Sequential injection analysis technique for the concentration, stoichiometry and formation constant studies of promethazine hydrochloride complexed with palladium(II) in hydrochloric acid

The sequential injection analysis (SIA) technique was successfully applied to the determination of promethazine hydrochloride in drug formulations. The chemical system is based on the complexation reaction of promethazine hydrochloride with Pd(II) in 8.0 x 10^-4 mol dm^-3 HCl and measurement of the absorbance at 504 nm. Promethazine was determined in the range 50-400 ppm using 1.0 x 10^-3 mol dm^-3 Pd(II) with an aspiration volume of 147.5 μl. The SIA technique was utilized for the determination of the concentration, stoichiometry and formation constant of the complexation reaction. The technique was found to be superior to flow injection analysis. The SIA method was statistically compared with the official British Pharmacopoeia method and showed comparable accuracy, but with the advantages of selectivity, simplicity, speed and amounts of reagents consumed.