Colorimetric sensing of palladium ions based on in situ generation of palladium nanoparticles as an activator for thionine-hydrazine reaction

Palladium is a lustrous silver-white transition metal that is used in modern industrial applications including dentistry, jewelry, medical instruments, electrical devices, fuel cell and catalytic converters in automobile nowadays [1-4]. On the other hand, these applications have led to increasing concentration of palladium in the atmosphere and environmental matrices. It is well known that palladium could affect human health. It may cause skin and eyes sensitization and at high concentration level can bind to thiol containing amino acids, proteins, and other biomolecules causing serious physiological disorders Therefore it is important from analytical viewpoint to monitor palladium concentration in the environment and attentions are made to develop new sensitive method for this purpose. In this new work, attention has been devoted to in situ generation of palladium nano particles (PdNPs) and its catalytic effect on the reduction reaction of thionine by hydrazine. Upon entrance of Pd2+ ions into a medium including hydrazine and thionine, Pd2+ ions were reduced by hydrazine to produce PdNPs which caused depigmentation of thionine by surplus hydrazine. This phenomenon was followed spectrophotometrically by measuring the change in maximum absorbance intensity of thionine (599 nm) versus time. Initially to approve the synthesis of PdNPs, UV-VIS spectroscopy, average particle size and TEM imaging were performed. Then several factors influencing analytical performance of the method such as concentration of reactants and electrolyte, pH of the sample solution and temperature were investigated to achieve the optimum conditions and highest sensitivity. This method showed a linear range from 8-1200 ng mL-1 concentration of palladium ions with a limit of detection of 6.7 ng mL-1. The relative standard deviation was 3.8% and 1.3 % (n=8) for two concentrations of 60 and 300 ng mL-1, respectively. The method was successfully applied to the determination of palladium in river water, pond water and soil samples.