A comparison of isotope dilution mass spectrometric methods for the assay of copper in copper ore reference materials

The trend toward lower assays in the repeated determination of copper in copper ore, Standard Reference Material 332, have resulted in the withdrawal of this reference material due to material instability. Recent analyses by both isotope dilution thermal ionisation mass spectrometry (TIMS) and isotope dilution inductively coupled plasma mass spectrometry (ICP-MS) have confirmed this change in copper assay. In this study ICP-MS was shown to be an excellent method for the determination of the concentration of copper in copper ore and therefore may be capable of relatively high precision for a number of elements in inorganic matrices. Two experiments were designed to study the relationship between the high loss of volatile components on drying and the corresponding low copper assay. The slow oxidation of CuS to CuSO4 was confirmed. The accelerated moisture study indicated that exposure to changes in temperature and relative humidity did not cause this oxidation. Microwave drying provided additional information about moisture associated with the samples that had been oxidised. (author)