Desorption and Ionization of Amino Acid Compounds Observed by Negative Ion Mode　Surface-Assisted Laser Desorption/Ionization Mass Spectrometry (SALDI-MS) using Titanium Oxide Nanoparticles

Abstract

Surface-assisted laser desorption / ionization mass spectroscopy (SALDI-MS) in negative mode of various amino acids with commercial TiO₂ nanoparticles as the DI assisting material is reported. SALDI-MS gives clear spectra of these low molecular weight negative ions, such as drugs and bio-related organic compounds. With commercially available TiO₂ nanoparticles, 20 common amino acids used could be clearly detected as [M-H]^- molecular ions. The ion intensity of [M-H]^- molecular ions is well linear correlated with the gas-phase acidity but less correlation with the hydrophobicity. But the concentration of the amino acids on the TiO₂ nanoparticle surface also affected the ion intensity.