Charge detection mass spectrometry for single ions with a limit of detection of 30 charges

Abstract

A charge detection mass spectrometer (CDMS) with a limit of detection of 30 elementary charges (e) for a single ion is described. The new CDMS consists of an electrospray source coupled to a dual hemispherical deflection analyzer (HDA) followed by a modified cone trap incorporating an image charge detector. Ions are energy selected by the dual HDA prior to entering the trap. The fundamental oscillation frequency of the trapped ion is extracted by a fast Fourier transform (FFT). The oscillation frequency and kinetic energy provide the m/z. The magnitude of the FFT at the fundamental frequency is proportional to the charge. Simulations indicate that the charge is measured with an average uncertainty of 3.2 e. The mass of each ion is obtained from the m/z and the charge. Mass distributions have been measured for bovine serum albumin (BSA). The BSA ions were trapped for up to 1139 cycles. BSA monomer and multimer ions are evident in the measured mass distribution. The width of the monomer mass distribution (14kDa) is consistent with the predicted uncertainty in the charge.