JP2020159927A - Method for measuring chlorine concentration in silica - Google Patents

Abstract

To improve accuracy and stability of analysis in a method for measuring chloride ion concentration in silica by applying an ion chromatography method.SOLUTION: A method for measuring chlorine concentration in silica heats silica dispersion by an alkaline aqueous solution to dissolve silica such as dry silica, treats the obtained silica solution by H type cation exchange resin, particularly H type strong acid cation exchange resin, and analyzes a chloride ion in the solution by an ion chromatography method.SELECTED DRAWING: None

Description

The present invention relates to a method for measuring the chlorine concentration in silica.

Silica is an important chemical material used in various applications such as raw materials for glass and optical fibers, reinforcing agents for silicone resins, fillers for semiconductor encapsulants, and fluidity imparting agents. In particular, dry silica has a lower water content than wet silica and is an indispensable material for silicone and electronic material applications.

Dry silica is synthesized by burning the raw material silane in a hydrofluoric acid flame, so it has a higher purity than wet silica, but it is still derived from the raw material silane and may contain various metal impurities. Inevitable. Further, as the raw material silane, chlorosilane such as silicon tetrachloride is the most versatile, and in this case, hydrochloric acid is also adsorbed in a significant amount. These impurities cause deterioration of the quality of dry silica when it is used for the above-mentioned use. For example, the hydrochloric acid is a corrosive substance, and its reduction is strongly desired for the semiconductor use and the like. ..

Therefore, a technique for quantitatively analyzing a trace amount of impurities contained in dry silica is a very important technique. The analysis of metal impurities can be performed by, for example, an inductively coupled plasma (ICP) emission spectrometry method. However, practically, only a method using silver nitrate, mercury thiocyanate, or the like has been known for analysis of chlorine-based impurities. That is, it is a method of measuring the chloride ion concentration by colorimetric analysis (titration or absorbance measurement). However, among the reagents used in this method, mercury thiocyanate is a toxic substance, and therefore, the application of this method has a high environmental load, and caution is required in its application (for example, Non-Patent Document 1). In addition, the measurement accuracy is low, and the lower limit of quantification of the silver nitrate titration method is about 20 ppm, which is not suitable for microanalysis. Although the mercury (II) thiocyanate absorbance analysis method is about 0.1 ppm in the solution state, it dissolves silica. Considering the amount of the solvent in this case, it is about 10 ppmw in terms of solid (Non-Patent Document 2), which is not sufficiently satisfactory for accurately measuring the chlorine concentration in silica, which is required to have high purity year by year.

On the other hand, as a method for analyzing the chloride ion concentration in an aqueous solution, a method for detecting chloride ions by an ion chromatography method is known (Patent Documents 1 and 2), but in this method, the measurement target is an aqueous solution. is there. Therefore, in order to apply this to the measurement of chloride ion concentration in silica in powder form, it is necessary to obtain a silica solution by dispersing silica in an alkaline aqueous solution and heating to dissolve it (Patent Document 3). ..

JIS K 1200-3-1 "Industrial Sodium Hydroxide-Part 3: How to Determine Chloride Content-Section 1: Mercury (II) Thiocyanate Absorptiometry" Concrete Engineering Vol. 25, No. 2. Feb. 1987 "Test method for chloride content of fresh concrete"

Japanese Unexamined Patent Publication No. 11-13301 JP-A-2018-54302 Chinese Patent Application Publication No. 109060976

According to the method of dissolving the above silica in an alkaline aqueous solution and measuring the chloride ion concentration in the obtained silica solution by an ion chromatography method, the chloride ion concentration is considerably high by a simple method having a low environmental load. It can be measured with accuracy.

However, in order to sufficiently dissolve silica, the alkaline aqueous solution must use a strong alkali, and therefore the silica solution exhibits considerably strong alkalinity. That is, the silica solution is contaminated with a large amount of alkaline cations as well as chloride ions. Therefore, when the chloride ion concentration is measured with higher accuracy and higher stability, the alkali cations have an adverse effect, and the peak separability of chloride ions in the ion chromatography method is now improved. One step was not enough, and the ion chromatocolumn and detector were easily damaged, and there was room for improvement.

Against the above background, an object of the present invention is to further improve the accuracy and stability of analysis in the method for measuring the chlorine concentration in silica to which the ion chromatography method is applied.

In view of the above problems, the present inventors have continued diligent studies. As a result, they have found that the above-mentioned problems can be solved by treating a silica solution in which silica is dissolved in an alkaline aqueous solution with a cation exchange resin and then subjecting it to an analysis of chloride ions by the ion chromatography method. The present invention has been completed.

That is, in the present invention, a silica dispersion liquid with an alkaline aqueous solution is heat-treated to dissolve silica, the obtained silica solution is treated with an H-type cation exchange resin, and then chloride ions in the liquid are subjected to an ion chromatography method. It is a method for measuring the chlorine concentration in silica, which is characterized by the above-mentioned analysis.

According to the method of the present invention, the chlorine concentration in silica can be measured more accurately and more stably. Specifically, even if the elution time is shortened, the separability of the chloride ion peak is good, and the risk of damage due to the adsorption of alkaline cations on the ion chromatocolumn or detector can be reduced. The operation is simple and does not use reagents that have a large environmental load, so it is extremely meaningful in industry.

It is a chromatogram when the silica solution of Example 1 was analyzed by an ion chromatography method. It is a chromatogram when the silica solution of Comparative Example 1 was analyzed by an ion chromatography method.

The silica to be measured in the present invention is not particularly limited, and examples thereof include wet silica (hydrous silicic acid) and dry silica (silicic anhydride). Among them, dry silica having few impurities can exert more effect. .. As the dry silica, so-called fumed silica obtained by a method of hydrolyzing chlorosilane such as silicon tetrachloride in an oxyhydrogen flame can be particularly preferably applied. That is, in fumed silica, chlorine is adsorbed in a considerable amount due to the hydrolysis of chlorosilane as a raw material, and it is of great significance to measure the content with high accuracy, which is the object of measurement of the present invention. Especially preferable as silica. As the fumed silica, one having a specific surface area of 10 to 400 m ² / g, preferably 50 to 400 m ² / g is usually used.

The surface of these silicas is usually covered with silanol groups and exhibits hydrophilicity, but in the present invention, it can also be applied to hydrophobic silica having a hydrophobic group introduced into the surface. The treatment for introducing the hydrophobic group is carried out by surface treatment with a treatment agent such as a silylating agent, silicone oil, siloxanes, metal alkoxides, fatty acids and metal salts thereof. In particular, silica having a dimethylsilyl group or a methyl group introduced on the surface by a silylating agent or silica surface-treated with silicone oil is preferable.

Such hydrophobic silica preferably has a carbon content of 0.4% by mass or more, more preferably 0.4% by mass or more and 10% by mass or less, and preferably 0.6% by mass or more and 8% by mass or less. Is more preferable. The amount of carbon can be measured by a carbon amount measuring device (for example, "Sumigraph NC-TR22" manufactured by Sumika Analytical Center Co., Ltd.) by a commonly used combustion method.

In the present invention, the chloride ion (CL ⁻ ) contained in such silica is measured by applying an ion chromatography method, which is a method for analyzing the chloride ion concentration in an aqueous solution, as described above. That is, usually, silica in powder form cannot be accurately measured in chloride ion concentration even if it is made into a suspension in water and subjected to the ion chromatography method. On the other hand, in the present invention, the chloride ion concentration can be measured with high accuracy by subjecting silica to the measurement by the ion chromatography method as a silica solution heated and dissolved in an alkaline aqueous solution. ..

To elaborate on the procedure for obtaining a silica solution in which silica is dissolved in an alkaline aqueous solution, first, the silica to be measured is dispersed in the alkaline aqueous solution to obtain a silica dispersion. The pH of the silica dispersion is preferably adjusted and used so that the pH (25 ° C.) of the silica solution obtained by the heat treatment described later is 10 or more, more preferably 10 to 14. That is, the strongly alkaline aqueous solution is mixed with silica so that the pH of the obtained silica solution is maintained in the above range even if the alkali is neutralized by the dissolution of silica. When the silica dispersion has such an alkaline strength, the solubility in silica is maintained high during the heat treatment, and the undissolved residue of silica is suppressed, which is preferable.

As the alkali used in the alkaline aqueous solution, an inorganic alkali is generally used, and specific examples thereof include sodium hydroxide, potassium hydroxide, and sodium carbonate. Among these, sodium hydroxide is preferably used from the viewpoint of the solubility of silica and the ease of handling. The cleaner the water that dissolves the alkali is, the more preferable it is, and ultrapure water is usually used.

The amount of the alkaline aqueous solution for dispersing silica may be at least the minimum amount at which silica is dissolved in the heat treatment in the next step, and is usually preferably 5 mL or more per 1 g of silica. On the other hand, if the amount of the alkaline aqueous solution is too large, the workability is deteriorated. Therefore, it is usually preferable to keep the amount at 150 mL or less, more preferably 50 mL or less per 1 g of silica. More specifically, if the alkaline aqueous solution is a 5N sodium hydroxide aqueous solution, it is preferable to use 8 to 30 mL per 1 g of silica.

In order to dissolve the silica dispersion thus obtained in the heat treatment of the next step and further subject the obtained silica solution to an ion chromatography method to measure the chloride ion concentration, the silica dispersion is used. Is preferably 10 mL or more, more preferably 20 to 150 mL, as a solution in a concentration state of the silica and an alkaline aqueous solution. Therefore, this amount of silica dispersion may be prepared directly by mixing the above-mentioned required amount of alkaline aqueous solution with silica, but since operability deteriorates when the amount of liquid is large, alkaline aqueous solution or water may be used. It may be used to once obtain a concentrated silica dispersion, and then an alkali, an aqueous alkali solution, or water may be appropriately blended to prepare the desired amount of the silica dispersion.

As described above, hydrophobic silica is difficult to be compatible with an alkaline aqueous solution. Therefore, when the silica is hydrophobic silica, it is preferable to coexist with a dispersion aid in the alkaline aqueous solution in order to improve the dispersibility in the alkaline aqueous solution, and it is particularly preferable to coexist with alcohol. .. As the alcohol, lower alcohols such as methanol and ethanol are preferable, and among them, methanol is more preferable because it has excellent compatibility with an alkaline aqueous solution.

The amount of alcohol to coexist is preferably 15% by mass or less, more preferably 12% by mass or less, in order to facilitate the subsequent evaporation and removal of alcohol. On the other hand, from the viewpoint of enhancing the dispersibility of the hydrophobic silica and sufficiently dissolving it in the heat treatment of the next step, it is 2% by mass or more, more preferably 3.5% by mass or more in the alkaline aqueous solution. Is preferable. In particular, it is desirable that the alcohol is contained in the alkaline aqueous solution in an amount of 1 to 25 mL, more preferably 2 to 20 mL per 1 g of silica.

The silica dispersion thus obtained is then heated to dissolve the silica. This heating gives a silica solution. The heating temperature is preferably 80 ° C. to the temperature at which the hydrophobic silica dispersion liquid boils. In order to sufficiently increase the solubility of silica, the heating temperature is preferably 80 ° C. or higher, more preferably 85 ° C. or higher. If the heating time is too long, workability is poor, and if it is too short, silica is not sufficiently dissolved. Therefore, it is usually adopted from 20 to 120 minutes.

The silica solution thus obtained exhibits considerably strong alkalinity due to the use of the alkaline aqueous solution. For this reason, a large amount of alkaline cations are contaminated, and due to this effect, even if this solution is used for measuring the chloride ion concentration by an ion chromatography method, the measurement accuracy will decrease, and further, columns, detectors, etc. There is also a risk of damaging.

Thus, the greatest feature of the present invention is that the silica solution thus obtained is treated with an H-type cation exchange resin and then subjected to the measurement by the ion chromatography method. As a result, the alkaline cations can be removed, and the accuracy and stability of the measurement in the ion chromatography method can be improved.

The type of H-type cation exchange resin used in the above treatment is not limited as long as it can exchange alkaline cations with hydrogen ions, and known ones can be applied. Strongly acidic cation exchange resins and weakly acidic cation exchange resins Any of these can be used. A strongly acidic cation exchange resin is preferable from the viewpoint of high removability of cation metal impurities.

Examples of the base material of the H-type cation exchange resin include styrene resin, acrylic acid resin, and methacrylic acid resin. Of these, styrene-based resins are preferable, and styrene-divinylbenzene copolymers are even more preferable. Examples of the resin structure of the H-type cation exchange resin include a gel type and a porous type, and a gel type having a large ion exchange capacity and high physical strength is preferable. The micropores formed on the cation exchange resin preferably have a pore diameter of 30 Å or more.

Examples of the cation exchange group of the H-type cation exchange resin include a sulfonic acid group, a carboxyl group, a phosphoric acid group and the like, and among them, a sulfonic acid group is preferable.

The cation exchange capacity of the H-type cation exchange resin is preferably 1.2 mm equivalent or more, more preferably 1.5 mm equivalent or more, with respect to 1 mL of the swelling resin. The water content of the H-type cation exchange resin is preferably 70% or less, more preferably 60% or less.

A commercially available product may be used as such an H-type cation exchange resin, and if it is a strongly acidic cation exchange resin, for example, "Amberlite IR120B", "Amberlite IR124", "Amberlite" manufactured by Organo Corporation. "Light 200CT", "Orlite DS-1", "Orlite DS-4"; "Dowex HCR-S", "Dowex HCR-W2 (H)", "Dowex Marathon Series", "Dowex Marathon Series" manufactured by Dow Chemical Corporation Dowex Monosphere Series ”;“ Diaion SK Series ”,“ Diaion UBK Series ”,“ Diaion PK Series ”, etc. manufactured by Mitsubishi Chemical Corporation.

As the H-type cation exchange resin, a Na-type resin may be used by passing an inorganic acid such as hydrochloric acid or sulfuric acid through the resin in advance and exchanging the counterion with the H-type resin.

The amount of the H-type cation exchange resin for treating the silica solution is not particularly limited, but the total ion exchange capacity is the alkaline equivalent of the silica solution to be passed, considering the efficiency of removing alkaline cations. It is preferable that the amount is twice or more that of. If the removal efficiency of alkaline cations is made higher and the amount of resin is too large, the operability is lowered. Therefore, the amount is more preferably 3 to 10 times the alkaline equivalent of the silica solution.

As a specific method for treating the silica solution with an H-type cation exchange resin, first, the silica solution is defined in a volumetric flask or the like. The capacity at this time is not particularly limited as long as the silica does not precipitate or gel, but 10 to 200 mL is preferable from the viewpoint of ease of operation.

Alkaline cations can be removed by, for example, a batch method in which the above-mentioned silica solution after volume transfer is transferred to a beaker, an ion exchange resin is added and stirred, but the efficiency of removing alkali cations is high. From the viewpoint of operability, it is preferable to fill a column or cartridge with an H-type cation exchange resin and pass a silica solution through the column or cartridge. In the case of such a filling method, even when the silica solution contains a solid such as undissolved silica, this can be removed by filtration, which is preferable.

In the filling method, columns and cartridges filled with a cation exchange resin are first washed by passing ultrapure water through them, then co-washed with a silica solution, and then the alkali cations of the silica solution are used. It is preferably subjected to an ion removal treatment. The co-washing operation is preferably performed once or more, preferably twice or more.

After the co-washing, a silica solution is passed through the mixture to obtain a treatment liquid to be subjected to an ion chromatography method. At this time, it is preferable to confirm the pH of the treatment liquid with a pH test paper or the like to check whether the alkali cations have been sufficiently removed in the treatment liquid. The pH of the silica solution varies depending on the concentration of silica and the surface modifying group, but since silicate ions generally show neutral to weak acidity, the pH of the silica solution after the ion exchange treatment is usually less than 10, and more. The treatment may be preferably performed so as to be less than 7. To check the pH, a pH test paper or a pH meter may be used as appropriate.
In the present invention, the chloride ion contained in the silica solution prepared as described above is analyzed by an ion chromatography method, thereby determining the chlorine concentration in the silica used for the measurement. Here, the ion chromatography method is a chromatograph in which an ion exchange resin is used as a stationary phase, and each ion is separated by utilizing differences in the permeation rate and diffusion rate of a plurality of ions contained in a sample. This is a quantitative method for measuring the amount of ions by measuring physical properties such as electrical conductivity of the separated ions.

The separation column used in ion chromatography may be appropriately selected from known columns for measuring anions. Examples of the stationary phase anion exchange resin include basic anion exchange resins such as a quaternary ammonium group and a tertiary sulfonium group as functional groups, and styrene-based and phenol-based polymer bases thereof. , Acrylic, methacryl and other synthetic polymers are used. Further, as the anion exchange resin, a latex type anion exchange resin or a coating type anion exchange resin can also be used. As the eluent (mobile phase), one used in a usual ion chromatography method can be appropriately selected. Specifically, a dilute aqueous solution containing sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, or the like alone or mixed. Is used. Examples of the detector include an ion conductivity detector, a visible absorptiometry detector, an electrochemical detector, etc., but usually, it is general-purpose to measure by a change in ion conductivity, and only an ion component is detected. Since it is a measurement method, it is preferable to use an ion conductivity detector. In addition, a commercially available ion chromatography analyzer equipped with a liquid feed pump, a sample introduction unit, a concentrator, a stationary phase column, a constant temperature bath, and the like can be used. An autosampler can be used to introduce the sample into the ion chromatograph, but the sample may gel due to aging depending on the concentration of silica dissolved in the silica solution and the surface modifying group. It is desirable to measure immediately after the treatment with the cation exchange resin, preferably within 24 hours.

The chloride ion concentration in the silica solution by the ion chromatography method is preferably determined by using a calibration curve prepared in advance. For the calibration line, prepare a plurality of chloride ion aqueous solutions having known chloride ion concentrations, analyze them by an ion chromatography method, and analyze the chloride ion concentration ppm (mg / L) and the peak area of chloride ions. That is, if the detector is an ion conductivity detector, a graph showing the relationship between the ion conductivity (μS / cm) and the detection time (min) may be linearly approximated by the minimum square method.

The chloride ion concentration in the silica solution thus obtained by the ion chromatography method may be used to determine the chlorine concentration in the silica used for the measurement. Specifically, it can be calculated by the following formula. The chloride ion concentration of the blank solution is the chloride ion concentration obtained by carrying out the same procedure as above without dispersing silica in the alkaline aqueous solution.

Chloride ion concentration (ppmw) = (Chloride ion concentration (mg / L) obtained from the calibration curve-Chloride ion concentration of blank solution (mg / L)) × Silica solution volume (L) ÷ Silica amount (g) ) × 1000

Hereinafter, examples will be shown for the purpose of specifically explaining the present invention, but the present invention is not limited to these examples. In the examples, the analysis conditions of the ion chromatography method are as follows, and the calibration curve used for determining the chloride ion in the silica solution was prepared by the following method.
(Analytical conditions for ion chromatography)
An "ICS-2100" (manufactured by Nippon Dionex Co., Ltd.) was used as the ion chromatography apparatus, and "IonPac AS18" (manufactured by Thermo Fisher Scientific Co., Ltd.) was used as the anion column. As the detector, an ion conductivity detector was used. As the eluent, a 34.5 mmol / L potassium hydroxide aqueous solution was used. The eluent was passed through the device at a flow rate of 1.0 mL / min.
(Method of creating a calibration curve for determining chloride ions in a silica solution)
A 1000 mg / L chloride ion standard solution is diluted with ultrapure water, and chloride ion aqueous solutions having concentrations of 0.05, 0.1, 0.2, 0.5, and 1.0 mg / L are added to each. Prepared. When these chloride ion aqueous solutions were analyzed by an ion chromatography method under the above conditions, the chloride ion peak could be confirmed with a detection time of 4.2 minutes. Each aqueous chloride ion solution is analyzed by ion chromatography, and the chloride ion concentration ppm (mg / L) is on the horizontal axis, and the peak area of chloride ions, that is, ion conductivity (μS) × detection time (min). A calibration curve was created by linearly approximating the scale on the vertical axis and the minimum square method.
Example 1 and Comparative Example 1
As silica, 1.00 g of "Leoloseal QS-09" (hydrophilic fumed silica, specific surface area of about 85 m ² / g) manufactured by Tokuyama Corporation was weighed and added to a 200 mL (25 ° C.) plastic container. Subsequently, 10 mL of a 5N thorium hydroxide aqueous solution was added and shaken gently. Further, 30 mL of ultrapure water was added and shaken lightly in the same manner. That is, the total amount of the alkaline aqueous solution used to disperse 1 g of silica was 40 mL.

Subsequently, the obtained silica dispersion was heated at 100 ° C. for 20 minutes using a water bath. The dissolution of silica was confirmed at the end of heating. The plastic container was taken out from the water bath, cooled to 25 ° C., and then the solution was transferred to a 100 mL volumetric flask, and the solution in the plastic container was washed with ultrapure water and increased to 100 mL to obtain a silica solution. The pH (25 ° C.) of this silica solution was about 14. When this silica solution was analyzed as it was by an ion chromatography method, an interfering peak was observed as shown in FIG. 2, and a chloride ion peak appeared at 4.0 minutes and was broad (Comparative Example 1).

Therefore, this silica solution was washed with 10 mL of pure water and then passed through a cation exchange solid-phase extraction cartridge co-washed with 2 mL of an actual sample. As the cation exchange solid phase extraction cartridge, an H-type strongly acidic cation exchange resin (the base material is a styrene resin, the ion exchange group is a sulfonic acid group, and the ion exchange capacity is 2 for 1 mL of the swollen resin. The cartridge was filled with "OnGuard II H" (manufactured by Thermo Fisher Scientific), which had an equivalent of .0 to 2.2 mm.

When the pH of the treatment liquid passed through the cation exchange solid-phase extraction cartridge was confirmed with a pH test paper, it showed about 5. When this treatment liquid was analyzed by an ion chromatography method, as shown in FIG. 1, the influence of the interfering peak was small, and the chloride ion peak could be separated cleanly. The peak area of chloride ions was 0.1243 μS / cm · min. When the chloride ion concentration in the silica solution was determined by the calibration curve method using the peak area of the chloride ion, it was 0.347 mg / L. Further, the chloride ion concentration of the blank solution obtained by carrying out the same procedure as above without dispersing silica in the alkaline aqueous solution was also measured and found to be 0.006 mg / L. From these results, the following formula chloride ion concentration (ppmw) = (chloride ion concentration (mg / L) obtained from the calibration curve-blank chloride ion concentration (mg / L)) × silica solution volume (L) ) ÷ Silica amount (g) x 1000
When the chlorine concentration in the silica used for the measurement was calculated using the above, it was 34.1 μg / g (ppmw).
Example 2
In order to confirm the accuracy of the analysis, a repeated experiment of the cation exchange operation of Example 1 was carried out. The same sample as in Example 1 was repeatedly analyzed 5 times by the same operation, and the chlorine concentration was calculated by an ion chromatography method. The results were 36.4, 35.3, 34.3, 34.9, and 34, respectively. It became .5.
The average value of these was 35.1, the standard deviation was 0.816, and the relative standard deviation was 2.33%. It was better than the relative standard deviation of 3.24% of the ion chromatography method and the relative standard deviation of 17.8% of the silver nitrate titration method shown in Patent Document 3.

Claims (12)

The feature is that the silica dispersion liquid with an alkaline aqueous solution is heat-treated to dissolve silica, the obtained silica solution is treated with an H-type cation exchange resin, and then the chloride ions in the liquid are analyzed by an ion chromatography method. A method for measuring the chlorine concentration in silica. The method for measuring chlorine concentration in silica according to claim 1, wherein the H-type cation exchange resin is a strongly acidic cation exchange resin. The method for measuring the chlorine concentration in silica according to claim 2, wherein the base material is a styrene resin and the ion exchange group is a sulfonic acid group in the H-type strongly acidic cation exchange resin. The silica solution is treated with an H-type strongly acidic cation exchange resin, the cation exchange resin is filtered off by a filter, and the obtained filtrate is subjected to chloride ion analysis by an ion chromatography method. The method for measuring the chlorine concentration in silica according to any one of the above. The chlorine concentration in silica according to any one of claims 1 to 4, wherein the pH of the silica dispersion is adjusted so that the pH (25 ° C.) of the silica solution obtained by the heat treatment becomes 10 or more. Measuring method. The chlorine concentration in silica according to any one of claims 1 to 5, wherein the treatment with the H-type cation exchange resin of the silica solution is carried out so that the pH (25 ° C.) of the treatment liquid is less than 10. Measuring method. The method for measuring chlorine concentration in silica according to any one of claims 1 to 6, wherein the alkaline aqueous solution is a sodium hydroxide aqueous solution. According to any one of claims 1 to 7, the amount of the alkaline aqueous solution for dispersing 1 g of silica is not more than the minimum amount for dissolving 1 g of silica at the heating temperature of the silica dispersion and not more than 150 mL. The method for measuring the chlorine concentration in silica according to the above. The method for measuring chlorine concentration in silica according to any one of claims 1 to 8, wherein the heating temperature of the silica dispersion is in the range of 80 ° C. to the temperature at which the silica dispersion boils. The chlorine concentration in silica according to any one of claims 1 to 9, wherein the analysis of chloride ions in the silica solution by an ion chromatography method is performed by measuring the chloride ion concentration due to a change in ion conductivity. Measuring method. The method for measuring chlorine concentration in silica according to any one of claims 1 to 10, wherein the silica is hydrophobic silica and alcohol is allowed to coexist in an alkaline aqueous solution in which silica is dispersed. The method for measuring chlorine concentration in silica according to any one of claims 1 to 11, wherein the alcohol is methanol.