Laser-Based Mass Spectrometric Assessment of Asphaltene Molecular Weight, Molecular Architecture, and Nanoaggregate Number

Unbiased analysis of asphaltene molecules by mass spectrometry requires that the three fundamental steps in mass spectrometry-volatilization, ionization, and mass analysis-are performed reliably and with nearly equivalent efficiency for nearly all of the diverse components in asphaltenes. Here, we examine these three processes and the overall analysis mechanism in two forms of laser-based mass spectrometry: laser desorption laser ionization mass spectrometry (L2MS) and surface-assisted laser desorption/ionization mass spectrometry (SALDI). In L2MS, volatilization occurs by laser desorption, which is a thermal process not selective for any particular molecular configuration; ionization occurs by single-photon ionization, which is a soft and universal method applicable to virtually all organic molecules and aggregates; and mass analysis occurs by time-of-flight mass spectrometry, which has a nearly constant sensitivity across a broad mass range. These factors suggest that L2MS should analyze asphaltenes wit...