When a material is exposed to an ion beam, atomic interactions occur that give off EM radiation of wavelengths in the x-ray part of the electromagnetic spectrum specific to an element.
PIXE is a powerful, yet non-destructive elemental analysis technique now used routinely by geologists, archaeologists, art conservators and others to help answer questions of provenance, dating and authenticity.
[1] Recent extensions of PIXE using tightly focused beams (down to 1 μm) gives the additional capability of microscopic analysis.
This technique, called microPIXE, can be used to determine the distribution of trace elements in a wide range of samples.
Three types of spectra can be collected from a PIXE experiment: Quantum theory states that orbiting electrons of an atom must occupy discrete energy levels in order to be stable.
Because only relative concentrations are calculated there are only minimal systematic errors, and the results are totally internally consistent.
The relative concentrations of DNA to protein (and metals) can also be measured using the phosphate groups of the bases as an internal calibration.
Excessive amounts of chlorine in the buffer should also be avoided, since this will overlap with the sulfur peak; KBr and NaBr are suitable alternatives.
Due to the low penetration depth of protons and heavy charged particles, PIXE is limited to analyzing the top micrometer of a given sample.