Detection method of ammonium fluoride

Abstract

The invention belongs to the technical field of detection, and particularly relates to a detection method of ammonium fluoride. The detection method comprises the following steps: S1, detecting the concentration of free acid in an ammonium fluoride product by adopting a titration method, S2, adding a formaldehyde aqueous solution into the product obtained after detection in the step S1, and S3, detecting the concentration of ammonium fluoride in the product in the step S2 by adopting a titration method. Compared with an existing detection method in which the concentrations of the free acid and the ammonium fluoride are respectively detected, the method has the advantages that two independent steps are combined into two continuous steps, the processes of reagent preparation and the like are reduced, the detection efficiency is improved, the method is more suitable for automatic detection, and the efficiency and the accuracy are further improved. During manual acid-base titration, bromothymol blue is used as an indicator, and compared with bromocresol purple and phenolphthalein which are used as titration indicators in the prior art, the titration end point judgment is accurate and is closer to neutral, so that the obtained concentrations of free acid and ammonium fluoride are more accurate compared with the prior art.

Description

Technical Field

[0001] The invention belongs to the field of detection technology, and in particular relates to a method for detecting free acid and ammonium fluoride concentration in ammonium fluoride, and is particularly suitable for detecting electronic-grade ammonium fluoride. Background Art

[0002] Ammonium fluoride (NH4F) is an important compound with widespread applications in corrosion protection, disinfection, and chemical engineering. In the semiconductor industry, ammonium fluoride plays an increasingly important role, used for etching silicon wafers, as a cleaning agent, and as a polishing fluid. Electronic-grade ammonium fluoride used in the semiconductor industry is subject to stringent requirements for purity, particle size, moisture content, and acidity to ensure its effectiveness and reliability in semiconductor manufacturing.

[0003] Existing electronic-grade ammonium fluoride is typically produced by reacting ammonia (NH3) and hydrogen fluoride (HF). For example, Chinese patent publication number CN102557076A heats industrial-grade liquid ammonia to produce ammonia gas, which is then subjected to activated carbon adsorption and deoxidation to obtain high-purity ammonia gas. This is then absorbed with high-purity hydrofluoric acid to produce an electronic-grade aqueous ammonium fluoride solution. Another example is Chinese patent publication number CN117165961A, which reacts a hydrogen fluoride solution with ammonia water or ammonia gas. During the reaction, hydrogen fluoride is supplemented to control the pH to ≤5.0 to obtain a crude product. This crude product is then purified by ion exchange and ethanol dropwise dissolution to obtain electronic-grade ammonium fluoride.

[0004] However, even if the raw materials and crude products are purified as disclosed in the above patent application, the products may still contain free acids (mainly HF, NH4HF2), which will affect the etching effect, corrode the equipment, and affect the environment, so they need to be strictly controlled.

[0005] Existing detection methods typically use manual acid-base titration with sodium hydroxide as the titrant and bromocresol purple as the indicator to determine the free acid content. The titration endpoint is reached when the solution turns purple. Similarly, existing methods for detecting ammonium fluoride content also use manual acid-base titration. Formaldehyde solution is added to an ammonium fluoride solution, followed by titration with sodium hydroxide and 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 base consumed.

[0006] However, in the above detection method, the bromocresol purple and phenolphthalein indicators used cannot accurately indicate when the solution is neutral. When the pH value of phenolphthalein changes color, it has reached 8, and the concentration calculated from this will have a large error; and bromocresol purple changes from yellow to grayish brown and then to purple from acidic to neutral and then to alkaline. The boundary between grayish brown and purple is not obvious, and it is not easy to determine the titration end point. Different testers choose different equivalence points, so the test results will also be quite different. Secondly, the detection of free acid and ammonium fluoride content is carried out twice independently, and at least two ammonium fluoride samples need to be prepared for detection, and the detection efficiency is low. Summary of the Invention

[0007] The purpose of the present invention is to overcome the problems of inaccurate ammonium fluoride detection results and low detection efficiency in the prior art, and to provide a method for detecting free acid and ammonium fluoride concentration in ammonium fluoride.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for detecting ammonium fluoride comprises the following steps:

[0010] S1: Determine the concentration of free acid in the ammonium fluoride product by titration;

[0011] S2: adding formaldehyde aqueous solution to the product obtained after detection in step S1;

[0012] S3: Detect the concentration of ammonium fluoride in the product of step S2 by titration.

[0013] In the present invention, the ammonium fluoride product refers to an ammonium fluoride aqueous solution.

[0014] The method of the present invention combines the two independent detection methods of free acid and ammonium fluoride concentration in the prior art into a two-step continuous detection method. In step S1, the free acid content is detected and the free H + Regarding the impact on subsequent ammonium fluoride detection, the obtained product can be tested for ammonium fluoride content again after being treated with formaldehyde, thereby reducing the time for reagent preparation, container cleaning, etc. and improving detection efficiency.

[0015] In the present invention, the terms "content" and "concentration" are not strictly distinguished. This is because the concentration (molar concentration) can be calculated by the content (mass or molar amount) of a substance according to the following formulas (1) and (2). Therefore, when the method of the present invention is used to detect the free acid and ammonium fluoride obtained, both the content and the concentration can be easily interchanged. Therefore, in the present invention, the terms "content" and "concentration" are no longer distinguished and are used interchangeably, and the meanings expressed are the same.

[0016] Concentration = molar amount / volume (1)

[0017] Molar amount = mass / molar mass (2)

[0018] Preferably, in step S1, the concentration of the free acid is determined by titration. Titration is a mature and reliable method for determining the concentration of acid. In one embodiment of the present invention, manual acid-base titration is used to determine the concentration of the free acid. In other embodiments of the present invention, potentiometric titration or other suitable methods may also be used.

[0019] Preferably, the titration method in step S1 is a manual acid-base titration method or a potentiometric titrator detection method. When manual acid-base titration is used, titration solution I and indicator I are added to the ammonium fluoride product. The titration endpoint is determined when the solution changes color, and the free acid concentration is calculated based on the amount of titration solution I consumed. When potentiometric titration is used, the potential jump is detected as the titration endpoint, and the free acid concentration is calculated based on the amount of titration solution I consumed. Preferably, in step S2, formaldehyde is added as a solution. In one embodiment of the present invention, formaldehyde is added as an aqueous solution. There is no specific requirement for the concentration of the formaldehyde aqueous solution, but the requirement is that it reacts quickly and completely with ammonium fluoride. For example, the concentration can be 35-45% by mass, specifically 35%, 37%, 40%, 42%, or 45%, or any concentration range thereof. After the addition of formaldehyde, the reaction between ammonium fluoride and formaldehyde can be ensured to be complete by allowing the solution to stand for a while, for example, to form hexamethylenetetramine and acid, which provide conditions for the next step of detection. In step S2, the formaldehyde solution is added and then allowed to stand for 10-60 minutes. In other embodiments of the present invention, the formaldehyde solution may be slowly stirred after addition to promote the reaction.

[0020] Preferably, when in step S1, the amount of ammonium fluoride product used is 1-3 g and the concentration (mass fraction) is 32-38%, in step S2, the amount of formaldehyde aqueous solution added is 15-30 mL.

[0021] Preferably, the titration method in step S3 is an acid-base manual titration method or a potentiometric titrator detection method. When the acid-base manual titration is adopted, titration solution II and indicator II are added to the product of step S2. When the solution changes color, it is the titration end point. The concentration of ammonium fluoride is calculated based on the amount of titration solution II consumed. When the potentiometric titrator is adopted for detection, the potential jump point is the titration end point. The concentration of the free acid is calculated based on the amount of titration solution II consumed.

[0022] Preferably, in step S3, H is detected by titration. + Based on step S2, ammonium fluoride reacts with formaldehyde to generate acid, which can be detected by manual acid-base titration. +In other embodiments of the present invention, potentiometric titration or other suitable methods can also be used to determine the concentration of H + The concentration of ammonium fluoride. According to the equation of ionization and hydrolysis of ammonium fluoride, the hydrolyzed H + The content is the amount of ammonium fluoride, so the H + The concentration is the concentration of ammonium fluoride.

[0023] Preferably, in the above steps S1 and S3, bromothymol blue can be used as the indicator for both indicator I and indicator II, and the titration endpoint is when the solution turns green or blue.

[0024] Preferably, the concentration of indicator I or indicator II is 1-5 g / L.

[0025] Preferably, in the above steps S1 and S3, the titration solution I and the titration solution II may both be aqueous solutions of inorganic bases.

[0026] In one embodiment of the invention, in step S1, detect the content of free acid with acid-base manual titration, wherein bromothymol blue is as titration indicator, and its color-changing pH range is 6.0-7.6, and when solution is acidic state, it is yellow, along with the increase of pH, when reaching neutrality (pH is about 7), presents light green, and pH continues to increase and reaches alkalescence and is then changed into blue.And the color change of bromothymol blue is crisp, does not have obvious transition color, therefore judges that terminal point is accurate, and the influence of different people's judgment error is less.Therefore in the ammonium fluoride solution containing free acid, along with the adding of inorganic alkali, solution acidity can be reduced gradually, alkalescence strengthens, and solution is titrated to reach terminal point when being changed into green or blue by yellow, and by the concentration of titration solution, volume and the volume of solution to be tested, the content of free acid in solution to be tested can be calculated.

[0027] In another embodiment of the present invention, in step S3, bromothymol blue is used as a titration indicator, and an inorganic base is used to titrate the amount of the acid obtained after the reaction of ammonium fluoride and formaldehyde, and the molar amount of ammonium fluoride is equal to the H of the acid obtained after the reaction of ammonium fluoride and formaldehyde. + As mentioned above, the color change of bromothymol blue is crisp and the error is small, so the amount of acid obtained by the reaction of ammonium fluoride can be accurately obtained and the amount of ammonium fluoride can be calculated.

[0028] In the present invention, bromothymol blue is selected, and its characteristics of obvious and crisp color change and pH value color change range being in the neutral range are utilized. It can realize accurate titration endpoint indication by itself without the need to be combined with other indicators, such as neutral red.

[0029] It should be noted that bromothymol blue shows a light green color at a pH of about 7, which is the optimal endpoint of the titration. However, considering that the concentration of the acid obtained by the reaction of free acid and ammonium fluoride is low, with the addition of the inorganic base titration solution, there is a certain amount of titration solution added that causes the acid-containing solution to be tested to change from acidic to alkaline, that is, the acid in it is not only completely neutralized, but there is still excess OH - , and the probability of this possibility occurring is relatively high. Usually, the acid content obtained in this case is within the allowable error range, so the blue color of the solution is also allowed to be used as the endpoint of the titration.

[0030] The titration solution I and titration solution II in the present invention refer to standard solutions with known concentrations, which are added dropwise to the solution to be tested containing the free acid and the indicator to separate the free acid / H + Reagents for the reaction.

[0031] Preferably, the inorganic base is sodium hydroxide or potassium hydroxide. Sodium hydroxide or potassium hydroxide is a strong base that reacts quickly with acid, is cheap and readily available, has little side reaction, and provides accurate test results.

[0032] Further preferably, in step S1, when titrating the free acid, considering that the free acid concentration is low, a 0.1 mol / L inorganic base titration solution can be selected. For example, in one embodiment of the present invention, a 0.1 mol / L NaOH solution is selected for titrating the free acid. For another example, in another embodiment of the present invention, a 0.1 mol / L KOH solution is selected for titration. Of course, the concentration of the titration solution I in step S1 is not limited to 0.1 mol / L, and can also be any value within a range of concentrations such as 0.05 mol / L, 0.08 mol / L, 0.12 mol / L, 0.15 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.8 mol / L, 1 mol / L, or the like, or a range of concentrations thereof, preferably 0.05 to 1 mol / L. For example, in another embodiment of the present invention, a 0.5 mol / L KOH solution or a NaOH solution is selected.

[0033] Further preferably, in step S3, when titrating ammonium fluoride, a 1mol / L inorganic base titration solution can be selected. In one embodiment of the present invention, a 1mol / L NaOH solution is selected for titrating ammonium fluoride. For example, in other embodiments of the present invention, a 1mol / L KOH solution is selected for titration. Of course, the titration solution in step S3 is not limited to 1mol / L, and can also be any value in the range of concentrations such as 0.2mol / L, 0.3mol / L, 0.5mol / L, 0.7mol / L, 0.8mol / L, 1.1mol / L, 1.2mol / L, 1.5mol / L, 1.8mol / L, 2mol / L, or the like, or the interval composed of the above concentrations, preferably 0.2 to 2mol / L. For example, in another embodiment of the present invention, a 0.5mol / L NaOH solution or a KOH solution is selected.

[0034] Preferably, the ammonium fluoride is electronic grade ammonium fluoride. Electronic grade ammonium fluoride has strict requirements on impurity content and ammonium fluoride concentration, while the solution of the present invention can obtain high-precision concentration detection results, and is therefore particularly suitable for the detection of electronic grade ammonium fluoride.

[0035] Preferably, in step S1, a potentiometric titrator can be used to detect the content of free acid, and in step S3, a potentiometric titrator can be used to detect the content of H + In one embodiment of the present invention, the detection method in step S1 and step S3 can be detected simultaneously using a potentiometric titrator, and the titration end point is determined by the sudden change of potential, thereby determining the content of free acid and ammonium fluoride.

[0036] Compared with the prior art, the advantages of the present invention are:

[0037] 1. Compared with the existing detection method in which the free acid and ammonium fluoride concentrations are detected separately, the detection method of ammonium fluoride disclosed in the present invention combines two independent steps into two continuous steps, thereby reducing the preparation of reagents and other processes, improving the efficiency of detection, and being more suitable for automated detection. For example, through the potentiometric titration method, both efficiency and accuracy are further improved.

[0038] 2. In the manual acid-base titration of the present invention, bromothymol blue is used as an indicator. Compared with the prior art using bromocresol purple and phenolphthalein as titration indicators, the titration endpoint is accurately judged and closer to neutrality. Therefore, the obtained free acid and ammonium fluoride concentrations are more accurate than those in the prior art. DETAILED DESCRIPTION

[0039] 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.

[0040] 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.

[0041] The ammonium fluoride products (aqueous solutions) 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.

[0042] The NaOH solutions used in the following examples and comparative examples were self-prepared NaOH solutions with 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.

[0043] In the following examples and comparative examples, the titration apparatus, beaker, and other equipment and containers were cleaned before each experiment. Furthermore, the titrator's tubing, electrodes, container, stirring paddle, and other related components were cleaned with distilled water before each experiment to avoid residue from the previous experiment.

[0044] In the following examples and comparative examples, the concentrations of free acid and ammonium fluoride are expressed in mass percentages, wherein the free acid is expressed as HF.

[0045] In the following examples and comparative examples, the ammonium fluoride product refers to an aqueous solution of ammonium fluoride.

[0046] In the following examples and comparative examples, the terms "content" and "concentration" are not strictly distinguished. This is because the concentration (molar concentration) can be calculated by the content (mass or molar amount) of a substance according to the following formulas (1) and (2). Therefore, when testing according to the method of the present invention, the free acid and ammonium fluoride obtained can be simply interchanged in terms of both content and concentration. Therefore, in the present invention, the terms "content" and "concentration" are no longer distinguished and are used interchangeably, and the meanings expressed are the same.

[0047] Concentration = molar amount / volume (1)

[0048] Molar amount = mass / molar mass (2)

[0049] Example 1

[0050] A method for detecting ammonium fluoride adopts manual titration, and the specific steps are as follows:

[0051] S1: The concentration of free acid in the ammonium fluoride product (aqueous solution) (standardized concentration 34%) was detected 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 about 30 mL of water. The solution was titrated with 0.1 mol / L NaOH standard solution and 3 drops of 1 g / L bromothymol blue 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%;

[0052] S2: Add 20 mL of 35% formaldehyde solution to the product obtained in step S1, shake well, and let it stand for 40 minutes;

[0053] S3: The product obtained in step S2 is titrated by acid-base titration to measure 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.

[0054] Example 2

[0055] A method for detecting ammonium fluoride adopts manual titration, and the specific steps are as follows:

[0056] S1: The concentration of free acid in the ammonium fluoride product (aqueous solution) (standardized concentration 40%) was detected by acid-base titration. Specifically, 2.6354 g of the sample (ammonium fluoride product) was weighed into a 250 mL ground-joint sealed conical flask pre-filled with about 30 mL of water. The solution was titrated with 1 mol / L NaOH standard solution and 3 drops of 1 g / L bromothymol blue 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 0.36 mL), the free acid concentration in the ammonium fluoride was calculated to be 0.27%;

[0057] S2: Add 15 mL of 40% formaldehyde solution to the product obtained in step S1, shake well, and let it stand for 60 minutes;

[0058] S3: The product obtained in step S2 is titrated by acid-base titration to measure H +The concentration is titrated with 1 mol / L NaOH standard titrant. The titration endpoint is when the solution color changes from yellow to blue. At this time, the amount of NaOH standard titrant used is V2 (specifically 24.51 mL). Therefore, the volume of NaOH consumed in this step is V2-V1, and H is calculated from this. + The concentration is 33.91%, which is the concentration of ammonium fluoride.

[0059] Example 3

[0060] A method for detecting electronic grade ammonium fluoride, comprising the following steps:

[0061] S1: Use a potentiometric titrator to detect the concentration of free acid in the ammonium fluoride product (aqueous solution) (standardized concentration 34%). Specifically, weigh 1.5364 g of sample into a 100 mL polytetrafluoroethylene beaker pre-added with about 50 mL of water, place it on the titration table of a Metrohm OMNISTitrator potentiometric titrator, and titrate with 0.1 mol / L NaOH solution at a titration rate of 4 mL / min. When the potential jumps, it is the end point. The potentiometric titrator automatically records the consumption of NaOH standard titrant (specifically 0.6609 mL) and calculates the free acid concentration, which is 0.0861%;

[0062] S2: Add 18 mL of 38% formaldehyde solution to the product obtained in step S1, shake well, and let it stand for 15 minutes;

[0063] S3: The product obtained in step S2 is titrated by acid-base titration to measure H + The concentration of 1g / L bromothymol blue was added as an indicator, and titrated with 0.8mol / L NaOH solution. The titration endpoint was when the solution color changed from yellow to blue. Based on the volume of NaOH consumed in this step (specifically 17.79mL), H + The concentration of , that is, the concentration of ammonium fluoride, is 34.27%.

[0064] Example 4

[0065] A method for detecting electronic grade ammonium fluoride, comprising the following steps:

[0066] S1: Use a potentiometric titrator to detect the concentration of free acid in the ammonium fluoride product (aqueous solution) (standardized concentration 34%). Specifically, weigh 1.5657 g of the sample into a plastic cup pre-filled with 40 mL of water. Place the cup on the titration platform of a Metrohm OMNIS Titrator potentiometric titrator and titrate with 0.1 mol / L NaOH standard titrant at a titration rate of 4 mL / min. When the potential jump reaches the first equivalence point, the potentiometric titrator automatically records the consumption of NaOH standard titrant (specifically 0.7250 mL) and calculates the free acid concentration, which is 0.0927%;

[0067] S2: Titration was continued using a potentiometric titrator with a 1 mol / L NaOH standard titrant. When the potential jumped, the second equivalence point was reached. Based on the volume of the consumed NaOH standard titrant (specifically, 14.4040 mL), the concentration of ammonium fluoride was calculated to be 34.03%.

[0068] Comparative Example 1

[0069] The concentrations of free acid and ammonium fluoride in electronic grade ammonium fluoride are determined using traditional methods as follows:

[0070] S1: Use acid-base titration to detect the concentration of free acid in the ammonium fluoride product (aqueous solution): take about 1g of ammonium fluoride aqueous solution, add bromocresol purple indicator (0.1g bromocresol purple dissolved in 100mL 95% ethanol as an indicator), and use 0.1mol / L NaOH solution as the titrant to perform acid-base titration. When the color of the solution turns purple, it is the titration endpoint. The free acid concentration is calculated based on the consumption of NaOH and is 0.30%;

[0071] S2: Use acid-base titration to detect the concentration of ammonium fluoride. Take about 0.5g of ammonium fluoride, add 40mL of 35% formaldehyde solution, shake evenly, and let it stand for 40 minutes. Then add 2 drops of phenolphthalein as an indicator and titrate with 1mol / L NaOH solution. When the solution turns pink, the titration reaches the endpoint. Record the volume of NaOH consumed and calculate H + The concentration of , that is, the concentration of ammonium fluoride, is 34.15%.

[0072] As can be seen from Comparative Example 1, the data of Examples 1-4 obtained according to the scheme of the present invention have ammonium fluoride concentrations that are within a reasonable error range compared to the concentration of Comparative Example 1; as for the concentration of the free acid, the results of Examples 1-2 and Comparative Example 1 using manual titration in the present invention show that the concentration detection results are also within the same range, thereby demonstrating the rationality and accuracy of the scheme of the present invention.

[0073] It should also be noted that, through Examples 3-4, it can be found that the concentration obtained by using the potentiometric titrator is much lower than the result of manual titration. It can be seen that the titration endpoint judgment of the potentiometric titrator is more accurate and sensitive, and more accurate, and its application in the detection of ammonium fluoride is also extremely valuable.

[0074] Choice of titration indicator:

[0075] Table 1 Color change range of each indicator

[0076] Indicator name Bromothymol blue Bromocresol purple Phenolphthalein pH 6.0-7.6 5.2-6.8 8.2-10.0 color Yellow-Blue Yellow-Purple Colorless-pink

[0077] As can be seen from Table 1 above: the color change range of the bromothymol blue indicator just spans the neutral point (pH 7.0) and is more suitable for indicating whether the pH changes from weak acidity to weak alkalinity. The titration endpoint is closer to neutrality and the color is easy to observe. The bromocresol purple indicator indicates a weak acid endpoint, and the purple color change is not as easy to observe as the blue color. The phenolphthalein indicator shows a weak alkalinity at the titration endpoint (pH 8.2> pH 7.0) as can be seen from the color change range. It cannot be used as the best indicator for titrating the free acid and concentration of ammonium fluoride. Therefore, the bromothymol blue indicator is the best indicator for titrating the free acid and concentration of ammonium fluoride.

[0078] Selection of detection method:

[0079] Table 2 Differences between manual test and instrument test

[0080] Test Method Auxiliary reagents Titration endpoint Detection time Manual testing formaldehyde Visual judgment, large deviation 50min Instrument testing unnecessary Instrument judgment, small deviation 15min

[0081] As can be seen from Table 2 above: titration test can be performed without adding formaldehyde using potentiometric titrator, while reducing detection time, greatly improving work efficiency while saving energy, reducing emissions and consumption.

[0082] 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: S1: Determine the concentration of free acid in the ammonium fluoride product by titration; S2: adding formaldehyde aqueous solution to the product obtained after detection in step S1; S3: Detect the concentration of ammonium fluoride in the product of step S2 by titration.

2. The method according to claim 1, wherein The titration method in step S1 is an acid-base manual titration method or a potentiometric titrator detection method. When manual acid-base titration is used, titration solution I and indicator I are added to the ammonium fluoride product. When the solution changes color, it is the titration end point. The concentration of the free acid is calculated based on the amount of titration solution I consumed. When a potentiometric titrator is used for detection, the potential jump point is the titration end point. The concentration of the free acid is calculated based on the amount of titration solution I consumed.

3. The method according to claim 1, wherein In step S2, the mass concentration of the formaldehyde aqueous solution is 35-45%.

4. The method according to claim 1, wherein In step S2, the formaldehyde aqueous solution is added and then allowed to stand for 10-60 minutes.

5. The method according to claim 2, wherein The titration method in step S3 is an acid-base manual titration method or a potentiometric titrator detection method. When the acid-base manual titration is adopted, titration solution II and indicator II are added to the product of step S2. When the solution changes color, it is the titration end point. The concentration of ammonium fluoride is calculated based on the amount of titration solution II consumed. When the potentiometric titrator is used for detection, the potential jump point is the titration end point. The concentration of the free acid is calculated based on the amount of titration solution II consumed.

6. The method according to claim 5, wherein In steps S1 and S3, both indicator I and indicator II use bromothymol blue as an indicator, and the titration endpoint is when the solution turns green or blue.

7. The method according to claim 5, wherein In steps S1 and S3, titration solution I and titration solution II are both aqueous solutions of inorganic bases; The inorganic base is sodium hydroxide or potassium hydroxide.

8. The method according to claim 5, wherein When titrating the free acid in step S1, the concentration of the titration solution I is 0.05-1 mol / L.

9. The method according to claim 5, wherein When titrating ammonium fluoride in step S3, the concentration of titration solution II is 0.2-2 mol / L.

10. The method according to claim 1, wherein The ammonium fluoride is electronic grade ammonium fluoride.