Analytical characterization of the electrospray ion source in the nanoflow regime.
A detailed characterization of a conventional low-flow electrospray ionization (ESI) source for mass spectrometry (MS) using solution compositions typical of reversed-phase liquid chromatography is reported. Contrary to conventional wisdom, the pulsating regime consistently provided better ESI-MS performance than the cone-jet regime for the interface and experimental conditions studied. This observation is supported by additional measurements showing that a conventional heated capillary interface affords more efficient sampling and transmission for the charged aerosol generated by a pulsating electrospray. The pulsating electrospray provided relatively constant MS signal intensities over a wide range of voltages, while the signal decreased slightly with increasing voltage for the cone-jet electrospray. The MS signal also decreased with increasing emitter-interface distance for both pulsating and cone-jet electrosprays due to the expansion of the charged aerosol plume. At flow rates below 100 nL/min, the MS signal increased with increasing flow rate due to increased number of gas-phase ions produced. At flow rates greater than 100 nL/min, the signal reached a plateau due to decreasing ionization efficiency at larger flow rates. These results suggest approaches for improving MS interface performance for low-flow (nano- to micro-) electrosprays.
Marginean
Ioan
I
Biological Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA.
Kelly
Ryan T
RT
Prior
David C
DC
LaMarche
Brian L
BL
Tang
Keqi
K
Smith
Richard D
RD
D036103:Nanotechnology / Q000379:methods*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*