Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 2/1/1997
Publication Date: N/A
Technical Abstract: The retention characteristics of fatty acid methyl esters and triacylglycerols on silver ion chromatographic columns are influenced not only by the number and/or configuration of the double bonds in the molecules, but also by the number of carbon atoms in the fatty acid chains. A mixture of 16:0 monoacyl-, diacyl- and triacylglycerols was analyzed by silver ion HPLC (Chrompack Chromspher 5 Lipids (TM)). Tripalmitoylglycerol eluted first (12 min), then the monoacetate triacylglycerols, the diacetate triacylglycerols and triacetin (70 min). Silver ion chromatographic separations are generally attributed to the interaction of silver ions with carbon-carbon double bond pi-electrons, a condition absent in the 16:0 series. (Saturated fatty acids are assumed to be non-contributors to fatty acid methyl ester and triacylglycerol retention.) The phenomenon of increasing retention with shorter fatty acid chain length was observed in the separation of a 6- to 18-carbon fatty acid methyl ester mixture and of an 8- to 54-carbon triacylglycerol mixture. Substrate interactions with the more polar silica backbone of the AG-HPLC column packing (some 30% of the hydroxy groups remain) are believed to contribute to the observed differences in retention. Thus, normal-phase effects must certainly be included in attempts to predict the elution orders of FAME and TAG containing FA of widely-differing chain lengths.