Trace Analysis

Since X-ray fluorescence spectrometry is essentially a method which counts atoms, the question naturally arises as to what is the minimum number of atoms which are required in order to give a measurable signal above background. Analyses based on the measurement of a small number of atoms fit conveniently into two categories, the first where the number of analysed atoms is small in comparison with the total number of atoms making up the sample i.e. in the analysis of low concentrations and second, where the number of atoms is small because the total sample weight is small i.e. in the analysis of limited quantites of material. These two cases must be considered separately since, as will be seen later, they have little in common.