Abstract: A complex emitting orange yellow fluorescence were generated by the mixture of the alizarin red and excessive Al³⁺ at pH = 5.2. The maximum fluorescence excitation and emission wavelength of the colored complex were located at 469 nm and at 585 nm, respectively, The fluorescence intensity of the alizarin red-Al³⁺ system could be quenched by a certain amount of Cu²⁺,and the fluorescence quenching value showed a linear relationship with the concentration of Cu²⁺ within limits, thus establishing a sensitive and switching method for the determination of Cu²⁺. The optimal factors of the determination system were investigated,such as the dosage ratio, reaction temperature, reaction time,pH and buffer solution. The results showed that the standard working curve was ΔF=19.7c+101.21(R²=0.999 5), the linear range was 0.2~30 μmol/L, and the detection limit was 0.022 μmol/L. The method shows high accuracy, high sensitivity, good selectivity, and could be used for the detection of trace copper ion in water.

Key words: alizarin red Al³⁺, copper ion, fluorescence probe of switching type