Key concept: - Ionization. Every commercially available mass spectrometer on the market today uses some form of ionization to bring a molecule from the liquid or solid phase into the gas phase for measurement and analysis. The ionization process imparts a charge on the molecule which can be measured by the instrument.

History of Mass Spectrometry

Mass Spectrometry is generally recognized to have been started with the work of Sir Joseph John "JJ" Thomson. His work on conduction of electricity through ionized gasses lead to his being awarded the Nobel Prize for Physics in 1906, though his best known work on mass spectrometry came later in 1911. Later his son, John Paget Thomson, won the Nobel Prize for Physics in 1937, making JJ Thomson one of few Nobel Laureates who lived to see their child win a Nobel Prize as well.

Thomson's best known work in mass spectrometry was in demonstrating the presence of atomic isotopes of gasses - atoms of the same element with differing masses. Thomson's work in mass spectrometry has lead to the name of Thomson being applied to the mass-to-charge ratio of an ion, which is the most common measurement in mass spectrometry. While pure physicists often use the term "q" to indicate charge, most applications of mass spectrometry use the letter "z", hence the mass-to-charge ratio in mass spectrometry is generally designated with "m/z" (generally pronounced as "m over z").