Probing the Effects of Popular Substrates on Laser Desorption of Ions and Neutrals

摘要

For SALDI, very similar spectra were obtained using porous Si and graphite despite the differences in the substrate electronic structure and surface chemistry. Interestingly SALDI does not occur initially using single crystal Si(100) substrates, however, adsorption of water at 130 K produces a spectrum similar to that observed from porous Si and graphite. SALDI spectra produced protonated molecular ion peaks. The absence of molecular ions indicates that analyte molecules were not directly ionized by photons in the gas phase. An increase in sample solution acidity resulted in an increase in ion yield for all amino acids, indicating important roles of surface/interface layer acidity and proton affinity of desorbing amino acid. Multiphoton induced ionization of interfacial water and terminal-OH derived surface states may be important in SALDI. Surface morphologies which lead to the adsorption of water matrices with dispersed analytes are most effective since they enhance and maximize protonated complex formation and escape. This data collectively indicates that SALDI depends more on the presence of water and the intrinsic proton or hydronium ion content than the substrate bulk electronic structure.