FT-ICR — Basics in Mass Spectrometry

In FT-ICR, ions are trapped in a strong magnetic field and orbit in circles (cyclotron motion). The orbit frequency depends on m/z — light ions orbit fast, heavy ions slow. The orbiting ions induce a tiny image current, which is Fourier-transformed into a spectrum.

The full cycle

Three linked panels: ions orbit → they induce a beating transient → a Fourier transform turns it into peaks.

orbit → transient (beating) → Fourier transform → spectrum

light ion → orbits fast → high frequency heavy ion → orbits slow → low frequency more ions of a mass → taller peak (intensity) signal decays as ions dephase (FID)

The key difference from other analyzers: FT-ICR does not slam ions into a detector. It “listens” to the ions orbiting and decodes the signal mathematically. The longer it listens, the finer the frequency resolution — which is why FT-ICR reaches the highest resolving power of any mass analyzer.

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