Fluorescent Studies of Salicylaldehyde and Other Related Carbonyl Compounds for the Selective and Sensitive Detection of Zinc(II) Ions in Aqueous Solution

Salicylaldehyde was found to have a high selectivity for zinc ions with simultaneous enhancement of fluorescence in aqueous buffer solution at optimum pH 8.5. The stoichiometry of the complex was determined to be 1:1 with a Ka value of 3.4 × 104 M−1 at 298 K. The fluorescence of the complex is not affected by common anions and Zn2+ binds preferentially to salicylaldehyde in the presence of alkali, alkaline earth and heavy metal cations (Hg2+, Cd2+, Cr3+ and Ni2+). This property is not observed with related phenolic compounds bearing a carbonyl group such as esters, amides, carboxylic acids and ketones.