Method for preparing impurity content test solution in titanium tetrachloride by mixed acid method and detection method

Abstract

The invention discloses a method for preparing an impurity content test solution in titanium tetrachloride by a mixed acid method and a detection method, and belongs to the technical field of component detection and analysis. The preparation method and the detection method comprise the following steps: adding water into a titanium tetrachloride sample to react until a precipitate is dissolved and no thick white smoke is generated; heating and evaporating the obtained product to dryness under the condition that the temperature is not higher than 100 DEG C; then adding a hydrofluoric acid solution, a nitric acid solution and a proper amount of water, heating under the condition that the temperature is not higher than 150 DEG C until the titanium matrix is completely dissolved to obtain a clear and transparent solution, and adding water to dilute and fix the volume to obtain a titanium tetrachloride impurity content test solution with the hydrofluoric acid concentration and the nitric acid concentration both smaller than 2%; and determining the impurity content in the solution by adopting ICP-MS or ICP-OES. The method disclosed by the invention is simple to operate, effectively avoids the pollution risk of external elements, and reduces the operation error, thereby greatly improving the accuracy and reliability of an analysis result.

Description

Technical Field

[0001] The present invention belongs to the technical field of component detection and analysis, and relates to a method for preparing a test solution for impurity content in titanium tetrachloride by a mixed acid method and a detection method, and specifically relates to a method for preparing a sample test solution and an analysis method for detecting the content of trace, trace and ultra-trace levels of metal impurities and other elements in titanium tetrachloride. Background Art

[0002] TiCl4 is a key intermediate product in the chloride process for producing titanium sponge and titanium dioxide. The quality of TiCl4, including its impurity content, severely restricts the quality and application of the final titanium metal and titanium oxide products. With the rapid development of integrated circuit technology, TiCl4 is widely used as a precursor for high-temperature TiN deposition in memory chips such as DRAM and 3D NAND, as well as in logic chips. For example, it is used to deposit TiN as the metal electrode layer in memory chips and reacts with TEA to deposit TiAl or TiN as the work function layer in logic chips. However, TiCl4 used in the semiconductor industry requires a purity of at least 99.99999%, and strict limits are imposed on the content of over 20 metallic impurities, including vanadium, arsenic, tin, silver, bismuth, gallium, and iron, with each impurity limited to no more than 1 ppb. Therefore, analytical methods for detecting trace, trace, and ultra-trace impurity elements in TiCl4 are essential supporting technologies for production control and product application.

[0003] The document "Determination of Impurity Elements in Titanium Tetrachloride Liquid by Inductively Coupled Plasma Atomic Emission Spectrometry" dilutes the TiCl4 sample solution with relatively high concentrations of dilute hydrochloric acid or dilute nitric acid and uses inductively coupled plasma atomic emission spectrometry (ICP-OES) to determine inorganic impurity elements such as Si, Fe, V, and Al. However, the ICP-OES detection method used in this method is limited by its performance indicators such as its lower detection limit and cannot meet the requirements for the determination of trace and trace element contents. In addition, the sample pretreatment method of using a large amount of high-concentration dilute hydrochloric acid solution to dilute TiCl4 will cause the concentrations of hydrogen ions and chloride ions in the test solution to be far higher than the upper limit that the ICP-OES can tolerate, resulting in a significant impact on the accuracy of the results due to matrix effects and mass spectrometry interference, and severe corrosion of valuable components such as the interface cone of the ICP-MS instrument.

[0004] The document "Determination of 13 element impurities in refined titanium tetrachloride by acid hydrolysis-ICP-MS" slowly adds a titanium tetrachloride sample to a hydrochloric acid solution for hydrolysis reaction to generate a white milky hydrolysis solution; then adds nitric acid and heats it at low temperature to digest it, and finally uses hydrochloric acid solution to make up the volume to obtain the hydrolysis solution to be tested. The content of 13 element impurities in refined titanium tetrachloride is analyzed by external standard quantitative method. This method cannot solve the problem of high concentration of Cl coexisting in TiCl4. - The influence of mass spectrometric interferences such as polyatomic ions on element determination caused by high concentrations of H+ The problem of instrument corrosion. In addition, this method uses a large amount of hydrochloric acid and nitric acid solutions in the preparation of the test solution, and the amount of reagents used is much larger than the amount of TiCl4 sample. This adds the serious impact of impurities present in the blank background of the reagents on the determination, and requires extremely high reagent purity. It also needs to consider eliminating the interference of polyatomic ion spectra caused by nitrogen oxides.

[0005] The document "Determination of Arsenic in Titanium Tetrachloride by Inductively Coupled Plasma Mass Spectrometry" established an analytical method for the determination of arsenic in titanium tetrachloride by inductively coupled plasma mass spectrometry (ICP-MS). The test solution was decomposed with nitric acid, and the mass spectrometry interference during the measurement was investigated. The dynamic reaction cell (DRC) was used to eliminate the interference. NH3 was used as the reaction gas. Under the optimal Rpq value of 0.45 and DRC gas flow rate of 0.5 mL / min, the interference was eliminated. 75 ArCl 75 Interference from As. This method uses only nitric acid for the hydrolysis reaction, which is prone to incomplete dissolution reactions. Centrifugation or filtration is required to remove fine particles such as titanium oxide suspended in the test solution that could clog instrument components. The clear solution must be aliquoted and rediluted to a fixed volume before elemental content determination can be performed on the instrument. This not only increases the number of operational steps and the risk of contamination of trace elements, but the secondary aliquoting and dilution also leads to increased errors in the test results.

[0006] Therefore, the existing technology has the disadvantages of complicated operation, long process cycle, high inspection cost, multiple interference factors and large error in test results. Therefore, the development of an analytical method that can accurately detect trace, trace and ultra-trace impurity elements in TiCl4 is of vital importance for its production control and practical application. Summary of the Invention

[0007] The technical problem to be solved by the present invention is that during the TiCl4 detection process, high concentration Cl - 、H + The reliability of the test results is affected by matrix effects, acidity effects, mass spectrometry interference, etc., as well as the corrosion of the detection instrument caused by strong acidic medium solutions.

[0008] To achieve the above application objectives, the technical solutions adopted in this application are as follows:

[0009] First, in order to completely eliminate the high concentration of Cl in the TiCl4 sample solution - 、H + In order to understand the influence of coexisting components on the test results and instrument operation, the present invention provides a method for preparing a test solution for impurity content in titanium tetrachloride by a mixed acid method, comprising the following steps:

[0010] S1. Add an appropriate amount of water to the titanium tetrachloride sample to be tested, allow to react at room temperature to generate a yellow flocculent precipitate, and then continue to add water to react until the precipitate is dissolved and no longer produces thick white smoke;

[0011] S2. The product obtained in step S1 is heated and evaporated to dryness at a temperature not higher than 100°C to obtain a titanium-based solid mainly composed of anatase-type titanium dioxide;

[0012] S3. Add hydrofluoric acid solution, nitric acid solution and an appropriate amount of water to the titanium-based solid obtained in step S2, and heat at a temperature not higher than 150 ° C until the titanium matrix is ​​completely dissolved to obtain a clear and transparent solution;

[0013] S4. After the solution obtained in step S3 is cooled, water is added to dilute the solution to a constant volume to obtain a test solution for the impurity content in titanium tetrachloride in which the concentrations of hydrofluoric acid and nitric acid are both less than 2%.

[0014] In the above step S1, the volume ratio of the titanium tetrachloride sample to be tested to the water added for the first time is 1:0.5-3, and the volume ratio of the titanium tetrachloride sample to be tested to the water added for the second time is 1:0.5-3.

[0015] In step S1 above, the addition of water to the titanium tetrachloride sample triggers a vigorous hydrolysis reaction, resulting in the rapid release of a large amount of HCl gas. To avoid an excessively vigorous reaction, water should be added dropwise to the titanium tetrachloride slowly to control the reaction rate and prevent safety issues caused by the release of large amounts of HCl gas. This also prevents volatile impurities from escaping and being lost along with the HCl gas during the vigorous hydrolysis process.

[0016] In the above step S2, the temperature of the heating and evaporation is 90-100°C.

[0017] In the above step S3, the volume ratio of the titanium tetrachloride sample to be tested to the hydrofluoric acid solution is 1:0.5-1, and the volume ratio of the titanium tetrachloride sample to be tested to the nitric acid solution is 1:0.5-1.

[0018] In the above step S3, the concentration of the hydrofluoric acid solution is ≥40%, and the concentration of the nitric acid solution is 65% to 68%.

[0019] In the above step S3, the amount of water added should ensure that the titanium-based solid is completely dissolved.

[0020] In the above step S3, the temperature of the heating and dissolving is 100-150°C.

[0021] In the above step S4, the volume ratio of the titanium tetrachloride sample to be tested to the impurity content test solution in titanium tetrachloride is 1:20-250.

[0022] The present invention makes full use of the property that TiCl4 is easily hydrolyzed in water to generate titanium precipitate and a large amount of HCl smoke, and provides a simple, fast and efficient method for removing Cl in TiCl4. - 、H + The sample test solution pretreatment preparation method of the coexisting components is as follows. Only water is added to the TiCl4 sample solution, and secondary precipitation and secondary dissolution precipitation are repeated through controlled hydrolysis reaction or evaporation, so as to promote the large amount of Cl - and H + The volatile HCl and other forms escape and are expelled; at the same time, the generated titanium dioxide precipitate exists in an anatase crystal structure that is easily soluble in acid, so that it can be quickly and completely redissolved by a very small amount of hydrofluoric acid and nitric acid.

[0023] The present invention reduces the ethanol volatilization loss by limiting the heating temperature conditions of the dissolution reaction, and the Ti in the test solution 4+ With F - The generated complex ions can be stably maintained in a low-acidity medium, ensuring that the high-concentration titanium matrix does not re-hydrolyze to form a precipitate in an extremely low-acidity test solution. In addition to the titanium matrix, the test solution only contains hydrofluoric acid at a concentration of no more than 2.0% and nitric acid at a concentration of no more than 2.0%, which do not interfere with the determination. The test solution prepared by this method greatly reduces the acidity and purifies the coexisting medium system compared to the original TiCl4 sample mother solution, effectively eliminating the interference of chloride ions and the corrosive effects of the strong medium on the instrument. The amount of hydrofluoric acid and nitric acid reagents used in this method is extremely small, greatly reducing the analysis cost and the impact of reagent blank background contamination on the results. The precipitate produced by the titanium base hydrolysis reaction is completely redissolved, and the solution is clear and transparent without suspended or settled insoluble particles. There is no problem of insoluble particles adsorbing, entrapping, or encapsulating the elements to be measured, thereby affecting the reliability of the test results. This method is simple to operate and has a short process, which greatly shortens the test cycle and reduces the risk of contamination in the determination of trace and ultra-trace elements during the preparation of the test solution, thereby improving the accuracy and reliability of the results.

[0024] In a second aspect, the present invention provides a method for detecting the impurity content in titanium tetrachloride, which is characterized by simple operation and a short inspection process and can quickly determine the content of trace, trace, and ultra-trace metal impurities in TiCl4. The specific method comprises: preparing a titanium tetrachloride impurity content test solution according to the above-mentioned mixed acid method, and determining the content of the impurity elements in the solution by ICP-MS or ICP-OES; the impurity elements include Li, Be, Na, Mg, Al, K, Ca, V, Cr, Mn, Fe, Co, Sb, Cu, Zn, Ga, As, Ni, Mo, Cd, Sn, Sr, Pb, Ba, Bi, Th, and U.

[0025] Furthermore, when the volume ratio of the titanium tetrachloride sample to be tested to the impurity content test solution in titanium tetrachloride is 1:100-250, or when the impurity content in the titanium tetrachloride sample to be tested is less than or equal to 0.5 mg / L, ICP-MS detection is adopted; the detection parameters are: tandem mass spectrometry; RF power 1200-1350W; He\O2\NH3 collision reaction mode; 103 Rh internal standard correction mode; standard addition method\calibration curve method.

[0026] Furthermore, when the volume ratio of the titanium tetrachloride sample to be tested to the impurity content test solution in titanium tetrachloride is 1:20 to <100, or when the impurity content in the titanium tetrachloride sample to be tested is greater than 0.5 mg / L, ICP-OES detection is adopted; the detection parameters are: RF power 1200-1350W; standard addition method\calibration curve method.

[0027] Furthermore, both the ICP-MS and ICP-OES may use instrument components made of glass materials, including a quartz glass concentric nebulizer or a quartz glass cyclonic spray chamber, which have higher atomization and transmission efficiency.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] This method involves directly hydrolyzing titanium tetrachloride with pure water, and then heating and evaporating the solution after the reaction to completely remove the coexisting chloride ions and hydrogen ions. Subsequently, only a very small amount of hydrofluoric acid and nitric acid is required to completely dissolve the generated titanium-based precipitate, and pure water is used alone for dilution and volume adjustment. Finally, the content of impurity elements in the test solution is determined by ICP-MS or ICP-OES. The key lies in utilizing the hydrolysis reaction to effectively drive out the highly interfering chloride ions and corrosive hydrogen ions, thus solving the problems of matrix component interference and corrosion of instruments and equipment by strong acid solutions. At the same time, relying on the complex formed by fluoride ions and titanium ions, titanium can remain dissolved in a low-acidity medium, ensuring that the precipitate is quickly and completely dissolved, and the resulting solution is clear and transparent without any insoluble solid particles. Hydrolysis will not occur even if diluted with water alone, and the prepared test solution does not require additional steps such as centrifugation or filtration separation. It can be directly measured on the machine after a single dilution and volume adjustment.

[0030] This method effectively eliminates polyatomic ion interference caused by chloride ions in mass spectrometry analysis and further addresses the issue of high-concentration hydrogen ion corrosion on the instrument's sample injection system and nebulizer. Furthermore, due to the extremely low acid dosage, its concentration in the test solution used for ICP-MS / ICP-OES analysis is controlled below 2%. This significantly reduces interference with mass spectrometry from impurities introduced by the reagent background blank and nitrogen oxides produced by nitric acid, thereby improving the accuracy of trace element detection.

[0031] The present invention has a simple operating process and few steps, effectively avoiding the risk of foreign element contamination that may be caused by intermediate links such as solution transfer, centrifugation / filtration separation, secondary extraction and dilution, reducing operational errors, thereby greatly improving the accuracy and reliability of the analysis results. At the same time, ethanol is used in small amounts as an organic solvent, and the background level of inorganic impurity elements contained therein is much lower than that of inorganic strong acid reagents such as nitric acid. In addition, hydrofluoric acid and nitric acid have characteristics such as low boiling points and high volatility, and can be purified by routine sub-boiling distillation in the laboratory, further reducing the impact of reagent impurities on ultratrace analysis. DETAILED DESCRIPTION

[0032] In order to make the technical problems, technical solutions and beneficial effects to be solved in the present application clearer, the present application will be further described in detail below in conjunction with the embodiments. It will be understood by those skilled in the art that the following examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Unless otherwise defined, all scientific and technological terms used herein have the same meanings understood by those of ordinary skill in the art.

[0033] The invention discloses a method for preparing a solution for testing the impurity content in titanium tetrachloride by a mixed acid method and a detection method thereof. The method comprises the following steps: adding an appropriate amount of water to a titanium tetrachloride sample to be tested, reacting the solution at room temperature to generate a yellow flocculent precipitate, then continuously adding water to react until the precipitate dissolves and no longer generates thick white smoke; heating the obtained product to dryness at a temperature not higher than 100°C to obtain a titanium-based solid mainly composed of anatase-type titanium dioxide; adding a hydrofluoric acid solution, a nitric acid solution and an appropriate amount of water to the titanium-based solid, heating the solution at a temperature not higher than 150°C until the titanium matrix is ​​completely dissolved to obtain a clear and transparent solution; and after the solution is cooled, diluting the solution with water to a constant volume to obtain a solution for testing the impurity content in titanium tetrachloride having a hydrofluoric acid concentration and a nitric acid concentration both less than 2%. ICP-MS or ICP-OES is used to determine the content of impurity elements in the solution; the impurity elements include Li, Be, Na, Mg, Al, K, Ca, V, Cr, Mn, Fe, Co, Sb, Cu, Zn, Ga, As, Ni, Mo, Cd, Sn, Sr, Pb, Ba, Bi, Th, and U.

[0034] In one embodiment of the present invention, the volume ratio of the titanium tetrachloride sample to be tested to the water added for the first time is 0.5 to 1:3, and the volume ratio of the titanium tetrachloride sample to be tested to the water added for the second time is 1:0.5 to 3. As a non-limiting example, the volume ratio of the titanium tetrachloride sample to be tested to the water added for the first time can be 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, or any ratio therebetween, and the volume ratio of the titanium tetrachloride sample to be tested to the water added for the second time can be 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, or any ratio therebetween.

[0035] In one embodiment of the present invention, the temperature of the heating and evaporation is 90-100° C. As a non-limiting example, the temperature of the heating and evaporation is 90° C., 100° C., or a range consisting of any two of the above values.

[0036] In one embodiment of the present invention, the volume ratio of the titanium tetrachloride sample to be tested to the hydrofluoric acid solution is 1:0.5 to 1, and the volume ratio of the titanium tetrachloride sample to be tested to the nitric acid solution is 1:0.5 to 1. As a non-limiting example, the volume ratio of the titanium tetrachloride sample to be tested to the hydrofluoric acid solution can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, or any ratio therebetween, and the volume ratio of the titanium tetrachloride sample to be tested to the nitric acid solution is 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, or any ratio therebetween.

[0037] In one embodiment of the present invention, the temperature for heating and dissolving is 100-150° C. As a non-limiting example, the temperature for heating and dissolving is 100° C., 110° C., 120° C., 130° C., 140° C., 150° C., or a range consisting of any two of the above values.

[0038] In one embodiment of the present invention, the volume ratio of the titanium tetrachloride sample to be tested to the impurity content test solution in titanium tetrachloride is 1:20 to 250. As a non-limiting example, the volume ratio of the titanium tetrachloride sample to be tested to the impurity content test solution in titanium tetrachloride can be 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, 1:100, 1:110, 1:120, 1:130, 1:140, 1:150, 1:160, 1:170, 1:180, 1:190, 1:200, 1:210, 1:220, 1:230, 1:240, 1:250 or any ratio therebetween.

[0039] Example 1

[0040] (1) Take 0.5 mL of TiCl4 sample solution (sample 1#) and place it in a 50 mL PFA quantitative tube. Slowly add about 1.0 mL of water dropwise, which reacts completely with the TiCl4 liquid to form a yellow flocculent precipitate and a large amount of thick white HCl smoke. Then continue to add water until the precipitate dissolves. When no thick white smoke escapes from the container, place the container in a 90°C water bath and heat until the solution evaporates to dryness. Add 0.5 mL of HF solution (40%), 0.5 mL of HNO3 solution (65%) and 10 mL of water, place on a 100°C hot plate and heat until the precipitate dissolves completely and the solution becomes clear and transparent. Dilute to 50 mL with water. Use ICP-MS to determine the element content in the test solution. The detection parameters are: RF power 1300 W; He\O2\NH3 collision reaction mode. 103 Rh internal standard correction mode; calibration curve method;

[0041] (2) Take 1.0 mL of TiCl4 sample solution (sample 2#) and place it in a 100 mL PFA quantitative tube. Slowly add about 2 mL of water dropwise, which reacts completely with the TiCl4 liquid to form a yellow flocculent precipitate and a large amount of thick white HCl smoke. Then continue to add water until the precipitate dissolves. When no thick white smoke escapes from the container, place the quantitative tube in a 100°C water bath and heat until the solution evaporates to dryness. Add 1.0 mL of HF solution (40%), 1.0 mL of HNO3 solution (65%) and 15 mL of water, place on a 120°C low-temperature electric hot plate and heat until the precipitate dissolves completely and the solution becomes clear and transparent. Dilute to 100 mL with water. Use ICP-MS to determine the element content in the test solution. The detection parameters are: RF power 1300 W; He\O2\NH3 collision reaction mode. 103 Rh internal standard correction mode; calibration curve method;

[0042] (3) Take 5.0 mL of TiCl4 sample solution (sample 3#) and place it in a polytetrafluoroethylene beaker. Slowly add about 10 mL of water dropwise to react with the TiCl4 liquid to form a yellow flocculent precipitate and a large amount of thick white HCl smoke. Then continue to add water dropwise until the precipitate dissolves. When no thick white smoke escapes from the vessel, place the beaker in a 100°C water bath and heat until the solution evaporates to dryness. Place 2.5 mL of HF solution (40%), 5.0 mL of HNO3 solution (65%) and 20 mL of water on a 150°C low-temperature electric hot plate and heat until the precipitate dissolves completely and the solution becomes clear and transparent. Dilute to 100 mL with water. Use ICP-OES to determine the element content in the test solution. The detection parameters are: RF power 1200-1350 W; calibration curve method.

[0043] (4) Take 2.5 mL of TiCl4 sample solution (sample 4#) and place it in a polytetrafluoroethylene beaker. Slowly add about 6 mL of water dropwise, which reacts completely with the TiCl4 liquid to form a yellow flocculent HCl precipitate with thick white smoke escaping; then continue to add water dropwise until the precipitate dissolves. When no thick white smoke escapes from the vessel, place the beaker in a 95°C water bath and heat until the solution evaporates to dryness; add 2.0 mL of HF solution (40%), 2.0 mL of HNO3 solution (65%) and 15 mL of water, place on a 150°C low-temperature electric hot plate and heat until the precipitate dissolves completely and the solution becomes clear and transparent, then dilute to 100 mL with water; use ICP-OES to determine the element content in the test solution, and the detection parameters are: RF power 1200~1350W; calibration curve method.

[0044] The test solution preparation and element content determination were repeated 8 times according to the above (1) to (4), and the average value and relative standard deviation (RSD) of the 8 measurement results were statistically calculated to evaluate the detection precision level of the method of the present invention. The results are shown in Table 1.

[0045] Table 1 Precision test (n=8)

[0046]

[0047]

[0048] As shown in Table 1, the relative standard deviation (RSD) of the elements with a value of ≥0.01 mg / kg determined by the method of the present invention is ≯25%, indicating that the results of repeated determinations are consistent, the repeatability and reproducibility of the method are good, and the method has a high level of precision.

[0049] Example 2

[0050] The effectiveness of the method of the present invention in solving the problem of chloride ions and hydrogen ions affecting the detection results and causing corrosion to the detection instrument during the detection process of titanium tetrachloride was evaluated.

[0051] 1. Targeting chloride ions

[0052] Determine the chloride ion content in the test solution prepared according to (1) to (4) above by comparing it with the solution without removing Cl - Cl in the test solution - The theoretical concentration of 200mg / L was used to evaluate the removal rate of chloride ions by the method of the present invention. The results are shown in Table 2.

[0053] Table 2 Chloride ion removal effect verification test

[0054]

[0055] As can be seen from Table 2, the rate of chloride ion removal by the method of the present invention is greater than 80%, which effectively reduces the corrosion to instruments and equipment and the interference effect on the determination of the components to be treated.

[0056] 2. Targeting hydrogen ions

[0057] The original mother liquor of titanium tetrachloride contains almost no hydrogen ions. In traditional methods, to prevent titanium tetrachloride from hydrolyzing in low-acidity media to form titanium oxide precipitates, large amounts of acid must be added during dilution, introducing a large number of hydrogen ions. These hydrogen ions not only affect the accuracy of test results but can also corrode the testing equipment. The method of the present invention requires only minimal addition of acid during the dilution process, significantly reducing the concentration of introduced hydrogen ions. Compared to traditional methods that use higher acid concentrations for dilution, the method of the present invention reduces hydrogen ion concentration by orders of magnitude.

[0058] Calculations show that the hydrogen ion concentration in the test solution prepared by methods (1) to (4) above is significantly lower than that obtained by conventional methods. This indicates that the method of the present invention can effectively control and significantly reduce the hydrogen ion concentration in the test solution, thereby reducing its interference with the test results and the risk of corrosion to the instrument.

Claims

1. A method for preparing a solution for testing impurity content in titanium tetrachloride by a mixed acid method, characterized in that: The steps include: S1. Add an appropriate amount of water to the titanium tetrachloride sample to be tested, allow to react at room temperature to form a yellow flocculent precipitate, and then continue to add water to react until the precipitate dissolves and no longer produces thick white smoke; S2. The product obtained in step S1 is heated and evaporated to dryness at a temperature not higher than 100°C to obtain a titanium-based solid mainly composed of anatase-type titanium dioxide; S3. Add hydrofluoric acid solution, nitric acid solution and an appropriate amount of water to the titanium-based solid obtained in step S2, and heat at a temperature not higher than 150 ° C until the titanium matrix is ​​completely dissolved to obtain a clear and transparent solution; S4. After the solution obtained in step S3 is cooled, water is added to dilute the solution to a constant volume to obtain a test solution for the impurity content in titanium tetrachloride in which the concentrations of hydrofluoric acid and nitric acid are both less than 2%.

2. The method for preparing a solution for testing impurity content in titanium tetrachloride by a mixed acid method according to claim 1, wherein: In step S1, the volume ratio of the titanium tetrachloride sample to be tested to the water added for the first time is 1:0.5-3, and the volume ratio of the titanium tetrachloride sample to be tested to the water added for the second time is 1:0.5-3.

3. The method for preparing a solution for testing impurity content in titanium tetrachloride by a mixed acid method according to claim 1, wherein: In step S2, the temperature of heating and evaporating to dryness is 90-100°C.

4. The method for preparing a solution for testing impurity content in titanium tetrachloride by a mixed acid method according to claim 1, wherein: In step S3, the volume ratio of the titanium tetrachloride sample to be tested to the hydrofluoric acid solution is 1:0.5-1, and the volume ratio of the titanium tetrachloride sample to be tested to the nitric acid solution is 1:0.5-1.

5. The method for preparing a solution for testing impurity content in titanium tetrachloride by a mixed acid method according to claim 1, wherein: In step S3, the concentration of the hydrofluoric acid solution is ≥40%, and the concentration of the nitric acid solution is 65% to 68%.

6. The method for preparing a solution for testing impurity content in titanium tetrachloride by a mixed acid method according to claim 1, characterized in that: In step S3, the temperature of the heating and dissolving is 100-150°C.

7. The method for preparing a solution for testing impurity content in titanium tetrachloride by a mixed acid method according to claim 1, characterized in that: In step S4, the volume ratio of the titanium tetrachloride sample to be tested to the impurity content test solution in titanium tetrachloride is 1:20-250.

8. A method for detecting impurity content in titanium tetrachloride, characterized in that: A test solution for impurity content in titanium tetrachloride is prepared according to the method of any one of claims 1 to 7, and the content of impurity elements in the solution is determined by ICP-MS or ICP-OES; The impurity elements include Li, Be, Na, Mg, Al, K, Ca, V, Cr, Mn, Fe, Co, Sb, Cu, Zn, Ga, As, Ni, Mo, Cd, Sn, Sr, Pb, Ba, Bi, Th, and U.

9. The method for detecting impurity content in titanium tetrachloride according to claim 8, wherein: When the volume ratio of the titanium tetrachloride sample to be tested to the impurity content test solution in titanium tetrachloride is 1:100-250, or when the impurity content in the titanium tetrachloride sample to be tested is less than or equal to 0.5 mg / L, ICP-MS detection is adopted; Detection parameters were: tandem mass spectrometry; RF power 1200–1350 W; He\O2\NH3 collision reaction mode; 103 Rh internal standard correction mode; standard addition method\calibration curve method.

10. The method for detecting impurity content in titanium tetrachloride according to claim 8, wherein: When the volume ratio of the titanium tetrachloride sample to be tested to the impurity content test solution in titanium tetrachloride is 1:20 to <100, or when the impurity content in the titanium tetrachloride sample to be tested is greater than 0.5 mg / L, ICP-OES detection is adopted; The detection parameters are: RF power 1200~1350W; standard addition method\calibration curve method.

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