Preparative soft and reactive landing of gas-phase ions on plasma-treated metal surfaces

Soft landing of singly charged gas-phase ions on dry metal surfaces that were pretreated in situ by oxygen plasma results in 0.1-2% total yields of recovered intact compounds. Lysine, peptides, crystal violet dye, and a biotin conjugate are found to survive soft landing of hyperthermal ions of up to 50-eV kinetic energy. Soft landing at 40-50-eV ion kinetic energies of a fluorescence-labeled biotin conjugate results in an immobilized fraction that cannot be washed from the surface and is found to contain an intact biotin moiety. The present results represent an approximately 10(4) fold improvement in soft-landing efficiency and indicate that plasma-treated metal surfaces can be useful for preparative separation of organic and biological molecules by mass spectrometry. The substantial improvement in soft-landing yields results from a high transmission of electrosprayed ions into the vacuum system, efficient and nondestructive discharge of ions on the metal oxide surface, and facile analyte recovery in the absence of a matrix.