In Clark-lubs buffer of pH 9.0, tetracycline antibiotics (TCs) such as doxycycline (DOTC), oxytetracycline (OTC), tetracycline (TC) and chlortetracycline (CTC) react with sodium tungstate to form 1∶1 anion chelates. It results in the change of the absorption spectra of TCs, but the resonance Rayleigh scattering (RRS) intensities are not increased. When the anion chelates further react with ethyl violet, the great enhancements of RRS intensities are observed and new RRS spectra appear. Their spectral characteristics are similar, and the maximum RRS wavelengths are at 328 nm. The linearity range and detection limits of four TCs are 0.047～4.8 μg•mL^－1 and 14.1 ng•mL^－1 (DOTC), 0.078～5.0 μg•mL^－1 and 23.5 ng•mL^－1 (OTC), 0.081～5.7 μg•mL^－1 and 24.4 ng•mL^－1 (TC), 0.122～7.7 μg•mL^－1 and 36.6 ng•mL^－1 (CTC), respectively. The composition of the ternary ion-association complex is investigated, and the structure of the complex and its reaction mechanism are discussed. A high sensitive, simple and fast method is proposed to the determination of TCs.

Key words: resonance Rayleigh scattering, tetracycline antibiotics, sodium tungstate, ethyl violet