Fourier-Transform Mass Spectrometry

Introduction

Fourier-transform mass spectrometry takes advantage of ion-cyclotron resonance to select and detect ions.

Ions in a magnetic field will move in a circular path of radius:

r = mv/eB

and frequency:

f = eB/m

Ions moving at their cyclotron frequency can absorb RF energy at this same frequency. A pulse of RF excites the ions in the magnetic field. The ions re-emit the radiation, which is picked up by the reciever plates. The decay produces a free-indcution decay signal that can be Fourier transformed to produce the emitted frequencies, and therefore the masses of the ions present.

Instrumentation

Schematic of a FT-MS

FTMS can provide very high resolution, 10⁶, which its main advantage compared to other mass spectrometers.

Related topics:

• Mass spectrometry (Intro)
• Ionization methods
• Ion detectors