262 



G. R. WYATT 



TABLE III 

 Ultraviolet Absorption Data on Purine and Pyrimidine Derivatives 



" Not, in all cases, the precise absorption maximum. 



TABLE IV 

 Ultraviolet Absorption Data on Purine and Pyrimidine Derivatives 



Substance 



Solvent 



Absorption Reference 



Maximum, wavelength, 



mju m/i 



Difference in 



£i°« at the 



two wavelengths 



of 1.5 to 5 Mg- of nucleic acid is applied in a volume of about 0.5 ^1. to a strip of filter 

 paper 0.5 to 1 mm. broad, which is subjected to chromatography in the ordinary way. 

 A contact print of the dried strip chromatogram is made on a process plate with light 

 of wavelengths 257 and 275 m^ from rotating cadmium electrodes, then the darkening 

 of the plate is measured with a recording microphotometer, the image of a rotating 

 sector serving for calibration. This refined technique will undoubtedly be of value in 

 certain biological problems; however, the equipment is not available in the average 

 laboratory, and one may note that by using narrow strips of paper as described by 

 Edstrom to prevent spreading of the spots, and eluting the bands for extinction 

 measurement in microcells'* on the spectrophotometer, comparable sensitivity could 



«* E. Volkin and C. E. Carter, J. Am. Chem. Soc. 73, 1516 (1951). 

 '6 J. McT. Ploeser and H. S. Loring, J. Biol. Chevi. 178, 431 (1949). 

 96 O. H. Lowry and O. A. Bessey, J. Biol. Chem. 163, 633 (1946). 



