Electron capture negative ion mass spectra of some typical matrix-assisted laser desorption/ionization matrices

A series of seven typical matrix‐assisted laser desorption/ionization (MALDI) matrices has been investigated by means of electron capture negative ion mass spectrometry (ECNI‐MS). It has been shown that the most effective matrices form deprotonated negative ions predominantly in the low‐energy region. Relative dissociative cross sections have been measured for all molecules under investigation. The relative integrated abundance of [M − H]− ion formation in the series changes by four orders of magnitude. It has been shown that 2,5‐DHB (gentisic acid), one of the most effective MALDI matrices, has maximal relative intensity of [M − H]− formation at the energy ∼0.8 eV. This result is in accordance with a finding of Frankevich and Zenobi [Book of s, Workshop‐school “Mass spectrometry in chemical physics, bio‐physics and environmental sciences”, Zvenigorod, Russia, April, 25–26, 2002, p. 40] that a probable origin of negative ions in MALDI is the process of low‐energy (0.5–1 eV) dissociative electron capture by matrix molecules. Copyright © 2002 John Wiley & Sons, Ltd.