366 RIBOFLAVIN 



tion is much superior. De Ritter et al}^ also compared several methods for 

 the determination of riboflavin in urine and concluded that the method 

 of Slater and Morell gave results most comparable to the microbiological 

 assay. Pearson and Schweigert-^ fovmd the fiuorometric method to give 

 very large errors when applied to the urine of sheep or goats given large 

 doses of riboflavin when compared to the microbiological assay, but rat 

 and human urine gave comparable results by either method. 



(6) Comment. It may probably be taken as a truism that, when many 

 methods are in use for the determination of the same substance, none is 

 really satisfactory. This may be a little severe in the present case, since 

 very few authors have attempted careful examination of several methods. 

 The work of Morell and Slater-" ■ " and that of De Ritter et al?^ are com- 

 mendable exceptions. Most studies compare "their" method with another, 

 usually the microbiological. It is certainly safe to conclude that no "best 

 method" for all materials can be selected at this time. Several of the meth- 

 ods undoubtedly give reasonably accurate and comparative values when 

 applied to materials of a generally similar origin, meats for example, and 

 which contain reasonable amounts of riboflavin. On the other hand, many 

 materials of plant origin are very low in riboflavin and yield highly colored 

 extracts containing numerous and varied pigments. These present numer- 

 ous problems, and, indeed, each extract to some degree may present a special 

 problem. Not only is the problem difficult but it has received relatively less 

 study, since such materials are not usually important riboflavin sources in 

 the diet and the knowledge that they are low may often be a sufficient 

 answer. On the other hand, as Morell and Slater point out, the principal 

 interest in urinalysis is usually in the samples which are very low and where 

 methods fail or become undependable. Their work appears promising here. 



h. Methods Utilizing the Fluorescence of Lumiflavin 



The transformation of riboflavin into the chloroform-soluble derivative, 

 lumiflavin, by irradiation in alkaline solution would appear to offer promise 

 as a specific method of determination, especially if combined with some of 

 the procedures now in common use. It is said^- ^^ that the transformation 

 is not quantitative and difficult to standardize, but very few workers in 

 the United States appear to have investigated its possibihties. Foreign 

 workers continue to improve and use the method. Roth,^^ Jansen,^ and 



28 E. De Ritter, M. E. Moore, E. Hirschberg, and S. H. Rubin, ./. Biol. Chem. 176, 



883 (1948). 

 23 P. B. Pearson and B. S. Schweigert, /. Nulrilion 34, 443 (1947). 

 3" P. Karrer, in Ergebnisse der Vitamin und Hormonforschung, Vol. II, p. 381. 



Akademische Verlagsgesellschoff, Leipzig, 1939. 

 31 H. Roth, Biochcm. Z. 320, 355 (1950). 



