Once formed (either by direct ionization of a neutral molecule or
as a product of a decomposition reaction of a larger ion), ions are
accelerated and focused into a mass analyzer. There are several common
ways to accomplish mass analysis: time-of-flight, magnetic field,
quadrupole field and ion cyclotron resonance.
All mass spectrometers measure mass-to-charge ratio (m/z) as opposed to simple mass. For this discussion, we assume all masses are singly charged. However, there are common cases (napthalene and similar compounds, for example) for which doubly (or higher) charged ions are often observed. In addition, mass spectrometry uses the atomic mass unit (amu), which is sometimes called the dalton (da), not kg, g or other macroscopic unit.