Chemical and GC-MS characterization of marine dissolved lipids

Abstract

The chloroform-extractable ‘lipid’ fraction of dissolved organic matter in seawater was analyzed by gravimetry, liquid chromatography, gas chromatography (GC), and gas chromatography—mass spectrometry (GC—MS). Gravimetric concentrations of dissolved lipids in the Gulf of Mexico were in the range of 60–160 μg 1 −1 in near-surface waters and 61–116 μg 1 −1 in near bottom waters and accounted for ∼4% of the dissolved organic carbon. Over a 12-h sampling period and a 5-d sampling period extensive variability in dissolved lipid quantity and quality were observed. The major percentage of extractable weight was collected in the polar liquid chromatographic fraction (55–95%). Gas chromatographic concentrations of the aliphatic fractions were in the range of 0.014-0.187 μg 1 −1. Concentrations derived from gas chromatography were consistently lower than gravimetrically-derived concentrations. A number of compounds were tentatively identified by a combination of GC, GC—MS, and authentic standards. The major components of the analyzable dissolved lipids were n-alkanes (C 16C 32), pristane, phytane, methyl, ethyl and propyl esters of fatty acids. Minor components included olefins and cycloalkanes, aromatics, short-chained acids, and possibly a lactone and an alcohol. All concentrations and compounds were indicative of a fairly pristine environment. The n-alkane distribution appears to be the result of marine and terrestrial inputs superimposed on a chronic low-level background of oil pollution. It is suggested that the fatty acid esters and other fragment molecules are the résult of the degradation of humic substances. A number of potential indicators of source were isolated.