CHEMICAL-IONIZATION OF NEUTRAL PEPTIDES PRODUCED BY MATRIX-ASSISTED LASER-DESORPTION

The cationization in the gas phase of neutral peptides formed under th e conditions of matrix-assisted laser desorption (MALD) has been demon strated. The beam of neutral peptides formed by MALD using one laser w as intercepted several hundred micrometers above the sample surface by a beam of cations produced using a second laser. The intensity of cat ionized neutral gramicidin S formed in this way was comparable to the ion signal produced by conventional matrix-assisted laser desorption/i onization (MALDI). The threshold fluences for MALD of neutral peptides have been shown to be lower than those for formation of ions from the same samples by MALDI. (C) 1998 Elsevier Science B.V.