Intercomparison of Boron isotope and concentration measurements: Part I: Selection, preparation and homogeneity tests of the intercomparison materials.

In 1999 the Istituto di Geoscienze e Georisorse (IGG), with the support of the International Atomic Energy Agency (IAEA), undertook the collection, preparation and distribution of eight geological materials intended for a blind interlaboratory comparison of measurements of boron isotopic composition and concentration. The materials come from Italian sources and consist of three natural waters (Mediterranean seawater and two groundwaters) and five rocks and minerals (tourmaline, basalt, obsidian, limestone and clay). The solid materials were crushed, milled and mixed, in preparation for distribution. Extensive assays performed at IGG on these materials demonstrate that their boron isotopic and chemical compositions are homogeneous. Additional homogeneity tests were carried out on solid material fragments at the GeoForschungsZentrum Potsdam, with the specific objective of investigating the suitability of some of them for the calibration in situ of micro-analytical techniques. Two materials, B4, tourmaline, and B6, obsidian, proved to be isotopically homogeneous and may become excellent references for in situ microanalyses of boron. The materials described here were used as the basis of a major laboratory intercomparison study and are now available for further distribution from either the IAEA (solid materials) or the IGG (waters).