Spectrophotometric studies on the photostability of some thiazide diuretics in ethanolic solution.

First derivative and dual-wavelength spectrophotometric methods were used in the quantum yield determination of the photochemical decomposition reactions of three thiazide diuretics (chlorothiazide, hydrochlorothiazide and trichloromethiazide) in ethanolic solution. The radiation absorbed by the compounds was measured using iron(III) oxalate actinometry based on absorption spectrophotometry. An apparatus is described in which the drugs were irradiated in quartz cuvettes cooled by water in a stand built on a magnetic stirrer. The wavelength region available to the reaction cuvette was restricted to 313 nm with chemical potassium chromate filter solutions and a Corning filter plate. Chlorothiazide proved to be more photostable than hydrochlorothiazide and trichloromethiazide in ethanol.