SU440593A1 - Method for the polygraphic determination of cobalt in the presence of copper, nickel and zinc - Google Patents

Description

one

This invention relates to analytical chemistry, in particular, to polarographic methods for the determination of cobalt in cobalt containing products in the presence of copper, nickel and zinc.

A known method for determining cobalt in the presence of copper in a nickel solution containing a mixture of ammonium chloride, ammonia and potassium ferricyanide is characterized by the coincidence of the reduction potentials of copper and cobalt and the need to fix the total current of copper and cobalt in polarographic measurements. The cobalt content is determined by measuring the difference between two signals: a signal corresponding to the sum of the concentrations of copper and cobalt, and a signal corresponding to the concentration of copper.

The aim of the invention is to develop a method for the direct polarographic determination of cobalt without an auxiliary determination of the concentration of copper (nickel and zinc are not displaced).

This goal is achieved by introducing pyridine into the solution and measuring the current of the pyridine complex of cobalt (1P) at a potential of 0.7 v (nke).

When pyridine is added to a known electrolyte containing a mixture of ammonium chloride, ammonia, and potassium ferricyanide, a cobalt (P1) pyridine complex is formed.

This complex is reduced at a more negative potential than the ammonium complex of cobalt (P1), resulting from the oxidation of cobalt (II) with ferricyanide

potassium in ammonia environment. When polarizing a solution of cobalt with the addition of pyridine, separate currents of copper and cobalt (111) are observed: the current of copper is at a potential of 0.4 V and the current of a complex of cobalt (P1) at a potential of 0.7 V. The reduction potentials of nickel and zinc are in a more negative region, namely: 1.1 volts. This allows the determination of the cobalt content in the presence of copper, nickel and zinc without determining the total concentration of cobalt and copper. The advantage of the proposed method consists in selectivity and increasing the accuracy of measuring the concentration of cobalt. The proposed method allows the determination of the cobalt content from 0.25 mg / l and above, while the following ratios of cobalt and interfering elements are allowed: Co: Cu 1: 20; Co: Ni 1: 100 and Co: Zn - 1: 100. In the presence of nickel and zinc, the above ratios are not the limit.

The proposed method is carried out as follows. To 2-3 ml of a synthetic solution containing cobalt (II) copper, zinc and nickel, with

In order to oxidize cobalt (II) to cobalt (III), 50 ml of ammonia (25%), 5 g of ammonium chloride and 0.22 g of potassium ferricyanide are added. The solution is stirred and 2 ml of pyridine are introduced. The resulting solution is then made up to 100 ml with water and stirred again. Oxygen was removed from the 20 ml aliquot of the solution by blowing nitrogen. The cobalt containing solution thus treated is polarized in the potential range from -0.3 V to 0.9 (bottom mercury). The current measurement of the cobalt (II) pyridine complex is carried out at a potential of 0.7 pa vector-polarograph or PPT-1.

FIG. 1 presents two polygrams:

a) a semi-gram of the solution containing its cobalt (III) -pyridine complex, (Co) 5 mg / l;

b) a solution program containing a cobalt (III) complex - pyridine, copper, nickel and zinc.

(Co) 5 mg / l. : (C) 20 mg / l. : (Ni) (Zn) 100 mg / l.

FIG. Figure 2 shows the program of the Co (III) complex with pyridine in the presence of nickel (Co) 6 mg / l. (Ni) 20 mg / l.

As can be seen from the figures, when

polishing solution containing

pyridine supplemented cobalt observed

selective current of the cobalt (III) pyridine complex at a potential of 0.7 volts.

Nredmet of the invention

Claims (2)

1. A method for the polar determination of cobalt in the presence of copper, nickel and zinc on an ammonia background containing potassium ferricyanide, characterized in that pyridine is introduced into the solution in order to provide a selective determination of cobalt and increase the accuracy of the analysis. 2. A method according to claim 1, characterized in that 0.22 g of potassium ferricyanide and 2 ml of pyridine are introduced per 100 ml of solution. Rig / Fig .. 2