Time-of-flight mass spectrometry (TOFMS) is a method of mass spectrometry in which an ion's mass-to-charge ratio is determined via a time measurement. Using a reflector leads to a significant increase in resolution time-of-flight devices in compare with linear increases spectrometers and to an increase of mass determination accuracy. Selection of ionization source depends on substance state before ionization. Ionization is possible by electron impact or by laser radiation (photoionization).