NIST SRM 610, 611 and SRM 612, 613 multi-element glasses: Constraints from element abundance ratios measured by microprobe techniques

The SRM 600 series of glasses, SRM 611 to SRM 619, which nominally contain 500 (SRM 610, 611), so (SRM 612, 613), 1 (SRM 614, 615) and 0.02 (SRM 616, 617) mu g g-' of sixty one elements are now being extensively used as microprobe standards. Recent compilations of the trace element concentrations, which include many new multi-element bulk analyses, do not all give the some value within the stated uncertainty; this observation appears to raise questions about the degree of homogeneity on a microscale reported from probe measurements. The ion microprobe cannot give absolute concentrations, but can accurately measure the abundance ratios between glasses of similar major element chemistry Recent and new probe measurements show that although the absolute concentrations are significantly lower than the nominal values, the average dilution factors are 12 : 1 :0.02 :0.0004 and close to weighed amounts. The consistency between the ratios of random samples of glasses (SRM 610/SRM 612 and SRM 611/SRM 613) strongly supports a high degree of homogeneity on all scales. The measured abundance ratios between two glasses can, therefore, act as a useful check on bulk measurement accuracy. A clear correlation in the SRM 610, 611/SRM 612, 613 ratios measured by ion probe and SRM 612 trace concentrations measured by bulk techniques demonstrates that SRM 610, 611 has a much more uniform trace content than SRM 612, 613.