Identification of Organic Components in Uncured Rubber Compounds Using Mass Spectrometry

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Abstract
Three carbon-black-filled rubber compounds of known composition were analyzed by mass spectrometry. Direct thermal desorption was used with three different methods of ionization (EI, CI, FI). In addition, the three rubbers were examined by FAB-MS (without liquid matrix) as a means for surface desorption/ionization. Extracts of the rubbers were also examined using two different solvents (acetone and acetonitrile). Each extract was examined directly by five methods of ionization (EI, CI, FI, FD, FAB). Of the various vaporization/ionization methods, it appears that FI/FD is the most efficient for identifying typical organic additives in rubber stocks. The analysis can be carried out using either the untreated rubber (FI mode) or else a solvent extract (FD mode). Molecular ions are dominant, which facilitates the characterization of the complex organic additive mixtures that are present in typical compounded rubbers. For samples in which the identity of FD/FI molecular ions is unclear, further analysis using other methods (EI, CI, FAB, MS/MS, GC/MS, LC/MS, high resolution) can be carried out to gain additional information. We conclude that FD and FI yield the most useful information in the shortest period of time. The main difference between the results of this study and those of the volcanizate study is with respect to the curatives. Intact accelerator molecules could readily be observed in the spectra from the uncured stocks, while only accelerator fragments could be observed from the vulcanizates.

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