In Mass Spectrometry, proteins are identified following an analysis of different factors and series of steps. First, the masses of different proteins and peptides are determined through measuring the m/z ratio of their gas-phase ions. Mass spectrometers convert protein molecules into gas-phase ions using an ion source. Ionization radiation such as electrospray ionization and electron ionization are commonly used to ionize proteins. Next, a mass analyzer separates ionized analytes based on their m/z ratio. A detector then measures the number of ions present at each m/z value.  The acquired mass spectra are then put into a database to identify the proteins present in the sample. Proteins are identified by the best match between the observed mass spectra and predicted spectra.