Effect of different lipid extraction methods on δ¹³C of lipid and lipid-free fractions of fish and different fish feeds

Abstract

For many ecological applications of stable carbon isotope techniques, it is necessary to separate the lipid and lipid-free fractions. The effect of different lipid extraction methods on the isotope signature of the remaining lipid-free matter as well as the lipid fraction was tested. A hot extraction form of the Soxhlet method using petrol-ether was compared with two liquid-liquid extraction methods for lipid determination described by Bligh and Dyer and Smedes. Solid samples of fish and different natural food items were subjected to extraction and the carbon isotope ratios in lipid and lipid-free matter determined by IRMS. All methods were suitable for lipid extraction from all samples analysed here and did not cause biologically relevant differences (> 1%) in carbon isotopic ratios, except the Bligh and Dyer extraction method using chloroform which caused systematic errors for delta13C when applied to diatoms.

Stable isotopes and trace elements as indicators of diet and habitat use in cetaceans: predicting errors related to preservation, lipid extraction, and lipid normalization

“…Lipid extraction caused an enrichment of δ 13 C values that was within the range of those from a variety of tissues and aquatic organisms. The magnitude of 13 C depletion varied among studies, primarily as a result of fat content, with lipid-rich tissues generally showing the largest depletions (Todd et al 1997, Pinnegar & Polunin 1999, Kurle & Worthy 2002, Schlechtriem et al 2003, Sotiropoulos et al 2004, Kiljunen et al 2006, Murry et al 2006, Sweeting et al 2006, Bodin et al 2007, Ricca et al 2007, Smyntek et al 2007, Barrow et al 2008, Mintenbeck et al 2008. In these studies, the effects of lipid extraction on δ 15 N values were more variable but were generally toward a mean, not always significant, enrichment of ≤1.6 ‰, a range that encompassed values obtained in the present study.…”

“…The use of less-polar solvents for lipid extraction was proposed as a means to reduce undesired leaching of nitrogenous compounds (e.g. Degens et al 1968, Schlechtriem et al 2003, Sotiropoulos et al 2004, Søreide et al 2006, Sweeting et al 2006), but was recently proven to be inefficient in reaching this goal .…”

The Phytolith14C Puzzle: A Tale of Background Determinations and Accuracy Tests

“…However, chemical phytolith extractions for 14 C measurements should always avoid any source of extraneous carbon (Piperno 2006(Piperno , 2009. In a different study, lipid extraction methods for diatom samples (silicate with similar structure to opal phytoliths) were evaluated with and without the use of solvents (Schlechtriem et al 2003). Their findings suggested that carbon stable isotopic signatures were somehow altered when chloroform was used during extraction, which we speculate may have been due to strong adsorption of the solvent on silica and incomplete subsequent removal.…”

The place of diatoms in the biofuels industry

“…Although cell wall components are solid, the overall structure is composed of discrete siliceous substructures that are joined together by organic molecules. The individual parts are relatively easily disrupted, and organic solvents readily extract lipid and pigments [137,138]. The diatom cell wall is actually easier to break open than the wall of some green algae; for example, RNA isolation procedures for diatoms involve simply vortexing cells in the presence of Tri Reagent [139], whereas for some green algae frozen cells have to be ground in a mortar and pestle prior to extraction.…”