A SPECTROPHOTOMETRIC DETERMINATION OF THE AND PAPAVERINE DISSOCIATION CONSTANTS OF p-NITROPHENOL

Edwards 1 has recently described the use of the ultra-violet spectrophotometer to measure the dissociation constant of salicylamide. In a search for a method of analysis of the insecticide Parathion, it was noticed that one of its decomposition products, p-nitrophenol, had an ultra-violet spectrum of an unusually simple nature, consisting of two bands, one of which was enhanced in alkaline solution and the other in acid solution. In addition, it exhibited one of the clearest isobiestic points yet observed and from the absorption at a series of pH values it was possible to evaluate the dissociation constant. In continuation of a study of the analysis of alkaloidal mixtures by the spectrophotometer,2 it has been observed that the alkaloid papaverine has an absorption spectrum much less complex than those of the alkaloids in general, and again the absorption is so dependent on the pH of the system that the dissociation constant of the base can be evaluated with ease. In view of the interest which attaches to the work on salicylamide, it is worth while reporting briefly on these further applications of the spectrophotometric method.