EIMS Fragmentation and MRM quantification of bacterial metabolites of the sea ice biomarker proxy IP25in Arctic sediments.

RATIONALE: 3,9,13-trimethyl-6-(1,5-dimethylhexyl)-tetradecan-1,2-diol and 2,8,12-trimethyl-5-(1,5-dimethylhexyl)-tridecanoic acid appear to be produced during the bacterial metabolism of IP25, a highly branched isoprenoid lipid often employed for past Arctic sea ice reconstruction. Characterization and quantification of these metabolites in sediments are essential to determine if bacterial degradation may exert a significant influence on IP25-based palaeo sea ice reconstructions. METHODS: EIMS fragmentation pathways of 3,9,13-trimethyl-6-(1,5-dimethylhexyl)-tetradecan-1,2-diol and 2,8,12-trimethyl-5-(1,5-dimethylhexyl)-tridecanoic acid TMS derivatives were investigated. These pathways were deduced by: (i) low energy CID-GC/MS/MS, (ii) accurate mass measurement and (iii) deuterium labelling. RESULTS: CID-MS/MS analyses, accurate mass measurement and deuterium labelling experiments enabled us to elucidate the EIMS fragmentations of 3,9,13-trimethyl-6-(1,5-dimethylhexyl)-tetradecan-1,2-diol and 2,8,12-trimethyl-5-(1,5-dimethylhexyl)-tridecanoic acid TMS derivatives. Some specific fragment ions useful in addition to chromatographic retention times for further characterization could be identified. As an application of some of the described fragmentations, the TMS derivatives of these metabolites were characterized and quantified in MRM mode in different Arctic sediments. CONCLUSIONS: EIMS fragmentations of 3,9,13-trimethyl-6-(1,5-dimethylhexyl)-tetradecan-1,2-diol and 2,8,12-trimethyl-5-(1,5-dimethylhexyl)-tridecanoic acid TMS derivatives exhibit specific fragment ions, which appear to be very useful for the quantification of these bacterial metabolites of the palaeo tracer IP25in sediments.