DETERMINATION OF TRACE IMPURITIES IN HIGH-PURITY TUNGSTEN BY DIRECT SOLID SAMPLING ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY USING A TRANSVERSELY HEATED GRAPHITE TUBE

A modern electrothermal atomic absorption spectrometer with transverse ly heated graphite tube and a solid sampling system based on the boat technique was used for the development of a method for the direct dete rmination of Ca, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, and Zn in high-pur ity tungsten powders. The high background originating from tungsten ox ide was eliminated by using hydrogen as purge gas during pyrolysis. Qu antification of all elements could be performed by using calibration c urves measured with aqueous standard solutions. The analyte contents d etermined were between 0.02 (Zn) and 34.9 (Fe) mu g/g The results were in good agreement with those obtained in analysis of sample digests, and they were compared also with results provided by other methods in other laboratories. Owing to an almost complete freedom of blank and u nusually high sample amounts applied (5-100 mg), extremely low limits of detection, in the range between 0.01 (Mg) and 4 (Fe) ng/g, could be achieved.