UV-matrix-assisted laser desorption/ionization time-of-flight massspectrometry analysis of synthetic polymers by using nor-harmane as matrix

Abstract

The matrix-assisted ultraviolet laser desorption/ionization time-of-flight mass spectra (UV-MALDI-TOF-MS) analysis of some synthetic polymers was studied. The results obtained by using nor-harmane, gentisic acid (GA) and other UV-MALDI matrices, in positive and negative ion modes, were compared. Nor-harmane worked as an efficient matrix for the synthetic polymers belonging to the families of polyethylenglycol (PEG), polymethylmethacrylate (PMMA), polystyrene (PS) and poly(dimethyl)siloxane (PDMS). This behaviour was quite noticeable in negative ion mode for polar-protic polymers (PEG) and in both ion modes for non-polar polymers (PS). For the latter analysis the addition of Ag+ salts was not necessary for the ionization process. The formation of Ag clusters when Ag+ salts are used as the cationizing agent is discussed. Because the initiation of the UV-MALDI process is a photochemical reaction (matrix + h (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 briefly discussed. The excellent results obtained in the analysis of commercial synthetic polymers with nor-harmane allow us to propose these analyte-matrix systems for UV-MALDI-TOF-MS calibration.