Author
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Adlof, Richard |
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Submitted to: Journal of Chromatography A
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 8/29/2002 Publication Date: N/A Citation: N/A Interpretive Summary: While some dietary fats have been related to coronary heart disease, cholesterol levels, and other health problems; their isolation in quantities large enough for use as standards in the health and nutrition industry has been difficult. A method, the technical term of which is silver ion chromatography (Ag-HPLC), is extremely useful for analyzing dietary fats. In this work, that method was modified to analyze and purify specific kinds of dietary fats called conjugated linoleic acids (CLA). Very high purities (>96%) were achieved with small amounts of sample. The isolated materials can now be supplied in quantities large enough to serve as standards for both industry and consumer groups in the screening and characterization of dietary fat samples and other fat formulations. Technical Abstract: Silver ion HPLC (Ag-HPLC) has been utilized to separate a variety of unsaturated fatty acid methyl esters (FAME) by configuration, location, or number of olefinic or acetylenic bonds. Most separations have been in the analytical range, with sample sizes of 0.5 to 150 µg. The application of Chrompack's ChromSpher Lipids© columns (Cat. No. 28313; 4.6mm I.D. x 250mm stainless steel; 5 micron particle size; silver ion impregnated; Chrompack International, Middelburg, The Netherlands) to the semi-preparative separation of FAME samples has been less-studied. A single Ag-HPLC column and an isocratic solvent system of acetonitrile (ACN) in hexane was used to study the relationships between sample size, solvent composition and FAME retentions. Two columns connected in series were utilized to fractionate milligram-sizes samples of a mixture of two deuterium-labeled isomers of conjugated linoleic acid (CLA; 9-cis,11-trans- and 9-trans, 11-trans-octadecadienoic acid-17,17,18,18-d4). Resolution of the two isomers, which decreased with increasing weights of sample injected, was maintained by decreasing the percentage of ACN in the isocratic hexane/ACN solvent system. By careful adjustment of solvent composition, "baseline" resolution (>95%) could be maintained for injected samples of 10-15 mg, with optimum speed and resolution achieved with a 10 mg sample. Final chemical purities of the isolated FAME was >96% by GC. |
