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

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 Pt-195 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.