EXTERNAL ACCUMULATION OF IONS FOR ENHANCED ELECTROSPRAY-IONIZATION FOURIER-TRANSFORM ION-CYCLOTRON RESONANCE MASS-SPECTROMETRY

Electrospray ionization (ESI) in combination with Fourier transform io n cyclotron resonance (FTICR) mass spectrometry provides for mass anal ysis of biological molecules with unrivaled mass accuracy, resolving p ower and sensitivity. However, ESI FTICR MS performance with on-line s eparation techniques such as liquid chromatography (LC) and capillary electrophoresis has to date been limited primarily by pulsed gas assis ted accumulation and the incompatibility of the associated pump-down t ime with the frequent ion beam sampling requirement of on-line chromat ographic separation. Here we describe numerous analytical advantages t hat accrue by trapping ions at high pressure in the first rf-only octu pole of a dual octupole ion injection system before ion transfer to th e ion trap in the center of the magnet for high performance mass analy sis at low pressure. The new configuration improves the duty cycle for analysis of continuously generated ions, and is thus ideally suited f or on-line chromatographic applications. LC/ESI FTICR MS is demonstrat ed on a mixture of 500 fmol of each of three peptides. Additional impr ovements include a fivefold increase in signal-to-noise ratio and reso lving power compared to prior methods on our instrument. (C) 1997 Amer ican Society for Mass Spectrometry.