"...Mass spectrometry is the art of "weighing" individual atoms and molecules to determine their masses or molecular weights. Such mass or weight information is sometimes sufficient, frequently necessary and always useful in determining the identity of a species. To practice this art one puts charge on the molecules of interest, i.e., the analyte, then measures how the trajectories of the resulting ions respond in vacuum to various combinations of electric and magnetic fields. Clearly the sine qua non of such a method is the conversion of neutral analyte molecules into ions. For small and simple species the ionization is readily carried by gas-phase encounters between the neutral molecules and electrons, photons or other ions. In recent years the efforts of many investigators have led to new techniques for producing ions of species too large and complex to be vaporized without substantial, even catastrophic, decomposition..." - This excerpt is quoted from John B. Fenn, who shared the 2002 Nobel Prize in Chemistry for his contributions to mass spectrometry.

For an easy-to-understand introduction to what mass spectrometry is and for what it may be used,

visit "About Mass Spectrometry" on the website of the American Society for Mass Spectrometry.