Surface characterization and depth profiling of biological molecules by electrospray droplet impact/SIMS

Electrospray droplet impact (EDI) was applied to the analysis of peptides. The etching rate of bradykinin was estimated to be similar to 2 nm/min. This value is about one order of magnitude greater than the etching rate for SiO2 (0.2 nm/min). Considering that the etching rate of argon cluster ions Ar-700(+) for organic compounds is more than two orders of magnitude larger than that for inorganic materials, the rather small difference in etching rates of EDI for organic and inorganic materials is unique. When water/ethanol (1/1, vol%) solution of gramicidin S and arginine was dried in air, [gramicidin S + H](+) was observed as a predominant signal with little [Arg + H](+) right after the EDI irradiation, indicating that EDI is capable of detecting the analytes enriched on the sample surface. Copyright (C) 2011 John Wiley & Sons, Ltd.