Separation of osmium from geological materials by solvent extraction for analysis by thermal ionisation mass spectrometry

The solvent extraction of Os from geological samples digested in aqua regia has been investigated. A straightforward procedure has been developed in which OsO4 is partitioned directly from the aqua regia digest solution into an organic phase, either CCl4 or CHCl3, and is then recovered by back extraction into concentrated HBr. Following a simple micro-distillation step, the purified sample is ready for thermal ionisation mass spectrometry (TIMS). This new approach avoids hightemperature fusion, ion exchange or large-scale distillation techniques, while the simplicity of the handling procedures and the potential use of small reagent volumes ensures that blank contributions are kept to a minimum.