Determination method of phosphate radicals in fluosilicic acid

Abstract

The invention discloses a method for determining phosphate radicals in fluosilicic acid, which comprises the following steps: pretreating a fluosilicic acid stock solution sample and adjusting the pH value to obtain a pH-adjusted sample solution; carrying out interfering ion masking treatment on the pH-adjusted sample solution through a boric acid solution to obtain a pretreated to-be-detected solution; carrying out phosphomolybdenum blue chromogenic reaction treatment on the pretreated to-be-detected solution to obtain a chromogenic detection solution; performing spectrophotometric determination treatment on the developed determination solution to obtain sample absorbance and a standard curvilinear equation; and calculating the concentration based on the sample absorbance, the standard curve equation and the dilution ratio to obtain the content of phosphate radicals in fluosilicic acid. Interference of fluorine ions and silicic acid is effectively eliminated, and accurate, rapid and economical determination of phosphate radicals in fluosilicic acid is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of chemical industry, and more particularly relates to a method for determining phosphate in fluosilicic acid. BACKGROUND

[0002] As an important inorganic chemical raw material, fluosilicic acid is widely used in fluoride preparation, metal surface treatment, glass etching, water treatment and other industrial fields. With the rapid development of electronic industry and photovoltaic industry, the demand for high-purity fluosilicic acid is increasing. As a key impurity index in fluosilicic acid, the content of phosphate directly affects the product quality and application performance. In particular, in high-end applications such as semiconductor cleaning and solar cell manufacturing, the content of phosphate needs to be strictly controlled at the ppm level. Therefore, it is of great significance to establish an accurate and reliable method for determining phosphate for the development of fluosilicic acid industry.

[0003] In related technologies, the methods for determining phosphate mainly include phosphomolybdenum blue spectrophotometry, ion chromatography, ICP-AES method, etc. However, these methods all have significant problems in the fluosilicic acid system: when directly applied, the phosphomolybdenum blue spectrophotometry competes with molybdate for reaction, resulting in incomplete color development and serious underestimation of the determination results; although the ion chromatography has good selectivity, the strong corrosiveness of fluosilicic acid can damage the chromatographic column and detector, and the equipment maintenance cost is high; in the ICP-AES method, high concentration of fluoride ions causes unstable plasma and serious matrix interference, and the instrument is expensive and not suitable for routine detection; in addition, the existing methods generally ignore the problem of polymerization and precipitation of silicic acid in the fluosilicic acid system during pH adjustment, resulting in co-precipitation loss of phosphate and affecting the accuracy of determination.

[0004] Therefore, how to effectively eliminate the interference of fluoride ions and silicic acid and realize accurate, rapid and economical determination of phosphate in fluosilicic acid is an important problem for those skilled in the art. SUMMARY

[0005] The purpose of the present application is to provide a method for determining phosphate in fluosilicic acid, which effectively eliminates the interference of fluoride ions and silicic acid and realizes accurate, rapid and economical determination of phosphate in fluosilicic acid.

[0006] In view of the above defects or improvement needs of the prior art, the present application provides a method for determining phosphate in fluosilicic acid, comprising: Pretreating and pH adjusting a fluosilicic acid stock solution sample to obtain a pH-adjusted sample solution; Interfering ion masking the pH-adjusted sample solution with a boric acid solution to obtain a pretreated test solution; Phosphomolybdenum blue color development reaction of the pretreated test solution to obtain a color-developed determination solution; The spectrophotometric determination process is performed on the developed color determination solution to obtain sample absorbance and standard curve equation; Based on the sample absorbance, the standard curve equation, and the dilution multiple, the concentration is calculated to obtain the phosphoric acid radical content in fluosilicic acid.

[0007] Optionally, the fluosilicic acid stock sample is pretreated and pH adjusted to obtain a pH-adjusted sample solution, including: The deionized water and the dilution concentration are used to dilute the fluosilicic acid stock sample to obtain a diluted fluosilicic acid sample solution, and the dilution multiple is recorded; The ammonia solution and the target pH are used to adjust the pH of the diluted fluosilicic acid sample solution to obtain the pH-adjusted sample solution, and the amount of ammonia water is recorded.

[0008] Optionally, the pH-adjusted sample solution is subjected to interference ion masking treatment by boric acid solution to obtain a pretreated test solution, including: The boric acid solution is added to the pH-adjusted sample solution, and stirred for a predetermined time to form a fluoro-boric acid complex, obtaining a fluorine ion masked solution, and the amount of boric acid is recorded; The potassium sodium tartrate solution is added to the fluorine ion masked solution to obtain a pretreated test solution, and the amount of potassium sodium tartrate is recorded.

[0009] Optionally, the pretreated test solution is subjected to phosphomolybdate blue color development reaction treatment to obtain a developed color determination solution, including: The ammonium molybdate, sulfuric acid, and ascorbic acid reagents are used to prepare a color developer and a reducing agent; The color developer and the reducing agent are sequentially added to the pretreated test solution, and the developed color determination solution is obtained after mixing.

[0010] Optionally, the developed color determination solution is subjected to spectrophotometric determination to obtain sample absorbance and standard curve equation, including: The sample absorbance and blank absorbance are obtained by determining the developed color determination solution and blank control solution with a spectrophotometer; The standard curve equation is obtained by determining the standard curve based on a series of phosphoric acid radical standard solutions.

[0011] Optionally, the standard curve equation is obtained by determining the standard curve based on a series of phosphoric acid radical standard solutions, including: The phosphoric acid radical standard solution series is subjected to color development reaction to determine the absorbance of the solution under each standard; The standard curve equation is determined based on the absorbance of the solution under each standard.

[0012] Optionally, the concentration is calculated based on the sample absorbance, the standard curve equation, and the dilution multiple to obtain the phosphoric acid content in the fluosilicic acid, comprising: The concentration is calculated based on the sample absorbance, the standard curve equation, the dilution multiple, the amount of ammonia, the amount of boric acid, and the amount of potassium sodium tartrate to obtain the phosphoric acid content in the fluosilicic acid.

[0013] The method for determining the phosphoric acid content in fluosilicic acid provided by the present application comprises: pretreating and pH adjusting a fluosilicic acid stock solution sample to obtain a pH-adjusted sample solution; performing interference ion masking treatment on the pH-adjusted sample solution by using a boric acid solution to obtain a pretreated test solution; performing phosphomolybdate blue color development reaction treatment on the pretreated test solution to obtain a color-developed determination solution; performing spectrophotometric determination treatment on the color-developed determination solution to obtain a sample absorbance and a standard curve equation; and calculating the concentration based on the sample absorbance, the standard curve equation, and a dilution multiple to obtain the phosphoric acid content in the fluosilicic acid.

[0014] The method has the following beneficial effects: Through the pretreatment and pH adjustment steps, the matrix interference of the fluosilicic acid is effectively reduced, and suitable reaction conditions are created; the boric acid complexation masking technology is used to completely eliminate the interference of fluorine ions on the phosphomolybdate blue reaction; the optimized color development reaction conditions ensure the complete color development and stability of the phosphoric acid; the spectrophotometric determination combined with the standard curve method realizes accurate quantification; and the volume correction calculation method eliminates the systematic error caused by the pretreatment process. The entire method is simple to operate, the reagents are easy to obtain, and the cost is low, which is suitable for routine laboratory development, overcomes the technical difficulties of the prior art in determining the phosphoric acid content in the fluosilicic acid system, provides a reliable analysis means for the quality control of the fluosilicic acid product, and has important industrial application value. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiment or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only embodiments of the present application, and those skilled in the art can obtain other drawings according to the provided drawings without creating any inventive labor.

[0016] Figure 1 The flowchart of the method for determining the phosphoric acid content in fluosilicic acid provided by the embodiments of the present application. DETAILED DESCRIPTION

[0017] The application aims to provide a method for determining phosphate in fluosilicic acid, so as to effectively eliminate the interference of fluorine ions and silicic acid, and realize accurate, rapid and economical determination of phosphate in fluosilicic acid.

[0018] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0019] The method for determining phosphate in fluosilicic acid provided by the present application is described below through an embodiment.

[0020] Reference is made to Figure 1 , Figure 1 The flowchart of the method for determining phosphate in fluosilicic acid provided by the present application is shown in the embodiment.

[0021] The method can include the following steps in the embodiment: S101, pretreating and pH adjusting the fluosilicic acid stock solution sample to obtain a sample solution after pH adjustment; This step aims to pretreat and pH adjust the fluosilicic acid stock solution sample to obtain a sample solution after pH adjustment. The fluosilicic acid stock solution has strong acidity and high concentration characteristics. Direct determination of phosphate will cause multiple problems: high concentration of fluorine ions causes serious matrix interference; the phosphomolybdenum blue color reaction cannot be normally performed in a strong acidic environment; and high ionic strength affects the accuracy of spectrophotometric determination. Therefore, the fluosilicic acid stock solution must be pretreated and pH adjusted to create conditions suitable for determination of phosphate. The core purpose of pretreatment is to reduce the concentration of fluosilicic acid to a controllable range, and pH adjustment is to create an optimal acidity environment for subsequent color reaction.

[0022] Optionally, this step can include the following steps: Step 1, diluting the fluosilicic acid stock solution sample with deionized water and diluting the concentration to obtain a diluted fluosilicic acid sample solution, and recording the dilution multiple; Step 2, adjusting the pH of the diluted fluosilicic acid sample solution with an ammonia solution and a target pH to obtain a sample solution after pH adjustment, and recording the amount of ammonia water.

[0023] Optionally, this step can further include the following steps: Firstly, sample dilution: accurately take 1.0-5.0 mL of fluosilicic acid stock solution, place it in a 100 mL volumetric flask, dilute to the mark with deionized water, so that the concentration of the diluted fluosilicic acid is controlled in the range of 0.5-2.0%. This concentration range can effectively reduce the matrix interference, and can ensure that the concentration of phosphate is within the detection range. During the dilution process, water should be added slowly and mixed thoroughly to avoid local high concentration and heat effect.

[0024] Then, pH adjustment: transfer the diluted sample solution to a beaker, slowly add ammonia solution (concentration 10-15%) under magnetic stirring, and monitor the pH value of the solution in real time using a pH meter. The addition speed is controlled at 1-2 mL / min to avoid excessive local alkalinity leading to rapid precipitation of silicic acid. Stop adding when the pH value reaches 1.5-2.5, and continue stirring for 2-3 minutes to make the system uniform. This pH range is the optimal acidity for the phosphomolybdate blue reaction, which can ensure that molybdate reacts fully with phosphate, and can avoid excessive pH value leading to massive precipitation of silicic acid.

[0025] Through this step, the concentration of fluosilicic acid is reduced to an appropriate range, effectively reducing the interference of fluoride ions on subsequent determination; the pH value is adjusted to the optimal range, creating ideal acidity conditions for the phosphomolybdate blue color reaction; the dilution and pH adjustment process is controllable, ensuring the reproducibility of the method; the whole process is simple and fast, suitable for routine analysis applications.

[0026] S102, the sample solution after pH adjustment is treated with boric acid solution to mask interfering ions, obtaining a pretreated sample solution; Based on S101, this step aims to mask interfering ions in the sample solution after pH adjustment by boric acid solution, obtaining a pretreated sample solution.

[0027] It can be seen that the fluoride ion in the fluosilicic acid system is the main interference source for phosphate determination, and its interference mechanism is as follows: fluoride ion forms a stable fluoromolybdate complex with molybdate, consuming molybdate reagent for phosphate development; fluoride ion also competes with phosphomolybdic acid for coordination, destroying the structure of the color complex, resulting in reduced absorbance. The traditional method of determining phosphate does not consider the interference of fluoride ions, and the direct determination error can be more than 30%. Boric acid, as a specific masking agent for fluoride ions, can form a stable fluoroboric acid complex (BF4-) with fluoride ions, effectively eliminating the interference of fluoride ions on the phosphomolybdate blue reaction. The advantage of choosing boric acid masking is that the fluoroboric acid complex has a large stability constant (lgK=19.8), and the masking effect is complete; boric acid itself does not interfere with the phosphomolybdate blue reaction; the formed fluoroboric acid complex has no absorption at the determination wavelength.

[0028] Optionally, this step can include: Step 1, add boric acid solution to the pH-adjusted sample solution and stir for a preset time to form a fluoroboric acid complex, obtain a solution after fluorine ion masking, and record the amount of boric acid used; Step 2, add potassium sodium tartrate solution to the solution after fluorine ion masking to obtain a pretreated solution to be measured, and record the amount of potassium sodium tartrate used.

[0029] Optionally, this step can also include: According to the content of fluorine ions in the sample, calculate the amount of boric acid used according to the molar ratio of fluorine ions to boric acid of 1:3-5. Prepare a 3-5% boric acid solution to ensure complete dissolution of boric acid. Place the pH-adjusted sample solution on a magnetic stirrer, slowly add the calculated amount of boric acid solution after starting stirring. The addition speed is controlled at 2-3 mL / min to avoid local high concentration. After the addition of boric acid is completed, continue to stir for 5-10 minutes to ensure that the fluorine ions react with the boric acid to form a fluoroboric acid complex. The solution remains clear and transparent during the reaction without precipitation.

[0030] For the possible polymerization interference of silicic acid, a 5-10% potassium sodium tartrate solution (10%) can be added to the sample volume. Its role is to form a soluble complex with silicic acid to prevent silicic acid from polymerizing and precipitating in subsequent processing. The entire masking process is carried out at room temperature without heating or special conditions.

[0031] As can be seen, in this step, the fluorine ions are completely complexed into fluoroboric acid, eliminating their interference with the phosphomolybdate blue reaction and significantly improving the accuracy of the determination results. The masking reaction conditions are mild and easy to operate, suitable for batch sample processing. The amount of boric acid can be flexibly adjusted according to the fluorine content, and the method has strong applicability. The stability of the masked solution is good, and the entire masking process does not introduce new interference, ensuring the selectivity of the method.

[0032] S103, pretreated solution to be measured is subjected to phosphomolybdate blue color reaction treatment to obtain a colored determination solution; Based on S102, this step aims to pretreat the solution to be measured to obtain a colored determination solution.

[0033] The phosphomolybdate blue color reaction is a classical method for quantitative analysis of phosphate, which is based on the principle that under acidic conditions, orthophosphate reacts with ammonium molybdate to form yellow phosphomolybdate heteropoly acid, which is reduced to blue phosphomolybdate blue complex by a reducing agent, with maximum absorption at 880 nm. The key to the color reaction is to control the reaction conditions, including acidity, ammonium molybdate concentration, reducing agent type and amount, reaction temperature and time, etc. After the aforementioned pretreatment and masking treatment, the interference factors in the test solution have been effectively eliminated, creating ideal conditions for the phosphomolybdate blue reaction. Compared with the traditional stannous chloride, ascorbic acid is selected as the reducing agent, which has the advantages of moderate reducing ability, stable color development, non-toxicity and environmental friendliness.

[0034] Optionally, this step can include: Step 1, ammonium molybdate, sulfuric acid, ascorbic acid reagent for color developing agent preparation and reducing agent preparation, to obtain color developing agent and reducing agent; Step 2, the pretreated test solution is added with color developing agent and reducing agent in sequence, and after mixing, the colored test solution is obtained.

[0035] Optionally, this step can also include: First, prepare the color reagent, including ammonium molybdate-sulfuric acid mixed solution (ammonium molybdate 2.5 g / L, sulfuric acid 0.5 mol / L) and ascorbic acid solution (10 g / L). The reagent should be prepared and used immediately, especially the ascorbic acid solution should be prepared within 30 minutes before use to avoid oxidation failure. Accurately transfer 25 mL of pretreated test solution into a 50 mL colorimetric tube, add 5 mL of ammonium molybdate-sulfuric acid mixed solution in sequence, mix thoroughly, and then add 2 mL of ascorbic acid solution. The order of addition must not be reversed, the phosphomolybdate heteropoly acid must be formed first, and then the reduction reaction is carried out.

[0036] After adding the reagent each time, it needs to be mixed immediately, which can be done by inversion mixing or vortex mixing. After mixing, place the colorimetric tube in a constant temperature water bath and react at 25±2℃ for 15 minutes. Temperature control is crucial, too low temperature will slow down the reaction speed and the color development will not be complete; too high temperature will cause the decomposition of phosphomolybdate blue, affecting the accuracy of the determination. After the reaction is completed, the solution presents a stable blue color, and the color depth is proportional to the concentration of phosphate.

[0037] The color reaction in this step is complete, reproducible, and the relative standard deviation is less than 2%; the color product is stable, and the absorbance changes less than 1% within 2 hours at room temperature; the reaction conditions are mild and controllable, suitable for routine laboratory operation; the reagent consumption is small, the cost is low, and the environment is friendly; the color development sensitivity is high, and the detection limit can reach 0.05 mg / L; the linear range is wide, which can cover the phosphate concentration of 0.1-10 mg / L.

[0038] S104, the colored test solution is subjected to spectrophotometric determination to obtain the sample absorbance and the standard curve equation; On the basis of S103, this step aims to perform spectrophotometric determination on the developed determination solution to obtain the sample absorbance and the standard curve equation.

[0039] The spectrophotometric determination is based on the Lambert-Beer law, i.e., the absorbance of a solution is proportional to the concentration of the light-absorbing substance in the solution. The phosphomolybdate blue complex has a characteristic absorption peak at 880 nm, and the absorption of other substances at this wavelength is minimal. By determining the absorbance of the developed solution at 880 nm, the content of phosphate can be quantitatively analyzed. The spectrophotometric method has the advantages of widespread instruments, simple operation, and satisfactory precision, and is the preferred method for routine analysis of phosphate. The establishment of the standard curve is the basis for quantitative analysis, and the linear relationship between absorbance and concentration is established through a series of known-concentration phosphate standard solutions, providing a basis for the quantitative analysis of unknown samples.

[0040] Optionally, this step can include: Step 1: Based on the developed determination solution and the blank control solution, the spectrophotometer is used to determine the sample absorbance and the blank absorbance. Step 2: Based on the series of phosphate standard solutions, the standard curve is determined to obtain the standard curve equation.

[0041] The determination of the standard curve based on the series of phosphate standard solutions includes: performing color reaction on the series of phosphate standard solutions, determining the absorbance of the solution under each standard, and determining the standard curve equation based on the absorbance of the solution under each standard.

[0042] Optionally, this step can also include: Firstly, sample determination: After color development, the determination solution is transferred to a 1cm-path cuvette, and the reagent blank (without phosphate color system) is used as the reference to determine the absorbance at 880 nm on the spectrophotometer. The instrument needs to be preheated for 30 minutes before determination to ensure the stability of the light source and detector. The cuvette needs to be rinsed with the sample solution for 2-3 times, and the outer wall needs to be wiped clean to avoid fingerprints and stains affecting the determination. Each sample needs to be determined at least 3 times, and the average value is taken as the sample absorbance As.

[0043] Secondly, standard curve establishment: Prepare a phosphate standard stock solution (100mg / L), and dilute it step by step to obtain a series of standard solutions of 0.1, 0.5, 1.0, 2.0, 5.0, and 10.0mg / L. Each standard solution is treated under the same color development conditions as the sample to determine the absorbance. The phosphate concentration is taken as the abscissa, and the absorbance is taken as the ordinate to draw the standard curve. The least squares method is used for linear regression to obtain the standard curve equation A=kC+b, where A is the absorbance, C is the phosphate concentration, k is the slope, and b is the intercept. The correlation coefficient r 2Should be greater than 0.999, indicating a good linear relationship.

[0044] The wavelength selected in this step is 880 nm, which avoids the absorption interference of other substances and has good selectivity. The reagent blank correction is used to eliminate the background absorption of reagents and solvents. The standard curve method is used for quantification to avoid the influence of instrument response fluctuation. The linear range is wide (0.1-10 mg / L), which can cover the common concentration range of phosphates in fluorosilicic acid. The determination precision is high, and the RSD of parallel determination is less than 1%. The detection limit of the method is low (0.05 mg / L), which meets the requirements of trace analysis.

[0045] In S105, the concentration of phosphates in fluorosilicic acid is calculated based on the sample absorbance, standard curve equation, and dilution factor.

[0046] On the basis of S104, this step aims to calculate the concentration of phosphates in fluorosilicic acid based on the sample absorbance, standard curve equation, and dilution factor.

[0047] Concentration calculation is the data processing process of converting the measured absorbance signal into the actual content of phosphates. Since the sample has undergone multiple pretreatments such as dilution, pH adjustment, and masking agent addition, the phosphorus concentration of the determination solution is not equal to the concentration in the original fluorosilicic acid sample, and strict conversion is required. The calculation process must consider all dilution and volume change factors to ensure the accuracy of the results. This method innovatively introduces a volume correction factor to compensate for the volume change caused by the addition of reagents, which significantly improves the analysis accuracy.

[0048] Optionally, this step can include: calculating the concentration of phosphates in fluorosilicic acid based on the sample absorbance, standard curve equation, dilution factor, ammonia usage, boric acid usage, and potassium sodium tartrate usage.

[0049] Further, it can include: First, calculate the net absorbance: ΔA = As - A0, where As is the sample absorbance and A0 is the reagent blank absorbance. The net absorbance eliminates background interference.

[0050] Then, calculate the concentration of phosphates in the determination solution according to the standard curve equation: Cmeas = (ΔA - b) / k, where k and b are the slope and intercept of the standard curve.

[0051] Next, calculate the volume correction factor: f = (V1 + Va + Vb + Vt) / V1, where V1 is the initial sample volume after dilution, Va is the amount of ammonia added during pH adjustment, Vb is the amount of boric acid added during masking treatment, and Vt is the amount of potassium sodium tartrate added. This correction factor reflects the total volume change during the pretreatment process.

[0052] Finally, the content of phosphate in the original fluosilicic acid sample is calculated: C original = C measured x n1 x f, wherein n1 is the initial dilution multiple.

[0053] If expressed in mass percentage, it can be further converted: w (%) = C original (mg / L) / (p x 10000) x 100%, wherein p is the density of fluosilicic acid (g / mL).

[0054] Through the concentration calculation of the system, the accuracy and reliability of the analysis results are ensured: the introduction of the volume correction factor eliminates the systematic error caused by ignoring the volume change in the traditional method, and the result accuracy is improved by more than 5%; the calculation process considers all dilution and processing steps, ensuring the complete traceability of the data; the result can be flexibly expressed as mass concentration (mg / L) or mass fraction (%), meeting different application requirements; the calculation method is standardized, facilitating programming to realize automatic calculation and reducing human error.

[0055] In summary, the embodiment effectively reduces the matrix interference of fluosilicic acid and creates suitable reaction conditions through the pretreatment and pH adjustment steps; the interference of fluoride ions on the phosphomolybdenum blue reaction is completely eliminated by using the boric acid complex masking technology; the optimized color reaction conditions ensure the complete color development and stability of phosphate; the spectrophotometric determination combined with the standard curve method realizes accurate quantification; the volume correction calculation method eliminates the systematic error caused by the pretreatment process. The whole method is simple to operate, the reagents are easy to obtain, and the cost is low, which is suitable for routine laboratory development, overcomes the technical difficulties of the prior art in determining phosphate in fluosilicic acid system, provides a reliable analysis means for fluosilicic acid product quality control, and has important industrial application value.

[0056] The embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the related parts can be referred to the method part.

[0057] The above describes in detail a method for determining phosphate in fluosilicic acid provided by the present application. In this paper, specific examples are used to illustrate the principles and implementation modes of the present application. The above embodiment is only used to help understand the method and its core idea. It should be pointed out that for ordinary skilled persons in the technical field, without departing from the principles of the present application, some improvements and modifications can be made to the present application, and these improvements and modifications also fall within the protection scope of the claims of the present application.

Claims

1. A method for determining the amount of phosphate in fluosilicic acid, characterized in that, The method comprises the following steps: The fluorosilicic acid sample is pretreated and pH adjusted to obtain a sample solution after pH adjustment; The sample solution after pH adjustment is subjected to interference ion masking treatment by boric acid solution to obtain a pretreated test solution; The pretreated test solution is subjected to phosphomolybdenum blue color reaction treatment to obtain a color-developed test solution; The color-developed test solution is subjected to spectrophotometric determination treatment to obtain a sample absorbance and a standard curve equation; The concentration of phosphates in fluorosilicic acid is calculated based on the sample absorbance, the standard curve equation and the dilution multiple.

2. The assay method according to claim 1, characterized by The fluorosilicic acid sample is pretreated and pH adjusted to obtain a sample solution after pH adjustment, comprising: The fluorosilicic acid sample is diluted by deionized water and diluted to a certain concentration to obtain a diluted fluorosilicic acid sample solution, and the dilution multiple is recorded; The diluted fluorosilicic acid sample solution is subjected to acid-base adjustment by ammonia solution and target pH to obtain the sample solution after pH adjustment, and the amount of ammonia water is recorded.

3. The assay method according to claim 2, characterized in that, The sample solution after pH adjustment is subjected to interference ion masking treatment by boric acid solution to obtain a pretreated test solution, comprising: Boric acid solution is added to the sample solution after pH adjustment, and stirred for a preset time to form a fluoroboric acid complex to obtain a fluorine ion masked solution, and the amount of boric acid is recorded; Potassium sodium tartrate solution is added to the fluorine ion masked solution to obtain a pretreated test solution, and the amount of potassium sodium tartrate is recorded.

4. The assay method according to claim 3, characterized in that, The pretreated test solution is subjected to phosphomolybdenum blue color reaction treatment to obtain a color-developed test solution, comprising: Ammonium molybdate, sulfuric acid and ascorbic acid reagent are used to prepare a color developing agent and a reducing agent to obtain the color developing agent and the reducing agent; The pretreated test solution is sequentially added with the color developing agent and the reducing agent, and mixed to obtain the color-developed test solution.

5. The assay method according to claim 4, characterized in that, The color-developed test solution is subjected to spectrophotometric determination treatment to obtain a sample absorbance and a standard curve equation, comprising: The color-developed test solution and a blank control solution are determined by a spectrophotometer to obtain the sample absorbance and a blank absorbance; A standard curve equation is obtained by standard curve determination based on a series of phosphate standard solutions.

6. The assay method according to claim 5, characterized in that, A standard curve equation is obtained by standard curve determination based on a series of phosphate standard solutions, comprising: The series of phosphate standard solutions are subjected to color reaction to determine the absorbance of the solution under each standard; The standard curve equation is determined based on the absorbance of the solution under each standard.

7. The assay method according to claim 6, characterized in that, The concentration of phosphates in fluorosilicic acid is calculated based on the sample absorbance, the standard curve equation and the dilution multiple, comprising: The concentration of phosphates in fluorosilicic acid is calculated based on the sample absorbance, the standard curve equation, the dilution multiple, the amount of ammonia water, the amount of boric acid and the amount of potassium sodium tartrate.

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