Spatially Resolved and Bulk Trace Element Analysis by Laser Ablation - Inductively Coupled Plasma - Mass Spectrometry (LA-ICP-MS)

In this contribution, the analytical capabilities of the Laser Ablation - Inductively Coupled Plasma - Mass Spectrometer (LA-ICP-MS) instrumentation installed at the Earth Sciences Department of Perugia University are evaluated. The instrumental set up and the analytical protocols for single-phase spatially-resolved and bulk trace-element analyses are presented. Spatially-resolved analysis allow 'in situ' trace element determinations with lateral resolutions ranging from less than 20 mu m to more than 80 mu m. Precision (expressed as relative standard deviation) is better than 10% with the only exception of Cs (14% with a 20 mu m laser beam diameter) whereas accuracy (expressed as relative deviation from the reference value) is better than 11%. Precision and accuracy increase as increasing the laser beam diameter. The extreme versatility of the instrument permits to analyze with excellent results compositions of crystals, melt inclusions, ceramics, archaeological, and environmental samples. Bulk configurations are utilized to perform whole-rock trace-element determination on samples prepared as fusion beads. Both flux-free and lithium tetraborate fusion sample preparation for whole rock trace element determination are investigated. Results show that the lithium tetraborate fusion produces beads with higher degrees of homogeneity compared to the flux-free method, resulting in more precise and accurate trace-element determinations. In detail, for the lithium tetraborate fusion precision is better than 10% for elements with concentrations above 2 mu g/g with the only exception of Ph (similar to 15%). For elements with concentrations below 2 mu g/g the precision decreases to about 15%. Accuracy values are always better than 10% with the only exception of Pb.