International Proficiency Tests for Analytical Geochemistry Laboratories: An Assessment of Accuracy and Precision in Routine Geochemical Analysis

The results of Second International Proficiency Test (GeoPT2) obtained at the Geochemical Laboratory of National Geophysical Research Institute are presented. Estimation of 33 trace elements including all the fourteen rare earths obtained by ICP-MS in Bardon Volcanic Tuff Samples (OU-1) are compared with the assigned values. Sample decomposition method and other relevant details of the analytical procedures adopted are presented. Depending upon the 'Z-scores' calculated, the fitness of the data for either "pure geochemistry" or "applied geochemistry" was assessed. An overview of 'Z-score' results indicates that about 2/3rds of the data contributed from our laboratory fell within the -2<z<2 range which included majority of the trace and rare earth elements used normally in several pure geochemical investigations. These results allowed us to further investigate the analytical discrepancies observed in the data and optimize necessary aspects such as sample preparation by the use of more effective dissolution methods like microwave digestion and minimise the interference effects by the use of matrix matching calibrations.