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

A preconcentration method for low concentrations of Ag, As, Au, Cd, Cu,Pb a nd Se in water, using cloud point extraction is proposed. The analytes in t he initial aqueous solution, acidified with hydrochloric acid, are complexe d 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. A fter phase separation, by increasing the temperature above 20 degrees C, de pending on the cloud point of the mixture, and dilution of the surfactant-r ich 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 c oupled plasma mass spectrometry, using ultrasonic nebulization, injecting 1 00 mu l 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 facto rs are obtained. After optimization of the complexation (pH and DDTP concen tration), of extraction conditions, sample introduction (FI and ultrasonic nebulizer parameters) and spectrometer conditions, the method was applied t o the analysis of riverine water, sea water and enriched water reference ma terials, and good agreement with the certified values was obtained. By intr oducing the organic extract with the FI system and using ultrasonic nebuliz ation, no carbon deposits on the interface cones and lens were observed, al lowing extensive use of the spectrometer without cleaning and re-optimizati on. (C) 2000 Elsevier Science B.V. All rights reserved.