Abstract: A method of separating ions according to mass in a mass spectrometer includes establishing a stream of ions traveling in a generally cycloidal path in an electric field and a magnetic field, subsequently causing the electric field to terminate for a predetermined period of time while maintaining the magnetic field thereby causing the electrons to travel in a generally circular path for a predetermined time period and subsequently reestablishing the electric field to cause further travel in a cycloidal path and providing a detector for receipt of some of the ions. A suitably programmed microprocessor is employed to control operation of the mass spectrometer and to receive electrical signals responsive to ions impacting on the detector to thereby provide information regarding the ions. Corresponding apparatus is provided.