Contribution to the analysis of some Phenothiazines

In this work, eleven phenothiamine drugs were determined spectrophotometrically. The method is based on the oxidation of the phenothiszine nucleus by N-bromoscuccinimide in sulphuric acid medium (30 – 70 % v/v). The conditions of the reaction were optimized in order to produce the most intense and stable colour.The following experimental variables were studied :a) Effect of different acid species.b) Effect of various concentrations of sulphuric acid.c) Effect of NBS concentration.d) Effect of the order of addition or reaction components.e) Effect of temperature on production and stability of chromogen.f) Effect of time on the development and stability of colours.On the basis of this study, the general assay procedure includes the addition of the specified volume of nulphuric acid to aqueous phenothiazine sample solution and then addition of the required concentration of the aqueous NBS solution. The volume was completed with distilled water to 5.0 ml and absorbance was then read at the specified wavelength after the colour was well developed (20 – 30 min. at room temperature).In conclusion : The proposed method has several advantages :- It is simple, can be carried out at room temperature, consumes a relatively short time and its reagents are available.- The reactions involved are quite selective being of red ox type and so inhibit interferences. These reactions were discussed and chemically represented by equations.- The produced chromogen are lightly stable with time and the method is considered to be reproducible and moderately sensitive.- The determination of studied phenothiazines in their dosage forms was successful. The acid extraction procedure has advantage over the official methods were the step of chloroform extraction of the free base is omitted. So, the proposed method not only introduces good results that are well comparable with the official methods, but also it saves time and material. Besides, no interferences of the excipients commonly present in the dosage form were found.- Approximately, the absorptivity increases to the double when NBS was used in conjunction with sulphuris acid in comparison with those obtained by using sulphuric acid alone.- Sulphuric acid was found to be the most effective acid among the tried acids, perchloric, or thophosphoric, hydrocholoric, nitric and acetic. On the other hand, NBS produces the most intense coloures relative to the other studied oxidizing agents.