Analytical Sciences

Enhanced Reduction and Determination of Trace Thyroxine at Carbon Paste Electrode in the Presence of Trace Cetyltrimethylammonium Bromide

Chengguo HU,* Qiong HE,*^,** Qing LI,* and Shengshui HU*

*Department of Chemistry, Wuhan University, Wuhan 430072, China
**Department of Chemistry, Qujing Normal College, Qujing 655000, China

The electrochemical response of thyroxine (T₄) 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 T₄ at CPE was greatly enhanced in the presence of CTAB, due to the interactions between T₄, CTAB and the hydrophobic electrode surface. The electrode process of T₄ 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 T₄ via a special interaction with the iodine atoms on T₄, which would activate the reduction of T₄. The sensitive and selective reduction of T₄ in this system was applied to the determination of T₄ in drugs; a detection limit of 6.5 × 10^-9 M was obtained (σ = 3).

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