Development of a fluorescent chelating ligand for gallium ion having a quinazoline structure with two Schiff base...

A novel chelating ligand, 2,4-[bis-(2,4-dihydroxybenzylidene)]-dihydrazinoquinazoline (DBHQ), was synthesized, and the fluorescence characteristics of its complex with metal ions were investigated. Thirty-five different metal ions were tested for the emission of fluorescence in the presence of DBHQ in aqueous solutions in a pH range of 3.0-10.5 (at a difference of 0.5 for each metal). It was observed that DBHQ fluoresces intensely at 470nm with an excitation wavelength of 405nm in the presence of Ga(3+) or Al(3+) in the pH range 3.0-4.0. The other metal ions did not show fluorescence with DBHQ. Although the presence of Cu(2+), Co(2+) and Fe(3+) decreased the fluorescence intensity of DBHQ-Ga(3+), the addition of a fluoride ion (NaF) recovered the fluorescence by masking the interfering ions. In addition, the fluoride ions were found to enhance the sensitive determination of Ga(3+) because the fluorescence intensity of DBHQ-Ga(3+) was further increased approximately 2.5-fold in the presence of F(-) (phi=0.658) from that in the absence of F(-) (phi=0.401). The fluoride ions also masked the Al(3+) ions, which emit fluorescence on chelation with DBHQ. Therefore, a selective and sensitive detection of Ga(3+) was achieved by using DBHQ in the presence of F(-). The detection limit of Ga(3+) was approximately 50nmolL(-1) (3.5ppb). The proposed method was applicable to determine Ga(3+) in river water.