Fabrication of a novel palladium membrane sensor for its determination in environmental and biological samples

A novel sensitive, specific, and reversible optical sensor for the palladium(II) ion was created by impregnating an agarose membrane with 4-(2-amino-3-hydroxypyridine-4-ylazo)1,5-dimethyl-2-phenyl-1,2-dihydropyrazol-3-one (AHDDO). Spectrophotometric studies of complex formation between the AHDDO base ligand and Mn²⁺, Cd²⁺, Co²⁺ Hg²⁺, Zn²⁺, Cu²⁺, Pd²⁺, Sr²⁺, Al³⁺, Fe³⁺, Au³⁺, and Ag⁺ metal ions in an ethanolic solution indicated a substantially larger stability for the palladium ion complex. Therefore, the AHDDO was immobilized on a clear agarose film and used as a suitable ionophore for building a selective Pd²⁺ optical sensor. By combining the sensing membrane with Pd²⁺ ions at pH 5.75, a transparent color change from orange to violet was observed. On the immobilization of AHDDO, the effects of ionophore concentration, pH, temperature, stirring, and reaction time were investigated. A linear relationship was observed between the membrane absorbance at 633 nm and Pd²⁺ concentrations in a range from 15 to 225 ng mL⁻¹ with detection (3σ) and quantification (10σ) limits of 4.25 and 14.25 ng mL⁻¹, respectively. For the determination of Pd²⁺ ions, no significant interference from at least 400-fold excess concentrations of a number of possibly interfering ions was found. The sensor exhibits remarkable selectivity for Pd²⁺ ions and can be regenerated through exposure to 0.15 M HNO₃. The sensor has been successfully used to find palladium in biological, soil, road, and water samples.