RU2227290C1 - Process of extraction and separate detection of osmium (vi) and osmium (iv) - Google Patents

Abstract

FIELD: analytical chemistry, separation and detection of osmium (VI) and osmium (IV) in process solutions. SUBSTANCE: process of extraction and separate detection of osmium (VI) and osmium (IV) includes preparation of solutions containing mixture of osmium (VI) and osmium (IV), their consistent transfer to complex compound and measurement of diffuse-reflection factor. Consistent extraction of osmium under different degrees of oxidation from solutions is performed with one sorbent-silica gel chemically modified by mercaptal groups. Diffuse- reflection factor is measured at 440 nm in case of extraction of osmium (VI) and at 550 nm in case of extraction of osmium (IV) in presence of tin chloride. EFFECT: simplified process and reduced limit of detection of osmium (VI) and osmium (IV).

Description

The invention relates to the field of analytical chemistry, namely to methods of separation and determination, and can be used for the separate determination of osmium (VI) and osmium (IV) in technological solutions.

The described methods for the determination of osmium do not provide for a separate determination of osmium in solution in various degrees of oxidation. As a rule, before determining osmium in various degrees of oxidation, they are transferred to one oxidation state (+8 or +4) and then they are already determined according to known methods [I].

There is a method of isolation and separate determination of trace amounts of osmium (VI) and osmium (IV), simultaneously present in solution [2]. The method includes adding to the solution simultaneously containing chlorine complexes of osmium (IV) and osmium (VI) hydrochloric acid to a concentration of 0.1-3 M, adding a sorbent-silica gel chemically modified with benzoylthiourea, stirring for 5 minutes, separating the sorbent from the solution, drying it and measuring the diffuse reflection coefficient of the sample at 490 nm. At this stage, osmium (VI) is isolated from the solution.

To the solution remaining after sorption, add another sorbent-silica gel, chemically modified with allylthiourea, 1 ml of a 10% solution of tin (II) chloride, and stirred for 60 min at 95 ° C, the sorbent is separated from the solution and the diffuse reflection coefficient is measured air-dry sample at 550 nm. In this way, osmium (IV) is isolated and determined.

The disadvantages of this method include the use of two types of sorbents, as well as the insufficiently high sensitivity of the determination of osmium in various oxidation states.

This method is selected as a prototype.

The technical result is to simplify the technique and reduce the detection limit of osmium (VI) and osmium (IV).

The specified technical result is achieved by the fact that in the method for determining osmium, which includes the preparation of solutions containing a mixture of osmium (VI) and osmium (IV), their sequential conversion into a complex compound and measurement of the diffuse reflection coefficient, the sequential isolation of osmium in various degrees is new oxidation by a single sorbent - silica gel, chemically modified by mercapto groups, measurement of the diffuse reflection coefficient at 440 nm in the case of osmium (VI) separation and 550 nm in the case of osmium ( Iv) in the presence of tin (II) chloride.

At the first stage, to a 0.1-3 M solution of hydrochloric acid, containing simultaneously osmium (VI) and osmium (IV) chlorocomplexes, a weighed portion of sorbent-silica gel chemically modified by mercapto groups is added. The mixture is shaken for 1-2 minutes at room temperature, the sorbent is separated, washed with 1 M Hcl. The sorbent is placed in a fluoroplastic cell and the diffuse reflection coefficient of the sample is measured at 440 nm. At the first stage, the sorbent selectively selects only osmium (VI), which is quantified. All osmium (IV) remains in solution.

Next, a new sample of a sorbent-silica gel chemically modified by mercapto groups is added to the solution, 1 ml of a 10% solution of tin (II) chloride is added, and sorption is carried out with vigorous stirring at 95 ° C for 40 min. The sorbent is separated from the solution by decantation, placed in a fluoroplastic cell and the diffuse reflection value is measured at 550 nm. In this case, osmium (IV) is determined.

The essence of the invention lies in the fact that under the optimal conditions found, the sorbent provides sequential isolation and separate determination of osmium (VI) and osmium (IV). Under conditions of sorption of osmium (VI) (room temperature), osmium (IV) is practically not recovered (its degree of extraction does not exceed 0.5%). Osmium (IV) is adsorbed only in the presence of a 300-fold excess of tin (II) chloride, which is used as a lab-enhancing additive.

The proposed method allows to isolate and determine 0.1-1000 μg of osmium (VI) and 1-1000 μg of osmium (IV) per 0.1 g of sorbent.

The optimal acidity of the extraction is selected experimentally. With an increase in acidity of more than 3 mol / L by HCl, the sorbent is destroyed, and the osmium (VI) in solution is reduced to osmium (IV), and the degree of extraction decreases. The decrease in the concentration of Hcl below 0.1 M leads to the appearance of hydrolyzed forms of osmium (VI) and osmium (IV) and, as a consequence, to a decrease in the degree of extraction. The time and temperature of sorption were chosen experimentally from the curves of the dependence of the degree of extraction on the phase contact time and temperature. A decrease in the time and temperature of sorption leads to a decrease in the degree of extraction of osmium (IV). An increase in the phase contact time leads only to an increase in the analysis time.

The experiments performed to study the effect of the amount of tin (II) chloride on the completeness of osmium (IV) extraction showed that the equilibrium of the sorption reaction shifts toward quantitative sorption only with a 200-fold excess of tin (II) chloride relative to osmium (IV). The decrease in the ratio leads to a decrease in the degree of extraction. The completeness of extraction is already achieved with a 200-fold excess of tin (II) chloride, which in terms of 0.8-1.0 ml of a 10% solution (II).

In the proposed method, the content of osmium (VI) and osmium (IV) in an arbitrary volume of the solution should not be less than 0.03 and 0.3 μg, respectively. This amount of osmium (VI) and osmium (IV) per 0.1 g of sorbent is the minimum concentration that can be recorded on existing devices relative to the background signal.

For a better understanding, the following examples are suggested.

Example 1 (prototype). 10 ml of the analyzed solution containing 150 μg of osmium (VI) and 20 μg of osmium (IV) is acidified with Hcl to a content of 0.1-3 M. 0.1 g of silica gel chemically modified with benzoylthiourea is added to the solution, the mixture is shaken for 5 minutes at room temperature. The sorbent is separated from the solution by decantation, dried, placed in a fluoroplastic cell and the diffuse reflection coefficient is measured at 490 nm. The content of osmium (VI) is found according to the calibration schedule. Found (147 ± 6) μg osmium (VI).

To the filtrate was added 0.1 g of silica gel chemically modified with allylthiourea, 1 ml of a 10% solution of tin (II) chloride, the mixture was placed in a thermostatic tube with a ground stopper. The tube is installed in a mechanical shaker and stirred for 60 min at a temperature of 95 ° C. The sorbent is separated by decantation, dried, placed in a fluoroplastic cuvette and the diffuse reflection coefficient is measured at 550 nm. The content of osmium (IV) is determined by the calibration graph. Found (20 ± 1) mcg of osmium (IV).

Example 2 (prototype). 10 ml of the analyzed solution containing 5 μg of osmium (VI) and 200 μg of osmium (IV) is acidified with HC1 to a content of 0.1-3 M. 0.1 g of silica gel chemically modified with benzoylthiourea are added to the solution, the mixture is shaken for 5 minutes at room temperature. The sorbent is separated from the solution by decantation, dried, placed in a fluoroplate cuvette and the diffuse reflection coefficient is measured at 490 nm. The content of osmium (VI) is found according to the calibration schedule. Found (4.7 ± 0.6) μg osmium (VI).

To the filtrate was added 0.1 g of silica gel chemically modified with allylthiourea, 1 ml of a 10% solution of tin (II) chloride, the mixture was placed in a thermostatic tube with a ground stopper. The tube is installed in a mechanical shaker and stirred for 60 min at a temperature of 95 ° C. The sorbent is separated by decantation, dried and the diffuse reflection coefficient is measured at 550 nm. The content of osmium (IV) is found according to the calibration schedule. Found (195 ± 6) μg osmium (IV).

Example 3 (the proposed method). 10 ml of the analyzed solution containing 5 μg of osmium (VI) and 1000 μg of osmium (IV) is acidified with HCl to a content of 0.1-3 M. 0.1 g of silica gel chemically modified with mercapto groups are added to the solution, the mixture is shaken for 5 minutes at room temperature. The sorbent is separated from the solution by decantation, placed in a fluoroplastic cell and the diffuse reflectance of wet sorbates is measured at 440 nm. Determine the content of osmium (VI) according to the calibration schedule. Found (4.8 ± 0.3) μg osmium (VI).

0.1 g of silica gel chemically modified with mercapto groups, 1 ml of a 10% solution of tin (II) chloride are added to the filtrate, the mixture is placed in a thermostatic tube with a ground tube, the tube is fixed in the cells of a mechanical shaker and stirred for 30 min at a temperature of 95 ° C. The sorbent is separated by decantation and the diffuse reflection coefficient of wet sorbates is measured at 550 nm. The content of osmium (IV) is found according to the calibration schedule. Found (1000 ± 14) mcg of osmium (IV).

Example 4 (the proposed method). 10 ml of the analyzed solution containing 0.5 μg of osmium (VI) and 100 μg of osmium (IV) is acidified with HC1 to a content of 0.1-3 M. 0.1 g of silica gel chemically modified with mercapto groups are added to the solution, the mixture is shaken for 5 min at room temperature. The sorbent is separated from the solution by decantation, placed in a fluoroplastic cell and the diffuse reflectance of wet sorbates is measured at 440 nm. Determine the content of osmium (VI) according to the calibration schedule. Found (0.48 ± 0.07) mcg of osmium (VI).

0.1 g of silica gel chemically modified with mercapto groups, 1 ml of a 10% solution of tin (II) chloride are added to the filtrate, the mixture is placed in a thermostatic tube with a ground tube, the tube is fixed in the cells of a mechanical shaker and stirred for 30 min at a temperature of 95 ° C. The sorbent is separated by decantation and the diffuse reflection coefficient of wet sorbates is measured at 550 nm. The content of osmium (IV) is found according to the calibration schedule. Found (100 ± 4) mcg of osmium (IV).

Thus, in comparison with the prototype, the proposed method allows the separation and separate determination of osmium (VI) and osmium (IV) using one type of sorbent and with lower detection limits.

The analysis time is reduced from 1 h 40 min to 60 min, while only operations are carried out to bring the solution to a certain acidity by HC1, sequential sorption with two weighed portions of one sorbent and subsequent photometry.

Sources of information

1. Ginzburg S.I., Yezerskaya N.A., Prokofieva I.V. et al. Analytical chemistry of platinum metals. - M .: Nauka, 1972, 613 p.

2. RF patent 2112238 Method for the isolation and separate determination of osmium (VI) and osmium (IV) / Bakhvalova IP, Bakhtina MP, Losev VN Priority June 4, 1996 // Received May 27, 1998. Bull. invented No. 15, 1998 (prototype).

Claims (1)

The method of isolation and separate determination of osmium (VI) and osmium (IV), including converting them into complex compounds and measuring the diffuse reflection coefficient, characterized in that osmium (VI) is isolated from solutions with silica gel, chemically modified mercapto groups, at room temperature and measure the coefficient diffuse reflection of the osmium complex with mercapto groups at 440 nm on the surface of the sorbent, and osmium (IV) is isolated from solutions by silica gel, chemically modified mercapto groups, at 95 ° C in the presence of ol and (II) and measure the diffuse reflectance of mixed-ligand complex of osmium merkaptolovohloridnogo on the surface at 550 nm.