Determinação de compostos organosulfurados como marcadores dos processos de envelhecimento em matrizes asfálticas brasileiras

Abstract

The involvement of organosulfur species in the aging processes of Brazilian asphalt cements was studied using analytical methodologies such as ultra high performance liquid chromatography with atmospheric pressure photoionization and detection by tandem mass spectrometry (UHPLC-APPI-MS / MS), differential pulse voltammetry (DPV) in non-aqueous medium and immobilized microparticle voltammetry (VIMP). A model group of organosulfur compounds was listed as markers to evaluate the distribution and changes occurring during the forced incidence of UV radiation and high temperatures and pressure by RTFOT / SUNTEST and RTFOT / PAV, respectively on asphalt. The ionization method (APPI) presented several advantages such as the non-use of dopant, which reduce the possibility of interference of matrice compounds like PAHs in the determination of the sulfur compounds. The method still showed an acceptable matrix effect, ranging from 70.58 to 118.18%, regarding the complexity of the asphalt matrix. Good results were obtained in the validation of the method and the lower quantification and detection limits were observed for sulfoxides and sulfones, which was explained by the different ionization mechanisms observed between classes. The electrochemical monitoring of the samples by DPV in non-aqueous medium prior to the chromatographic characterization demonstrated the necessity of cleaning the asphalt matrices for the determination of the markers compounds. The optimization results of the clean-up method demonstrated that a redissolution of the samples in acetone followed by solid phase extraction with stationary phase of aminopropyl gives good recovery results (62.07 to 114.85%). In addition, the electrochemical behavior of the solid-state organosulfur compounds allowed the evaluation of these species in the aging processes of asphaltic matrices by VIMP. The results demonstrated that in addition to oxidation, sulfur compounds, mainly thiophenes and sulfides, are involved in polymerization mechanisms during aging. The determination of organosulfur markers such as thianthrene, 4,6-dimethyl dibenzothiophene, 4-methyl dibenzothiophene, dimethyl sulfoxide and dodecyl sulfoxide by UHPLC-APPI-MS/MS in the different fractions studied corroborated with the results obtained by VIMP. This allowed the establishment of possible reactions routes for these markers during the different aging processes.The Brazilian asphalt samples also demonstrated the presence of dimethyl sulfoxide and dodecyl sulfoxide in significant contents even before submitted to the processes of forced aging.