Peaks eluting at 28 min were assigned as isomers of highly
branched isoprenoid (HBI) thiolanes, presumably derived from
the sulfurization of diatom HBI lipids. Mass spectra do not decisively
establish whether the sulfur functionality is a thiolane or
thiane, although the spectra share all major fragment ions with
published HBI thiolane spectra (Kohnen et al., 1991). A single double
bond in the molecule is indicated by the M+ ion at m/z 380. HBI
thiolanes have been observed in Cariaco Basin sediments (Werne
et al., 2000) and were isolated for conventional sulfur isotopic analysis
(Werne et al., 2008). Similar to the C20 isoprenoid thiophenes,
identical HBI thiolanes were observed in both the apolar (F1) and
polar (F3) fractions, with a higher abundance in F3 (5–63 nmol/g
OC) than in F1 (2–18 nmol/g OC).