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The first reported use of gas chromatography in the separation of fatty acids was by James and Martin' at the Oxford Congress of Analytical Chemistry in 1952. They described the separation of acids from formic through dodecanoic on silicone-stearic acid columns, and detected the eluted acids by titration.In 1953, Cropper and Heywood2 extended the gas chromatographic separation to the methyl esters of the even-numbered fatty acids from Clz to Czz. They used Dow Corning high vacuum silicone grease on Celite columns and employed a platinum-wire thermal conductivity cell as the detector. The efficiency of their columns allowed only a separation based on differences in chain length, and methyl oleate and methyl stearate were not separated.A major contribution to the field of fatty ester separation and to gas chromatography in general was made with the invention of the gas density balance detector by Martin and James3 in 1953. The high sensitivity of this ingenious device was largely responsible for improvements in the separation of the methyl esters of the fatty acids containing from 8 to 26 carbon atoms by James and Martin,4e6 James and Wheatley," and Beerthuis and Keppler? The high sensitivity allowed the use of extremely small samples that, in turn, reduced the band spreading that results from overloaded columns. These. workers found Apiezon M or Apiezon L vacuum greases on Celite to be the preferred partition medium and reported the successful separation of saturated and monounsaturated methyl esters of the same carbon chain length, as well as some branched chain fatty esters prepared from natural lipid sources. However, methyl linoleate and methyl linolenate were not separated. ' and Lipskylo have reported further refinements in the separation of high molecular weight fatty esters using Apiezon greases. These refinements resulted from improved technique in the preparation of the coated Celite and in the packing of columns. Lipskylo found that improvements could be made in the separation by precise control of the temperature of the detector, in this case a high-sensitivity thermal conductivity cell, through use of proportional controllers. Using Apiezon L and temperatures in the range of 200 to 250' C., Lipsky and Insull and James obtained excellent separations of methyl stearate, methyl oleate, and methyl linoleate. In no case, however, was it possible to resolve methyl linoleate and methyl linolenate on Apiezon L. TABLE 1 summarizes data taken from the best curves published by the above authors and gives the efficiencies of the separations obtained. Theoretical plate calculations are based on the methyl stearate peak and the percentage impurities were calculated using the method of Glueckauf," with a separation factor of 1.15 for methyl stearate relative to metbyl oleate. The factor R is 649 More recently Insull and Jamess#

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Conclusion The Twitchell and infrared isooleic methods have been compared. Assuming that all trans‐isooleic acids are of equal significance as regards influence on shortening plasticity as “solid unsaturated acids,” the infrared method is superior. This method has all the advantages of speed and accuracy of spectrophotometric methods. It handles simple and complex isoleate mixtures with equal ease in view of identical infrared absorption for trans‐isomers of different double bond position. The Twitchell method was shown, on close analysis, to have fair accuracy for simple trans‐acid mixtures but give very low values (errors of 35 to 45%) with ordinary hydrogenated oils. The reason for the failure of the Twitchell method apparently lies in the increasing lead isooleate solubility with increase in the number of trans‐isooleic acids.