UV Derivative Spectrophotometric Study of the Photochemical Degradation of Thioridazine Hydrochloride

Abstract A rapid, selective, and accurate method, based on derivative spectra is proposed for the quantification of thioridazine hydrochloride in the presence of its main degradation product—thioridazine sulphoxide, and vice versa. The determination of thioridazine hydrochloride was made using the second order of derivative (Δλ = 22 nm, third polynomial degree) at 280 nm, while the determination of its sulphoxide is possible by applying the first order derivative spectra (Δλ = 22 nm, second polynomial degree) based on measurements of derivative height at 312 nm. The calibration graphs were linear up to 30 and 50 µg/mL for thioridazine and its sulphoxide, respectively. The limits of detection were 2.91 and 0.77 µg/mL. The elaborated method was applied successfully for determination of the photostability of thioridazine hydrochloride in aqueous solution and in solid phase.