Improved Methods for the Purification of the Common Carotenoids, and the Quantitative Measurement of Their Absorption Spectra

Simple improved methods for the purification of three of the common carotenoids have been developed. The methods of Tswett and Escher have been combined for the purification of the carotene isomers. The methods are described in detail. 2. A critical discussion of chromatographic analysis has been made. The necessary precautions are listed. 3. The quantitative absorption spectra of alpha and beta carotene, leaf xanthophyll, and lycopene were measured with an error of 2.0 per cent or less between 3950 and 5500 A. units. These spectra were measured by a spectro-photoelectric method which is accurate and precise. 4. Spectroscopic data show that certain tests of purity which have been considered accurate are only approximate. It is concluded that a critical examination of the absorption spectrum is the most reliable. 5. The absorption spectra of the carotenoids are employed as the basis for quantitative spectral analytical methods which have been applied to binary mixtures. 6. The preparative procedure includes and employs the precaution of excluding oxygen in the important steps of purification.