The concept of X-ray flourescence (XRF) has been around since the early 1900’s, but it wasn’t until the late 1970’s that both theory and engineering caught up to make the technique feasible. Using the behavior of atoms when they interact with x-rays, allows this technique to be robust in the analysis of major and trace elements in both natural and anthropogenic materials. Sample materials are excited by x-rays and become ionized. If the energy of the radiation is sufficient to dislodge an inner electron (tight-bond), the atom becomes unstable and an outer electron (weaker-bond) replaces the missing inner electron. When this happens, energy is released due to the decreased binding energy of the inner electron orbital compared with an outer one. The emitted radiation is of lower energy than the primary incident X-rays and is termed fluorescent radiation. Because the energy of the emitted photon is characteristic of a transition between specific electron orbitals in a particular element, the resulting fluorescent X-rays can be used to detect the abundances of elements that are present in the sample.
This technique is ideal for relatively large samples (typically > 1 gram), which can be homogenized and prepared in powder form, Materials for which compositionally similar, well-characterized standards are available, and materials containing high abundances of elements for which absorption and fluorescence effects are reasonably well understood. If your samples do not meet all of the considerations there are sample preparation techniques and instrument filters that can increase the sensitivity of detection limits. This technique cannot determine isotopes or valence states of individual elements.
The Center’s EDAX Orbis micro-XRF has a Ruthenium X-ray tube and the sample chamber can be at atmospheric pressure or in a vacuum.
Liquid, solid, or powders can be run in this analyzer as long as they fit onto the platform. It does allow for a non-destructive analysis of precious and rare samples.
The detection limit is variable depending on sample type, filter use, chamber environment, and z-number.
This technique is particularly well-suited for investigations that involve bulk chemical analyses of major (e.g. Si, Ti, Al, Fe) and minor elements (e.g. Ba, Cu, Ni) in rock and sediment. Detection limits for trace elements are typically on the order of a few parts per million.