Lipids of aquatic sediments, recent and ancient

Abstract

Computerized gas chromatography - mass spectrometry (g.c.-m.s.) is now an essential tool in the analysis of the complex mixtures of lipids (geolipids) encountered in aquatic sediments, both Recent (less than 1 Ma (10 ⁶ years) old) and ancient. Most geolipid studies have been performed in the e.i. mode at low resolution but the techniques now being applied include c.i. and h.r.m.s. The large quantities of data acquired from capillary g.c.-m.s. runs necessitate fast data acquisition and data processing, including the capability for the automatic selection and refinement of key spectra. Even so, the chemist is faced with the identification and/or recognition of at least several hundred good quality spectra from a single run. Fast routine search procedures are useful here, especially for known compounds, while classification routines based on established rules for manual interpretation can be of assistance even with novel compounds. Examples from recent studies (at Bristol) of contemporary, Recent and ancient sediments, are presented. Geolipids show abundance patterns of homologous series which, while related to those of known organisms, display many novel features, including extensive carbon number ranges and stereospecific distributions. Additionally, certain carbon skeleton types, commonly thought to be rare as natural products, are major components of geolipid fractions, presumably reflecting the composite inputs and early microbial diagenetic activity.