Editing Mass spectrum (section)

===History of x-axis notation===
[[Image:Dempster mass spectrum.gif|right|thumb|300 px|Mass spectrum of sodium and potassium positive ions from [[Arthur Jeffrey Dempster|Arthur Dempster]]'s 1918 publication "A new Method of Positive Ray Analysis " ''Phys. Rev.'' '''11''', 316 (1918)]]
In 1897 the mass-to-charge ratio <math>m/e</math> of the [[electron]] was first measured by [[J. J. Thomson]].<ref>{{cite web|url=http://web.lemoyne.edu/~giunta/thomson1897.html|title=J. J. Thomson 1897|work=lemoyne.edu}}</ref> By doing this he showed that the electron, which was postulated before in order to explain electricity, was in fact a particle with a mass and a charge and that its mass-to-charge ratio was much smaller than the one for the hydrogen ion H<sup>+</sup>. In 1913 he measured the mass-to-charge ratio of [[ion]]s with an instrument he called a parabola spectrograph.<ref>{{cite web|url=http://web.lemoyne.edu/~giunta/canal.html|title=Joseph John Thomson|work=lemoyne.edu}}</ref> Although this data was not represented as a modern mass spectrum, it was similar in meaning. Eventually there was a change to the notation as ''m/e'' giving way to the current standard of ''m/z''.{{Citation needed|date=July 2011}}

Early in mass spectrometry research the [[Resolution (mass spectrometry)|resolution]] of mass spectrometers did not allow for accurate mass determination. [[Francis William Aston]] won the Nobel prize in Chemistry in 1922.<ref>{{Cite web |url=http://nobelprize.org/chemistry/laureates/1922/aston-lecture.pdf |title=Archived copy |access-date=18 April 2006 |archive-date=13 May 2006 |archive-url=https://web.archive.org/web/20060513215609/http://nobelprize.org/chemistry/laureates/1922/aston-lecture.pdf |url-status=dead }}</ref> "For his discovery, by means of his mass spectrograph, of isotopes, in a large number of non-radioactive elements, and for his enunciation of the [[Whole Number Rule]]." In which he stated that all atoms (including isotopes) follow a whole-number rule<ref>{{cite web|url=http://web.lemoyne.edu/~giunta/aston.html|title=F. W. Aston|work=lemoyne.edu}}</ref> This implied that the masses of atoms were not on a scale but could be expressed as integers (in fact multiple charged ions were rare, so for the most part the ratio was whole as well). There have been several suggestions (e.g. the unit thomson) to change the official mass spectrometry nomenclature <math>m/z</math> to be more internally consistent.