Comparison of infrared spectrophotometric and lead salt‐alcohol methods for determination of trans octadecenoic acids and esters

Abstract

Summary The scope and limitations of the lead salt‐alcohol method (11, 19) have been defined as a result of observations in the authors' laboratories and in others. Trans octadecenoic acids and esters are not determined specifically by this method, and when large amounts of cis acids or esters are present, they are also isolated with the solid acid fraction. The infrared spectrophotometric method, previously described by the authors (14), and the lead salt‐alcohol method have been applied to a variety of synthetic mixtures of known composition and to other materials. Comparison of the data indicates that the infrared method is more rapid, specific, and accurate than the lead salt‐method; it is directly applicable to the determination of trans isomers in acid or ester mixtures; only small samples are required; and they can be recovered if necessary. The infrared method is suggested as a necessary tool to investigators conducting research on the oxidation, isomerization, polymerization, composition, and hydrogenation of fats and their components and derivatives, and on the preparation of pure unsaturated acids and esters.