Powerfully Solvating Matrices for MALDI-TOF Spectroscopy of Aromatic Polyesters

The starting premise of this work was that matrices containing powerfully solvating groups would enhance the quality of MALDI-TOF spectra of condensation polymers. The solvating groups in these matrices would pry the polymer aggregates apart and make it easy for individual ionized polymer molecules to “fly”. Ten polyfluorinated azobenzenes and stilbenes were synthesized. The laser desorption ionization spectra of the pure fluorinated matrices show the formation of radical cations (M•+) and anions (M•-) in addition to the more conventional [M + H]+ and [M−H]- ions. Dimerization followed by loss of fluorine is also observed. The effectiveness of these compounds as MALDI matrices was tested with four aromatic polyesters: poly(3-ethyleneoxybenzoate) (3EOB), Vectra, poly(1,4-dimethylenecyclohexane terephthalate) (CHDT), and poly(ethylene terephthalate) (PET). The azobenzene-containing matrices were much better than their stilbene analogues and gave good quality positive ion spectra, better than those obtained with the conventional matrix dithranol. With the best matrix, 4,4‘-dihydroxyoctafluoroazobenzene, ions up to m/z 12 000 were detected for the CHDT and PET polymers.