Fundamental Aspects of the Photoionization of Molecules

Abstract

The component techniques currently used for mass spectrometry can be divided roughly into three: ionization of a sample, mass analysis, and detection. Among these steps, ionization is the most fundamental, and various methods are used for the ionization of a sample. Historically, electron ionization (EI) was the first technique used for mass spectrometry, and is still widely used because of the abundant database of mass spectra for many molecules. In EI, an electron beam having energy of around 70eV is usually used, since beams of this energy are easy to control, and provide a relatively high ionization efficiency. In EI, however, not only parent ions but also fragment ions are produced. Therefore, in the mass spectrometry of a complicated molecule or a mixed sample, the interpretation of the mass spectrum may become difficult.