Spectrophotometric determination of diclofenac in pharmaceutical preparations assisted by microwave oven

Abstract

In this work, an effective and low-cost method for the determination of sodium or potassium
diclofenac is proposed in its pure form and in their pharmaceutical preparations. The method is based on the
reaction between diclofenac and tetrachloro-p-benzoquinone (p-chloranil), in methanol medium. This reaction
was accelerated by irradiating of reactional mixture with microwave energy (1100 W) during 27 seconds,
producing a charge transfer complex with a maximum absorption at 535 nm. The optimal reaction conditions
values such as reagent concentration, heating time and stability of the reaction product were determined.
Beer’s law is obeyed in a concentration range from of 1.25x10 -4 to 2.00x10 -3 mol l -1 with a correlation
coefficient of 0.9993 and molar absorptivity of 0.49 x10 3 l mol -1 cm -1 . The limit of detection (LOD) was
1.35x10 -5 mol l -1 and the limit of quantification (LOQ) was 4.49x10 -5 mol l -1 . In the presence of the common
excipients, such as glucose, lactose, talc, starch, magnesium stearate, sodium sulphite, titanium dioxide,
polyethyleneglycol, polyvinylpirrolidone, mannitol and benzilic alcohol no interferences were observed.
The analytical results obtained by applying the proposed method compare very favorably with those given
by the United States Pharmacopeia standard procedure.