Molecular ion yield enhancement in static secondary ion mass spectrometry by soft landing of protonated water clusters

An effective online method for molecular ion yield enhancement in static secondary ion mass spectrometry (SIMS) is demonstrated using a custom-built soft landing (SL) instrument equipped with SIMS capabilities. Dramatic molecular ion yield enhancement has been observed for amino acids and peptides on silica substrates after soft landing a mixture of protonated water clusters [H(H2O)(n)](+) (n = 4 to >100). Image current measurements and experiments on semiconducting and metal substrates confirmed that protonation of the analyte molecule and effective charge retention on the substrate is the reason for the observed phenomenon. Enhancement could also be observed-less conveniently-by offline treatment of the surface using electrospray deposition of 2% acetic acid in methanol/water solution. Copyright (C) 2010 John Wiley & Sons, Ltd.