RU2326049C2 - Method of obtaining silicon dioxide, modified by molybdophosphoric heteropolycompound, and an indication tube - Google Patents

Abstract

FIELD: analytical chemistry; food industry.

SUBSTANCE: method of obtaining silicon dioxide, modified by molybdophosphoric heteropolycompound, involves hydrolysis of tetraethoxysilane in a medium of ethanol in the presence of ammonium hexafluosilicate, molybdophosphoric heteropolycompound and a transition metal compound, which can be reduced, and with subsequent drying of the mature gel using microwave radiation with power from 800 to 1000 W. The indicator tube is made from a transparent tube made from glass or polymer material. The cavity of the tube is filled with powdered modified molybdophosphoric heteropolycompound silicon dioxide. The invention allows to obtain a porous modified silicon dioxide for determining 0.2-50 mg/l of diamides, 100-2000 mg/l ascorbic acid; 20-100 mg/l tin (II).

EFFECT: obtaining of porous modified silicon dioxide.

10 cl, 3 dwg, 1 tbl

Description

The invention relates to the field of chemistry, food industry and other industries where the rapid determination of metal ions, anions and organic compounds is necessary, and in particular to methods for producing silicon dioxide modified with a molybdophosphoric heteropoly compound, and to indicator tubes.

A known method of producing silicon dioxide is to introduce ethanol and water into a mixture of tetraethoxysilane in the presence of an ammonium hexafluorosilicate of a molybdophosphoric compound and a copper (II) compound. After gel maturation, drying is carried out with a 600 W microwave radiation (Morosanova E.I., Reznikova E.A., Velikorodny A.A., Journal of Analytical Chemistry, 2001, V. 56, No. 2, pp. 195-200).

The porous material obtained in a known manner is used to determine 0.3-3 mg / l of hydrazines and 10-400 mg / l of ascorbic acid. The determination of high contents of reducing agents is not possible due to leaching of immobilized heteropoly compounds. For the same reason, the known material does not allow the determination of tin (II) compounds.

In a known solution in the determination of reducing agents, the material is used as an indicator powder. The determination is made both using analytical instruments (spectrophotometers), and visually colorimetrically using color scales.

The technical result of the invention is to obtain silicon dioxide modified with an analytical reagent in the form of a molybdophosphoric heteropoly compound, which allows to extend the range of detectable concentrations of hydrazines and ascorbic acid. The material allows to determine 0.2-50 mg / l of hydrazines, 100-2000 mg / l of ascorbic acid, as well as 20-100 mg / l of tin (II). In addition, the invention solves the problem of creating a tool in the form of an indicator tube, which provides the possibility of rapid analysis in the specified concentration range.

The technical result of the invention is achieved in that the method of producing silicon dioxide modified with an analytical reagent includes the hydrolysis of tetraethoxysilane in ethanol in the presence of ammonium hexafluorosilicate, a molybdophosphoric heteropoly compound and a transition metal compound capable of reduction, as well as subsequent drying of the ripened gel with microwave radiation with a power of 800-1000 Tue

The following ions can be used as a transition metal ion capable of reduction: iron (III), titanium (IV), or copper (II). The reduction of molybdophosphoric heteropoly compounds in the presence of these ions is autocatalytic. The reaction activators are intermediate mixed complexes formed at the initial moment of reduction, which include transition metal ions. In the subsequent reaction, the transition metal ion leaves the complex and the end product of the reaction is the reduced form of heteropoly compounds.

As molybdophosphoric heteropoly compounds, molybdophosphoric heteropoly compounds of 12 and 18 rows can be used, including molybdophosphoric acids, their salts, mixtures of acids and salts.

According to the invention, the indicator tube is made in the form of a transparent tube of glass or of a polymeric material, which is filled with the modified silicon dioxide obtained as described above.

The inner diameter of the transparent tube lies in the range of 0.5-3 mm, and its length is in the range of 40-200 mm. As an inert porous material for sealing the ends of the tube can be used pulp and paper non-woven material. When using a tube of polymeric material, a tube of polyethylene or polyacrylamide is used.

Due to the physicochemical characteristics of the silicon dioxide powder (specific surface area and porosity) obtained by the method according to the invention, the interaction products of the immobilized heteropoly compound are retained in the volume of the powder particles. This leads to the expansion of the ranges of the determined contents of inorganic and organic reducing agents. The indicator powder can be used to determine reducing agents in aqueous solutions in various forms, including using indicator tubes.

Possessing redox properties, silicon dioxide having a porous structure modified with a molybdophosphorus heteropoly compound reacts with various reducing agents to form intensely colored “blue” reduction products. The method used to determine various organic and inorganic reducing agents, including ascorbic acid, hydrazines, and tin (II), is based on the use of this rather widely known reaction. Thanks to the fixed (immobilized) molybdophosphoric heteropoly compounds, it is possible to significantly simplify and speed up the analysis procedure, to make it possible to perform in off-laboratory conditions, which is achieved, in particular, using analytical tubes.

The possibility of carrying out the invention is illustrated by the following examples of the preparation of silicon dioxide indicator powder modified with a molybdophosphoric heteropoly compound.

Example 1

50 ml of a saturated solution of molybdophosphoric heteropoly acid in ethanol, 15 ml of a 0.05 M aqueous solution of ammonium hexafluorosilicate and 5 ml of a 0.2 M aqueous solution of titanium (IV) are added to 20 ml of tetraethoxysilane.

The resulting solution was left at room temperature until the gel fully ripened.

After 2 hours, the ripened gel is dried under the influence of microwave radiation with a power of 800 W to constant weight for 6 minutes.

The dried sample is crushed and dispersed into fractions. The yellow color of the obtained powder is due to the presence of molybdophosphoric heteropoly acid in it.

When using the material as an indicator powder, the range of the determined hydrazine contents in the variant of solid-phase spectrophotometry is 0.2-10 mg / l, in the variant of visual colorimetry - 0.2-50 mg / l.

Example 2

50 ml of ethyl alcohol, 10 ml of an aqueous solution of a mixture of molybdophosphoric heteropoly acids 12 and 18 rows, 15 ml of a 0.1 M aqueous solution of ammonium hexafluorosilicate and 5 ml of a 0.2 M solution of copper (II) are added to 20 ml of tetraethoxysilane.

The resulting solution was left at room temperature until the gel fully ripened.

After 1.5 hours, the ripened gel is dried under the influence of microwave radiation with a power of 900 W to constant weight for 5 minutes.

The dried sample is crushed and dispersed into fractions. The resulting powder is yellow due to the presence of molybdophosphoric heteropoly acids in it.

When using the material as an indicator powder, the range of ascorbic acid contents determined in the solid-state spectrophotometry variant is 2-600 mg / L, in the visual colorimetric variant - 10-1000 mg / L, in the indicator tube variant 100-2000 mg / L.

Example 3

0.5 g of ammonium molybdophosphate is carefully ground and added to 50 ml of ethyl alcohol. After that, 20 ml of tetraethoxysilane, 15 ml of a 0.1 M aqueous solution of ammonium hexafluorosilicate, 5 ml of a 0.2 M aqueous solution of iron (III) are quickly added to the mixture.

The mixture is stirred and left at room temperature until the gel is fully ripened.

After 15 minutes, the ripened gel is dried under the influence of microwave radiation with a power of 1000 W to constant mass for 2 minutes.

The dried sample is crushed and dispersed into fractions. The resulting powder is yellow due to the presence of ammonium molybdophosphate in it.

When using the material as an indicator powder, the range of the determined tin (II) contents in the indicator tube variant is 20-100 mg / l.

The results of the determination of reducing agents are presented in the Table.

In the solid-state spectrophotometric determination, 25 ml of the analyzed solution is poured to 0.3 g of the indicator powder. The suspension is stirred for 15 minutes, then the optical density of the powder is measured at 680 nm and the concentration of the reducing agent is determined according to a predefined calibration schedule.

In the variant of visual colorimetry, 0.2 ml of the analyzed solution is poured to 0.2 g of the indicator powder. The suspension is stirred for 15 minutes, then the color of the indicator powder is compared with the color scale and the concentration of the reducing agent is determined.

In the variant of indicator tubes: the indicator tube is lowered into the analyzed solution to a depth of 2-3 mm. After raising the liquid front to the upper end, the indicator tube is removed and the length of the blue-green colored zone is measured and the concentration of the reducing agent is determined according to a pre-constructed calibration schedule.

Table Detectable substance Definition Option The range of determined contents, mg / l Analysis time, min Object of analysis Hydrazines Solid State Spectrophotometry 0.2-10 twenty Technological solutions, extracts from soils Visual colorimetry 0.2-50 twenty Vitamin C Solid State Spectrophotometry 2-600 7 Juices, pharmaceuticals Visual colorimetry 10-1000 7 Indicator tube 100-2000 5 Tin (II) Indicator tube 5-100 mcg / vial 5 Reagents for the production of radiopharmaceuticals

The indicator tube is made as follows.

A glass transparent tube is taken with an inner diameter of 1.5 mm and a length of 60 mm. First, one end of the tube is sealed with a pulp and paper non-woven material, then, from the side of the second end, crushed powder of modified silicon dioxide is poured into the tube. When filling the powder, it is compacted by shaking the tube and tapping on it. The second end of the tube is also sealed with a pulp and paper non-woven material. After both ends of the tube are sealed, pouring powder inside it is not allowed.

Claims (10)

1. A method of producing silicon dioxide modified with a molybdophosphoric heteropoly compound, including the hydrolysis of tetraethoxysilane in ethanol in the presence of ammonium hexafluorosilicate, a molybdophosphoric heteropoly compound and a transition metal compound capable of reduction, as well as subsequent drying of the ripened gel with 1000 W microwave power. 2. The method according to claim 1, characterized in that as a transition metal compound capable of reduction, a compound of iron (III), titanium (IV) or copper (II) is used. 3. The method according to claim 1, characterized in that as the molybdophosphoric heteropoly compounds can be used molybdophosphoric heteropoly compounds of 12 and 18 rows. 4. The method according to claim 1, characterized in that as molybdophosphoric heteropoly compounds can be used molybdophosphoric acids, their salts, mixtures of acids and salts. 5. The indicator tube, made in the form of a transparent tube made of glass or of a polymeric material, the tube cavity is filled with powdered modified molybdophosphoric heteropoly compound of silicon dioxide obtained by hydrolysis of tetraethoxysilane in ethanol in the presence of ammonium hexafluorosilicate, a molybdisophosphoric compound restoration, followed by drying of the ripened gel with microwave radiation with a power of 800-1000 W, while the ends of the tube are sealed with an inert porous material. 6. The tube according to claim 5, characterized in that as the transition metal compound capable of reduction, a compound of iron (III), titanium (IV) or copper (II) is used. 7. The tube according to claim 5, characterized in that as the molybdophosphoric heteropoly compounds can be used molybdophosphoric heteropoly compounds of 12 and 18 rows. 8. The tube according to claim 5, characterized in that the inner diameter of the transparent tube lies in the range of 0.5-3 mm, and its length is in the range of 40-200 mm. 9. The tube according to claim 5, characterized in that the pulp and paper non-woven material is used as an inert porous material. 10. The tube according to claim 5, characterized in that when using a transparent tube of a polymeric material, a tube of polyethylene or polyacrylamide is used.