Performance of mu-XRF with SEM/EDS for trace analysis on the example of RoHS relevant elements - measurement, optimisation and prediction of the detection limits

For ten years mu-XRF (micro-focus X-ray fluorescence) analysis has been performed with SEM/EDS (scanning electron microscope with an energy dispersive X-ray detector) so that non-destructive analysis of elements at trace level concentrations below 100 mu g g(-1) becomes possible. This can be considered as a valuable completion of the classical electron probe microanalysis by EDS, an analytical method suffering from rather poor limits of detection in the range of one to two orders of magnitude higher than those of mu-XRF. Based on a representative actual application, namely analysis of RoHS relevant elements at trace concentration levels, the performance of the rather new analytical method with respect to its limits of detection is systematically evaluated. CRMs (certified reference materials) specially prepared to support the quantitative XRF analysis of RoHS relevant elements were employed. On the other side, based on calculations of mu-XRF spectra according to a recently developed physical model the optimization of the analytical performance is also successfully undertaken.