Determination of impurities in tungsten metal: Determination of iron

A method is proposed for the determination of iron present as an impurity in tungsten. 4,7-diphenyl-1,10-phenanthroline forms a stable complex with iron (present as the ferrous ion) which can be extracted by chloroform, in presence of alcohol, and determined absorptiometrically. Tungsten is complexed as citrate, and iron is reduced with sodium dithionite.