Method for detecting chloride ions in methyl silicate

Abstract

The invention discloses a method for detecting chloride ions in methyl silicate, which comprises the following specific steps: step 1, adding water into a methyl silicate sample to be detected for hydrolysis, adding concentrated nitric acid after hydrolysis to completely hydrolyze the methyl silicate and ensure that the methyl silicate is completely converted into silicic acid, then adding a sodium hydroxide solution to generate sodium silicate, and adjusting the pH value of the sodium silicate to obtain a solution to be detected; and 2, detecting the to-be-detected solution treated in the step 1 by using ion chromatography.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical detection, and particularly relates to a method for detecting chloride ions in methyl silicate. Background Art

[0002] As an important organosilicon compound, methyl silicate has a wide range of applications in many fields. For example, it is used as a silicon source in organic synthesis, and in the coatings and adhesives industries to improve product performance. However, the chloride ion content in methyl silicate can have a significant impact on its application performance. For example, in the preparation of electronic materials, trace amounts of chloride ions may cause problems such as corrosion and unstable performance of the product; in the synthesis of precision catalysts, chloride ion impurities will interfere with the catalytic reaction process and reduce the activity and selectivity of the catalyst.

[0003] Currently, there are many detection methods for chloride ions in chemical products, such as the detection method for chloride ions in electronic-grade tetraethyl orthosilicate. However, there are various types of tetraethyl orthosilicate, and the silicon dioxide content is different, and the reagent addition amount is also different during the sample treatment process, which easily leads to incomplete reaction of silicon dioxide and inability to perform subsequent detection. At the same time, due to the high silicon dioxide content in methyl silicate, this method is not applicable to methyl silicate, and there are many problems with conventional detection methods. The potentiometric titration method is affected by the conductivity of methyl silicate itself and chemical reactions, and the end point judgment error is large; in ion chromatography, the organic components of methyl silicate are likely to contaminate the chromatographic column, resulting in a decrease in column efficiency. At the same time, it is difficult to accurately quantify chloride ions in the complex separation process. Summary of the Invention

[0004] Aiming at the above-mentioned deficiencies existing in the prior art, the purpose of the present invention is to provide a method for detecting chloride ions in methyl silicate to solve the problems of poor accuracy and easy interference when detecting chloride ions in the methyl silicate system in the prior art.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions: A method for detecting chloride ions in methyl silicate, the specific steps are as follows: Step 1: Add water to the methyl silicate sample to be tested for hydrolysis. After hydrolysis, add concentrated nitric acid to completely hydrolyze the methyl silicate and ensure that the methyl silicate is completely converted into silicic acid. Then add sodium hydroxide solution to form sodium silicate and adjust its pH to obtain the test solution; Among them, the mass-volume ratio of the sample to water is 10g:(2 - 4)mL; the mass-volume ratio of the sample to concentrated nitric acid is 10g:(0.2 - 0.4)mL; the mass-volume ratio of the sample to sodium hydroxide solution is 10g:(10 - 13)mL; the concentration of concentrated nitric acid is 65wt% - 69wt%; the concentration of sodium hydroxide solution is 600g / L; Step 2: Detect the test solution processed in Step 1 using ion chromatography.

[0006] Preferably, in Step 1, after adding concentrated nitric acid, heat the mixture to 50°C - 60°C.

[0007] Preferably, in Step 1, adjust the pH value to 8 - 10.

[0008] Preferably, before Step 1, plot the chloride ion standard working curve.

[0009] Preferably, the steps for plotting the chloride ion standard working curve are as follows: S1: Prepare chloride ion standard solutions with different concentrations respectively; among them, the concentrations of the chloride ion standard solutions are 0 mg / mL, 0.5 mg / L, 2 mg / L, 5 mg / L, 7 mg / L, and 10 mg / L respectively; S2: Detect the chloride ion standard solutions prepared in S1 using ion chromatography to obtain the chloride ion standard working curve; among them, plot the standard working curve with the chloride ion concentration as the abscissa and its peak area as the ordinate.

[0010] Preferably, the detection conditions of the ion chromatography in Step 2 are exactly the same as those of the ion chromatography in S2.

[0011] Preferably, the detection conditions of the ion chromatography are as follows: Eluent flow rate: 1.0 mL / min; Column temperature: 35°C; Injection volume: 25 μL; Suppressor: Anion suppressor, the current of the suppressor is 70 mA; Chromatographic column: TYPE SH-AC-11 anion chromatographic column, the mobile phase is: KOH concentration 15 mmol Preferably, in Step 1, before the hydrolysis of the methyl silicate sample to be tested, first add silver nitrate. If there is no turbidity, the detection is terminated; if there is turbidity, then add water for hydrolysis.

[0012] Compared with the prior art, the present invention has the following beneficial effects: 1. When studying the detection method of chloride ions in methyl silicate, it was found that the methyl silicate system has particularities. It is prone to rapid polycondensation after hydrolysis, which in turn produces by-products and affects the accuracy of detection. Due to this characteristic, the existing detection methods for chloride ions in ethyl silicate cannot be directly applied to the detection of methyl silicate. Based on this, the present invention has improved the pretreatment method of the sample. Through specific hydrolysis and separation steps, the interference of the organic structure of methyl silicate on the chloride ion detection is effectively eliminated. Combining with the high sensitivity and high-precision detection ability of ion chromatography, the accuracy of the detection result is greatly improved.

[0013] 2. The detection method of the present invention can detect chloride ions at a concentration of 0.0001 mg / L, meeting the strict quality control requirements for chloride ions in methyl silicate, applicable to the detection of methyl silicate products of various purity grades, and having a wide application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is the instrument test flow chart in the present invention.

[0015] Figure 2 It is the chloride ion standard working curve in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] The present invention will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the present invention belong to the scope of protection of the present invention.

[0017] Unless otherwise specified in specific circumstances in the present invention, the numerical ranges listed herein include the upper and lower limit values, as well as all integers and fractions within this range, rather than the specific values listed when defining the range.

[0018] I. A detection method for chloride ions in methyl silicate Step 1: Add water to the methyl silicate sample to be tested for hydrolysis. After hydrolysis, add concentrated nitric acid to completely hydrolyze the methyl silicate and ensure that the methyl silicate is completely converted into silicic acid. Then add sodium hydroxide solution to form sodium silicate and adjust its pH to obtain the solution to be tested. Among them, the mass-volume ratio of the sample to water is 10 g : (2 - 4) mL; the mass-volume ratio of the sample to concentrated nitric acid is 10 g : (0.2 - 0.4) mL; the mass-volume ratio of the sample to sodium hydroxide solution is 10 g : (10 - 13) mL; the concentration of concentrated nitric acid is 65 wt% - 69 wt%; the concentration of sodium hydroxide solution is 600 g / L. Step 2: Detect the solution to be tested processed in Step 1 by ion chromatography.

[0019] In some embodiments of the present invention, in step 1, after adding concentrated nitric acid, the mixture is heated to 50°C - 60°C to enable the complete hydrolysis of methyl silicate and ensure the complete conversion of methyl silicate into silicic acid. The present invention discovers that there are existing detection methods for chloride ions in ethyl silicate in the prior art. These methods all involve the hydrolysis of ethyl silicate. In some technical solutions, in order to make the hydrolysis more complete, direct addition of water and rapid oscillation are adopted. However, during the centrifugation process, the chloride ions in the bottom solid particles are not completely extracted, and there is silicic acid in the supernatant, which will undoubtedly affect the detection results. And in some technical solutions, HF is used to hydrolyze ethyl silicate to detect the concentration of chloride ions in ethyl silicate. But this solution has problems. The SiF4 generated by HF further reacts with the water in the detection system to form fluosilicic acid (H2SiF6). This substance reacts with the mobile phase sodium hydroxide in ion chromatography to form insoluble fluorosilicates (such as Na2SiF6), resulting in column blockage or baseline interference, thereby affecting the detection accuracy. At the same time, since the raw material may itself contain free chloride ions, they are easily carried away during the reaction process, resulting in a large deviation in the detection results. Based on this, the present invention considers adding concentrated nitric acid, which will not have the above-mentioned situations. Concentrated nitric acid can enable the complete hydrolysis of methyl silicate and ensure its complete conversion into silicic acid, avoiding other reactions during the hydrolysis process and thus affecting the accuracy of the detection results. After adding concentrated nitric acid, the temperature of the mixture is controlled between 50°C and 60°C. If the temperature is too low, the hydrolysis rate will be slow, which will affect the reaction degree and lead to too long reaction time; but if the temperature is too high, the hydrolysis rate may be too fast, resulting in side reactions and the formation of other substances. Therefore, the temperature of the mixture can be controlled at 50°C, 55°C or 60°C, or within the numerical range formed by any two of the above specific values as endpoints; it should be understood that in the implementation scheme, any of the above ranges can be combined with any other range.

[0020] In some embodiments of the present invention, in step 1, sodium hydroxide solution is added to generate sodium silicate, and this process is maintained for 20 min - 30 min to ensure that all silicic acid can react to form sodium silicate. The pH value is adjusted with concentrated nitric acid to be between 8 and 10. If the pH value is lower than 8, a small amount of silicic acid will be formed in the sample to be measured, affecting the normal detection of the instrument; but if the pH value is greater than 10, sodium silicate is a strong base, and direct injection will cause the loss of the stationary phase, which will also affect the detection results. Therefore, the pH value adjusted with concentrated nitric acid can be 8, 9 or 10, or within the numerical range formed by any two of the above specific values as endpoints; it should be understood that in the implementation scheme, any of the above ranges can be combined with any other range.

[0021] In some embodiments of the present invention, before performing the detection operation, a chloride ion standard working curve can be drawn in advance. The steps for drawing the chloride ion standard working curve are as follows: S1: Prepare chloride ion standard solutions with different concentrations respectively; among them, the concentrations of the chloride ion standard solutions are 0 mg / mL, 0.5 mg / L, 2 mg / L, 5 mg / L, 7 mg / L, and 10 mg / L respectively; S2: Use ion chromatography to detect the chloride ion standard solutions prepared in S1 to obtain a chloride ion standard working curve; among them, a standard working curve is drawn with the chloride ion concentration as the abscissa and its peak area as the ordinate.

[0022] In some embodiments of the present invention, the detection conditions of the ion chromatography in step 2 are exactly the same as those of the ion chromatography in S2. The detection conditions of the ion chromatography are as follows: Eluent flow rate: 1.0 mL / min; Column temperature: 35 °C; Injection volume: 25 μL; Suppressor: Anion suppressor, the current of the suppressor is 70 mA; Chromatographic column: TYPE SH-AC-11 anion chromatographic column, mobile phase: KOH solution with a concentration of 15 mmol / L.

[0023] Among them, this anion chromatographic column can better separate the sample to be tested after pretreatment. Compared with other types of ion chromatographic columns, it can make the detection results more accurate.

[0024] In some embodiments of the present invention, in step 1, before hydrolyzing the sample of methyl silicate to be tested, first add silver nitrate dropwise. If there is no turbidity phenomenon, it indicates that the sample does not contain chloride ions, and the detection is terminated; if there is a turbidity phenomenon, then add water for hydrolysis, so as to further perform the detection method described in the present invention to quantitatively detect the chloride ions in the sample.

[0025] II. Specific implementation situations The water used in the present invention complies with the provisions of GB / T 33087, nitric acid is (65-69%) of superior grade purity, the chlorine content is less than 0.01 mg / L, and the concentration of the sodium hydroxide solution is 600 g / L.

[0026] 1. Drawing of the chloride ion standard working curve (1) Chloride ion standard solution: 1000 mg / L. Accurately weigh 1.648 g of the dried reference substance, dissolve it and make up the volume to 1000 ml in a volumetric flask.

[0027] (2)Respectively pipette 0 mL, 0.05 mL, 0.2 mL, 0.5 mL, 0.7 mL, and 1 mL of chloride ion standard solution into 100 mL volumetric flasks, dilute with water and make up to the mark in sequence to obtain chloride ion standard samples for determination.

[0028] (3)Inject samples into the ion chromatograph through an autosampler, detect the ion standard solutions with different concentrations using the ion chromatograph, plot the standard working curve with the chloride ion concentration as the abscissa and its peak area as the ordinate, as Figure 2 shown.

[0029] 2. Examples and Comparative Examples Example 1 Step 1: Take 10 g of methyl silicate sample in a 250 mL beaker, add 3 mL of water, and stir and hydrolyze for 10 min.

[0030] Step 2: To the mixture obtained in Step 1, dropwise add 0.2 mL of concentrated nitric acid with a concentration of 69%, and continue to stir for 10 min for sufficient hydrolysis.

[0031] Step 3: Heat the solution obtained in Step 2 to 50 °C, and gradually add 10 mL of 600 g / L sodium hydroxide solution dropwise until completely dissolved.

[0032] Step 4: Adjust the pH to 10 with nitric acid solution, filter, and take the filtrate to determine chloride ions in the ion chromatograph. Among them, the detection conditions of the ion chromatograph are as follows: Eluent flow rate: 1.0 mL / min; Column temperature: 35 °C; Injection volume: 25 μL; Suppressor: Anion suppressor, suppressor current is 70 mA; Chromatographic column: TYPE SH-AC-11 anion chromatographic column, mobile phase: KOH solution with a concentration of 15 mmol / L.

[0033] Example 2 Step 1: Take 10 g of methyl silicate sample in a 250 mL beaker, add 4 mL of water, and perform ultrasonic-assisted hydrolysis for 15 min.

[0034] Step 2: To the mixture obtained in Step 1, dropwise add 0.3 mL of concentrated nitric acid with a concentration of 69%, and continue to stir for 15 min for sufficient hydrolysis.

[0035] Step 3: Heat the solution obtained in Step 2 to 50 °C, and gradually add 12 mL of 600 g / L sodium hydroxide solution dropwise until completely dissolved.

[0036] Step 4: Adjust the pH to 10 with nitric acid solution, filter through a 0.45 μm filter membrane, and then determine the chloride ions using an ion chromatograph. The detection conditions of the ion chromatograph are as follows: Eluent flow rate: 1.0 mL / min; Column temperature: 35 °C; Injection volume: 25 μL; Suppressor: Anion suppressor, with a suppressor current of 70 mA; Chromatographic column: TYPE SH-AC-11 anion chromatographic column, mobile phase: KOH solution with a concentration of 15 mmol / L.

[0037] Example 3 Step 1: Take 10 g of methyl silicate sample in a 250 mL beaker, add 2.5 mL of water, and stir and hydrolyze for 18 min.

[0038] Step 2: Add 0.4 mL of concentrated nitric acid with a concentration of 69% dropwise to the mixture obtained in Step 1, and continue to stir for 25 min for sufficient hydrolysis.

[0039] Step 3: Heat the solution obtained in Step 2 to 50 °C, and gradually add 13 mL of 600 g / L sodium hydroxide solution until completely dissolved.

[0040] Step 4: Adjust the pH to 10 with nitric acid solution, filter, and take the filtrate to determine the chloride ions using an ion chromatograph. The detection conditions of the ion chromatograph are as follows: Eluent flow rate: 1.0 mL / min; Column temperature: 35 °C; Injection volume: 25 μL; Suppressor: Anion suppressor, with a suppressor current of 70 mA; Chromatographic column: TYPE SH-AC-11 anion chromatographic column, mobile phase: KOH solution with a concentration of 15 mmol / L.

[0041] Three methyl silicate products were used as samples, and the chloride ions in the three methyl silicate samples were determined through Examples 1 to 3. Subsequently, a chloride ion standard solution with a concentration of 2 mg / L was prepared, an equal amount of sodium chloride solution was added to the three methyl silicate samples, and then these three samples were detected respectively by the methods of Examples 1 to 3. The detection results are as follows.

[0042] Table 1 As can be seen from Table 1: (1)When the sodium chloride solution was not added, the chloride ion concentrations in the three examples were very low, with values close to each other and extremely small fluctuations (the range was only 0.003 mg / L), indicating that the background chloride ion content in the samples was low and the detection results of the method described in the present invention had high reproducibility.

[0043] (2)After adding the sodium chloride solution with a concentration of 2 mg / L, there were obvious changes in the detection results, indicating that the method described in the present invention could effectively respond to the added chloride ions, and the detection sensitivity met the requirements of trace analysis.

[0044] (3)The RSD of Examples 1 to 3 was 1.02%. The relatively low relative standard deviation (<2%) indicated that the data dispersion degree of the three parallel determinations in Examples 1 to 3 was extremely small, and the repeatability of the method described in the present invention was excellent.

[0045] (4)The recovery rates of the examples were close to 100%, all close to the theoretical values, indicating that the method described in the present invention had no significant systematic error and could accurately determine the chloride ion content in actual samples.

[0046] (5)The method described in the present invention had high sensitivity (able to detect chloride ions as low as 0.15 mg / L), high repeatability (RSD ≤1.02%), and high accuracy (recovery rate 99.95% - 100.5%), and was suitable for the quantitative analysis of trace chloride ions in electronic-grade methyl silicate; at the same time, it also proved the reliability of the method described in the present invention and could meet the strict requirements of the semiconductor industry for raw material impurity detection.

[0047] Comparative Example 1 Adopting the technical solution of CN110646539A, the chloride ions in the methyl silicate sample detected in Example 1 were detected.

[0048] 0.4 g of sodium carbonate, 20 mL of water, and 40 mL of absolute ethanol (according to 0.02 g of sodium carbonate, 1 mL of water, and 2 mL of ethanol in the patent technical solution) were used for preparation. During the preparation process, the solubility of sodium carbonate was poor and flocculates appeared. Subsequently, 6 g of methyl silicate sample was weighed and 3 mL of sodium carbonate mixed solution was added. After heating at 50 °C for 10 min, silicon dioxide was formed. 2 mL of hydrofluoric acid with a concentration of 4% was added to the formed silicon dioxide. Subsequently, after heating at 50 °C for 24 h, the silicon dioxide did not completely react and remained as solid silicon dioxide, which could not be used for ion chromatograph detection. After in-depth research on this solution, it was found that the content of silicon dioxide in methyl silicate was relatively high. According to the above technical solution, the hydrofluoric acid added could not completely react with the silicon dioxide in methyl silicate, resulting in the continuous presence of silicon dioxide in the sample. Subsequently, the amount of hydrofluoric acid was gradually increased. Although the amount of silicon dioxide decreased significantly, after increasing the amount of hydrofluoric acid, the SiF4 generated by HF further reacted with the water in the detection system to form hexafluorosilicic acid (H2SiF6). This substance reacted with sodium hydroxide in the mobile phase of ion chromatography to form insoluble fluorosilicates (such as Na2SiF6), resulting in column blockage or baseline interference, thereby affecting the detection accuracy. This indicates that the detection method for chloride ions in ethyl silicate is not applicable to methyl silicate, and even after certain adjustments, it is still not applicable.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those of ordinary skill in the art should understand that any modifications or equivalent replacements made to the technical solutions of the present invention without departing from the spirit and scope of the present technical solution should be covered within the scope of the claims of the present invention.

Claims

1. A method for detecting chloride ions in methyl silicate, characterized in that, The specific steps are as follows: Step 1: Add water to the methyl silicate sample to be tested for hydrolysis. After hydrolysis, add concentrated nitric acid to completely hydrolyze the methyl silicate and ensure that the methyl silicate is completely converted into silicic acid. Then add sodium hydroxide solution to form sodium silicate and adjust its pH to obtain the test solution. Among them, the mass-volume ratio of the sample to water is 10 g:(2 - 4) mL; the mass-volume ratio of the sample to concentrated nitric acid is 10 g:(0.2 - 0.4) mL; the mass-volume ratio of the sample to sodium hydroxide solution is 10 g:(10 - 13) mL; the concentration of concentrated nitric acid is 65 wt% - 69 wt%; the concentration of sodium hydroxide solution is 600 g / L. Step 2: Detect the test solution processed in Step 1 by ion chromatography.

2. The detection method according to claim 1, wherein In Step 1, after adding concentrated nitric acid, heat the mixture to 50°C - 60°C.

3. The detection method according to claim 1, characterized in that, In Step 1, adjust the pH value to 8 - 10.

4. The detection method according to claim 1, wherein Before Step 1, draw a chloride ion standard working curve.

5. The detection method according to claim 4, wherein The steps for drawing the chloride ion standard working curve are as follows: S1: Prepare chloride ion standard solutions with different concentrations respectively; among them, the concentrations of the chloride ion standard solutions are 0 mg / mL, 0.5 mg / L, 2 mg / L, 5 mg / L, 7 mg / L, 10 mg / L respectively. S2: Detect the chloride ion standard solutions prepared in S1 by ion chromatography to obtain the chloride ion standard working curve; among them, draw the standard working curve with the chloride ion concentration as the abscissa and its peak area as the ordinate.

6. The detection method according to claim 4, characterized in that, The detection conditions of the ion chromatography in Step 2 are exactly the same as those in S2.

7. The detection method according to claim 6, wherein The detection conditions of the ion chromatography are as follows: Eluent flow rate: 1.0 mL / min; Column temperature: 35°C; Injection volume: 25 μL; Suppressor: Anion suppressor, the current of the suppressor is 70 mA; Chromatographic column: TYPE SH-AC-11 anion chromatographic column, the mobile phase is: KOH concentration 15 mmol.

8. The detection method according to claim 1, wherein In Step 1, before hydrolyzing the methyl silicate sample to be tested, first add a few drops of silver nitrate. If there is no turbidity, the detection is terminated; if there is turbidity, then add water for hydrolysis.

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