A sector instrument is a general term for a class of mass spectrometer that uses a static electric (E) or magnetic (B) sector or some combination of the two as a mass analyzer. Popular combinations of these sectors have been the EB, BE, three-sector BEB and four-sector EBEB (electric-magnetic-electric-magnetic) instruments. Most modern sector instruments are double-focusing instruments in that they focus the ion beams both in direction and velocity.

Josef Mattauch was a nuclear physicist and chemist. He was known for the development of the Mattauch-Herzog double-focusing mass spectrometer, for his work on the investigation of isotopic abundances using mass spectrometry, and the determination of atomic weights. Much of his career was spent at the Kaiser Wilhelm Institute for Chemistry.