20 /^-AMINOBENZOIC ACID 



Several advantages derive from the use of this amine: ease of purification 

 of the diamine, rapid couphng, greater solubiUty of the dye, increased sensi- 

 tivity, eHmination of the use of buffer, and stability of the color. 



Prior to the use of N-(l-naphthyl)ethylenediamine as the coupUng agent, 

 N ,N-dimethyl-l-naphthylamine^'^ and N-ethyl-1-naphthylamine^ had been 

 advocated as coupling agents. The determination of PABA in which N,N- 

 dimethyl-1-naphthylamine is the coupling agent has been described by 

 Eckert.^ 



CH3 CH3 H C2H5 



\ / \ / 



N N 



N, N-Dimethyl-1-naphthylamine N-Ethyl-1-naphthylamine 



In the original Marshall method in which the couphng agent is N,N- 

 dimethyl-I-naphthylamine,^ metals^ and thiocyanate interfere with color 

 production.^ Presumably these objections also apply to the improved 

 method where the coupUng agent is N-(l-naphthyl)ethylenediamine.^ 



A disadvantage in the Bratton-Marshall method for the determination 

 of PABA is that the color reaction is not specific and a variety of biological 

 compounds all give essentially the same color reaction. Among the known 

 biological compounds that interfere are 5(4)-amino-4(5)-imidazolecarboxa- 

 mide,^' ^^ kynurenine,'^ • ^^ anthranihc acid,'' tryptophan,'^ and indole.'* 



The Bratton-Marshall method has been applied extensively in studies 

 of PABA and/or other arylamines formed by sulfonamide-sensitive and 

 -resistant strains of staphylococci.'^' '^ 



3 E. K. Marshall, Jr., K. Emerson, Jr., and W. C. Cutting, /. Am. Med. Assoc. 108, 



953 (1937). 

 ' E. K. Marshall, Jr., Proc. Soc. Exptl. Biol. Med. 36, 422 (1937). 

 5 E. K. Marshall, Jr., J. Biol. Chem . 122, 263 (1937-1938). 

 «G. Hecht, Dermatol. Wochschr. 106, 261 (1938). 

 ' H. W. Eckert, J. Biol. Chem. 148, 197 (1943). 



^M. I. Gregersen and E. E. Painter, Am. J. Physiol. 123, 83 (1938). 

 « W. Shive, W. W. Ackermann, M. Gordon, M. E. Getzendaner, and R. E. Eakin, 



/. Am. Chem. Soc. 69, 725 (1947). 

 !» M. R. Stetten and C. L. Fox, Jr., /. Biol. Chem. 161, 333 (1945). 



11 M. G. Sevag and M. N. Green, /. Bacteriol. 48, 615 (1944). 



12 J. Tabone and C. Magis, Bull. soc. chim. biol. 28, 744 (1946). 



13 H. W. Eckert, ./. Biol. Chem. 148, 205 (1943). 



" M. Landy, N. W. Larkum, K. J. Oswald, andF. Streightoff, Science 97, 265 (1943). 

 "^ W. W. Spink, L. D. Wright, J. J. Vivino, and H. R. Skeggs, ./. Expfl. Med. 79, 331 

 (1944). 



