The primary function of an MS is to determine the mass of a compound. Also, through fragmentation of the parent compound, information about the chemical structure can be deduced.

Mass Spectrometers are equipped with different sources in an effort to generate ions depending on the class of the compound.

Volatile organic compounds are usually separated first with Gas Chromatography then ionized by electron impact (EI). Nonvolatile organic compounds are typically separated first with Liquid Chromatography then ionized with electrospray (ESI) or atmospheric pressure (APCI or APPI). Metals are usually ionized using Induced Coupled Plasma (ICP) at 5,000-6,000 K.