Tin(II) chloride in the analytical chemistry of the platinum metals: From the “purple of cassius” to polyurethane foams

Abstract

Tin(II) chloride has played a central role in the non-instrumental analytical chemistry of the platinum group metals, the characteristic reaction between tin(II) chloride and platinum(II/IV) chloride having been documented for more than 180 years. The intense colour of hydrochloric acid solutions containing small amounts of Pt(II/IV) and tin(II) chloride constituted one of the first trace colorimetric methods for the determination of Pt in the sub parts per million range. Similar spectrophotometric methods of trace analysis for Rh have been known for more than half a century. Remarkably the detailed nature of the interaction of tin(II) chloride with the platinum group metals has only been elucidated relatively recently, and there is evidence of recent renewed interest in platinum group metal complexes involving the SnCl 3 − moiety as ligand. We wish here to give a brief history of the use of tin(II) chloride in the analytical chemistry of the platinum group metals, highlighted by some of our recent work involving the selective immobilization of chloro(trichlorostannato)platinum/rhodium complex anions by polyurethane foams as a means of separation and pre-concentration of small amounts of Rh and Pt.