Study of Reactions of Triiodide and Alizarin Red S with Some Important Phenothiazines. Development of an Indirect Titrimetric and a Spectrophotometric Method for the Assay of Phenothiazine Derivatives

Abstract

AbstractThe reactions of a triiodide ion and alizarin red S with some N‐substituted phenothiazine drugs have been studied for the development of two simple, rapid, sensitive and accurate indirect titrimetric and extractive‐spectrophotometric methods for determining these drugs. Spectroscopic studies and chemical analysis showed that the protonated forms of phenthiazines, (PhenH2)2+, react with triiodide ions forming highly stable and insoluble ion pair products as (PhenH2)(I3)2. Formation of ion association complexes have been applied to the development of an indirect visual titrimetric method for the determination of chlorpromazine hydrochloride (CPH), trifluoperazine hydrochloride (TFPH), fluphenazine hydrocholoride (FPH) and promethazine hydrochloride (PMH) over the range 10−5–10−2 M. The extractional‐spectrophotometric method is based on the formation of (1:1) ion‐association complexes between drugs and alizarin red S as chromogenic reagents in acidic citrate buffer that are extractable into chloroform with an absorption maximum at 425 nm. The effect of different factors such as organic solvents, pH, and reagents concentration, were studied. CPH, TFPH and FPH can be determined over the range 9–57, 14–77 and 7–71 ppm, respectively. The proposed methods were applied for the analysis of the studied drugs in pure forms and their commercial preparations. Results are in good agreement with those obtained by official methods.