Improved methods for the isolation and study of the C₁₈, C₂₀ and C₂₂ monoethylenic fatty acid isomers of biological samples: Hg adducts, HPLC, AgNO₃‐TLC/FID, and ozonolysis

Abstract

The monoethylenic isomers of C18, C20 and C22 chain lengths of the depot fat of a nonhominid primate (cynomolgus monkeys,Macaca fascicularis), fed a partially hydrogenated herring oil (IV=76.0) for 30 months, were examined by 2 different approaches. The first isolation method involved preparative gas liquid chromatography and argentation thin layer chromatography (TLC). The second sequence involved a chain-length fractionation system based on the TLC of the methoxy-bromomercuri quence involved a chain-length fractionation system based on the TLC of the methoxy-bromomercuri adducts of the total methyl esters to isolate groups of acids of common degrees of unsaturation, and then high performance liquid chromatography on a reverse-phase column. In both cases, the monoethylenic isomer distribution was determined by ozonolysis in BF3/MeOH. Comparable results were obtained with the 2 methods. The second approach is recommended for small biological samples, especially for those containing a relatively high proportion of di- and other polyethylenic isomers which might interfere.

Determination ofcis andtrans‐Octadecenoic acids in margarines by gas liquid chromatography‐infrared spectrophotometry

“…Margarines and other dietary fats made from partially hydrogenated vegetable oils contain substantial amounts of trans-and cis-octadecenoic acids (1)(2)(3)(4)(5). Accurate determination of the total c/s and transoctadecenoic isomers is a difficult task, as there is no one-step, simple procedure for the separation of the trans-octadecenoic acids (18:lt) as a group from that of the c/s (18:1 c) isomers (6)(7)(8)(9). Direct analysis by gas liquid chromatography (GLC) on the very polar cyanosilicone liquid phases has been recommended for cis-trans isomeric separations (10)(11)(12)(13).…”

Hydrogenation of a menhaden oil: II. Formation and evolution of the C20 dienoic and trienoic fatty acids as a function of the degree of hydrogenation

“…From the other two fragments (diester and acetate ester), the position of the ethylenic bond closest to the carboxyl group can be determined. The GLC analyses of the diester fragments were also corrected for both the extraction procedure and the flame ionization response factor (35). However, under the GLC conditions used, it was not practical to correct the acetate ester data for the FID response factor (36) due to a partial decomposition of these compounds with higher molecular weights during the GLC analysis.…”

Analysis of conjugated and trans fatty acids after derivatization (in French)

“…Aussi, la position et la géométrie de la liaison éthylénique dans chaque monoène représentent celles de la molécule de départ. Les monoènes sont ensuite fractionnés par chromatographie liquide haute performance et chromatographie sur couche mince impré-gnée au nitrate d'argent [54] et la géométrie de chaque liaison éthylénique est déterminée par CPG-IRTF. La position de la liaison éthylénique est déterminée par CPG-SM après transformation en dérivés DMOX [41].…”