Qualitative and quantitative end-group analysis of a small molecular weight polyester by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry was used for qualitative and quantitative end-group analysis of a small molecular weight polyester, poly(2-butyl-2-ethyl-1,3-propylene p hthalate), The presence of carboxyl-terminated linear and cyclic polyester oligomers was confirmed with the help of simple sample preparation methods. The presence of carboxyl end-groups in the polyester chains was verified t hrough their formation of carboxylate salts with alkali metal cations, Cycl ic oligomers were identified through deuterium exchange of the exchangeable protons of the polyester. Various inorganic salts were tested for salt for mation of the carboxyl end-groups, but only the alkali metal salts proved e ffective. The influence of the alkali metal salts on the results of the qua ntitative end-group analysis was also studied. The relative amounts of diff erently terminated and cyclic oligomers were calculated when the alkali met al salts were used with different matrices. The results showed that both th e salts and the matrices used in sample preparation can have a marked effec t on the quantitative results of the end-group analysis. The measurements w ere carried out using 2,5-dihydroxybenzoic acid (DHB), 1,8,9-trihydroxyanth racene (dithranol), and 2-(4-hydroxyphenylazo)benzoic acid (HABA) as matrix compounds. Dithranol and HABA repeatably exhibited similar results, and th ese results differed from those obtained with DHB probably because of the d ifferent ionization mechanisms in the MALDI process. Copyright (C) 2000 Joh n Wiley & Sons, Ltd.