An isotope dilution procedure using 185W has been developed for the determination of tungsten in high alloy steels. Tungsten is determined spectrophotometrically with hydroquinone in sulphuric acid medium, after homogeneous precipitation from a nitric acid-hydrogen peroxide solution.For molybdenum-vanadium-tungsten alloy steels no further chemical separations are required. The radiometric correction is applied to the residual tungsten so as to minimize counting errors. Analyses carried out on N.B.S. samples showed good accuracy and precision.For high alloy steels containing niobium, tantalum and titanium a chemical separation of tungsten is necessary to avoid interference in the subsequent spectrophotometric determination. Although the recovery of tung5,ten is quite low, the magnesia method is entirely satisfactory.The method was succesfully tested on a number N.B.S. high alloy steels to which varying amounts of tantalum and titanum were added.The quantitative determination of tungsten in high alloy steels is beset with a number of difficulties, which are unavoidable with classicalanalytical techniques. They are mainly due to the fact that the precipitation of tungstic acid is not quantitative, even with organic reagents such as cinchonine and p-naphthoquinoline.Furthermore, the precipitate is impure, as a number of other elements e.g. Si, Ti, Mo, V, Nb and Ta, are coprecipitated or adsorbed. It is obvious that an isotope-dilution procedure can considerably simplify the chemical separations, as quantitative recovery of tungsten is not necessary.
Choice of isotope and counting techniquesNeutron activation of natural tungsten gives rise to 3 radioactive species, namely 181W (T, = 145d), 185W (T, = 75 d) and 187W (Ti =
