R.G. Ackman

A proposed basis for the systematic identification of unsaturated fatty acid esters through gas-liquid chromatography on polyester substrates.

Abstract Systematic separation factors may be established among various unsaturated fatty acid methyl esters analysed by gas—liquid chromatography on polyester substrates. These are apparently dependent on differences in the magnitude of the carboxyl end chain and end carbon chain parts of the fatty acid chain.

Flame ionization detector response for the carbonyl carbon atom in the carboxyl group of fatty acids and esters

Abstract The response of the carboxyl group in free fatty acids, although markedly less than the equivalent response for a methylene carbon atom in the lower fatty acids, approaches this value in acids with six or more carbon atoms. The relative responses for these higher fatty acids are then proportional to the relative weight percent carbon content on a weight basis. In esters a complex molar response pattern is evident, apparently due to scission of the ester linkage with the lower acids to give an alcohol with a response of half a methylene carbon atom, and an acid or carboxyl group fragment with little or no response. In the methyl esters of saturated fatty acids with nine or more carbon atoms the net loss in response falls to the equivalent of one methylene carbon atom and the relative response is the proportional to the relative weight percent carbon content based on the number of carbon atoms in the fatty acid chain. Formate esters apparently give slightly higher responses than other esters of the same net number of carbon atoms. This suggests that the difference observed in the various esters may be due in the cases of those esters with higher responses to formation of a hydrocarbon in lieu of an alcohol during the initial scission of the ester group linkages. Alternatively in the esters other than formates the carboxyl group may give an increasing response as the fatty acid chain length increases.

Calculation of ECL values in the gas-liquid chromatography of multiple-branched fatty acids.

Abstract The generation from literature data of fractional chain length (FCL) values for single methyl substituents in esters of isomeric monomethyl-branched fatty acids is described. The addition of FCL values to the basic chain length gives good agreement between calculated and experimental equivalent chain length (ECL) values for esters of several multiple-branched fatty acids of known structure and is used to verify the structure tentatively assigned to another multiple-branched fatty acid ester.

Direct determination of elemental phosphorous by gas—liquid chromatography

Abstract A rapid and sensitive method for the analysis of elemental phosphorous is described. Phosphorous is extracted into a suitable organic solvent, isolated by gas—liquid chromatography, and measured in a highly sensitive and specific flame photometric detector. Phosphorus levels as low as 10−12 g (corresponding to sensitivities of about 2 parts in 1012 in concentrated extracts) can be measured in a few minutes. Application of this method to the analysis of water, mud and biological samples is described.

Additivity of retention data for ethylenic functions in aliphatic fatty acids : II. Polar liquid phases

Abstract The elution order of two mono- cis ,di- trans -isomers of the methyl esters of 9,12,15-octadecatriethylenic acids for two polar liquid phases is indicated by the equivalent chain lengths calculated from fractional chain length values determined for methyl esters of monoethylenic C 18 acids with Δ 9 , Δ 12 and Δ 15 ethylenic unsaturation. The application of appropriate diethylenic coupling corrections is demonstrated. All eight octadecatriethylenic isomers, and related mono- and diethylenic isomers, were examined on the polar liquid phases butanediol succinate and SILAR-5CP.

Additivity of retention data for ethylenic functions in aliphatic fatty acids : I. Apiezon L

Abstract The equivalent chain lengths of the methyl esters of eight isomeric 9,12,15-octadecatriethylenic acids for Apiezon L are compared with values calculated from fractional chain length values determined for methyl esters of monoethylenic C 16 acids with Δ 9 , Δ 12 and Δ 15 unsaturation. The necessity of further correction based on the appropriate two diethylenic couplings is shown, confirming published concepts, and the desirability of “particular” corrections ( i.e. based on the same column and same temperature) is discussed.

Temperature effects in the calculation of equivalent chain length values for multiple-branched fatty acid esters and ketones on polar and non-polar open tubular columns

Abstract Accurate equivalent chain length (ECL) values were determined for methyl esters of a variety of methyl-branched fatty acids. Only those with methyl substituents in the C2, C3 and ω1 (iso) position were particularly affected by changes in operating temperature on one type of polar open-tubular column, or were otherwise significantly affected by the polarity of different polyester columns. In other positional isomers ECL values dropped only very slightly with increasing temperature. On Apiezon L columns only the C2 isomer was significantly affected. Adjustments for temperature effects improved accuracy in calculating ECL values for multiple methyl-branched fatty acids and some corresponding ketones.

Phytanic acid l-menthyl esters : Gas-Liquid chromatographic separation of diastereoisomers

Abstract l -Menthyl esters of a naturally occurring (marine) phytanic acid, of an all-synthetic phytanic acid, and of a phytanic acid known to be of 3 d , 7 d , 11 d configuration were compared by GLC. As in the pristanates, the ldd and ddd diastereoisomers were the farthest apart, but in the marine phytanate only two diastereoisomers, presumably ldd and ddd , could be detected. A general guideline is proposed that in the GLC of l -menthyl esters of isoprenoid fatty acids with 2-methyl and 3-methyl substituents the ldd and ddd diastereoisomers will be, respectively, the first and last to elute.

Prediction of retention times in the GLC of diastereoisomers of methyl-branched fatty acids

Abstract Examination of the order of elution of certain diastereoisomers of a number of multiple methyl-branched fatty acid esters from polar GLC columns suggests a general guide based on molecular rotations. Thus diastereoisomers having molecular rotations of the highest magnitude should elute first followed by others in order by decreasing order of magnitude of molecular rotation. In lieu of experimental molecular rotations which are lacking for most diastereoisomers an attempt has been made to correlate additive molecular rotations Σ[ M ] D with GLC data. It is believed that some discrepancies from predicted order of elution are due to complex interactions among asymmetric centers which modify one or more of the [ M ] D values assigned on the basis of data for fatty acids with a single methyl branch.

KETOACID POLYMERS AS GAS-LIQUID CHROMATOGRAPHY SUBSTRATES.

Abstract A low molecular weight ketoacid polymer prepared from the cadmium salt of sebacic acid has been demonstrated to be a satisfactory substrate for the separation of the volatile fatty acids. With the addition of formic acid vapor to the carrier gas quantitative results may be obtained employing conventional supports. With a teflon-impregnated support the use of formic acid vapor, while probably helpful at very low concentrations of acids, is not strictly necessary . Separations of certain other materials and the thermal stability of the polymer are discussed. An instance of desensitization of a flame ionization detector has been noted.