SU373613A1 - METHOD FOR DETERMINING SELENA - Google Patents

Description

The invention relates to the field of analytical chemistry, in particular to methods for the determination of selenium.

A known method for determining selenium using a redox reaction catalyzed by a detectable element and with photometric recording of its velocity. As a catalyzed reaction, for example, the reduction reaction of methylene blue sodium sulfide in the presence of iron (III) and trilonate B is used. However, the known method requires the preliminary separation of copper, mercury and a number of other elements that give insoluble sulfides in an alkaline medium, with the addition of sodium sulfide reagent.

To increase the selectivity and sensitivity of the assay, it is proposed to use the reaction between bivalent iron trilonate and nitrate ions in the presence of an excess of trilon B at pH 2.0-2.5.

The reaction is accompanied by the formation of colored products, the maximum absorption of which lies in the blue part of the spectrum. The rate of formation of the reaction products, recorded photometrically, is proportional to the selenium content in the solution.

The sensitivity of determination of selenium at 25 ° C is 2-10-9 g / ml, at 55 ° C - g / ml; detection time 15-20 min;

accuracy of about 10%. In the presence of the masking substance in the solution — Trilon B, as well as, due to the specific nature of the reaction, the presence of copper (2-f), iron (2-f, 3+), ironing, aluminum, lead, cadmium, manganese, sulfur, phosphorus and others elements in amounts 3-5 times higher than the selenium content, does not interfere with the determination. The presence of nitrate ions in excess of 25 μg

interferes with the definition.

Example. Determination of selenium in the solution obtained after dissolving the ore.

To 1 ml of the test solution containing 5-10- -6-10-g selenium, for pH 2, add 8 ml of 40% sodium solution containing 5% of Trilon B. To the resulting solution add 1.5 ml of 10% a solution of Mohr's salt. At the same time prepare a blank solution, drain the reagents in the same sequence; the ore solution is replaced with water. The solutions are placed in cuvettes 2 cm in the cuvette holders of the FEK-M device, the arrow of the null-galvanometer is adjusted to zero using optical wedges and includes

stopwatch. There was a change in the optical density of the solution for 10 minutes, which passed from the MOiMeHTa to start the stopwatch. The determination is carried out at 20-25 ° C. At lower selenium contents, the temperature is respectively pevyshayut. 3 The subject of the invention The method of determining selenium using a redox reaction catalyzed by a detectable element and photometric registration of its speed, 5 4 characterized in that, in order to increase the selectivity and sensitivity of the avalysis, the reaction between the ferrous iron nitrous ions the presence of an excess of Trilon B at a pH of 2.0-2.5.