SU767033A1 - Method of amperomatric determination of chromium - Google Patents

Description

(54) METHOD OF AMPEGOMETRIC DETERMINATION OF HGOM

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The invention relates to the field of analytical chemistry and can be used in non-ferrous metallurgy, chemical, semiconductor, electronic and electronic industries, in the analysis of glass grades, building materials and ferrites.

Methods are known for determining chromium of various oxidation states.

The known method is the photometric determination of chromium (III) with chromazurol, based on the formation of a red-violet complex with a maximum light absorption of 70nm 11.

However, the disadvantages of the process are the interfering effect of chromium (VI), the need for special preheating of the reaction mixture, since the complex is formed by liyl. at boiling point.

A known method for the photometric determination of chromium (III), chromium (VI) and the total content of chromium in water. The method is based on the reaction of chromium (VI) in an acidic medium with cobalt (I) and ethylenediaminetetraacetic acid (EDTA) to form a colored compound 2.

The disadvantages of the method are the impossibility of direct determination of chromium (III) in the presence of chromium (VI), since an indirect method of determination is used, which reduces the accuracy of the determination.

The closest in technical essence and the achieved result is the method of the actorometric determination of chromium in the presence of nickel by titration on a rotating platinum disk electrode with a solution of complexon III or mora salt as titrants 3.

However, it is not possible to determine chromium (111) in the presence of chromium (Vi), vanadium (III) and vanadium (IV) in the known method; Amper15 metric titration of mixtures containing chromium and nickel is carried out with preliminary oxidation of chromium (III) with ammonium persulfate in the presence of silver nitrate; The error defined by chrome (VI) is 8-10% and so on.

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Claims (3)

The aim of the invention is to improve the accuracy of chromium (1I) determination not only separately, but also in a mixture with chromium (VI), vanadium (III) and vanadium (IV) without their separation and separation when they are present together, and also in the presence of other cations and anions. This goal is achieved by using the triphenylmethane series - eriochrome cyanine R as the titrant of an organic reagent by amperometric titration on a rotating platinum disk electrode, the concentration of eriochrome cyanine R being 0.001-0.5 M. This range is determined by the fact that at concentrations lower than 0.001 M, amperometric titration curves are fuzzy, and at concentrations higher than 0.5 M, the ernochrome cyanine R is insoluble in solutions and precipitates. Chromium (III) forms complex compounds of composition Cg (111): EHC 1: 1 and 1: 2 under optimum conditions with eriochrome cyanine R under optimal conditions. Complex compounds are formed at a pH of 1 -2 and their stability over time is also preserved ...; In order to eliminate the effects of chromium (VI), vanadium (1I) and vanadium (IV), the determination of chromium (III) is carried out in a solution with a pH of 1-3. The complex compounds of vanadium (III) and vanadium (IV) with eriochrome cyanine R, if they are formed, are easily destroyed at this solution pH value. A rotor plate electrode with a visual reading of amperage (galvanometer type) is used for amperometric titration. M 91 / A) and voltage. The overlap potential is equal to 0.8-1.0 V, with a given value of the overlap potential njpoHC, the complex compound of chromium (III) forms with the organic reagent Eriochrome cyanine R and the formation of complex compounds of simultaneously present chromium VI Vanadium (V) and others. - Example. In the analysis of alloys and steels. 0.2-0.5 g with a content of 0.10-1% chromium or 0.1 g with a content of 1-10% hrrma placed in a glass with a capacity of 100-150 ml and dissolved in sulfuric acid (1: 8) with moderate heating up. Carbides destroy nitric acid before removing oxides of nitrogen. The contents of the glass were transferred to a 100 ml volumetric flask and brought to the mark with distilled water. An aliquot portion of the test solution is then taken for analysis and placed in a cell (titration cup), 2 ml of 2 M sodium chlorate solution are added. The required pH value of the medium is 1-3, which is created by introducing acetate buffer solution (sodium acetate acetate) into the electrolyzer or by introducing 1N NaOH solution. The total volume of the cell is 10-20 ml. At 34, the prepared titration solution passes nitrogen through for 10-15 minutes to remove dissolved oxygen. Then it is titrated from a microburette while moving with a solution of eriochromo cyanine R of exact concentration (in the range of 0.001-0.5 M), waiting each time after adding the working solution (EHC) until the Constant current is established (for 20-30 s.). ). The overlap potential is 0.8-1.0V. A graph is plotted in coordinates: current strength (division of galvanometer gauges, mA) - reagent solution volume (ml). From the graph, the volume of the reagent solution consumed for the titration is determined from the inflection point, and the chromium (III) content is calculated using the formula A-52.-Uk-100 5,2-fa-UK. II J- H V H-4 -1000 where VK is the volume of the volumetric flask, ml; Vn-volume aliquot part, ml; H - sample weight, g .; b is the reagent volume at the equivalence point, ml., multiplied by the exact concentration of eriochrome cyanine R, M; 52 is the atomic weight of chromium. The proposed method has a high accuracy of application: the definition for the chromium (III) content (up to 1.5%) is on average 0.04-0.2%; for high contents (more than 1.5%), a minimum of 0.2%. The definition is not the proxy of Cr (Vl), K, md, NOj, s1H8o: su;, S47; H (V), V (lll), V (IV), Fe. Eriochromcy R is an inexpensive, light: available reagent, the production of which is widely established in the country, and is also supplied by the company Hemapol (GDR). DETAILED DESCRIPTION OF THE INVENTION A method for amperometric determination of chromium in solutions, including titration on a rotating dial of a platinum electrode using a titrant, characterized in that, in order to improve the accuracy of determination of chromium (III) in a mixture with chromium (VI), vanadium (III) and vanadium ( IV) at their joint presence, a solution of eriochromycyanine R. is used as a titrant. 2. According to claim 1, about 1 tl and h with the fact that the titration is carried out with 0.001-0.5 M solution of eriochromecyanine R 5 Sources of information taken into account during the examination 1. Malat. M., Collect. Czechosl. Cham, cammuns, 1964, 29, JC 10, 2484. 767033, " 2. US patent, N 3656908, cl. 23-230 R (G 01 N 21/20), published. IS.04.72. 3. Journal of Analytical Chemistry, 1975, 30 N 10, p. 2045 (prototype).