Colorimetric determination of thioxanthenes with tetracyanoethylene

A simple and rapid colorimetric method for the quantitative determination of the thioxanthene derivatives, chlorprothixene, tiotixene and metixene has been performed either in their pure form or in tablets. The procedure is based upon the formation of charge transfer complexes with the pi-acceptor tetracyanoethylene. The spectra of the complex show maxima at 415, 410 and 390 nm with a high apparent molar absorptivity which facilitates the determination of 5-100 micrograms X ml-1 of the studied compounds. The mean recoveries are 100.1 +/- 1.4%, 99.8 +/- 0.8% and 100.2 +/- 1.1% for chlorprothixene, tiotixene and metixene, respectively. This procedure is applied to determine these drugs in certain formulations and the results compare favourably to compendial methods.