Solution equilibria of palladium(ll) with 2-mercaptonicotinic acid and spectrophotometric determination of palladium

Abstract

The solution equilibria between palladium(ll) and 2-mercaptonicotinic acid (MENA) has been studied spectrophotometrically in 40% ethanol-water medium at 25±0.1°C and <i>I=</i>0.1 <i>M </i> NaCIO₄. The spectra of equimolar solutions and solutions containing an excess of one component reveal the formation of two complex species in the <i>p</i>H range ~ 0.5-4.5, depending on the acidity of the medium and the concentration of components. A sensitive, rapid and selective method has been developed for the determination of microgram amounts of palladium based on the formation of Pd (MENA) (1:1) complex at <i>p</i>H 3.5 (ɛ = 1 x 10⁴ I mol^-1 cm^-1 at 410 nm). The method has been applied for the determination of palladium in catalysts and in synthetic samples with compositions identical to those of some dental alloys.