Kinetic determination of methotrimeprazine, thioridazine and their mixture by use of a modular stopped-flow/diode-array detection system.
The oxidation reactions of methotrimeprazine and thioridazine by iron(III) were used to develop kinetic methods based on measurements of the formation rate of the corresponding coloured phenothiazinyl free radicals. The calibration graphs were linear over the range 0.8-60 microg/ml for methotrimeprazine and 1.1-60 microg/ml for thioridazine. The relative standard deviation was 1.1-3.4%. The method was used to determine the analytes in commercially available pharmaceutical preparations. The different absorption maxima of the oxidation products formed and also the different, high initial rates of the reactions for both analytes allow their simultaneous determination by using a stopped-flow module coupled to a diode-array spectrophotometric detector. Reaction rate and absorbance increment measurements of the kinetic curves obtained were used to resolve mixtures of both phenothiazines by using the proportional-equation method and establishing three different equation systems that allowed the results obtained in each case to be compared. Mixtures of methotrimeprazine and thioridazine in ratios between 8:1 and 1:8 were satisfactorily resolved.
de la Peña
L
L
Department of Analytical Chemistry, Faculty of Sciences, University of Córdoba, Córdoba, Spain.
Gómez-Hens
A
A
Pérez-Bendito
D
D