Orbitraps

Orbitraps are a class of mass analyzers used in mass spectrometry. They trap ions in an electrostatic field formed between a central spindle-like inner electrode and a coaxial outer barrel. Ions orbit around the central electrode while performing axial oscillations along the instrument axis. The axial oscillation frequency of each ion is largely determined by its mass-to-charge ratio (m/z). By detecting the image current induced by the moving ions on the outer electrodes and applying Fourier transform to the time-domain signal, a high-resolution mass spectrum is produced.

In practice, Orbitraps are used as standalone analyzers or as part of hybrid instruments, often combined with another mass analyzer such as a linear ion trap or a quadrupole (for example LTQ Orbitrap, Orbitrap Velos, Q Exactive, and Orbitrap Fusion). They are typically coupled to electrospray ionization and support tandem mass spectrometry (MS/MS) using fragmentation methods like CID or HCD. Orbitraps excel in high mass accuracy and high resolving power, enabling precise determination of elemental compositions and confident identification of molecules.

Performance characteristics include resolving powers from tens of thousands to well over 100,000 at m/z 400, with mass accuracy frequently in the low parts-per-million (ppm) range after calibration and lock-mass correction. Scan speeds are generally slower than some other analyzers, but advancements have improved duty cycles and sensitivity. Applications span proteomics, metabolomics, small-molecule analysis, and complex mixture profiling, where exact mass measurements improve identification and characterization.

The Orbitrap technology was developed by Anton Makarov and introduced in the early 2000s. Its name reflects the orbital motion of ions in the analyzer and has become a widely adopted platform in modern mass spectrometry.