Abstract
Analytical data reported for natural geological reference materials (GRMs) indicates uncertainty in the recommended element concentrations, varying levels of both inhomogeneity in the distribution of trace elements and chemical/physical instability. Two types of silica gel-based synthetic trace element reference materials (SynTERM) have been developed as alternatives to natural GRMs: (i) high-purity reference materials and (ii) standard additions to existing natural geological materials. Wide variations in the concentration and combination of trace elements have been successfully formulated. The gel is formed by the rapid alkaline hydrolysis of tetraethyl orthosilicate (TEOS). Depth profiling by X-ray photoelectron spectrometry indicates that the trace metals are homogeneously distributed throughout gel particles of mean size 25 µm. Relative variation in results for trace elements in the high-purity reference materials (inhomogeneity) was less than ± 1.5% for a 1 g sample and less than ± 12% for 0.05 g samples. Compared with many natural GRMs SynTERM reference materials are more homogeneous, cheaper to produce and of potentially infinite supply.
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