Photodegradation of chlorpromazine in aqueous solutions as studied by ultraviolet–visible spectrophotometry and voltammetry

Abstract

Chlorpromazine, a phenothiazine derivative, is well known for its photosensitivity toward sunlight. Photodegradation of the drug under near-u.v. radiation (λ_max= 366 nm) was monitored both by following its spectroscopic π–π* absorption band (256 nm) and by measuring the voltammetric oxidation peak current. In aqueous solutions of pH 1.5–6.5 and at a nearly constant temperature (22–24 °C), both techniques gave consistent results which could be interpreted to give the probable mechanism of the photochemical reaction. The photo-oxidation reaction obeyed zero-order kinetics. Evidence for chlorpromazine phenazathionium ion formation was found in spectra of 6 mol dm^–3 H₂SO₄ solutions of irradiated chlorpromazine.