CHEMISTRY OF EPINEPHRINE 81 



reaction should be carried out in slightly alkaline solution, 

 in the presence of an excess of ferric chloride. 553 The purplish 

 coloration thus produced is proportional to the molar concen- 

 tration of the catechol derivative present in the solution tested. 



The ease with which epinephrine is oxidized to give a red 

 coloration has given rise to a number of methods for its analy- 

 sis. For this purpose, many oxidizing agents have been sug- 

 gested — iodine, iodic acid, chlorine, mercuric chloride, persul- 

 fates, osmic acid, et cetera. 639 Iodic acid has been used by a 

 number of workers. 664 The addition of sulphanilic acid in- 

 creases the sensitivity of this method so that a dilution of as 

 little as 1 part of epinephrine in 5,000,000 is detectable. 341 

 Unfortunately this delicacy is not specific to epinephrine. 



The use of persulphate for the estimation of epinephrine has 

 recently been investigated by Barker, Eastland, and Evers. 37 

 These authors consider this reagent the most accurate for the 

 colorimetric determination of epinephrine. 



The use of iodine as an oxidizing agent in the colorimetric 

 determination of epinephrine has been revived by Euler 188 who 

 has worked out an exceedingly accurate procedure using the 

 spectrophotometer. This method is not interfered with by 

 the presence of reducing agents such as ascorbic acid. 



Perhaps the most widely used colorimetric method for the 

 determination of epinephrine is the method of Folin, Cannon 

 and Denis. 202 This consists in reducing tungstic acid to its 

 blue oxides. This is an exceedingly sensitive method capable 

 of detecting as little as 0.003 milligrams of epinephrine. Al- 

 though yielding accurate results when applied to pure solu- 

 tions, it is so non-specific as to yield erroneously high values 

 when other reducing substances are present. Uric acid, for 

 the determination of which the reagent was originally devised, 

 and ascorbic acid react like epinephrine to give the blue color. 

 Their presence in many biological fluids thus vitiates the re- 

 sults obtained in analyses of epinephrine. Although epineph- 

 rine is destroyed by the passage of air through its alkaline 



