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United States Department of Agriculture

Agricultural Research Service

Title: Improved GC/MS method for quantitation of n-Alkanes in plant and fecal material

Authors
item Smith, Lori
item Strickland, James

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 2, 2007
Publication Date: August 15, 2007
Citation: Smith, L.L., Strickland, J.R. 2007. Improved GC/MS method for quantitation of n-Alkanes in plant and fecal material. Journal of Agricultural and Food Chemistry. 55:7301-7307.

Interpretive Summary: Estimation of forage intake and dietary composition of grazing animals has been successfully accomplished using the naturally occurring “fingerprint” of n-alkanes present in the cuticular waxes of forage species. Comparing the n-alkane patterns in dietary plant materials to that acquired from the feces of an animal that has consumed the plants can be used to determine component species in the diet. However, current analytical methods are logistically difficult resulting in long sample analysis times and difficulty in maintaining precision. A gas chromatography-mass spectrometry method for the quantification of n-alkanes in forage and fecal samples has been developed. Automated solid-liquid extraction using elevated temperature and pressure minimized extraction time to 30 minutes per sample as compared to more than 24 hours for traditional gas chromatography – flame ionization detection methods that use saponification and liquid-liquid extraction. Extraction solvent requirements were also minimized to 10 mL per sample. The reported gas chromatography-mass spectrometry method permits simple, rapid and precise quantification of n-alkanes in plant and fecal material and reduces reagent and labor requirements over previously available methods.

Technical Abstract: A gas chromatography-mass spectrometry (GC/MS) method for the quantitation of n-alkanes (carbon backbones ranging from 21 to 36 carbon atoms) in forage and fecal samples has been developed. Automated solid-liquid extraction using elevated temperature and pressure minimized extraction time to 30 minutes per sample as compared to more than 24 hours for traditional GC – flame ionization detection methods that use saponification and liquid-liquid extraction. Extraction solvent requirements were also minimized to 10 mL per sample. Under optimal conditions, complete method recoveries, including extraction efficiency, were greater than 91%. The linear dynamic range was 5 to 100 nmol injected onto the column, with limits of quantitation less than or equal to 2.5 nmol. Intra-assay coefficients of variation for the analysis of annual ryegrass (Lolium rigidum), subterranean clover (Trifolium subterranean) and bovine feces ranged from 0.1% - 12.9%, where lower concentrations of n-alkane produced a higher degree of imprecision. The reported GC/MS method permits simple, rapid and precise quantitation of n-alkanes in plant and fecal material and reduces reagent and labor requirements.

Last Modified: 7/25/2014
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