We have used 23 keV C 60+ projectiles in the event-by-event bombardment and detection mode to investigate the emission of the gramicidin S [M - H] - ion embedded in a matrix of sinapic acid. We have observed an increase in the gramicidin S [M - H] - ion of approximately eight times by controlling the ratio of gramicidin S to sinapic acid. The maximum of the gramicidin S [M - H] - yield occurs at a matrix/analyte ratio of 10:1. This ratio is different from those typically used in matrix-assisted laser desorption/ionization. 2006 Elsevier B.V. All rights reserved.