Function dependent changes in the intracellular (i.c.) concentrations of calcium and sodium play a crucial role in the regulation of biological processes such as contraction of heart muscle. However, accurate measurements of both elements are difficult since in i.e. compartments they are present in low concentrations, hence the Ca and Na peaks show small count rates and small peak to continuum ratios. The accurate quantification of Ca and Na is rendered even more difficult by the partially overlap of the NaK with CuL peak and CaKα with KKβ peak. In some cases electrophysiologist substitute in the experiments K+ with Cs+ or the pathologist is interested in the storage of mercury. For analysis of such elements (Cs, Hg) with higher atomic number the stopping power of the EDS crystal play an important role for system sensitivity. Quantitative analysis of thin biological cryosections with the continuum method must be corrected for influence of X-rays emit from holder, supporting film and grid.