Simultaneous determination of copper, mercury and zinc in water with a tailored fluorescent bipyridine ligand entrapped in silica sol-gel.

A novel fluorescent ligand, (4-[(E)-2-(4'-methyl-2,2'-bipyridin-4-yl)vinyl]phenol) (abbreviated BSOH), has been designed and prepared for simultaneous determination of heavy metals in water. Its photophysical and photochemical properties in the absence and in the presence of Cd(II), Cu(II), Hg(II), Ni(II) and Zn(II) were determined, and the respective complexation constants (7.4 × 10(3)-2.8 × 10(8) l mol(-1)) and stoichiometries were extracted thereof. The Stern-Volmer emission intensity and lifetime plots indicate an efficient static quenching of the indicator dye with the heavy metals. The BSOH fluorescent reagent has been successfully immobilised in a silica sol-gel matrix for automation of the analytical method, and the sensing phase demonstrated a reversible response to Cu(II), Hg(II) and Zn(II) but not to Cd(II) and Ni(II). Characterisation of the sensor showed that its response to those heavy metals is linear in the 2.5 to 50 μmol l(-1) range, with a response time (t (90)) on the order of 100 min, providing detection limits of 9.0 × 10(-7), 4.7 × 10(-7) and 2.9 × 10(-7) mol l (-1) for Zn(II), Cu(II) and Hg(II), respectively. Due to the stability of the immobilised ligand, which presented no leaching from the sol-gel matrix, the simultaneous determination of the three cations in water was feasible by employing multivariate calibration techniques coupled to fluorescence quenching measurements. The sensor was validated with recovery tests by addition of Cu(II) and Hg(II) ions to spring waters, providing results with standard errors lower than 4.1 μmol l (-1).