Importance of geometry in biological sample analysis by x-ray fluorescence

The determining factors of a good analysis by x-ray fluorescence are discussed, emphasizing the importance of the geometrical arrangement, especially the excitation-source to analysis-material distance. The variation of the peak area of the Kalpha x-ray of Fe is evaluated as a function of the distance. Precautions are given for the analysis of low concentration samples as well as for obtaining the relative concentration of an element in a specific material or organ.