Structural identification and mass spectral interpretation of C_3nhighlybranched alkanes in sediment and aquatic extracts and evidencefor their anthropogenic origin

摘要

The structures of two distinctive series of C_(3n)highly branched alkanes (HBAs), previously detected in sed-imentary and aquatic extracts, were identified as polypropylene (PP) oligomers with different end groups,using gas chromatography (GC) and mass spectrometry (MS) correlation with diastereoisomeric mixturesof authentic C_(15)andC_(18)standards. AC_(15)member of the earlier eluting series was assigned as 2,4,6,8-tetramethylundecane and a C_(15)member of the later eluting series as 4,6,8-trimethyldodecane. TheC_(3n)HBA GC-MS profiles of extracts from a typical PP GC sample vial lid were also shown to closely matchthose previously detected in sediment and water extracts, providing convincing evidence that the pur-ported environmental occurrences are a result of PP contamination. Both C_(3n)series correspond to the firsteluting 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.