FTICR

FTICR, or Fourier Transform Ion Cyclotron Resonance, is a mass spectrometry technique that uses a strong magnetic field to trap ions in a Penning-type cell and detect their cyclotron motion. The image current produced by coherently moving ions is recorded as a time-domain transient and converted to a mass spectrum by Fourier transformation. The cyclotron frequency ωc = qB/m relates field strength, ion charge, and mass-to-charge ratio, enabling very high resolving power and mass accuracy.

Instrumentation and operation: A high-field superconducting magnet provides the magnetic field, and ions are confined in an ICR cell with detection electrodes. A vacuum system minimizes collisions. Ions generated by electrospray or MALDI enter the trap; radiofrequency excitation coheres their motion. The transient signal is Fourier-transformed and calibrated to m/z. Field strengths of 7–15 tesla are common; higher fields improve resolution and accuracy. FTICR systems support a wide dynamic range and enable advanced MSn experiments and isotope-resolved measurements.

Performance and limitations: FTICR can achieve resolving powers in the 10^5–10^6 range and mass accuracies in the low ppm range under optimal conditions. Its strengths include high resolution, precise isotope discrimination, and flexibility for fragmentation and tandem analysis. Limitations include high cost and ongoing maintenance of large superconducting magnets, substantial space requirements, demanding vacuum and cryogenics, and longer acquisition times for the highest resolution, which can limit throughput.

Applications: Used in proteomics, metabolomics, and analyses of complex natural products, as well as petroleomics and isotope pattern studies where fine mass discrimination is essential.

History: The method emerged in the 1960s–1970s, with key developments by Marshall and Comisarow who demonstrated the Fourier-transform approach to ion cyclotron resonance. Ongoing advances in magnets, detectors, and data processing have expanded its capabilities.