5.3.1 Mass Analysis by Ion Time-Of-Flight

All singly ions accelerated by a uniform electric field are given the same kinetic energy, which is given by

$$T=s\overrightarrow{E}=\frac{1}{2}m\overrightarrow{v}\,^{2}$$

where s is the acceleration distance, $\overrightarrow{E}$ is the electric field, m is the ion mass and v is the velocity. This simple equation shows that though the kinetic energy is the same for all ions (regardless of mass), the velocity is mass dependent. Less massive ions travel faster than more massive ions. If the flight distance is the same for all ions (regardless of mass or velocity), the time between acceleration and detection can be used to calculate the mass of a given ion.

TOF instruments have the advantage of data multiplexing. All ions can be detected as opposed to some of the other mass analysis techniques that filter (remove) unwanted ions. Historically, TOF was generally thought to be of limited analytical use due to the length of flight tube required to achieve adequate mass resolution. However, energy focusing devices such as a reflection or dynamic fields provide much higher resolution than simple, field free flight tubes.