SPECTROPHOTOMETRIC DETERMINATION OF SOME N-SUBSTITUTED PHENOTHIAZINE-DERIVATIVES USING N-BROMOPHTHALIMIDE

A simple, rapid and sensitive spectrophotometric method is described for the quantitative determination of N-substituted phenothiazines. The method depends on the formation of a stable phenothiazine free radical cation by the use of N-bromophthalimide as oxidising agent in a strong acid medium (methanol/sulphuric acid 1:1 v/v). The produced red or violet color possesses absorption maximum range from 500 to 530 nm. A linear relationship exists between the absorbance at (lambda(max)) and concentration in the range 5 to 40 mug ml-1 with apparent molar absorptivities range from 6 x 10(3) to 12 x 10(3) l mol-1 cm-1. The color is developed instantaneously for all the studied phenothiazines except for thioproperazine mesylate, trifluoperazine dihydrochloride and prochlorperazine mesylate that require 25, 15 and 25 min, respectively, for complete reaction. The developed colors are stable over 24 h. The average % recovery is 99.85 +/- 0.61 to 100.28 +/- 0.95. The method was applied successfully to the microdetermination of chlorpromazine HCl, promethazine HCl, pericyazine, thioproperazine mesylate, perphenazine, prochlorperazine mesylate, trimeprazine tartrate and trifluoperazine 2HCl either in pure form or incorporated in their pharmaceutical preparations. The results of analysis are in good agreement with those of the official B.P. 1988 and USP XXII.