Mass and Charge Dependent Ion Discrimination in a Linear Pulsed Time-of-Flight Mass Spectrometer

Abstract

Two potential sources of mass and charge discrimination in a linear pulsed time-of-flight mass spectrometer have been analyzed in detail. The first is a well known effect due to spreading of the ion beam in the drift tube. The ion flux density distribution at the detector has been calculated as a function of the ion source dimensions, initial ion kinetic energy, and drift tube length and voltage. The second effect results from motion of the ions in the ion source region prior to being accelerated into the drift tube. It is shown that by appropriate choice of the source parameters and operating conditions it is possible to store ions in the source region prior to extraction and thereby enhance ion count without introducing severe discrimination effects.