Voltammetric determination of methylthiouracil in animal feed using carbon fiber microelectrodes

Cylindrical carbon fiber microelectrodes (CFMEs) (8 mum in diameter, 8 mm in length) are used to develop a voltammetric method for the determination of the thyreostatic drug methylthiouracil (MTU) in animal feed samples. Methanol, containing 0.05 mol L-1 tetrabutylammonium perchlorate as supporting electrolyte, was selected as working medium because of the high MTU solubility in this solvent, which is also used for the extraction of MTU from real samples. Reproducible electroanalytical responses were obtained with no need of applying cleaning treatments to the CFME. The net-current square-wave (SW) oxidation signal of MTU was selected to be exploited analytically. Under the optimized SW conditions, a linear calibration plot for MTU was obtained in the 1.0 x 10(-6)-1.0 x 10(-4) mol L-1 range, with a detection limit of 3.8 X 10(-7) mol L-1. The SW voltammetric behavior of other thyreostatic drugs was checked. A simple extraction procedure with methanol, followed by a clean up step, was used for the determination of MTU in a commercial dry fodder sample spiked with this drug at the 500 mug g(-1) level. The detection limit in this type of sample was found to be 8.6 X 10(-6) mol L-1.