Chemical and GC-MS characterization of marine particulate lipids

The lipid fraction of particulate organic matter in seawater was analyzed by gravimetry, liquid chromatography, gas chromatography (GS), and gas chromatography—mass spectrometry (GS—MS). Gravimetric concentrations in the Gulf of Mexico were in the range of 12–70 μg 1^?1 for near-surface samples and 9–52 μg 1^?1 for near-bottom samples. The lipids accounted for ～20% of the particulate organic carbon. Particulate lipids were found to be a much more complex mixture of organic compounds than the dissolved lipids and their composition was much more variable. The majority of the extracted weight was recovered in the polar liquid chromatography fraction (49–85%). The major components of the analyzable particulate lipids were similar to those of the dissolved lipids, namely, n-alkanes, pristane, phytane, and methyl, ethyl and propyl fatty acid esters. Often olefins, alkylated benzenes, quinones, and the unresolved GC area contribute a substantial part to the total particulate lipids. Minor components included ketones, phenols, indanes, acids, benzoates, aromatics and possibly derivatives of inositol, dioxane, and pyran. The low concentrations observed confirm that the area is relatively pristine though some evidence for chronic low-level oil pollution was present. Seasonal, diurnal, vertical and areal variations were observed in the particulate lipids. Lipid concentrations not only decreased with depth but they were also a decreased percentage of the organic carbon present. This may indicate the loss of labile carbon with depth due to reworking in the euphotic zone. Anoxic conditions appeared to promote the preservation of lipid materials in the particulate phase, n-Alkanes and fatty acid esters were common to both the particulate and dissolved phases and had similar distributions.