200 



HUBERT S. LORING 



Uj 



9,4 00 



240mp^ 



220 230 



240 250 260 270 280 



WAVE LENGTH (mp) 



290 300 



Fig. 1. The ultraviolet absorption spectra of adenine and guanine in 0.1 A' HCl and 

 of cytidine and uridine in 0.01 A' HCl. 



are obtained of adenine, and guanine on the one hand and cytidine and uri- 

 dine on the other. ^^ The ultraviolet absorption spectra of each pair of com- 

 ponents in dilute acid as illustrated in Fig. 1«. 22, 49 are sufficiently different 

 to allow the estimation of the concentration of each component to an extent 

 limited only by the precision of the spectrophotometer and the degree to 

 which other ultraviolet-absorbing impurities may be present in either mix- 

 ture. [Cf. Beaven, Holiday, and Johnson, Chapter 14.] 



The analysis of a binary mixture of components, A and B, having different absorp- 

 tion spectra, is made on the assumption that the total optical density, D, at each of 



^* The relative amounts of the isomeric cytidylic and uridylic acids present in the 

 pyrimidine nucleotide fraction can be estimated directly^ by absorption spectro- 

 photometry without conversion to nucleosides. The uncertainty in such analyses 

 is larger, however, because the two isomeric cytidylic and uridylic acids present in 

 acid hydrolysates [H. S. Loring, N. G. Luthy, H. W. Bortner, and L. W. Levy, J. 

 Am. Chem. Soc. 72, 2811 (1950) ; W. E. Cohn, ibid. 72, 2811 (1950)] have somewhat 

 different absorption spectra.*' 



