It is difficult to determine estrogens directly by electrochemical methods because estradiol, estrone and estriol are hydrophobic and electroinactive. Thus, they are only determined by the indirect electrochemical techniques. In this paper, based on the voltammetric behavior of estrogens(estradiol, estrone and estriol) on the Nafion\|modified glassy carbon electrode in the presence of CTAB, a novel direct electroanalytical method for the determination of the total amounts of estradiol, estrone and estriol was developed. In pH=8.00 phosphate buffer and in the presence of 6×10\+\{-5\} mol/L CTAB, estradiol, estrone and estriol have very sensitive oxidation peaks at 0.38 V(\%vs\%. SCE) at Nafion\|modified glassy carbon electrode after being accumulated for 3 min at -0.50 V. This peak can be used to determine trace level of estradiol, estrone and estriol. It was found that estradol, estrone and estriol have the similar electrochemical responses on the Nafion\|modified electrode in the presence of other long\|chain cationic surfactants, such as CPB, STAB, CATAB, LTAB. It is observed that the enhancement effect is highest in the presence of CTAB, and the peak current is CTAB concentration\|dependent. However, in the presence of long\|chain anionic surfactants, such as SDBS, and long\|chain nonionic surfactants, such as Triton X\|100, estradiol, estrone and estriol have no voltammetric responses on the Nafion\|modified glassy carbon electrode. The mechanism for the oxidation of estradiol in this system has been discussed, and the reactant site for the oxidation of estradiol has been verified to be the hyrdoxyl group in A\|ring.
