Voltammetric and electrochemical quartz crystal microbalance study of antithyroid drugs

Methimazole (MTZ, 1-methylimidazole-2-thiol), carbimazole (CM, 1-ethoxycarbonyl-3-methyl-2-thio-4-imidazoline), methylthiouracil (MTU, 6-methyl-2-thiouracil) and propylthiouracil (PTU, 6-propyl-2-thiouracil) are antithyroid agents. The electrochemical properties of MTZ, CM, MTU and PTU were studied by cyclic voltammetry (CV) over pH range 1.0-13.0 using mercury, gold and glassy carbon electrodes. The anodic processes of MTZ, CM, MTU and PTU, on mercury electrode, lead to formation of a Hg complex or slightly soluble mercury salt. At solid electrodes those compounds undergo a diffusion controlled oxidation. These investigations allowed to propose new voltammetric methods for determination of antithyroid drugs in pure form. The calibration plot was linear from 5x10(-5) mol l(-1) to 1x10(-3) mol l(-1). An electrochemical quartz crystal microbalance (EQCM) with AT-cut, 10 MHz quartz crystals covered with vacuum deposited gold (area = 0.24 cm(2); mass sensitivity = 0.226 Hz cm(2) ng(-1)) was used as a very sensitive, dynamic, piezoelectric sensor.