Sequential voltammetric determination of ultratrace osmium, ruthenium and iridium. Application to superficial water.

The present work, regarding the determination of ultra-trace Os(VIII), Ru(III) and Ir(III) in superficial waters is an interesting example of the possibility to simultaneously, or better sequentially determine each single element in real samples by voltammetry. The method is based on the catalytic current of the Os(VIII)- and Ru(III)-bromate systems by square wave voltammetry and on the Ir(III) determination by square wave catalytic adsorptive stripping voltammetry. 0.5 mol L-1 acetate buffer pH 4.9 + 7.7x10-2 mol L-1 NaBrO3 and 0.5 mol L-1 acetate buffer pH 4.9 + 7.7x10-2 mol L-1 NaBrO3 + 2.3x10-5 mol L-1 cetyltrimethylammonium bromide (CTAB) + 0.2 mol L-1 KCl were employed as the supporting electrolytes. The analytical procedure was verified by the analysis of the standard reference materials: Sea Water BCR-CRM 403 and Fresh Water NIST-SRM 1643d. For all the elements, the accuracy, expressed as relative error e %, was satisfactory, being lower than 6%, while precision as repeatability, expressed as relative standard deviation sr %, was generally lower than 5%. Once set up on the standard reference materials, the analytical procedure was transferred and applied to superficial water sampled in proximity to superhighway and in the Po river mouth area.