RU2327983C1 - Photometric method of identifying rhodium - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method lies in that, rhodium (III) is separated from a solution using silica gel, chemically modified dithiocarbamate groups, at 90°C and the diffuse reflection factor of the complex of rhodium (III) with the dithiocarbamate groups at the surface of the silica gel is measured at 410 nm.

EFFECT: simplification; faster and increased sensitivity of analysis.

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Description

The invention relates to the analytical chemistry of platinum metals, in particular to the photometric determination of rhodium (III), for example, in technological solutions of refining production.

A known method for the photometric determination of rhodium (III) by coloring its chloride complex [Karpova L.V. Some issues of emission and molecular spectroscopy / Karpova L.V., Gutko A.D. - Krasnoyarsk: Central Bureau of Technical Information, 1960]. The method is characterized by a very low sensitivity for determining rhodium.

As a prototype, the method of photometric determination of rhodium (III) with sodium bismuthate was selected [S. Ginzburg et al. Guidelines for the chemical analysis of platinum metals and gold. - M .: Nauka, 1965].

During the oxidation of rhodium (III) in a sulfuric acid medium, its compounds are formed in higher oxidation states, staining the solution in violet color.

A solution of complex rhodium chloride (from 20 to 60 μg / ml) is evaporated to dryness in a water bath, 3-5 ml of nitric acid are added and evaporated several times to dryness; the residue is dissolved in 10-15 ml of water, 2-3 ml of HNO _{3 are} added (ρ = 1.14 g / cm ³ ), the solution is transferred into a 100 ml volumetric flask, adjusted to the mark with water and stirred. An aliquot of the solution (20 ml) is transferred into a glass with a capacity of 100 ml, 6 ml of H ₂ SO ₄ (ρ = 1.84 g / cm ³ ) are added and evaporated until sulfuric anhydride vapor is isolated, cooled, diluted with water, transferred to a volumetric flask with a capacity of 50 ml and adjusted to the mark with water. The solution is then transferred to a 150 ml conical flask. To the resulting solution was added 1 g of sodium bismuthate, stirred for 15 minutes, then filtered into a dry flask and after 5-7 minutes the optical density of the solution was measured at a wavelength of 550-570 nm.

The disadvantages of the method include a high detection limit, low sensitivity of the method, duration and complexity.

The technical result of the invention is to increase the sensitivity of the method, reducing the detection limit, reducing the duration of the analysis and simplification.

The technical result is achieved by the fact that in the method for the photometric determination of rhodium, including the preparation of a solution of rhodium (III), converting it to a complex compound and measuring the color intensity of the complex compound, it is new that rhodium (III) is isolated from the solution by silica gel chemically modified with dithiocarbamate groups at a temperature of 90 ° C and measure the diffuse reflectance of the complex of rhodium (III) with dithiocarbamate groups on the surface of silica gel at 410 nm.

Comparative analysis with the prototype shows that the claimed method is characterized in that rhodium (III) is isolated from the solution with silica gel chemically modified with dithiocarbamate groups at a temperature of 90 ° C and the diffuse reflection coefficient of the rhodium (III) complex with dithiocarbaminate groups on the surface of silica gel is measured at 410 nm Thus, the claimed device meets the criteria of the invention of "novelty."

When studying other well-known technical solutions in this technical field, the features that distinguish the claimed invention from the prototype were not identified, and therefore they provide the claimed technical solution with the criterion of "inventive step".

The essence of the method lies in the fact that on the surface of the modified silica, rhodium (III) is concentrated from its solution due to complexation with the functional groups of the sorbent, which makes it possible to determine lower concentrations in comparison with the prototype.

The method is implemented as follows. The analyzed sample containing rhodium is transferred into the solution by sintering with barium peroxide at a red heat, followed by leaching of 2 N. hydrochloric acid solution. In this case, rhodium passes into solution in the form of the H ₃ [RhCl ₆ ] complex, and the processes of its water absorption and hydration are excluded.

An aliquot of the solution containing 10-500 μg of rhodium (III), with a volume of about 10 ml, is placed in a thermostated tube with a ground stopper, 0.1 g of chemically modified silica is added, heated to 90 ° C and shaken for 20 minutes. In the process of sorption of rhodium (III), the initial solution of its chloride complex becomes discolored, and the sorbent turns red almost instantly. Then the solution is decanted, the silica gel is washed with distilled water, placed in a fluoroplastic cuvette and the diffuse reflectance of the wet sample is measured at 410 nm relative to the blank sample.

The diffuse reflection coefficient is transferred to the Gurevich-Kubelka-Munk function by the formula:

The content of rhodium (III) is found according to the calibration graph constructed in the coordinates C _{Rh (III)} - ΔF (R), where C _{Rh (III)} is the concentration of rhodium on silica, in μg / 0.1 g.

To construct a calibration graph, an aliquot (V = 10 ml) of a hydrochloric acid (2 N in HCl) solution of rhodium (III) with a content of 1-50 μg / ml is placed in temperature-controlled tubes with a ground stopper, 0.1 g of chemically modified silica is added, and heated to 90 ° C and shaken vigorously for 20 minutes. Then the sorbent is separated from the solution, placed in a fluoroplastic cell and the diffuse reflection coefficient is measured at 410 nm. The content of rhodium in the analyzed solution is found according to the calibration graph constructed in the conditions of determination. The detection limit of rhodium with a weighed sorbent of 0.1 g and a solution volume of 10 ml is 0.3 μg / ml. The calibration graph is linear in the range of rhodium concentrations of 1-50 μg / ml.

The introduction of chemically modified silica into the analyzed solution makes it possible to increase the sensitivity of the determination of rhodium (III) and makes it possible to determine it in an acidic environment characteristic of industrial solutions.

The correctness of the method for determining rhodium (III) was checked by the method of "entered - found." The data obtained are given in the table.

Table Photometric determination of rhodium (III) using silica gel chemically modified with dithiocarbaminate groups Rhodium introduced, mcg / ml Found rhodium content, mcg / ml 1,0 1.05 ± 0.05 5,0 4.9 ± 0.3 10.0 11.3 ± 0.5 30,0 31.1 ± 0.7 50,0 49.0 ± 0.4

These examples confirm the suitability of the proposed method for determining rhodium (III) in the concentration range of 1-50 μg / ml (at V = 10 ml). The detection limit for the proposed method is 0.3 μg / ml.

During sorption in dynamic mode, it is possible to determine rhodium (III) in solutions with a lower concentration and higher acidity, which is important in cases of analysis of technological solutions of refining production.

Claims (1)

A method for photometric determination of rhodium, including preparing a solution of rhodium (III), converting it to a complex compound and measuring the color intensity of the complex compound, characterized in that rhodium (III) is isolated from the solution by silica gel, chemically modified with dithiocarbamate groups, at a temperature of 90 ° C and measured diffuse reflectance of the rhodium (III) complex with dithiocarbaminate groups on the surface of silica gel at 410 nm.