High performance detection of biomolecules using a high magnetic field electrospray ionization source/Fourier transform ion cyclotron resonance mass spectrometer

Abstract

An improved, high-performance version of the concentric vacuum chamber design is shown for forming ions at high pressure in a strong magnetic field and detecting them in an adjacent Fourier transform ion cyclotron resonance mass spectrometry (FTICR) trapped ion cell. Improvements in system design, including primarily the addition of a mechanical shutter to halt the flow of neutrals to the trapped ion cell during FTICR detection, allow a more than 100-fold improvement in pressure drop between the source and analyzer chamber to be realized. Within a 20 cm distance, ions formed in an electrospray ion source at atmosphere are transported across five concentric tube conductance limits to a trapped ion cell at a shuttered pressure below 2×10−9 Torr. High resolution detection of electrosprayed proteins is demonstrated and, for example, mass resolutions of 1×105 for the +14 charge state of horse heart myoglobin (at m/z 1211) and 2×105 for +5 charge state of bovine insulin (at m/z 1147) are obtained. The original advantages of the concentric tube vacuum chamber are retained. Forming the ions within the magnetic field permits a 40-fold enhancement in sensitivity to be obtained. Narrow kinetic energy distributions are achieved because magnetic field confinement eliminates the need for complex electric focusing assemblies that exhibit mass discrimination and broaden the kinetic energy distribution. Finally, the shutter is demonstrated to serve effectively as an alternative to pulsed valve assemblies for the transient introduction of a collision gas to the trapped ion cell.