Ion Exchange Method for Determination of Caffeine in Presence of Antipyrine and Phenacetin

A new method is presented for the determination of caffeine in mixtures containing antipyrine and phenacetin. The mixture is first treated with hydrochloric acid in order to convert the phenacetin into p -phenetidine and then extracted with chloroform. After evaporation of the chloroform, the remaining residue containing caffeine and antipyrine is dissolved in water and passed through an ion exchange column filled with a resin in the ferric iron form. Owing to complex formation, antipyrine is quantitatively retained in the column. The caffeine, however, is completely displaced with water at elevated temperature and is spectrophotometrically determined in the ultraviolet region. This procedure has been found to be simple and to give a very satisfactory degree of accuracy.