Selective complexometric determination of palladium with sodium metabisulphite as releasing agent

Sodium metabisulphite has been proposed as a selective releasing agent for the rapid and selective complexometric determination of palladium. Pd(II) present in a given sample solution is first complexed with excess of EDTA and the surplus EDTA is back titrated with standard zinc sulphate solution at pH 5-5.5 (acetic acid-sodium acetate buffer) using xylenol orange as indicator. Sodium metabisulphite solution is then added to displace EDTA quantitatively from the Pd-EDTA complex. The released EDTA is back titrated with standard zinc sulphate solution as before. The method works well in the concentration range 2-20 mg of Pd with a relative error ≤ 0.40% and relative standard deviation ≥ 0.65%. The method has been applied to the determination of palladium in catalysts, alloys and complexes.