28 ISOLATION III 



4. CRYSTALLISATION 



The crystallisation of carotenoids requires considerable practice, especially 

 if small amounts of material are involved. It is not always possible to recrystal- 

 lise a carotenoid from a single solvent. Solvent mixtures consisting of one 

 component in which the pigment is easily soluble, and a second component in 

 which the pigment is sparingly soluble, sometimes have to be employed. No 

 attempt will be made here to give a complete list of all the solvents which have 

 been used, since more information on this point will be found in later sections 

 dealing with individual carotenoids. Epiphasic carotenoids can often be 

 recrystallised from light petroleum or from ether-methanol, or benzene- 

 methanol mixtures. For hypophasic pigments, benzene-methanol or ether- 

 methanol mixtures are often used. Methanol alone is also employed. Certain 

 carotenoids (e.g. violaxanthin, fucoxanthin, zeaxanthin) can be precipitated 

 by adding water to a methanolic solution of the pigment covered with a layer 

 of light petroleum. The water is added in very small portions and crystallisation 

 can often be induced by scratching the sides of the vessel with a glass rod. 



REFERENCES 



1. R. WiLLSTATTER and A. Stoll, Untersuchungen iiber aas Chlorophyll, Berlin 191 3; 

 Untersuchungen iiber die Assimilation der Kohlensaure, Berlin 1918. — Cf. also R. Kuhn 

 and H. Brockmann, Z. physiol. Chem. 206 (1932) 41. 



2. An extensive literature dealing with chromatography is available. The following mono- 

 graphs should be consulted: L. Zechmeister and L. v. Cholnoky, Die chromato- 

 graphische Adsorptionsanalyse, Berlin 1938. — H. Brockmann, Die chromatographische 

 Adsorption, in: Neuere Methoden der praparativen organischen Chemie, Berlin 1943. — 

 Gerhard Hesse, Adsorptionsmethoden im chemischen Laboratorium, Berlin 1943. — 

 H. G. Cassidy et al., "Chromatography" in: Annals of the New York Academy of 

 Sciences, 49 (1948) 141-326. 



3. M. TswETT, Ber. deut. botan. Ges. 24 (1906) 316, 384. — M. Tswett, The chromophylls 

 in the vegetable and animal kingdoms (in Russian), Warsaw, 1910. 



4. Cf. L. S. Palmer, Carotinoids and related Pigments, New York, 1922. 



5. C. Dhere, Compt. rend. 158 (1914) 64-66. — Cf. also C. Dhere, Candollea 10 (1943) 60. 



6. A. WiNTERSTEiN and G. Stein, Z. physiol. Chem. 220 (1934) 251. 



7. Cf. G. Hesse, Adsorptionsmethoden im chemischen Laboratorium, Berlin, 1943, p. 31. 



8. Cf. H. Brockmann, Die chromatographische Adsorption, in: Neuere Methoden der 

 praparativen organischen Chemie, Berlin, 1943. 



9. A. Winterstein and G. Stein, Z. physiol. Chem. 220 (1933) 273. — Cf. D. C. Castle, 

 A. E. GiLLAM, I. M. Heilbron and H. W. Thompson, Biochem. J. 28 (1934) 1702. 



