A method for determining the 1,10-phenanthroline content of technical 1,10-phenanthroline is described. The sample is dissolved directly in alcohol. The difference in absorbance of this solution at 323.5 mμ and 820 mμ is an approximate measure of the amount of 1,10-phenanthroline present. By differential comparison of a sample solution of technical 1,10-phenanthroline with a reference solution containing a known amount of pure 1,10-phenanthroline, a more exact determination can be made. Results obtained with the method were in close agreement with those obtained by a colorimetric method based on the formation of a red to orange complex by the reaction of 1,10-phenanthroline with ferrous ions. The standard deviation of the method based on five duplicate determinations is less than 0.2%.
P. J. Secrest, J. A. Pawley, and Claude A. Lucchesi, "Ultraviolet Spectrophotometric Determination of 1,10-Phenanthroline," Appl. Spectrosc. 13, 141-143 (1959)