Dissolution of Platinum Phosphide in a Mixture of Hydrochloric Acid and Nitric Acid after Heating in Concentrated Sulfuric Acid or Melted Sodium Disulfate for Determination of Platinum and Phosphorus

A platinum phosphide sample was constituted of PtP(2) and Pt(5)P(2) which were determined by X-ray diffraction. It had the shape of a thin plate (thickness of about 0.5 mm), and had a platinum-like color. It was not dissolved in aqua regia and other acids, because it was an acid-resistant substance. However, it could be dissolved in a mixture of hydrochloric and nitric acids, after it was heated sufficiently in concentrated sulfuric acid or melted sodium disulfate. Most of the phosphorus was first of all extracted from the phosphide by heat in concentrated sulfuric acid or melted sodium disulfate. On the other hand, most of the platinum remained in it, and the shape of the thin plate virtually remained the same. The platinum was dissolved in a mixture of hydrochloric and nitric acids. Platinum and phosphorus in the phosphide were determined by ICP optical emission spectrometry (ICP-OES) without their loss during dissolution.