Spectrophotometric determination of tungsten in rocks by an isotope dilution procedure

Samples are decomposed with hydrofluoric acid and perchloric acid in the presence of W¹⁸¹ tracer. Molybdenum is extracted from a hydrochloric acid solution with tributyl phosphate. Tungsten is separated from most other elements by extraction of the a-benzoinoximate into chloroform. Stannous chloride in concentrated hydrochloric acid is used to strip tungsten and reduce it to W⁺⁵ . The amount of tungsten is determined spectrophotometrically after extraction as the thiocyanate complex into amyl alcohol. The correction for chemical losses is determined by counting W¹⁸¹.