Potentiometric determination of silver(I), palladium(II) and gold(III) in mixtures by use of an iodide-selective electrode

Abstract

Two procedures are proposed for the potentiometric determination of Ag(I), Pd(II) and Au(III) in binary mixtures, by titration with potassium iodide solution, and use of a commercial iodide electrode as sensor. In the first procedure, two aliquots of the mixture are titrated, at pH 2.0 _+ 0.2 and 9.0 + 0.2, adjusted with dilute sulphuric acid and ammonia solution. At pH 2.0, the titrant reacts with both metals, whereas at pH 9.0, Ag(I) is the only reactant. The second procedure utilizes titration of two aliquots of the mixture in the presence and absence of a selective masking agent. The methods have been applied to the determination of these metals in some jewellery alloys. Experimental ReagentsAll solutions were prepared with doubly distilled water and analytical-reagent grade chemicals, unless stated otherwise. A standard 5 mM potassium iodide solution was used throughout. Silver nitrate, palladium(II) chloride and hydrogen tetrachloroaurate stock solutions (5 raM) were prepared. Solutions of the masking agents (0.1% dimethylglyoxime in ethanol, 0.1 M citric acid and 0.1 M potassium thiocyanate) were prepared from commercially available reagents. ApparatusThe potentiometric measurements were made with an Orion pH-ion meter (Model EA 920) fitted with an Orion solid-state iodide-sensitive electrode (Model 94-53) and an Orion single-junction reference electrode (Model 90-01). In pH adjustment an Orion pH-electrode (Model GX 91-05) was used.