Controlled-potential coulometric determination of plutonium in the presence of iron

A controlled-potential coulometry is proposed for the determination of plutonium in the presence of iron. Iron interferes because the differences in the formal potentials of the Fe^2--Fe³⁺ and Pu^3--Pu⁴⁺ couples are very small in sulfuric acid. Even small quantities of iron relative to plutonium can cause an appreciable error in the analysis, since the equivalent weight ratio of Pu : Fe is about 4 : 1. In order to remove the interference of iron, 1,10-phenanthroline was used as a complexing agent with iron. 1,10-phenanthroline reacts with iron(II) to form the complex, and the start of the oxidation potential was shifted to the positive side of about 100 mV from that of iron. To obtain the most accurate result, the mole ratio of 1.10-phenanthroline to iron was required to be more than 20-fold. The relative standard deviation was less than 0.3%.