~ ~ ~_ Matrix-assisted Laser Desorption of *Peptides in Transmission Geometry

The possibility of performing matrix-assisted laser &sorption experiments in trknsmission geometry is demonstrated for two neuropeptides (substance P and bombesin), for six analogs of the melanocyte-stimulating hormone (MSH) core and for collagenase enzyme substrates. Positive- and negative-ion spectra of several peptides are produced without the presence of a metallic substrate. Cationized quasi-molecular ions are abundant in the positive spectra. Peak broadening in the high-mass range can be the consequence of overlapping molecular and adduct ions. The presence of synthesis by-products can be identified readily from the spectra. Ultimately, picogram detection limits are possible for important bioactive peptides and other large molecules. Because of the clearlv demonstrated matrix-assisted laser ionization in a homogeneous environment, metal substrate participatioi in the volatilization mechanism seems less likely. The recent upsurge of laser-desorption studies orig-inated in the discovery of the matrix-assisted method.’ It has carved out a distinguished place in the schedule of several current conferences? Laser desorption seems to compete quite successfully with plasma desorption ’ and with electrospray ionization for bein