Ion and Ionization

Ions, being electrically charged, are much easier to manipulate and detect than electrically neutral atoms or molecules. The direction or speed of ions can be changed by application of electric and magnetic fields, similar to the way a magnet can move small pieces of a magnetic material. Ions can be detected simply by measuring the electric current produced by their movement. Consequently, ionization is frequently employed in scientific apparatus to transform neutral species to charged species so that they may be more easily studied.

Mass spectrometry is a powerful analytical technique based on the transformation of the neutral components of a sample to ions which are then separated according to their mass-to-charge ratio. The structure and composition of molecular species can be deduced by studying the masses of the molecular ion along with the smaller, fragment ions which are sometimes formed. There are several different types of ion sources which are used in mass spectrometers: electron impact, field ionization and chemical ionization are the most common, and are described below. Other instrumental analytical techniques which are based on ionization include spectroscopies which study the energy of the ejected electron as well as the positively charged ion. These methods typically employ electromagnetic radiation to supply the ionization energy (photoionization). The basic requirement for all ionization sources is that sufficient energy must be supplied to remove at least one electron.