Determination of squalene by-products during model compound vulcanization studies by LC-ESI-MS using silver nitrate as a post-column reagent

High Performance Liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESI-MS) using silver nitrate as a post-column reagent has been used for the determination of squalene by-products during model compound vulcanization studies. In this method, after all by-products were separated by reverse-phase liquid chromatography, analytes formed complexes with silver cation by mixing with a silver nitrate solution. The positive ion ESI mass spectra of squalene, squalene by-products and intermediates of vulcanization process showed [M+Ag]⁺ and/or [M+Ag+AgNO₃]⁺ ions. The method described in this paper overcomes the ESI technique limitations related to the ionization of hydrocarbon. Furthermore, results obtained working with this methodology helped to gain more insight into the natural rubber accelerated vulcanization process. In this sense the identification of the different crosslink types was determined, proving that the elution time increases with the decrease of sulfur chain length in the crosslink. Squalene with pendant group was also identified.