Ion trapping and manipulation in a tandem time-of-flight-Fourier transform mass spectrometer

Abstract

An external source tandem time-of-flight-Fourier transform mass spectrometer which provides programmed ion kinetic energy manipulation and trapping control is described. Design considerations are discussed and a detailed description of the instrument is provided. Typical ion injection efficiencies of 80–90% are obtained over an injection energy range of 30–500 eV. The instrument is capable of sensitive time-of-flight analysis of ions which have been injected into, and subsequently discharged from, the magnetic field. This allows a diagnostic treatment of ion injection and trapping performance independent of the Fourier transform mass spectrometry (FTMS) experiment. A theoretical treatment of the propagation characteristics of the ions detected in this manner is presented along with supporting data. Also described are new external source FTMS trapping procedures for pulsed injection that provide full control over the mass range of injected ions. Preliminary results for one such procedure are presented. In this example, a 230 dalton mass range is acquired in the trapped-ion cell for pulsed ion injection parameters that would ordinarily limit the acquired mass range to less than 150 daltons.