The alkali isomerization of a methyl docosahexaenoate and the spectral properties of conjugated fatty acids

Abstract

Summary The dependence of the ultraviolet absorption spectra for docosahexaenoate upon conditions used in alkali‐isomerization has been studied. The extinction coefficients at all wavelengths varied with sample size when 21% KOH‐glycol was used as the isomerization reagent at 180°C.; the effect of sample size was due to the solubility characteristics of 22‐carbon fatty acid esters in the isomerization reagent. Spectrophotometer slit width is an important consideration in the measurement of extinction coefficients at the absorption maximum at 374 mμ. Certain conditions which must be met for accurate analysis of hexaenoate in fatty acid mixtures are described. An extension of a theory of Lewis and Calvin has been used to clarify the number, position, and to some extent, intensity of the peaks in the ultraviolet absorption spectra of natural conjugated and alkali‐isomerized fatty acids.