Nanoelectrospray - More than just a minimized-flow electrospray ionizationsource

The comparison between electrospray ionization (ESI) mass spectra from NaCl solutions with and without analyte obtained under ionspray and nanospray c onditions reveals different mass spectral behavior of the two ESI technique s. This can be attributed to the different initial droplet sizes which are in the mu m range for ionspray, while in nanospray they are believed to be about one order of magnitude smaller. In the context of the widely accepted uneven-fission model, nanospray would then enter one fission generation la ter; in addition, a higher initial droplet surface charge density in nanosp ray results in early fissions without extensive evaporation and thus increa se in sample and salt concentration. This rationalizes that ionspray spectr a closely resemble nanospray spectra from solutions with about one order of magnitude higher salt concentrations, showing a higher tolerance of nanosp ray towards salt contamination. When the analyte is a peptide tin a solutio n containing a high molar surplus of salt), molecule ion formation effectiv ely competes with salt cluster ion formation; when the analyte is a sugar, it is detectable beside a high salt concentration only with nanospray, indi cating the supporting effect of surface activity on ion release in the case of peptides. A model is presented which explains the different mass spectr al behaviour of ionspray and nanospray by suggesting different "predominant fission pathways" depending on the size of the initial droplets. (C) 1999 American Society for Mass Spectrometry.