Sample digestion is a critical stage in the process of chemical analysis of geological materials by ICP-MS. We present a new HF ⁄ HNO 3 procedure to dissolve silicate rock samples using a high pressure asher system. The formation of insoluble AlF 3 was the major obstacle in achieving full recoveries. This was overcome by setting an appropriate digestion temperature and adding Mg to the samples before digestion. Sodium peroxide sintering was also investigated and the inclusion of a heating step to the alkaline sinter solution improved the recoveries of thirteen elements other than the lanthanides. The results of these procedures were compared with data sets generated by common acid decomposition techniques. Forty-one trace elements were determined using an ICP-QMS equipped with a collision cell. Under optimum conditions of gas flow and kinetic energy discrimination, polyatomic interferences were eliminated or attenuated. The measurement bias obtained for eight reference materials (BCR-2, BHVO-2, BIR-1, BRP-1, OU-6, GSP-2, GSR-1 and RGM-1) and intermediate precision (RSD) were generally better than ± 5%. The expanded measurement uncertainties estimated for two certified reference materials were mostly between 7 and 15%. New data sets for the reference materials are provided, including constituents with previously unavailable values and also for the USGS candidate reference material G-3.

Reference materials (RM) are essential to achieve traceability of measurements. Specific uses of RM in analytical laboratories are the validation of methods, the calibration of instruments, the quality control and the demonstration of proficiency. This paper describes the certification of a new geochemical reference material, named BRP‐1 (Basalt Ribeirão Preto), and acts as the certificate of analysis for this RM. The rock sample was crushed and pulverised at the USGS (Denver, USA), homogenised and split into 1920 bottles, with 55 g each. BRP‐1 was transported back to Brazil and the homogeneity between and within bottles was assessed to demonstrate sufficient homogeneity for certification. The chemical characterisation was performed by twenty‐five laboratories. Each laboratory received two bottles of BRP‐1 and one of BCR‐2 (Basalt Columbia River) used for quality control (QC). Reference values and uncertainties were calculated for forty‐four constituents of BRP‐1, following ISO Guide 35 recommendations and the IAG Protocol. The calculation of each reference value included data of proven traceability from at least ten laboratories using two or more analytical techniques and the uncertainties combines the characterisation and between bottle homogeneity contributions.

Reference materials (RM) are required for quantitative analyses and their successful use is associated with the degree of homogeneity, and the traceability and confidence limits of the values established by characterisation. During the production of a RM, the chemical characterisation can only commence after it has been demonstrated that the material has the required level of homogeneity. Here we describe the preparation of BRP‐1, a proposed geochemical reference material, and the results of the tests to evaluate its degree of homogeneity between and within bottles. BRP‐1 is the first of two geochemical RM being produced by Brazilian institutions in collaboration with the United States Geological Survey (USGS) and the International Association of Geoanalysts (IAG). Two test portions of twenty bottles of BRP‐1 were analysed by wavelength dispersive‐XRF spectrometry and major, minor and eighteen trace elements were determined. The results show that for most of the investigated elements, the units of BRP‐1 were homogeneous at conditions approximately three times more rigorous than those strived for by the test of “sufficient homogeneity”. Furthermore, the within bottle homogeneity of BRP‐1 was evaluated using small beam (1 mm2) synchrotron radiation XRF spectrometry and, for comparison, the USGS reference materials BCR‐2 and GSP‐2 were also evaluated. From our data, it has been possible to assign representative minimum masses for some major constituents (1 mg) and for some trace elements (1‐13 mg), except Zr in GSP‐2, for which test portions of 74 mg are recommended.

Isotope dilution (ID) mass spectrometry is a primary method of analysis suited for the accurate and precise measurement of several trace elements in geological matrices. Here we present mass fractions and respective uncertainties for Cr, Cu, Ni, Sn, Sr and Zn in 10 silicate rock reference materials (BCR‐2, BRP‐1, BIR‐1, OU‐6, GSP‐2, GSR‐1, AGV‐1, RGM‐1, RGM‐2 and G‐3) obtained by the double ID technique and measuring the isotope ratios with an inductively coupled plasma‐mass spectrometer equipped with collision cell. Test portions of the samples were dissolved by validated procedures, and no further matrix separation was applied. Addition of spikes was designed to achieve isotope ratios close to unity to minimise error magnification factors, according to the ID theory. Radiogenic ingrowth of 87Sr from the decay of 87Rb was considered in the calculation of Sr mass fractions. The mean values of our results mostly agree with reference values, considering both uncertainties at the 95% confidence level, and also with ID data published for AGV‐1. Considering all results, the means of the combined uncertainties were < 1% for Sr, approximately 2% for Sn and Cu, 4% for Cr and Ni and almost 6% for Zn.