The biogeochemistry of sterols in Trinity Bay, Newfoundland, and a new method (thin layer chromatography-pyrolysis-gas chromatography-mass spectrometry) for their analysis

Hudson, Edward D. (1999) The biogeochemistry of sterols in Trinity Bay, Newfoundland, and a new method (thin layer chromatography-pyrolysis-gas chromatography-mass spectrometry) for their analysis. Masters thesis, Memorial University of Newfoundland.

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Abstract

In the context of a multidisciplinary study to determine current and past ecosystem health, sterols were analyzed in plankton, settling particles and sediments from Trinity Bay, Newfoundland by saponification, derivatization to their TMS ethers and GC and GC/MS. Plankton net tow samples and settling particles contained C₂₇ and C₂₈ sterols typical of marine plankton. However, higher plant C₂₈ and C₂₉ sterols were prominent in sediments from both in-shore and off-shore sites, indicating an appreciable terrestrial contribution to sedimentary organic carbon and either degradation or effective recycling of marine sterols. No decrease in total or individual sterols was observed down the cores, suggesting good overall preservation. The fecal sterol coprostanol was not detected in offshore sediments, net tow material or settling particles, and was present only at low levels in certain in-shore sedimentary horizons. This suggests that sewage discharges in rural Newfoundland are being efficiently degraded or dispersed. -- Total free sterols in the samples were determined by Iatroscan TLC-FTD on Chromarods, a widely-used method which effectively separates and quantifies lipid classes but provides no further information on the species in each class. Thus, a new method (TLC- Pyrolysis-GC/MS) was developed in which lipid bands are desorbed directly from the silica Chromarod surface into a GC/MS for analysis. Twelve lipid classes were either desorbed without further treatment, converted to trimethylsilyl derivatives on the Chromarod, or analyzed following in situ thermochemolysis with tetramethylammonium hydroxide. The method's utility was demonstrated with lipids from settling particles, especially where TLC bands contained more than one lipid class (wax/steryl esters, acetone-mobile polar lipids). Wax esters up to C₄₂ were detected, with alkyl and acyl distributions consistent with a zooplankton source. The wax ester/steryl ester band contained no more than 8% steryl esters, suggesting that their contribution to this band is minimal but that their contribution to total sterols may be significant. The free sterol carbon number distribution in settling particles as determined by TLC-Pyrolysis-GC/MS matched that as determined by individual molecular species analysis (predominantly C₂₇). By extending the scope of Iatroscan TLC-FID, the new method should have applications in many fields besides marine environmental studies viz. food science, biomedical science and petroleum analysis.

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