Enhanced reduction and determination of trace thyroxine at carbon paste electrode in the presence of trace cetyltrimethylammonium bromide

The electrochemical response of thyroxine (T-4) at a carbon paste electrode (CPE) in the presence of cetyltrimethylammonium bromide (CTAB) was investigated. It gave a well-defined oxidation peak at 0.80 V and a sensitive reduction peak at 0.40 V. Compared with the indiscernible signal in the absence of CTAB, the reduction current of T-4 at CPE was greatly enhanced in the presence of CTAB, due to the interactions between T-4, CTAB and the hydrophobic electrode surface. The electrode process of T-4 was explored by cyclic voltammetry and chronocoulometry. The effect of surfactants on the reduction reaction proved that bromide ions (Br-) in CTAB might form special ion complexes with T-4 via a special interaction with the iodine atoms on T-4, which would activate the reduction of T4. The sensitive and selective reduction of T-4 in this system was applied to the determination of T4 in drugs; a detection limit of 6.5 x 10(-9) M was obtained (sigma = 3).