Structural identification and mass spectral interpretation of C3n highly branched alkanes in sediment and aquatic extracts and evidence for their anthropogenic origin

The structures of two distinctive series of C3n highly branched alkanes (HBAs), previously detected in sedimentary and aquatic extracts, were identified as polypropylene (PP) oligomers with different end groups, using gas chromatography (GC) and mass spectrometry (MS) correlation with diastereoisomeric mixtures of authentic C15 and C18 standards. A C15 member of the earlier eluting series was assigned as 2,4,6,8-tetramethylundecane and a C15 member of the later eluting series as 4,6,8-trimethyldodecane. The C3n HBA GC-MS profiles of extracts from a typical PP GC sample vial lid were also shown to closely match those previously detected in sediment and water extracts, providing convincing evidence that the purported environmental occurrences are a result of PP contamination. Both C3n series correspond to the first eluting diastereoisomer of the respective standards, also consistent with an industrial isotactic PP source. Mass spectra of all five standards are presented to help assignment of new polymethyl alkanes.