Microscopic X-ray fluorescence analysis (Micro-XRF or µXRF) uses X-rays to determine the spatial distribution of major, minor and trace elements in a sample. The basic principle is the same as in bulk-XRF. In the case of microanalysis the x-ray beam is focused to a small spot (in the µm range) onto the sample surface. Therefore only a small part of the sample is irradiated and only information from this area is being collected. The fluorescent radiation is usually detected by means of an energy dispersive detector. This allows simultaneous multi-element detection across a wide range of elements without prior knowledge about the sample contents. The sample is mounted on a motorized sample stage that allows precise positioning of the sample in the x-ray beam. The position of the sample can be seen through an optical microscope (usually on a screen) to be able to identify the measurement area. By moving the sample surface perpendicular to the beam and measuring at many points along a line (a so called linescan) or in an area (areascan) the distribution of elements in the sample can be obtained.
Micro-XRF can be done in the lab with with an X-ray tube as a source, however resolution and detection limits are worse and measurement time much longer when compared to synchrotron radiation induced micro-XRF (SR micro-XRF). The high flux of a synchrotron allows very short measurement times per point. Usually the beam is also monochromatized which leads along with the fact that synchrotron radiation is polarized to better detection limits. The spot size is also usually smaller at a synchrotron micro-XRF beamline. The smallest spot sizes obtained are today in the nm range!