Guest Editorial

Increasingly stringent quality demands are being made of geoanalysts, and in this respect, certified reference materials provide one of the most convenient means of demonstrating that these demands are being met. Nevertheless, with progressive improvements in the capabilities of analytical techniques, certified reference materials, however well-characterized, frequently fail to keep pace with changing quality requirements. Therefore, each evolutionary improvement in analytical capability creates new demands for CRMs.

The particular aspects of advances in analytical capability that create new requirements for CRMs include:
1) Expansion in the list of elements that can be determined routinely.
2) Better analytical repeatability requiring CRMs with smaller uncertainties.
3) Improvements in detection limit capabilities that create a demand for certified values at correspondingly low elemental concentrations in natural matrix CRMs.
4) The capability of being able to determine trace elements in progressively smaller test portions (e.g. by microprobe techniques).
These aspects, unmet by contemporary CRMs, represent one of the most pressing issues, which has the potential to hamper progress in modern geoanalysis.

Recent advances in microprobe instrumentation is one case in point. None of the CRMs currently available are certified for the microprobe analysis of geoanalytically important elements, because values are not certified for microanalytical test portion masses. Another instance is the analysis of the rare earths and the platinum group elements. Reference values are generally not known with sufficiently small uncertainty limits to ensure measurement quality for these key elements. These two examples overlap, in that microprobe techniques are frequently used to determine the REEs and PGEs in geological samples.

One of the topics for discussion at Geoanalysis 97 was the unmet requirements of CRMs. One option for satisfying these needs would be to improve certifications of existing materials, or alternatively to develop totally new ones. A proposal to extend and update the certification of the NIST glass SRMs 610-617 for microanalytical use illustrates the first option. Conversely, the characterisation of BCR-2 in both glass and powdered rock forms by the USGS as a replacement for BCR-1 illustrates the second. Regardless of whether the proposal is to characterise existing materials or new ones, the newest techniques often provide the most suitable data for that purpose.

Five papers in this volume were presented at or are associated with the workshop on CRM needs specific to microanalysis held at Geoanalysis 97. An improved UV laser ablation inductively coupled plasma-mass spectrometric technique for the determination of the PGE and Au is discussed in one of these papers, with data presented for these elements in several recently issued CRMs. Two papers discuss the NIST glasses, one reviewing the history of the original certification programme and the other considering current use of these samples in microanalysis, and suggesting how more suitable reference values for that use might be developed. Preliminary data in characterising USGS BCR-2g (basaltic glass form) are presented in a fourth paper. Specifically, homogeneity is evaluated by both ion and electron microprobe techniques, demonstrating homogeneity on a scale down to tens of micrometres. The last paper provides a review of the evolution of analytical techniques for geoanalysis and makes the case for the increasing importance of microprobe geochemistry.

This evolution of analytical techniques has not only changed the requirements for CRMs, but also has resulted in a significant improvement in the quality of data being contributed by laboratories to certification programmes. The process of improving analytical techniques is intimately linked to the demand for and development of CRMs. In turn, these materials are used both to calibrate and to assure the quality of measurements. The papers stemming from the Geoanalysis 97 workshop show the interconnectedness of these two concepts. It is our challenge as geoanalysts to continue this progressive evolution both in geoanalytical measurements and the CRMs that support them.

Jean S. Kane

Robert J. Kane Associates Inc.,
HCR 4, Box 231
Brightwood, VA 22715, USA

Geostandards Newsletter: The Journal of Geostandards and Geoanalysis
Vol. 22 No. 1 p. 5 (1998)

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