Preparation of calibration materials for microanalysis of Ti minerals by direct fusion of synthetic and natural materials: Experience with LA-ICP-MS analysis of some important minor and trace elements in ilmenite and rutile

Calibration materials for microanalysis of Ti minerals have been prepared b y direct fusion of synthetic and natural materials by resistance heating in high-purity graphite electrodes. Synthetic materials were FeTiO3 and TiO2 reagents doped with minor and trace elements; CRMs for ilmenite, rutile, an d a Ti-rich magnetite were used as natural materials. Problems occurred dur ing fusion of Fe2O3-rich materials, because at atmospheric pressure Fe2O3 d ecomposes into Fe3O4 and O-2 at 1462 degreesC. An alternative fusion techni que under pressure was tested, but the resulting materials were characteriz ed by extensive segregation and development of separate phases. Fe2O3-rich materials were therefore fused below this temperature, resulting in a form of sintering, without conversion of the materials into amorphous glasses. T he fused materials were studied by optical microscopy and EPMA, and tested as calibration materials by inductively coupled plasma mass spectrometry, e quipped with laser ablation for sample introduction (LA-ICP-MS). It was demonstrated that calibration curves based on materials of rutile co mposition, within normal analytical uncertainty, generally coincide with ca libration curves based on materials of ilmenite composition. It is, therefo re, concluded that LA-ICP-MS analysis of Ti minerals can with advantage be based exclusively on calibration materials prepared for rutile, thereby avo iding the special fusion problems related to oxide mixtures of ilmenite com position. It is documented that sintered materials were in good overall agr eement with homogeneous glass materials, an observation that indicates that in other situations also sintered mineral concentrates might be a useful a lternative for instrument calibration, e.g. as alternative to pressed powde rs.