Report on the 2007 Recertification of the Certified Reference Materials GAS (Serpentinite) and OShBO (Alkaline Granite)

A report is presented on the recertification of two certified reference materials (CRMs) initially prepared and certified by the Central Geological Laboratory of Mongolia (CGL), namely serpentinite GAS and alkaline granite OShBO. Subsequent work done in collaboration with the International Association of Geoanalysts (IAG) followed the International Organisation for Standardisation (ISO) guidelines for certification (ISO Guide 35, 2006) more closely than had been possible originally. The certification protocol followed was that of the International Association of Geoanalysts (IAG). The recertification added to the number of elements that were certified for OShBO (from 21 to 30), but not for GAS (decreased from 15 to 12) because of the greater analytical difficulties posed by that sample matrix in meeting the more stringent metrological requirements for recertification. Further, the uncertainties for these values were established in accordance with the Guide to Measurement Uncertainty; individual contributions of heterogeneity and bias are reported as appropriate for each of the certified constituents. Traceability of the certified values was demonstrated to the greatest possible extent, based on concurrent analyses of the matrix-matched existing CRMs, SW and GM, by all participating laboratories. The materials are now available from the CGL for use by laboratories in controlling data quality when analysing materials of similar matrices.