The principle of a FTMS spectrometer is based on ion containment. Ions are trapped for long period of time and can be manipulated using electric and magnetic fields. A force is exerted onto a particle when it is moving perpendicular to the magnetic field direction. The particle, (in our case an ion) is deflected into circular orbits, providing it doesn’t encounter any obstacle (vacuum). The cyclotron frequency is the frequency at which an ion of a given mass rotates inside a given magnetic field. This frequency depends only on the field magnitude and the ion’s mass-to-charge ratio. By solving the equation of motion, we obtain the following formula: ω_c=q.B/m with the units [rad/s]=[ Coulomb].[Tesla]/[ kg ]. 

The FTICR MS generates series of carefully timed events in order to measure the cyclotron frequency of the ions. 

Introduction of the neutral sample: A small quantity of gas is pulsed inside the vacuum chamber.Ionization of the neutral sample: Using electron impact, a short beam of electron is accelerated across the cell, effectively ionising the neutral gas sample. The resulting ions are trapped inside the cell by a combination of magnetic and electric fields.RF excitation of the ions: The ions are put into circular motion by using RF pulses. Each ion is rotating accordingly to its cyclotron frequency

Detection of the induced signal: When the ion’s orbit is close enough to the detection electrodes, they induce an image current that’s amplified and recorded, for all the ions simultaneously.Signal mathematical analysis : A Fourier Transform is performed on the raw signal in order to get a frequency spectra. A mass spectra is then easily obtain by applying the previous formula.