Determination of molybdenum and tungsten at trace levels in rocks and minerals by solvent extraction and X-ray fluorescence spectrometry.

Separation by solvent extraction followed by X-ray fluorescence spectrometry has been used for determination of molybdenum and tungsten in rocks and minerals. Samples are decomposed either by heating with a mixture of hydrofluoric acid and perchloric acid or by fusion with potassium pyrosulphate, followed by extraction of molybdenum and tungsten with N-benzoylphenylhydroxylamine in toluene from 4-5M sulphuric acid medium. The extract is collected on a mass of cellulose powder, which is dried in vacuum, mixed thoroughly and pressed into a disc for XRF measurements. The method is free from all matrix effects and needs no mathematical corrections for interelement effects. The method is suitable for determination of molybdenum and tungsten in geological materials down to ppm levels, with reasonable precision and accuracy.