Direct monitoring of the role played by a stabilizer in a solid sample of polymer using direct analysis in real time mass spectrometry: the case of Irgafos 168 in polyethylene.

Direct analysis in real time (DART) ionization method is used with a time-of-flight (TOF) mass spectrometer to perform the analysis of industrial polyethylene pellets free of additives or containing Irgafos 168 as stabilizing agent without any sampling step. The developed analytical method uses the [M + H](+) ion of the bis(2-ethylhexyl) phthalate (DEHP) for performing the exact mass measurements of the stabilizer and polymer ions using the mass drift compensation procedure available on the AccuTOF mass spectrometer. DEHP is in fact a plastic contaminant always presents on the mass spectra of the analyzed samples. The mass spectra allow one to characterize either the ions of the polyethylene and that of the Irgafos. The analysis of thermally treated samples show that the polymer does not undergo any degradation when the Irgafos is present in the bulk of the material, and the role played by the Irgafos 168 is that of an oxygen trapping agent. Under UV exposure, the DART-TOF MS analyses performed on the exposed polyethylene pellets shows that the Irgafos 168 behavior toward the UV radiations is different since this one reacts by cleavages of its P-O bonds to prevent the degradation of the polymer. These interpretations are supported by all the elemental formula determination of the detected ions.