Subambient pressure ionization with nanoelectrospray source and interface for improved sensitivity in mass spectrometry

A nanoelectrospray ionization mass spectrometry (ESI-MS) source and interface has been designed that enables efficient ion production and transmission in a 30 Torr pressure environment using solvents compatible with typical reversed-phase liquid chromatography (RPLC) separations. In this design, the electrospray emitter is located inside the mass spectrometer in the same region as an electrodynamic ion funnel. This avoids the use of a conductance limiting ion inlet, as required by a conventional atmospheric pressure ESI source, and allows more efficient ion transmission to the mass analyzer. The new subambient pressure ionization with nanoelectrospray (SPIN) source improves instrument sensitivity and enables new electrospray interface designs, including the use of multi-emitter approaches. Performance of the SPIN source was evaluated by electrospraying standard solutions at 300 nL/min and comparing results with those obtained from a standard atmospheric pressure ESI source that used a heated capillary inlet. This initial study demonstrated an approximately 5-fold improvement in sensitivity when the SPIN source was used compared to a standard atmospheric pressure ESI source. The importance of desolvation was also investigated by electrospraying at different flow rates, which showed that the ion funnel provided an effective desolvation region to aid the creation of gas-phase analyte ions.