Determination of tocopherol in autoxidizing methyl esters of fatty acids

Summary Autoxidizing methyl esters of fatty acids interfered with the determination of α‐tocopherol by ultraviolet spectrophotometry or by the bipyridine colorimetric method. Interference with the colorimetric method was removed by sulfuric acid treatment, but spectrophotometry was applicable only when the tocopherol was completely separated from oxidized fat. This separation could not be obtained by sulfuric acid treatment but was accomplished by room temperature saponification in an alcohol‐petroleum ether system protected by pyrogallol. The sensitivity of the spectrophotometric method was increased by oxidizing tocopherol quantitatively to the p ‐quinone with 2 N nitric acid.