Dispersive liquid–liquid microextraction for simultaneous preconcentration of platinum group elements (Pd, Os, Ir, and Pt) and selected transition elements (Ag, Cd, Ta, and Re) at parts per trillion levels in water and their determination by inductively coupled plasma-mass spectrometry

Abstract

A simple and environmentally friendly procedure for the simultaneous determination of platinum group elements (Pd, Os, Ir and Pt) and selected transition elements (Ag, Cd, Ta and Re) of industrial importance in water has been developed. The elements were extracted as their chloro and/or fluoro (anionic) complexes by dispersive liquid–liquid microextraction (DLLME) and determined by inductively coupled plasma quadrupole mass spectrometry (ICP-QMS). The anionic complexes formed in the presence of 1 mol L⁻¹ HCl and 0.5 mol L⁻¹ F⁻ were extracted into chloroform in the presence of Aliquat® 336 (tricaprylmethylammonium chloride) at room temperature. Analytes were back extracted from the chloroform layer with a mixture of perchloric acid and nitric acid for subsequent determination by ICP-MS. Effective parameters for the complex formation and its extraction, such as the concentration of HCl and KF, volume of the extractant/disperser solvent, extraction time and concentration of the surfactant, have been optimized. The effect of the interfering ions on the recovery of analytes was also investigated. Under optimum conditions, the preconcentration factors of the above elements ranged from 27–75 for 35 mL of water samples for determination by ICP-QMS. The calibration graphs were linear in the range of 10–500 ng L⁻¹ for the 8 elements, with limits of detection ranging from 0.04–0.3 ng L⁻¹. The precision was better than 5% R.S.D. (n = 6). The proposed DLLME procedure was applied to the analysis of lake water contaminated with industrial effluents and hospital wastes, collected from four different locations of a popular lake situated in the middle of the Hyderabad city of Telangana, India. The percentage recovery, spiked to 10 and 20 ng L⁻¹, was in the range from 92–101%. Subsequently, the method was validated by comparing the results obtained by HR-ICPMS with those obtained by spiked recovery using pure standards and a certified precious metal standard (CMS-2).