Editing Particle-induced X-ray emission (section)

== Protein analysis ==
[[Protein]] analysis using microPIXE allow for the determination of the elemental composition of liquid and crystalline proteins. microPIXE can quantify the metal content of protein molecules with a relative accuracy of between 10% and 20%.<ref>{{cite journal|pmid=15910917|year=2005|last1=Garman|first1=EF|last2=Grime|first2=GW|title=Elemental analysis of proteins by microPIXE|volume=89|issue=2|pages=173–205|doi=10.1016/j.pbiomolbio.2004.09.005|journal=Progress in Biophysics and Molecular Biology|doi-access=}}</ref>

The advantage of microPIXE is that given a protein of known sequence, the X-ray emission from [[sulfur]] can be used as an internal standard to calculate the number of metal atoms per protein monomer. 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 [[nucleotide|bases]] as an internal calibration.