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Although over recent years, sensitivity and precision of modern analytical techniques have continuously improved, traditional analytical specification for the particle size of samples has remained at 74 μm (‐200 mesh). For this reason, the uncertainty caused by inhomogeneity in test portions of the sample itself has become a more and more significant contribution to the total analytical uncertainty. Therefore, to reduce this total uncertainty, the first step is to improve the homogeneity by reducing the particle size of a sample. For this purpose, we have investigated a method for the preparation of ultra‐fine reference materials. Using the modern ultra‐fine crushing technique (jet mill), six marine sediment samples MSAn and MSCS‐1 to 5 were prepared and the particle distributions of these samples were measured using a laser particle‐analyser. The average particle size of these samples was 4–5 (im and the largest particle size was less than 30 (im. MSAn will be used as the sample for a future GeoPT(tm) proficiency testing round and MSCS‐1 to 5 will be prepared as reference materials. All geochemical laboratories are welcome to participate in this co‐operative research programme. The processing and use of ultra‐fine samples (< 30 μm) will have a significant influence on the future development of geoanalytical techniques as a consequence of the potential reduction in the mass of test portion and the development of new geoanalytical systems.

Seven soil geochemical certified reference materials (CRMs) GSS 10‐16 recently prepared by the Institute of Geophysical and Geochemical Exploration (IGGE), are mainly used for sample analysis in geochemical surveys of the overburden region in China. Fifteen Chinese institutes and central laboratories, which operated at a high level of analytical performance analysed these samples. More than ten reliable analytical methods based on different principles of measurement were adopted, of which ICP‐MS, ICP‐AES and NAA were taken as the primary analytical methods. In total, 23715 determinations were carried out, 5660 average data sets were obtained, seventy two elements and components were determined and certified values of sixty nine elements and components were assigned. Rhenium concentrations were measured by isotope dilution ICP‐MS in GSS‐10, GSS‐13, GSS‐15 and GSS‐16. Certified values of elements in GSS 10‐16 have good precision and for 90% of these values relative uncertainties are less than 10%.

Sulfide mineral certified reference materials GSO 1‐7, recently prepared by the Institute of Geophysical and Geochemical Exploration (IGGE), were analysed by twelve laboratories. Various reliable analytical methods based on different principles were adopted and classical chemical methods were taken as the primary analytical methods, by which 5729 determinations were carried out, 1425 average data were obtained, and twenty one to twenty seven elements and components were certified.

Two types of gold deposit with both good homogeneity and a high‐grade of gold were selected to prepare four gold ore reference materials (GAu‐19,GAu‐20,GAu‐21 and GAu‐22) by the Institute of Geophysical and Geochemical Exploration (IGGE),China.Seven laboratories participated in the certification programme. Volumetric methods for GAu19‐21 and atomic absorption spectrometry for GAu‐22 were used for the homogeneity testing,the coefficient of variation being found to be less than 3%.After sample digestion and preconcentration,the samples were analysed by flame atomic absorption spectrometry (AAS),colorimetry,neutron activation analysis (NAA)and volumetric analysis. The certified values for the gold concentration in GAu19‐22 are 18.3 μg g ‐1, 32.3 μg g ‐1, 53.0 μg g ‐1 and 5.72 μg g ‐1,respectively.

Certified or reference values for sixty six to sixty seven elements and element oxides are given for geochemical reference materials recently prepared by the Institute of Geophysical and Geochemical Exploration (IGGE), including limestone (GSR‐13), granitic gneiss (GSR‐14), amphibolite (GSR‐15), lake sediment (GSS‐9) and stream sediments (GSD‐1a, GSD‐13, GSD‐14). These samples supplement the GSR 1‐6, GSD1‐8 and GSD 9‐12 certified reference materials already prepared and characterized by the IGGE.

Unlike the situation for other elements, few reference materials certified for the platinum‐group elements are currently available. Therefore, the GPt1‐7 series of PGE geochemical CRMs, prepared by the IGGE, represent an important addition and comprise a range of matrix types, including a soil, stream sediment, Mg‐rich ultramafic rock, Fe‐rich ultramafic rock, platinoid ore depleted in Cu, Ni and Fe, and a chromitite. The concentration of PGE in these samples ranges over 4‐5 orders of magnitude and the samples were shown to have good homogeneity as assessed by a variance test. Analytical methods based on different principles were used in sample certification, including several fire assay and wet chemical procedures used for decomposition and preconcentration. Certified values for the elements Pt, Pd, Os, Ru, Ir, Rh and Au were determined by AAS, catalytic colourimetry (COL), catalytic polarography (POL), atomic emission spectrometry (AES), ICP‐MS and NAA. Recently, the GPt1‐7 samples were approved as national primary CRMs by the State Bureau of Technical Supervision of China.