An acid induced mixed-micelle mediated cloud point extraction for the separation and pre-concentration of platinum from road dust and determination by inductively coupled plasma mass spectrometry

Abstract

An acid induced mixed-micelle mediated cloud point extraction procedure is developed for the separation and pre-concentration of platinum from digested road dust matrices. The mixed-micelle is formed from the micelle–micelle interaction of cetyltrimethylammonium bromide (CTAB) (cationic) and Triton X-100 (nonionic) surfactants. Nitric acid induces the clouding as well as phase separation in these mixed-micelles. In the presence of mixed acids (HCl and HNO₃), platinum forms stable and extractable anionic species compared to palladium and rhodium, which provides the quantitative separation of platinum, from palladium and rhodium, by forming the hydrophobic ion-associated complex with quaternary ammonium head groups of mixed-micelles. This hydrophobic complex is subsequently pre-concentrated from a bulk aqueous phase into a small mixed-micelles rich phase, avoiding the addition of an external chelating agent. The potential oxide interference of Hf is eliminated effectively up to 1 mg L⁻¹ level, enabling interference free determination of ¹⁹⁵Pt using inductively coupled plasma mass spectrometry (ICP-MS). The parameters affecting the extraction process are optimized. Under the optimized conditions, the pre-concentration factor and detection limit are 13 and 10 pg g⁻¹, respectively. The recoveries are in the range 92–99% at 100–200 pg mL⁻¹ with relative standard deviation 2.0–3.5%. The accuracy of the procedure is evaluated by platinum determination in certified reference materials such as CCRMP PTC-1a Copper-Nickel sulfide concentrate and BCR 723 Road dust and the results agreed with the certified values with 95% confidence level, as well as being applied to road dust samples.