Spectrophotometric determination of tungsten in rocks by using zinc-dithiol

Tungsten is determined in 11 USGS standard rocks by a spectrophotometric procedure that measures the absorbance of the tungsten-dithiol complex. The results are compared with those obtained by other methods. After the samples are dissolved in HClO₄ and HF, the tungsten-dithiol complex is extracted into isoamyl acetate and then back-extracted into isoamyl acetate. The determination of 0.1 part per million in a 500-mg sample can be made routinely.