Coacervative extraction of trace lead from natural waters prior to its determination by electrothermal atomic absorption spectrometry

Abstract

In this work, a relatively simple and sensitive method for separation/preconcentration of trace lead from natural waters prior to its determination by electrothermal atomic absorption spectrometry has been proposed. The method is based on the extraction of Pb–dithizone chelate with coacervates made up of lauric acid in the presence of potassium ions and methanol. Several important factors affecting extraction efficiency such as pH, concentration of lauric acid and dithizone, ionic strength, incubation and centrifugation time were investigated and optimized. After separation of aqueous bulk solution from surfactant-rich phase, the final extract was redissolved by using 500μl of methanol acidified with 0.2moll−1 HNO3. Under the optimized conditions (using initial sample volume of 10ml), enrichment factor of 17.0, detection limit of 0.12μgl−1, quantification limit of 0.38μgl−1, relative standard deviation of 4.2% (for 2μgl−1 of Pb; n=26), linearity of the calibration graph in the range of 0.5–4.0μgl−1 (with correlation coefficient better than 0.995) were achieved. The method was validated by the analysis of certified reference material (TMDA-61). Extraction recoveries for the CRM, spiked model solutions and spiked natural water samples were in the range of 91–96%. Finally, the method was applied to the separation/preconcentration and determination of trace lead in natural waters.