IV. DETERMINATION 89 



sources of error. ^' ~' ]Men small amounts of moisture cause considerable 

 error, and furthermore the presence of unsaturated fats or indole derivatives 

 influence the development of the blue color. As the maximum of intensity 

 of the blue color is reached after 5 to 10 seconds, and then the "blue value" 

 drops quite rapidly, the measurement must be carried out during this short 

 period. This involves uncertainties and recjuires a greater number of control 

 measurements. For this reason the international arrangement gives chief 

 attention to the quantitative measurement of the ultraviolet absorption 

 maximum of vitamin A. But still the V . S. Pharma(H)peia demands the 

 control of this value bj'' the Carr-Price reaction,*^ which delivers useful 

 results if expertly performed. The spectrophotometric measurement of the 

 maxima of light absorption can be carried out with any spectrophotometer 

 or suitable spectral apparatus, but nowadays the preference is generally for 

 the much easier and more precise measurement by a spectrophotometer, 

 e.g., of the Beckman-DU type, to the old method by photography of the 

 spectrum and evaluation l)y quantitative photometry. Hilger's Vitameter^ 

 is also used for the determination of the vitamin A content. Here, too, a 

 special vitamin A standard preparation is useful, because it permits com- 

 parative measurement with the individual instrument and thereby enables 

 the analyst to compensate for faults of the apparatus. 



The influence of the solvent on the spectrum of vitamin A and of /3-caro- 

 tene has been investigated by several workers. ^"■^- Nowadays, the quantita- 

 tive measurement of the blue color of the Carr-Price reaction may appropri- 

 ately be carried out with a spectrophotometer, but in many countries 

 colorimetric measurement by the Lovibond Tintometer'^ is still in use. 

 The reaction solution is compared with glass standards having different 

 shades of blue color. Often the measurement is done by a Zeiss-Pulfrich 

 Stufen-Photometer with filter S61.'^' '^ Generally, the Carr-Price determina- 

 tion of vitamin A in fish liver oils, butter, and milk can be made only on 

 the unsaponifiable fraction, because the raw material contains substances 

 which interfere \\'ith the color reaction. (On the preparation and conserva- 

 tion of the Carr-Price reagent, see Miiller.'^) 



« M. J. Caldwell and D. li. Parrish, ./. Biol. Chem. 158, 181 (1945). 



' M. J. Caldwell and J. S. Hughes, J. Biol. Chem. 166, 565 (1946); 170, 97 (1947). 



* U. S. Pharmacopeia, 14th revision, pp. 784, 792, 1950. 



9 R. J. Taylor, Analyst 67, 248 (1942). 



i« A. E. Gillam and M. S. El Ridi, Biochem. J. 32, 1496 (1938). 

 n F. P. Zscheile and R. L. Henry, Ind. Eng. Chem. Anal. Ed. 14, 422 (1942). 

 '^ P. Karrer and E. Jucker, Carotinoide. Verlag Birkhauser, Basel, 1948. 

 1' O. Rosenheim and E. Schuster, Biochem. J .21, 1.329 (1927). 

 '^ L. Fuchs and E. Soos, Vitamine n. Hormone 4, 155 (1943). 

 »5 M. Lodi, Vitamine it. Hormone 4, 404 (1943). 

 >« P. B. Muller, Mitt. Gebiete Lebensm. u. Hyg. 40, 359 (1949) ; see also ref. 3. 



