Laser desorption ionization (LDI)/laser ablation (LA) time-of-flight mass spectrometry (TOFMS) studies are performed via back-illumination on thin silver films deposited with gramicidin S, a cyclic decapeptide (1141 Da). Experimental results indicate an electronic excitation mechanism at low laser fluences and a thermal process at high laser fluences. In a perpendicular orientation of the thin silver film with respect to the drift tube axis, better success of chemical ionization (CI) of neutral silver atoms/clusters and gramicidin S molecules by Ag+ monomer cations within the ablation plume is evident. When these LDI/LA studies are repeated under surface plasmon resonance (SPR) conditions, the neutral atoms/clusters/molecules undergo SPR LDI/LA via a different laser energy transfer process compared to direct LDI/LA. These results also indicate an electronic excitation mechanism, only with a lower laser fluence requirement. Upon addition of a matrix, 2,5-dihydroxybenzoic acid (DHB), CI of gramicidin S molecules by Ag+ monomer cations is hindered while the CI of gramicidin S molecules by Na+ cations can occur at an even lower laser fluence. Thus, SPR LDI/LA with matrix isolation is an excellent technique for the mass analysis of gramicidin S.

Chemical ionization, Electronic excitation mechanism, Laser desorption ionization, Matrix isolation, Silver film substrate, Surface plasmon resonance, Time-of-flight mass spectrometry
Journal of Photochemistry and Photobiology A: Chemistry
Department of Chemistry

Owega, S. (Sandy), Lai, E.P.C, & Mullett, W.M. (Wayne M.). (1998). Laser desorption ionization of gramicidin S on thin silver films with matrix isolation in surface plasmon resonance excitation. Journal of Photochemistry and Photobiology A: Chemistry, 119(2), 123–135.