Extractive-spectrophotometric determination of some phenothiazines with dipicrylamine and picric acid.

Dipicrylamine and picric acid have been tested as reagents for the determination of promethazine and perphenazine. They react in neutral media with these drugs forming the coloured compounds. The compounds are sparingly soluble in water and quantitatively extracted into organic solvents. The extracts are intensely coloured and very stable. These properties have been exploited for the extractive spectrophotometric determination of promethazine and perphenazine in pure solutions and pharmaceuticals. Linear calibration graphs were obtained in the concentration range 4-40, 3-30 microg ml(-1) of promethazine and 4-80, 8-60 microg ml(-1) of perphenazine for picric acid and dipicrylamine, respectively. The relative standard deviation (RSD) is less than 0.8%.