Kinetic determination of carbimazole, methimazole and propylthiouracil in pharmaceuticals, animal feed and animal livers

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Abstract
Kinetic methods are proposed for the determination of carbimazole(CBZ), methimazole(MMI) and propylthiouracil(PTU) based on their inhibitory effects on the palladium(II)-catalysed reaction between the pyronine G and hypophosphite ions. The reactions are monitored spectrophotometrically at 548 nm. The influence of reaction variables and the interfering effect of other substances were studied. Under the selected experimental conditions (CBZ: 3.6 × 10–5 mol l–1 pyronine G; pH 3.0; 0.7 µg ml–1 PdII and 0.2 mol l–1 H2PO2 –; MMI: 6 × 10–5 mol l–1 pyronine G, pH 3.0; 0.7 µg ml–1 PdII, 0.4 mol l–1 H2PO2 –; PTU: 3.6 × 10–5 mol l–1 pyronine G; pH 3.0; 0.7 µg ml–1 PdII and 0.3 mol l–1 H2PO2 –), these three antithyroids were determined in the following ranges: CBZ, 0.04–0.70 µg ml–1; MMI, 0.04–0.50 µg ml–1; PTU 0.08–1.00 µg ml–1. The methods were applied to the determination of CBZ, MMI and PTU, in pharmaceuticals, animal feed and animal livers.