8 OCCURRENCE. DETECTION, ESTIMATION I 



5. SPECTROSCOPY 



An important part of the characterisation of a carotenoid is the determi- 

 nation of its absorption maxima. (With regard to the relationships between 

 constitution and colour, and extinction curves, cf. page 53). On examining the 

 solution of a carotenoid, usually in carbon disulphide or petroleum ether, in a 

 spectrometer, two or three sharp absorption bands can usually be observed. 

 Their positions can be accurately determined (approximately to within 0.5 m/z) 

 and represent the wavelengths of the absorption maxima. These data are 

 characteristic for each carotenoid and together with other physical constants 

 are used for its identification. (Detailed light absorption data will be quoted 

 in the description of the individual pigments in later sections). By means of the 

 photographic method of determining solution spectra, as developed, for in- 

 stance, by VON Halban, Kortum and Szigeti^^, or by other suitable means, 

 the complete absorption curves can also be determined^'. 



6. COLORIMETRY 



There are numerous methods for the colorimetric determination of a caro- 

 tenoid, all of which have in common the comparison of an unknown quantity 

 of the pigment with a standard solution. Potassium dichromate^", azobenzene^^, 

 bixin22 and jS-carotene^^ have been used as standard substances. Instruments 

 not requiring standard solutions have also been employed^*. It is necessary to 



separate the carotenoids before their colorimetric determination, otherwise 



t. 

 misleading results are obtained. 



7. fluorescence spectra 



Following the determination of the fluorescence spectra of different diphenyl- 

 polyenes by Hausser and collaborators^^, Dhere^^ examined vitamin A, 

 j8-carotene and lycopene at — 180° in this respect. The determination of fluo- 

 rescence spectra has not, however, found general application. 



REFERENCES 



1. W. Menke, Naturwissenschaflen 28 (1940) 31. 



2. H. JuNGE, Z. physiol. Chem. 268 (1941) 179. 



3. A. M. GoLDOwsKi and M. S. Podolskaja, Chem. Centr. igjg II 2437. 



4. R. Savelli, Protoplasma 2g (1938) 601; C. igjS II 2126. 



5. H. MoLiscH, Ber. deut. Botan. Ges. 36 (1918) 281. — K. Noack, Biochem. Z. 183 (1927) 

 135. — A. GuiLLiERMOND, Compt. rend. 76^(1917) 232. — Courchet, tImm. Scj.wai. (7) 

 (1888) 263. — R. KuHN and H. J. Bielig, Ber. 73 (1940) 1080. 



6. Cf. W. Straus, Dissertation, Zurich, (1939) p. 50. 



