Quantitative electron probe x-ray microanalysis of biological bulk specimens.

X-ray microanalysis of thick biological specimens is of considerable practical interest. Quantitative analysis of this kind of specimens poses some difficulties, and quantitative methods are less well developed than for thin sections. In this tutorial, the various parts of the ZAF-corrections are examined in some detail, and special attention is given to possible problems with the use of the ratio model. In quantitative analysis of metals (Z greater than 20) in biological bulk specimens, attention should be given to secondary fluorescence by the continuum. Various types of standards are compared, both with respect to homogeneity and with respect to their effect of quantitation with the ZAF-correction method. In both respects, organic standards of the 'gelatin' or 'resin' type perform better than do crystal standards. The use of relative intensities (P/B-ratios) in quantitative analysis of biological bulk specimens is considered. In most, but not all, cases use of P/B-ratios has advantages over the use of absolute X-ray intensities.