RU2096754C1 - Method of preparing samples for determining iridium - Google Patents

Abstract

FIELD: analytical chemistry, more particularly determination of microamounts of iridium. SUBSTANCE: selected samples are opened and treated to obtain catalytically active iridium solution. Opened sample is treated with mixture containing 0.5-0.7 ml of concentrated sulfuric acid, 2.0-2.5 ml of concentrated nitric acid and 0.5-0.7 ml of 2•10^-2 potassium periodate solution at 92-98 C. EFFECT: more efficient determination method. 3 tbl

Description

 The invention relates to the field of analytical chemistry, in particular to the determination of trace amounts of iridium.

 A known method of sample preparation for determining iridium, in which they carry out the opening of the selected samples and processing them to obtain a catalytically active solution of iridium. Samples are treated with a solution of sulfuric acid diluted / 1: 1 / after opening by fusion with sodium peroxide or acid decomposition / I.I. Alekseeva, G.N. Latysheva, L.E. Romanovskaya and L.P. Tikhonova. "Highly sensitive selective kinetic method for the determination of iridium." Factory laboratory. M. "Metallurgy", 1984, v. 50, N 3, p. 5 6 /.

 The subsequent kinetic determination is carried out by a method based on the iridium catalysis of the mercury oxidation reaction / 1 / cerium / IV / / USSR copyright certificate N 775690, class. G 01 N 31/10, 1980 /.

 However, in the known method of sample preparation when processing them with sulfuric acid / 1: 1 /, such iridium solutions are obtained whose catalytic activity is low, which does not allow to achieve high sensitivity and selectivity of its kinetic determination.

 The technical result of this method is to increase the selectivity and sensitivity of the determination of iridium by the kinetic method.

To achieve a technical result in the method of sample preparation for determining iridium, in which the samples are opened and processed to obtain a catalytically active iridium solution, the opened sample is treated with a mixture containing 0.5 0.7 ml of concentrated sulfuric acid, 2.0 - 2.5 ml of concentrated nitric acid and 0.5 0.7 ml of 2 • 10 ^-2 M solution of potassium periodate, at a temperature of 92 -98 ^o C.

 An example implementation of the method.

 The proposed method is implemented as follows.

The analyzed solution obtained after opening the sample, with a volume of up to 5 ml and containing 0.05 0.5 μg of iridium, is treated with a mixture containing 0.5 ml of 2 • 10 ^-2 M solution of potassium periodate - / KIO ₄ /, 2 ml of concentrated nitrogen and 0.5 ml of concentrated sulfuric acid when heated to 95 ^o C, then evaporated to a volume of 0.15 0.20 ml, the solution was transferred into a volumetric flask and the volume was adjusted to 25 ml. The resulting catalytically active solution is used for kinetic measurements. To determine iridium, an aliquot of 0.1 to 2 ml is taken by the kinetic method and introduced into the reaction mixture of the indicator mercury oxidation indicator reaction / I / cerium / IV /. The iridium content is determined by the calibration graph, built on the comparison solutions, which are obtained by a method similar to the preparation of the analyzed solutions from the salt K ₃ IrCl ₆ .

 The results of the analysis of the solutions obtained by this method and the prototype are presented in table. one.

From the data given in table. 1, it follows that when preparing samples according to the proposed method, the detection limit is reduced to 2 • 10 ^-4 μg / ml, which allows the determination of iridium in the concentration range of 5.0 • 10 ^-4 0.2 • 10 ^-4 μg / ml.

 In addition, with an excess of ruthenium greater than 1:40 according to the prototype, it is impossible to obtain the correct iridium content / lines 3, 4 and 7, 8 of the table. 1 /, whereas in this method the correct iridium content is also obtained with large excesses of ruthenium up to 100-fold inclusive.

The need to maintain the composition of the mixture for processing and temperature in a given range of values is due to the fact that / cm. tab. 2, 3 /:
a) when the amount of acids decreases below 0.5 ml of H ₂ O ₄ and 2.0 ml of HNO _{3, the} catalytic activity of iridium solutions decreases, the permissible excess of ruthenium decreases;
b) with an increase in the amount of acids above 0.7 ml of H ₂ O ₄ and 2.5 ml of HNO _{3, the} oxidation of mercury / I / cerium / IV / without iridium is accelerated, which excludes the possibility of determining the latter;
in / with a decrease in the amount of periodate in the mixture below 0.5 ml of a 2 • 10 ^-2 M solution, the catalytic activity of iridium solutions decreases and the permissible excess of ruthenium decreases;
g / with an increase in the amount of periodate in the mixture above 0.7 ml of a 2 • 10 ^-2 M solution, the reproducibility of the analytical signal decreases, which makes the determination of iridium impossible;
d / lowering the temperature of the mixture below 92 ^o C leads to a decrease in the catalytic activity of iridium and the permissible excess of ruthenium.

 Studies have shown that the iridium solution obtained by this method, which is being determined, has increased catalytic activity due to the formation of the primary products of hydrolysis of complex iridium sulfate / IV /. In addition, ruthenium, usually associated with iridium in real objects of analysis, after the proposed treatment does not interfere with the determination of iridium.

Using the method of sample preparation provides:
1 / increase the sensitivity of the determination of iridium by 5 times,
2 / increase in the selectivity of the determination of iridium with respect to ruthenium / increase in the permissible excess of ruthenium with respect to iridium by 2.5 times /.

Claims (1)

A method of preparing samples for the determination of iridium, in which the opening of the selected samples and processing them to obtain a catalytically active solution of iridium, characterized in that the processing of the opened sample is carried out with a mixture containing 0.5 0.7 ml of concentrated sulfuric acid, 2.0 2, 5 ml of concentrated nitric acid and 0.5 0.7 ml of 2 • 10 ^{- 2} M solution of potassium periodate, at 92 98 ^o C.

Images