Matrix-Assisted Laser Desorption Ionization Mass Spectrometry of Compounds Containing Carboxyl Groups Using CdTe and CuO Nanoparticles

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Matrix-assisted laser desorption ionization mass spectrometry of compounds containing carboxyl groups was carried out by using semiconductor nanoparticles (CdTe and CuO) as the matrix. Salicylic acid (Sal), glucuronic acid (Glu), ibuprofen (Ibu), and tyrosine (Tyr) were ionized as deprotonated species (carboxylate anions) by using electrons ejected from CdTe after the photoexcitation. When CuO was used as the matrix, the peak intensity of Tyr became high compared with that obtained with CdTe. Measurements of model peptides, angiotensin II (AngII) and substance P (SubP), were also carried out but the obtained peak intensities were very low. In order to explain this result, the interaction between CdTe and AngII was confirmed by diffuse reflectance spectroscopy. The results suggest that electrostatic binding between semiconductor nanoparticles and AngII prevented the efficient desorption of AngII into the gas phase.