Abstract
A novel spectrophotometric method is proposed for the determination of procaine on the basis of solvent extraction. Tetrabromophenolphthalein ethyl ester (TBPE) anion, which is a monoacidic dye, is not extracted into 1, 2-dichloroethane layer from an aqueous solution. However, if TBPE is added to the aqueous solution containing procaine, the extract is colored red. Optimum pH range for the extraction of procaine from the aqueous solution is 8-9. The absorbance maximum of the extracts is at 580 nm, and the absorbance showed a linear relationship to the concentration of procaine in the aqueous solution over the range of 5×10-7 to 5×10-6 M. Procaine was found to form an associated ion-pair compound (1 : 1) with TBPE in 1, 2-dichloroethane. It seems that a kind of charge transfer complex is formed in the extract which shows a strong red color. On the other hand, when the aqueous phase contains quaternary ammonium salts, the extract is blue. In the quaternary ammonium system, it was found that an ion-pair extracted is readily dissociated in the organic phase and the blue color is attributed to the TBPE anion.
