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Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS)

Principles

The Fourier transform mass spectrometry (FTMS) is a special MS technique based on the principle of ion cyclotron resonance (ICR). Generally externally formed ions are trapped in a FTMS analyzer cell which is at the center of a strong magnetic field. A cyclotron motion results when the ions spiral rapidly around the magnetic field lines. The cyclotron frequencies of the different ions depend on their mass/charge ratios and the uniform magnetic field strength. Detection of the ions is performed by recording image current signals (transient) which are induced by the ions passing a pair of receiver plates. Frequencies are recorded more precisely than any other physical parameter leading to mass spectra with very high resolution and mass accuracies. For simultaneous measurement of ions with different mass/charge ratios Fourier transform analysis is used to convert the complex transient from a time-dependent to a frequency-dependent function which is the basis for generation the mass spectra.

Equipment

The LTQ FT Ultra from Thermo Fisher is a hybrid mass spectrometer consisting of a linear ion trap (LTQ) and a FT-ICR-MS. For separation of complex mixtures prior to FT-ICR-MS a HPLC system (Agilent 1200) can be coupled to the LTQ FT Ultra.

Ionization can be performed by the API techniques electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) as well as by the Nanomate from Advion which enables on/off-line nano-ESI.

API techniques are soft ionization techniques which generate intact pseudo-molecule ions from analyte molecules. Besides determination of the accurate mass MS-MS experiments are useful for additional structure information. The LTQ FT Ultra offers collision induced dissociation (CID) in the ion trap as well as fragmentation directly in the ICR cell (Infrared multiphoton dissociation (IRMPD): excitation of molecule vibrations by a CO2 laser; electron capture dissociation (ECD): bombardment of multiply-charged positive ions with electrons).

Examples

  • Structure elucidation of unknown organic compounds (signaling compounds, metabolites, products from chemical (side) reactions)
  • Characterization of the organic carbon in soil and sediments with the focus on humic substances
  • Characterization and sequencing synthetic and natural peptides and proteins (under construction)

Contact

Frau Dr. B. Santiago Schübel Tel.: 02461-61 4951


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