Determination of Ultra - Trace Amounts of Thorium in NIM-D and NIM-P Standard Geological Reference Materials Using Cation Exchange Chromatography - Spark Source Mass Spectrography

Ultra-trace (<1 ppm) amounts of thorium in NIM-D and NIM-P geochemical reference materials are determined by the technique of cation exchange chromatography - spark source mass spectrography. After dissolution, thorium is selectively separated from all other elements on a column of AG50W-X4 resin. The thorium eluate is concentrated and evaporated onto silver powder together with 1 000 ng of uranium which serves as the internal standard. Mass spectrographic analysis of this spiked silver powder is carried out with a spark source mass spectrograph.