Correction for extraneous background in quantitative X-ray microanalysis of biological thin sections: some practical aspects

The correction for extraneous continuum is of great importance in the quantitative analysis of thin sections of biological tissue. Although a theoretical model for this correction is available, its application in practice meets with problems. In this paper, a model system, consisting of sections of homogeneous plastic on copper mesh grids was used to identify sources of inaccuracies in the quantitative procedures. An unmodified electron microscope was operated under standard analytical conditions. It appeared that geometrical factors connected with the position of the analysis relative to the grid bars were of prime importance. The correction for the contribution of the support film to the continuum should ideally be carried out at the same location with respect to the grid bars as the matching measurement on the section. Also the position of the analysis with respect to its coordinates on the grids is important, in particular when the possibility of absorption of X-rays by the specimen holder exists. The use of slot grids (rather than mesh grids) may alleviate this problem at least in part. Additional factors of importance are differential mass loss in specimen and film, as well as undetected variations in specimen current