Determination of trace elements in water samples by ultrasonic nebulization inductively coupled plasma mass spectrometry after cloud point extraction

Abstract

A preconcentration method for low concentrations of Ag, As, Au, Cd, Cu, Pb and Se in water, using cloud point extraction is proposed. The analytes in the initial aqueous solution, acidified with hydrochloric acid, are complexed with ammonium O, O-diethyl-dithiophosphate, and 0.05% m/v Triton X-114 is added as surfactant. The complexation allows the separation of the analytes from alkali, alkaline earth and other elements, which are not complexed. After phase separation, by increasing the temperature above 20°C, depending on the cloud point of the mixture, and dilution of the surfactant-rich phase with a mixture of 60% v/v methanol and 40% v/v of 1% v/v aqueous nitric acid solution, the enriched analytes are determined by inductively coupled plasma mass spectrometry, using ultrasonic nebulization, injecting 100 μl of the enriched phase with a flow injection (FI) system. Since the initial volume is 40 ml and the final volume is 1 ml, good enrichment factors are obtained. After optimization of the complexation (pH and DDTP concentration), of extraction conditions, sample introduction (FI and ultrasonic nebulizer parameters) and spectrometer conditions, the method was applied to the analysis of riverine water, sea water and enriched water reference materials, and good agreement with the certified values was obtained. By introducing the organic extract with the FI system and using ultrasonic nebulization, no carbon deposits on the interface cones and lens were observed, allowing extensive use of the spectrometer without cleaning and re-optimization.