Abstract: A Fourier transform ion cyclotron resonance (ICR) mass spectrometer, with a vacuum housing comprising three differentially pumped regions allows spatial separation of the processes for generation, translocation, and detection of the ionic species. The ion source provides inlets for solid, liquid, and gaseous samples from direct injection or chromatographic interfaces. Provision is made for ionization by electron impact, chemical ionization, fast atom bombardment, and laser ionization. A system of electrostatic lenses accelerates, focusses, and decelerates the ions for transmission to the ion detector. The mass analyzer includes an ion cyclotron resonance cell in which the ionic motions are detected by amplification of a small "image" current induced in the walls of the cell and made to flow through external detection circuitry.