Biamperometric determination of platinum in some technical products

Abstract

A method is described for the determination of platinum based on the reduction of platinum (IV) to platinum (II) with an excess of copper (I) chloride and titration of the resulting solutions with a strong oxidant, such as cerium (IV). The reaction proceeds in two steps, the first corresponding to oxidation of an excess of copper (I), and the second to oxidation of platinum (II). The electrochemical characteristics of the systems involved appear to be ideal for biamperometric titration. Up to the first end-point the reversible systems copper (II)-copper(I) is present, after which the next system, platinum(IV)-platinum (II), formed in the course of further additions of the titrant, is strongly irreversible. An excess of the oxidant in acidic solution forms a reversible cerium (IV)-cerium (III) couple. In these systems a double bend titration curve is formed when a small voltage (100 mV) is applied. The only standardised solution required is cerium (IV) sulphate and removal of oxygen is, in general, unnecessary. The reaction is much faster at elevated temperatures and it is therefore convenient to warm the solution up to 80 °C before titration.

Depending on the concentration of the titrant (0·1 or 0·01 M) an amount of platinum from 5 to 50 mg can be determined with a relative standard deviation of about 0·14 per cent. This method has been applied to the determination of platinum in platinum-nickel alloys and platinum catalyst.