Characterization of homologous gasoline additive markers by DART ionization coupled with high-resolution tandem mass spectrometry

Less-volatile gasoline additives provide persistent molecular markers that can complement conventional hydrocarbon-based analysis of gasoline and gasoline residues. However, structural assignments of these compounds remain unresolved. In this study, high-resolution direct analysis in real time mass spectrometry (DART-MS), Kendrick mass defect (KMD) analysis, and higher-energy collisional dissociation tandem mass spectrometry (HCD-MS 2 ) were used to characterize additive-related homologous compounds in three commercial gasoline brands. KMD analysis revealed extensive C₄H₈- and C₃H₆O-based homologous complexity, from which five representative series were selected for detailed characterization. Four C₄H₈-spaced series were distinguished by their elemental compositions and MS 2 fragmentation behaviors and assigned to different polyisobutylene-derived structural classes, including phenolic Mannich-base and amine-containing families. A fifth series, separated by 58.0419 Da, exhibited compositions and fragmentation consistent with a poly(propylene oxide)-based monoamine family. The results demonstrate that a common homolog spacing does not necessarily indicate a common additive class and substantially refine structural interpretations based on nominal-mass patterns alone. Numerous additional homologous relationships observed in the KMD plots indicate that the five characterized series represent only a subset of the oligomeric complexity present in gasoline. Structural characterization of these less-volatile markers provides a strong justification for developing more selective extraction, enrichment, and targeted mass spectrometric methods for gasoline residue analysis.