An assessment of the suitability of NIST glass SRM literature data for the derivation of reference values

The NIST certified reference materials, SRMs 610-617, Trace Elements in Glass, are used extensively in geoanalysis as microanalytical reference materials; however, present practice is not in keeping with ISO guidelines. One reason is that these samples were originally certified as bulk reference materials, and homogeneity conclusions based on test portion masses of about 0.5 g may differ significantly from those based on the much smaller mass relevant to microprobe analysis. Another is that certified values are not available for all elements of interest in microanalytical applications. In this manuscript, published homogeneity data is reviewed to show that these samples are suitable for use as microanalytical reference materials. In addition, an evaluation is undertaken of data quality requirements for microanalytical applications which shows that data contributing to existing compilations are insufficiently repeatable to detect bias between the individual contributed data and the compilation mean. Furthermore, existing published compilations do not yield reference data that is entirely "fit for purpose", based on published criteria. To resolve these difficulties, it is proposed that a detailed measurement programme should be organised by the IAG with the intention of generating new data that would permit updating the certifications, and so greatly enhance current use of these glasses, and improve overall quality assurance in micro-analytical laboratories based on appropriate microanalytical fitness for purpose criteria.