric titration, using an aqueous solution of an inorganic base as the titrant to detect the free acid content and the ammonium fluoride content in ammonium fluoride. Continuous stirring is applied during the titration process to promote the acid-base neutralization reaction and increase the degree of ionization of ammonium fluoride.

[0018] Furthermore, the method continuously applies stirring at a rotation speed of 160-640 r / min during the detection process.

[0019] As mentioned in the above background, when the applicant used potentiometric titration of ammonium fluoride solution to detect the concentration of free acid and ammonium fluoride, the parallel detection results had a large deviation problem. Through experiments and analysis, the applicant found a control method that can simply improve the accuracy of detection and has a good concentration of parallel detection results, that is, to continuously apply strict stirring during the titration process, and control the stirring rate within the range of 320-800r / min. When the rotation speed is larger than 640r / min, the stirring intensity is large. First, in the process of determining the free acid, the ammonium fluoride is ionized to a greater extent under strong stirring, so the H generated by hydrolysis + There are more free acids, so the concentration of free acid detected actually includes free acid and acid hydrolyzed by ammonium fluoride, and the result is inaccurate; secondly, fast stirring speed will cause adsorption of bubbles, thus affecting the measurement data.

[0020] Furthermore, the potential jump point includes two, the first potential jump point is the equivalence point of the free acid, and the second potential jump point is the equivalence point of ammonium fluoride.

[0021] In the present invention, because ammonium fluoride contains free acid and the anions and cations formed after ionization of ammonium fluoride further hydrolyze, two potential jumps occur, i.e., there are two equivalence points during the titration process. The first potential jump point is the equivalence point of the free acid, at which point the titration of the free acid is complete; the second potential jump point is the equivalence point of the ammonium fluoride, at which point the reaction between the ammonium fluoride and the base is complete. The concentrations of the free acid and ammonium fluoride can be calculated based on the two potential jump points.

[0022] It should be noted that the solution of the present invention does not have only the above-mentioned two potential jump points. In one embodiment, the experimenter can choose to use an alkaline titration solution of suitable concentration for potentiometric titration to measure the concentration of ammonium fluoride in the ammonium fluoride solution, without considering the concentration of the free acid therein. Since the concentration of the titration solution is large and the addition rate is fast, the equivalence point of the free acid may be quickly crossed and thus not clearly recorded by the titration equipment. At this time, there is only one potential jump point, i.e., the equivalence point of ammonium fluoride. In another embodiment, depending on the composition of the selected ammonium fluoride solution, 3, 4 or even more potential jump points may also appear during the titration process. Those skilled in the art can determine the results represented by each equivalence point based on the preparation process and other detection means.

[0023] Furthermore, the method of the present invention does not add formaldehyde during the detection process. By controlling the rotation speed during the titration process, the present invention does not need to add aldehyde, especially formaldehyde, to promote the release of H from ammonium fluoride.+ , thereby reducing harmful effects on the environment and human body.

[0024] Furthermore, the detection method of ammonium fluoride comprises the following steps:

[0025] 1) Place the ammonium fluoride aqueous solution in a potentiometric titrator and stir continuously;

[0026] 2) starting the titrator, adding the titration solution at a certain rate for titration, and when the first potential jump point is detected, calculating the concentration of the free acid (hydrofluoric acid) based on the consumption and concentration of the titration solution;

[0027] 3) The titrator automatically switches to add titration solution at a certain rate for titration while continuously stirring. When the second potential jump point is detected, the concentration of ammonium fluoride is calculated based on the consumption and concentration of the titration solution.

[0028] Furthermore, an aqueous solution of an inorganic base is used as a titration solution.

[0029] Furthermore, the inorganic base is sodium hydroxide or potassium hydroxide.

[0030] Furthermore, when detecting the concentration of the free acid, the concentration of the titration solution is 0.10 mol / L. Of course, the present invention is not limited to 0.10 mol / L. Any other suitable concentration, such as 0.02 mol / L, 0.05 mol / L, 0.08 mol / L, 0.12 mol / L, 0.15 mol / L, or any concentration within a range thereof, is feasible, preferably 0.01 to 0.18 mol / L. Considering the low concentration of the free acid, a 0.10 mol / L NaOH solution is usually selected for titration for more accurate and efficient detection.

[0031] Furthermore, when detecting the concentration of the free acid, the titration rate of the titration solution is 1-10 mL / min.

[0032] Furthermore, when detecting the concentration of ammonium fluoride, the concentration of the titration solution is 1.00 mol / L. Of course, the present invention is not limited to 1.00 mol / L. Any other suitable concentration, such as 0.10 mol / L, 0.50 mol / L, 0.80 mol / L, 1.20 mol / L, 1.50 mol / L, 2.00 mol / L, or any range thereof, is feasible, preferably 0.10 to 2.00 mol / L. 1.00 mol / L NaOH solution is usually selected for titration.

[0033] Furthermore, when detecting the concentration of ammonium fluoride, the titration rate of the titration solution is 1-10 mL / min. This titration rate is coordinated with the concentration of the titration solution. Under these conditions, the titration rate is appropriate, providing sufficient time for the ionization of ammonium fluoride and ensuring detection efficiency.

[0034] Preferably, stirring at a rotation speed of 320-480 r / min is continuously applied in step 1) and step 2).

[0035] Preferably, in step 2), before starting the titrator, the stirring time in step 1) lasts for 10 to 20 seconds.

[0036] Preferably, in step 3), stirring is continuously applied at a rotation speed of 320-480 r / min.

[0037] Preferably, the present invention selects magnetic stirring or mechanical stirring, such as stirring with a stirring paddle; the rotation speed of magnetic stirring and mechanical stirring can be accurately controlled, and the speed adjustment is convenient.

[0038] Preferably, the ammonium fluoride to be detected in the present invention is electronic grade ammonium fluoride. In fact, the scheme of the present invention is particularly suitable for the detection of electronic grade ammonium fluoride, and the detection result is more accurate.

[0039] Furthermore, a second aspect of the present invention provides applications of the aforementioned ammonium fluoride detection method. Specifically, the aforementioned method is applied to the quality testing of electronic-grade ammonium fluoride, such as factory inspection of ammonium fluoride production, or incoming material inspection during downstream production or processing of ammonium fluoride. Electronic-grade ammonium fluoride has higher requirements for product concentration and impurity content, and the aforementioned detection method of the present invention is particularly suitable for the detection of electronic-grade ammonium fluoride.

[0040] Compared with the prior art, the advantages of the present invention are:

[0041] 1. The present invention adopts potentiometric titration, which is to add the titration solution to the liquid to be tested to carry out acid-base neutralization reaction, and the equivalence point of the titration is indicated by the potential jump. Since ammonium fluoride is a weak acid and weak base salt, during the titration process, the free acid first participates in the acid-base neutralization reaction to obtain the first potential jump point; the ionization and hydrolysis process of ammonium fluoride releases H + , thus generating a second potential jump point. By recording the consumption and concentration of the titration solution, the free acid and ammonium fluoride content in ammonium fluoride can be accurately calculated. This method is particularly suitable for the detection of electronic-grade ammonium fluoride, with high precision and accurate results.

[0042] 2. The detection method of the present invention overcomes the need to add formaldehyde to promote H in the traditional acid-base titration method. +The release of ammonium fluoride can cause environmental pollution and adverse health effects. Furthermore, the present invention overcomes the problem of inaccurate detection results for weak acid and weak base salts that are not completely ionized by potentiometric titration. The solution of the present invention provides accurate and efficient detection, and the concentration and content results obtained are more accurate than those obtained by manual titration. It is particularly suitable for inbound and outbound testing of electronic-grade ammonium fluoride. DETAILED DESCRIPTION

[0043] The following is a clear and complete description of the technical solutions of this application in conjunction with the embodiments. Obviously, the embodiments described are only a part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0044] The experimental methods in the following examples without specifying specific conditions were generally carried out under conventional conditions or conditions recommended by the manufacturers, and the raw materials and reagents used were conventional commercially available products unless otherwise specified.

[0045] The ammonium fluoride products used in the following examples and comparative examples are products produced by the applicant itself (specifically, ammonium fluoride products prepared by the reaction of electronic-grade hydrofluoric acid absorbing ammonia, produced by Duofuduo New Materials Co., Ltd.), and are all taken from the same batch of products for testing and comparison.

[0046] The NaOH solutions used in the following examples and comparative examples were prepared from purchased premium-grade pure reagents with calibrated concentrations of 0.1013 mol / L and 1.0041 mol / L, respectively. The two titration solutions are hereinafter referred to as 0.10 mol / L and 1.00 mol / L NaOH (titration) solutions, respectively.

[0047] The potentiometric titrator used in the following examples and comparative examples is a Metrohm OMNIS Titrator. Two independent titration solution containers are respectively filled with 0.10 mol / L and 1.00 mol / L NaOH solutions, and the titrator automatically switches to select the titration solution according to the set program.

[0048] In the following examples and comparative examples, before each experiment, the pipes, electrodes, containers, stirring paddles and other related components of the titrator were cleaned with distilled water to avoid residues from the previous experiment.

[0049] In the following examples and comparative examples, the concentrations of free acid and ammonium fluoride are all expressed in mass percentages.

[0050] Example 1

[0051] A method for detecting electronic grade ammonium fluoride, comprising the following steps:

[0052] 1) Place 1.3093 g of homemade electronic-grade ammonium fluoride product (aqueous solution) in the test solution container of a potentiometric titrator, insert a magnetic stirring rotor cleaned with distilled water, and start stirring at a stirring speed of 320 r / min. Before starting the titrator, stir for 10 s;

[0053] 2) Start the titrator and titrate by adding 0.10 mol / L NaOH solution at a rate of 4 mL / min (maintaining the stirring speed in step 1). The device automatically detects and analyzes the potential change. When the first potential jump point is reached, 0.4371 mL of NaOH solution is consumed, and the free acid (hydrofluoric acid) concentration is calculated to be 0.0677%.

[0054] 3) The titrator automatically switches to a 1.00 mol / L NaOH solution and titrates at a rate of 5 mL / min, while maintaining a rotational speed of 320 rpm. When the potentiometric titrator reaches the second potential break, 12.0144 mL of NaOH solution has been consumed, and the calculated concentration of ammonium fluoride is 34.125%.

[0055] Example 2

[0056] A method for detecting electronic grade ammonium fluoride, comprising the following steps:

[0057] 1) Place 1.8282 g of homemade electronic-grade ammonium fluoride product (aqueous solution) in the test solution container of a potentiometric titrator and stir with a mechanical stirring paddle at a stirring speed of 480 r / min. Stir for 10 s before starting the titrator.

[0058] 2) Start the titrator and titrate by adding 0.10 mol / L NaOH solution at a rate of 3 mL / min (maintaining the stirring speed in step 1). The device automatically detects and analyzes the potential change. When the first potential jump point is reached, 0.6749 mL of NaOH solution is consumed, and the free acid (hydrofluoric acid) concentration is calculated to be 0.0748%.

[0059] 3) The titrator automatically switches to a 1.00 mol / L NaOH solution for titration at a titration rate of 5 mL / min and an increase in rotational speed to 640 rpm. When the potentiometric titrator reaches the second potential break, 16.7560 mL of NaOH solution is consumed, and the calculated concentration of ammonium fluoride is 34.085%.

[0060] Example 3

[0061] A method for detecting electronic grade ammonium fluoride, comprising the following steps:

[0062] 1) Place 1.7975 g of homemade electronic-grade ammonium fluoride product (aqueous solution) in the test solution container of a potentiometric titrator, insert a magnetic stirring rotor cleaned with distilled water, and start stirring at a stirring speed of 640 r / min. Before starting the titrator, stir for 10 s;

[0063] 2) Start the titrator and titrate by adding 0.10 mol / L NaOH solution at a rate of 5 mL / min (maintaining the stirring speed in step 1). The device automatically detects and analyzes the potential change. When the first potential jump point is reached, 0.8012 mL of NaOH solution is consumed, and the free acid (hydrofluoric acid) concentration is calculated to be 0.0904%.

[0064] 3) The titrator automatically switches to a 1.00 mol / L NaOH solution for titration at a titration rate of 10 mL / min. The rotation speed is maintained at 640 rpm. When the potentiometric titrator reaches the second potential break, 16.4827 mL of NaOH solution is consumed, and the calculated concentration of ammonium fluoride is 34.101%.

[0065] Example 4

[0066] A method for detecting electronic grade ammonium fluoride, comprising the following steps:

[0067] 1) Place 1.8207 g of homemade electronic-grade ammonium fluoride product (aqueous solution) in the test solution container of a potentiometric titrator and stir with a mechanical stirring paddle at a stirring speed of 480 r / min. Stir for 10 s before starting the titrator.

[0068] 2) Start the titrator and select 1.00 mol / L NaOH solution for titration at a titration rate of 6 mL / min. The device automatically detects and analyzes potential changes. When the potential jump point appears in the potentiometric titrator analysis, 16.7188 mL of NaOH solution is consumed, and the calculated ammonium fluoride concentration is 34.115%.

[0069] In this example, we focused solely on the concentration of ammonium fluoride and ignored the effects of free acid. Therefore, we used a 1.00 mol / L NaOH solution for titration. Because the titration solution was highly concentrated, the first potential break was bypassed, and the potential break determined by the potentiometric titrator was the ammonium fluoride concentration.

[0070] Comparative Example 1

[0071] 1) Place 1.5860 g of homemade electronic-grade ammonium fluoride product (aqueous solution) in the test solution container of a potentiometric titrator and start a mechanical stirring paddle for stirring at a stirring speed of 160 r / min. Before starting the titrator, stir for 10 s.

[0072] 2) Start the titrator and titrate by adding 0.10 mol / L NaOH solution at a rate of 5 mL / min (maintaining the stirring speed in step 1). The device automatically detects and analyzes the potential change. When the first potential jump point is reached, 0.0205 mL of NaOH solution is consumed, and the calculated free acid (hydrofluoric acid) concentration is 0.0026%.

[0073] 3) The titrator automatically switches to a 1.00 mol / L NaOH solution and titrates at a rate of 5 mL / min, maintaining a stirring speed of 160 r / min. When the potentiometric titrator reaches the second potential break, 14.5781 mL of NaOH solution is consumed, and the calculated concentration of ammonium fluoride is 34.163%.

[0074] Comparative Example 2

[0075] The only difference between this comparative example and comparative example 1 is that 1.5689 g of ammonium fluoride product is weighed and titrated using magnetic stirring at the same speed and process, resulting in a free acid concentration of 0.0216% and an ammonium fluoride concentration of 33.372%.

[0076] Comparative Example 3

[0077] The only difference between this comparative example and comparative example 1 is that 1.5667 g of ammonium fluoride product is weighed and titrated according to the same rotation speed and process, resulting in a free acid concentration of 0.0600% and an ammonium fluoride concentration of 34.088%.

[0078] Through comparative examples 1, 2, and 3, it was found that under the same detection conditions, the concentration of free acid deviated greatly, and the concentration of ammonium fluoride also deviated to a certain extent. This deviation is unacceptable for the detection of ammonium fluoride, especially the detection of electronic-grade ammonium fluoride, and is a detection error.

[0079] Comparative Example 4

[0080] The free acid and ammonium fluoride concentrations of ammonium fluoride products are tested by manual titration:

[0081] 1) The concentration of free acid in the ammonium fluoride product (aqueous solution) (standardized concentration 34%) was determined by acid-base titration. Specifically, 2.5326 g of the sample (ammonium fluoride product) was weighed into a 250 mL ground-joint sealed conical flask pre-filled with approximately 30 mL of water. 0.1 mol / L NaOH standard titration solution was used, and 3 drops of 1 g / L bromothymol blue were added as an indicator. The titration endpoint was when the color of the solution changed from yellow to blue. Based on the NaOH consumption V1 (specifically 2.730 mL), the free acid concentration in the ammonium fluoride was calculated to be 0.22%;

[0082] 2) adding 35% formaldehyde aqueous solution to the product obtained in step 1), shaking evenly, and then letting it stand for 40 minutes;

[0083] 3) The product obtained in step 2) was measured by acid-base titration to determine H + The concentration is titrated with 1 mol / L NaOH standard titrant. The titration endpoint is when the solution changes from yellow to blue. The consumption of NaOH standard titrant is V2 (specifically 23.760 mL). Therefore, the volume of NaOH consumed in this step is V2. H is calculated from this. + The concentration is 33.84%, which is the concentration of ammonium fluoride.

[0084] In order to analyze the detection accuracy of the method of the present invention, multiple parallel experiments were conducted using the same sample at different rotational speeds. The detection results and their standard deviations were analyzed to obtain Table 1.

[0085] Table 1

[0086]

[0087] As can be seen from Table 1, for potentiometric titration, when the speed is 160 r / min, the standard deviation of the detection results of free acid and ammonium fluoride is the highest. This is because the test solution is not uniform at low speed and ammonium fluoride is ionized slowly. There is a large error or even an error in each test result. Therefore, the result at this speed is unreliable. As the speed increases, when the speed reaches 320-480 r / min, the standard deviation is smaller, indicating that the test result has a high accuracy and is suitable for the detection of ammonium fluoride.

[0088] Compared to manual chemical titration, the free acid concentration obtained using potentiometric titration is lower, indicating that potentiometric titration data is more accurate. This is because manual titration is more susceptible to human judgment of the titration endpoint for low-concentration test solutions, resulting in reading errors and the indicator's color change range not necessarily being exactly neutral (pH = 7). Furthermore, the base content in a single drop of titrated solution is often sufficient to cause the test solution to transition directly from acidic to neutral to alkaline, resulting in an overstated concentration reading. Potentiometric titration, on the other hand, has a controllable titration rate, a sensitive potential response, and automatic recording, making it more accurate in determining the equivalence point.

[0089] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for detecting ammonium fluoride, characterized in that: The following steps are involved: The ammonium fluoride aqueous solution is placed in a potentiometric titrator, and a titration solution is added for titration. When a potential jump point is detected, the free acid concentration and / or the ammonium fluoride concentration is calculated based on the titration solution consumption and concentration.

2. The method according to claim 1, wherein During the test, stirring was continuously applied at a speed of 160-640 r / min.

3. The method according to claim 1, wherein The potential jump points include two, the first potential jump point is the equivalence point of the free acid, and the second potential jump point is the equivalence point of ammonium fluoride.

4. The method according to claim 1, wherein The specific steps are: 1) Place the ammonium fluoride aqueous solution in a potentiometric titrator and stir continuously; 2) Start the titrator and add the titrant solution at a certain rate for titration. When the first potential jump point is detected, the concentration of the free acid is calculated based on the consumption and concentration of the titrant solution. 3) The titrator automatically switches to adding titrant solution at a certain rate for titration while continuously stirring. When the second potential jump point is detected, the concentration of ammonium fluoride is calculated based on the consumption and concentration of the titrant solution.

5. The method according to claim 4, wherein An aqueous solution of an inorganic base is used as the titration solution.

6. The method according to claim 5, wherein The inorganic base is sodium hydroxide or potassium hydroxide.

7. The method according to claim 4, wherein In step 2), when detecting the concentration of the free acid, the concentration of the titration solution used is 0.01-0.18 mol / L; and the titration rate of the titration solution is 1-10 mL / min.

8. The method according to claim 4, wherein In step 3), when detecting the concentration of ammonium fluoride, the concentration of the titration solution is 0.10-2.00 mol / L; and the titration rate of the titration solution is 1-10 mL / min.

9. The method according to claim 2 or 4, wherein: Stirring is continuously applied at a rotation speed of 320-480 r / min, wherein the stirring is magnetic stirring or mechanical stirring.

10. Use of the method according to any one of claims 1 to 9 in quality testing of electronic grade ammonium fluoride.

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