Spectrofluorimetric determination of 5-fluorouracil by fluorescence quenching of 9-anthracenecarboxylic acid

Photo-induced intermolecular electron transfer (PET) interaction between excited singlet (S1) state of 9-anthracene carboxylic acid (9-ANCA) and DNA bases of pyrimidines as uracil and 5-fluorouracil (5-FU) has been studied in water and ethanol solutions using steady-state fluorescence spectroscopy. The intensity of all emission bands of 9-ANCA was quenched in presence of uracil and 5-FU by electron transfer reaction without formation of an exciplex. It was found that uracil and 5-fluorouracil acts as effective electron donors and simultaneously quench the fluorescence of electron-accepting sensitizer 9-ANCA. The quenching by diffusion-controlled rate coincides well with the dynamic Stern–Volmer correlation. The bimolecular quenching rate constant (kqss) and electron transfer rate constant (ket) observed are seen to be much higher for 5-fluorouracil than those for uracil. The thermodynamic parameters estimated by using the Rehm–Weller equation were used to propose a suitable mechanism for PET occurring between uracils and 9-ANCA. The proposed method was used to determine 5-fluorouracil from pharmaceutical samples with satisfactory results. The technique is more selective, sensitive and relatively free from coexisting substances.