Detection of trace fatty acids in fats and oils by urea fractionation and gas‐liquid chromatography

The detection of trace fatty acids (<0.1%) in a fat or oil by gas‐liquid chromatography is possible when the methyl esters are fractionated with urea to provide a number of less complex fractions. Identification and estimation of trace fatty acids is simplified by quantitative removal of other fatty acids having similar gas chromatographic retention times. A detailed knowledge of the order in which inclusion compounds are formed was obtained by fractionating a complex mixture of marine and vegetable fatty acids. In addition, lanolin was fractionated to determine the preferential order in which saturated, branched chain ( iso‐, anteiso‐ ) and hydroxy acids form inclusion compounds. Using urea fractionation and gas chromatography, 52 trace fatty acids were tentatively identified in butter, 30 in lard, and 26 in walnut oil.