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-Cu2+ 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 mu M. The detection limit of this system was found to be 5.6 mu M and the relative standard deviation for five measurements of 78.7 mu M concentration was 5.2%. This fluorescent chemosensor also showed a high selectivity for copper ions over other metal ions, such as Al3+, Ca2+, Cd2+, Fe2+, K+, Me+, Na+, Pb2+, or Zn2+. 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.