Direct Insertion Analysis of Polymer-Modified Bitumen by Atmospheric Pressure Chemical Ionization Ultrahigh-Resolution Mass Spectrometry

Bitumen is a highly complex matrix, generally obtained as vacuum residues of the crude oil distillation. This material is majorly used as binder for the construction of asphalt pavement. Mechanical properties of bitumen are greatly influenced by its composition, including heteroatom-containing compounds, and by the use of additive cocktails. Polymer-modified bitumen (PMB) can be produced by the use of additives such as styrene-butadiene-styrene copolymer (SBS) to avoid asphalt stiffness and pavement cracking. To characterize a complex mixture such as bitumen at the molecular level, instruments such as Fourier transform ion cyclotron resonance are required. However, the size of SBS, which is typically >150 kDa, is far above the mass range of Fourier transform ion cyclotron resonance (FTICR) instruments. Direct insertion probe atmospheric pressure chemical ionization (DIPAPCI) can be used to pyrolyze SBS and observe its fragments within a PMB sample in a lower mass range. This technique does not require any sample preparation because the sample is analyzed in pure form and is also adapted to characterize heavy petroleum products with its ability to ionize a large range of molecules including nonpolar, polar, and aromatic species. DIP-APCI-FTICR was used with fixed and ramped temperature for the analysis of base bitumen, SBS, and PMB samples. It allowed for the characterization of the thermodesorption products of bitumen and the pyrolysis products of SBS. The main markers of SBS appear to be multimeric butadiene ions. This SBS ion series is clearly evidenced in PMB using DBE vs C# and modified Kendrick mass defect plots. Overall, this study presented a fast DIP-APCI-FTICR characterization of bitumen and PMB without any sample preparation.

Automated summary

The study discusses the analysis of modified bitumen using additives in FTICR instruments, which can accurately characterize bitumen and PMB without the need for sample preparation. The DIP-APCI technique allows for efficient decomposition of SBS and measurement of its fragments. Results show that the SBS ion series is clearly visible in PMB.