A novel approach to the estimation of aqueous solubility of some noble metal vapor species generated by reaction with tetrahydroborate (III)

The solubilities of stable, volatile metal species of Pd, Rh, Cd, Au and elemental Hg in an aqueous medium were estimated. Aqueous solutions were used to trap the species generated by reduction of the aquo ion with tetrahydroborate III. By continuously monitoring the headspace above the trap solution using ICP-MS detection, a saturation condition is readily discerned. Quantitation of the soluble fraction rapidly liberated by sparging the aqueous phase also permits its quantitation. The applicability of this approach was experimentally verified using cold vapour mercury generation to yield a solubility of elemental mercury of 40 ng/ml at 21 °C in a tin chloride reductant medium, in good agreement with a literature value of 44 ng/ml (after correction for salting out). The methodology was then applied to estimation of the solubilities of the gaseous species of Rh, Pd, Cd and Au, yielding values of 0.11, 3, >800 and 1.7 ng/l, respectively.