J. Rontani, L. Smik, S. Belt
Apr 21, 2020
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Rapid communications in mass spectrometry : RCM
Abstract
RATIONALE Some highly branched isoprenoid (HBI) alkenes are commonly used as proxies for palaeoceanographic reconstructions. However, there is a need to identify compounds that are sufficiently stable and abundant to be used as tracers of HBI oxidation in sediments. 2,6,10,14-tetramethyl-7-(3-methylpent-4-enyl)-pentadec-5(Z/E)-en-4-ols resulting from 2,6,10,14-tetramethyl-7-(3-methylpent-4-enyl)-pentadec-5-ene appear to be useful for this purpose. METHODS Comparison of EIMS mass spectra and retention times with those of standards allowed formal identification of autoxidation products of 2,6,10,14-tetramethyl-7-(3-methylpent-4-enyl)-pentadec-5-ene. EIMS fragmentations of TMS ethers of the main oxidation products (2,6,10,14-tetramethyl-7-(3-methylpent-4-enyl)-pentadec-5(Z/E)-en-4-ols) were deduced by GC/EI-MS, low energy CID-MS/MS and accurate mass measurements. These compounds were then quantified in Arctic sediment samples in MS/MS MRM mode using transitions based on the main fragmentation pathways elucidated. RESULTS 2,6,10,14-Tetramethyl-7-(3-methylpent-4-enyl)-pentadec-5(Z/E)-en-4-ols were identified after autoxidation of the HBI alkene 2,6,10,14-tetramethyl-7-(3-methylpent-4-enyl)-pentadec-5-ene. Low energy CID-MS/MS analyses and accurate mass measurement allowed the bEIMS fragmentation pathways of their TMS derivatives to be elucidated. Some specific fragment ions and chromatographic retention times were also useful for further characterization. As an application of some of the described fragmentations, TMS derivatives of these metabolites were characterized and quantified in MRM mode in Arctic sediments. CONCLUSIONS Due to: (i) their production in high proportion during autoxidation of their parent HBI diene, (ii) their apparent stability in sediments, and (iii) their specific EIMS fragmentations, (Z and E) 2,6,10,14-tetramethyl-7-(3-methylpent-4-enyl)-pentadec-5-en-4-ol TMS derivatives appeared to be useful tracers of HBI autoxidation in sediments.