Nor-Harmane (9H-Pyrido[3,4-b]indole) as Outstanding Matrix for UV-Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry Analysis of Synthetic and Bio-Polymers.

Abstract

In an effort to gain an understanding of the processes governing matrix-assisted ultraviolet laser desorption/ionization (UV-MALDI), we made a direct comparison of the mass spectra of synthetic (PEG, PMMA, PS, PDMS) and bio-polymers (neutral cyclic and acyclic, sulfated and basic mono- and polysaccharides) by using nor-harmane and gentisic acid (GA) as UV (337 nm) -MALDI-TOF-MS matrices in positive and negative ion modes in linear, reflectron and post-source decay (PSD) modes. The majority of the examples discussed shows nor-harmane working better as matrix than GA. This peculiarity is quite noticeable in negative ion mode. Because the initiation of the UV-MALDI process is a photochemical reaction (matrix+hν (337 nm) → matrix), the acid-base character of nor-harmane in the ground and the lower electronic excited singlet state, together with other photophysical properties are discussed in brief. Excellent results obtained with commercial synthetic polymers and commercial cyclodextrins with nor-harmane allow us to propose these analyte-matrix systems for UV-MALDI-TOF-MS calibration in positive and negative ion modes in linear, reflectron and PSD modes.