[Study on fluorescent properties of coumarin derivatives and determination of trace iron]

The fluorescence spectra of the succinic acid (7-hydroxy-coumarin) ester (SCE) of different concentration in water and ethanol solvents were studied. It was found that the peak wavelength changes not only with solvent, but also with the concentration. These phenomena of spectra have been discussed on the basis of solvent properties and dimerisation of SCE in hydrogen bonding solvents. The author thought that there are dimerisation phenomena in the SCE solutions at high concentration. The formation of dimer was caused by the aid of hydrogen bonding between SCE and solvent or between SCE themselves. Its acidic dissociation constant at excited state was determined based on the changes of the fluorescence spectra in water. And a simple and sensitive fluorescence quenching method for the determination of trace iron was developed. The method is based on the reaction of SCE with iron in hydrochloric acid medium. The fluorescence intensity was measured with excitation and emission wavelengths of 347 and 457 nm, respectively. The linear range for the determination of iron was 0.66-6.59 microg x L(-1). The detection limit was 51 ng x L(-1). The author contrasted SCE with 7-hydroxy-coumarin to determine Fe3+, and found the sensitivity of SCE is 10(4) higher than that of 7-hydroxy-coumarin. To our thinking there is a carboylate group in SCE, whose coordinate force with iron is stronger than hydroxide radical in 7-hydroxy-coumarin.