Inductively Coupled Plasma Mass Spectrometry Determination of Uranium and Thorium in High Purity Tungsten After Ion Exchange Separation

A method has been developed for the determination of uranium and thorium at parts per billion level in high purity tungsten metal by ICP-MS. The method consists of three steps: Sample dissolution with high purity acids, ion exchange separation from tungsten matrix and subsequent ICP-MS measurement. Tungsten metal was dissolved with HF HNO3 mixed acids (3:1), evaporated to dryness and redissolved in mixed acids (1 M HF-0.1 M HNO3). The solution was then passed through an anion exchange column. The effluent was evaporated to dryness, dissolved in 1% ni trie acid and analyzed by ICP-MS. The recoveries of U and Th were more than 90%. The detection limit for both metals rendered below 0.1 ppb, and the precisions were better than 5 % RSD at 10 ppb level.