Analysis of polymer additives by matrix-assisted laser desorption ionization/time of flight mass spectrometer using delayed extraction and collision induced dissociation

Matrix-assisted laser desorption/ionization (MALDI) in combination with mass spectrometry proved to be a viable method for identifying additives in polyethylene extracts. The MALDI mass spectra of additives standards were found to be very simple consisting of [M+H](+) and/or [M+Na](+) pseudo molecular ions with little fragment ions. For real samples, which often contain more than one additive, the production of only one or two ions for each additive makes the tentative assignment much easier. Collision induced dissociation (CID) of the pseudomolecular ion is used to confirm the tentative assignment. The analysis of high molecular weight additives, such as Chimassorb 944 and Tinuvin 622 indicated that MALDI was superior to other ionization techniques such as electrospray ionization (ESI), desorption chemical ionization (DCI) and fast atom bombardment (FAB) in the analysis of high molecular weight polymer additives. Sample preparation was found to be more critical than DCI in the analysis of real sample. The signals were interfered by the low molecule weight polyethylene molecules, which were co-extracted with the additives. This problem was partially overcome by using acetone instead of methanol to precipitate the low molecular weight polyethylene molecules.