L. Delapena et al., KINETIC DETERMINATION OF METHOTRIMEPRAZINE, THIORIDAZINE AND THEIR MIXTURE BY USE OF A MODULAR STOPPED-FLOW DIODE-ARRAY DETECTION SYSTEM, Talanta, 41(11), 1994, pp. 1895-1901
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 radi
cals. The calibration graphs were linear over the range 0.8-60 mu g/ml
for methotrimeprazine and 1.1-60 mu g/ml for thioridazine. The relati
ve standard deviation was 1.1-3.4%. The method was used to determine t
he 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 an
d absorbance increment measurements of the kinetic curves obtained wer
e used to resolve mixtures of both phenothiazines by using the proport
ional-equation method and establishing three different equation system
s that allowed the results obtained in each case to be compared. Mixtu
res of methotrimeprazine and thioridazine in ratios between 8:1 and 1:
8 were satisfactorily resolved.