Selective chemosensor for copper ions based on fluorescence quenching of a Schiff-base fluorophore

A Schiff base-based fluorescent chemosensor has been studied for divalent copper detection. The formation of 2-hydroxybenzaldehyde benzoylhydrazone-Cu(2+) complex induced a fluorescence quenching of this compound in a medium of water/ethanol (53% v/v) and 0.05 M phosphate buffer (pH 7.0). The continuous variations and mole-ratio plots of absorbance suggested a complex formation with a 1:1 metal-ligand stoichiometry. The conditional stability constant for the complex was evaluated to be 6 x 10(6) M(-1). A modified Stern-Volmer relationship was employed to obtain a linear calibration plot, obtaining a dynamic working range up to 157.4 microM. The detection limit of this system was found to be 5.6 microM and the relative standard deviation for five measurements of 78.7 microM concentration was 5.2%. This fluorescent chemosensor also showed a high selectivity for copper ions over other metal ions, such as Al(3+), Ca(2+), Cd(2+), Fe(2+), K(+), Mg(2+), Na(+), Pb(2+), or Zn(2+). The results of this investigation show a simple, rapid, low-cost, and selective method that can operate in neutral solutions and is useful for biological and environmental applications.