Chromatography of the isomeric methylene-interrupted methyl cis, cis-octadecadienoates

Prediction of gas chromatographic retention of polyunsaturated fatty acid methyl esters

Multivariate regression models were applied to predict retention indices as equivalent chain lengths (ECL) for methylene-interrupted polyunsaturated fatty acids. Simple molecular descriptors, the chain length, the number of double bonds and the position of the double bond system, were used as predictors. The merits of different variable combinations were evaluated. For general models, it was necessary to include the distance from the double bond system to both the carbonyl group (Delta-position) and the methyl end of the fatty acid (n-position). The best accuracy was found for models including higher order terms of Delta and n. For models restricted to n-3 and n-6 isomers, it was not necessary to include the n-position among the variables. The highest residuals for the most accurate models were below 0.06 ECL units, and root mean square error of prediction was below 0.030. The ECL data was achieved by three different temperature programs on a cyanopropyl column.

Mass spectra of the picolinyl esters of isomeric mono- and dienoic fatty acids

The picolinyl ester derivatives of the complete series of isomeric octadecenoates, methylene-interrupted octadecadienoates, and of octadec-9-ynoate have been subjected to gas chromatography-mass spectrometry. A fused-silica capillary column, coated with a cross-linked methyl silicone, was used for the separation. Electron impact spectra were determined at 70 eV. Earlier observations with a limited series of model compounds were confirmed, and it was shown that the picolinyl ester derivatives were of almost universal value in the location of double bonds in such isomers. Difficulties of interpretation arose mainly when the double bonds were close to the carboxyl group.

Fractionation of fish oil fatty acid methyl esters by means of argentation and reversed-phase high-performance liquid chromatography, and its utility in total fatty acid analysis

The utility of reversed-phase and argentation high-performance liquid chromatography (HPLC) as pre-fractionation methods in fatty acid analysis is discussed. Both HPLC modes were applied to cod liver oil fatty acid methyl esters. Apart from positional isomers, the fractions obtained by reversed-phase HPLC were analysed by gas-liquid chromatography and appear to be free of the usually occurring "critical pairs". The mechanism of retention of the fatty acid methyl esters on low-loaded silver nitrate-impregnated silicas is discussed. It is shown that argentation HPLC is a rapid semi-preparative pre-fractionation method for highly unsaturated fatty esters with 3-6 double bonds.

Fatty acids. VII. The gas-liquid chromatographic properties of all dimethylene interrupted methyl cis,cis-octadecadienoates

The gas-liquid chromatographic behaviour of all the dimethylene interrupted methyl cis,cis-octadecadienoates was studied on polar (Carbowax 20M, FFAP, DEGA, DEGS and Silar 10C), semi-polar (XE-60) and non-polar (SE-30, OV-101 and Apiezon L) stationary phases. The equivalent chain length of each isomer is recorded; the possibility of separation and the retention pattern of these isomers are discussed.

Fatty acids. IV. Synthesis of all the dimethylene-interrupted methyl octadecadiynoates and a study of their gas-liquid chromatographic properties

All the dimethylene-interrupted methyl octadecadiynoates have been synthesised and the gas-liquid chromatographic behaviour of these isomers was studied on polar [Carbowax 20M, FFAP, DEGA, DEGS and Silar 10C (recently renamed as Apolar 10C)], semi-polar (XE-60) and non-polar (SE-30, OV-101 and Apiezon L) stationary phases. The possibility of identification and separation of these isomers is discussed. The delta3a,7a isomer was found to decompose on most polar phases and the delta2a,6a isomer could not be eluted from the Carbowax 20M phase.

Fatty acids. II. The synthesis and gas-liquid chromatographic behaviour of five trimethylene-interrupted C18-diunsaturated fatty acids

Five trimethylene-interrupted methyl octadecadiynoates, C18 delta-2a,-7a; delta-3a,-8a; delta-4a,-9a; delta-5a,-10a and delta-6a,-11a, and the corresponding cis,cis-octadecadienoates were synthesized, and their gas-liquid chromatographic properties were studied on Apiezon L, diethylene glycol succinate polyester and Silac 10C stationary phases. The equivalent chain lengths of these esters have been determined, and the separation of mixtures and the prediction of gas chromatographic behaviour of these isomers are discussed.