Optimization of Extraction Procedure with Nonionic Surfactant for Determination of Trace Lead in Waters

Abstract

In this work, cloud point extraction was applied as a separation/preconcentration step for trace Pb prior to its determination by electrothermal atomic absorption spectrometry. After complexation with ammonium pyrrolidine dithiocarbamate, the analyte was quantitatively extracted to the phase rich in the non-ionic surfactant Triton X-114. Important factors affecting extraction efficiency were investigated in detail and optimized. After separation of aqueous bulk solution from surfactant-rich phase, the final extract was diluted by 200 μL of methanol acidified with 0.2 mol L^–1 HNO₃. After such a dilution, under the optimized conditions (using initial sample volume of 10 mL), the enrichment factor of 32, the detection limit of 0.06 μg L^–1, the quantification limit of 0.20 μg L^–1, the relative standard deviation of 3.8 % (for 2 μg L^–1 of Pb; n = 14), the linearity of the calibration graph in the range of 0.2–2.4 μg L^–1 (with the correlation coefficient higher than 0.995) were achieved. The optimized method was validated by the analysis of a certified reference material (TMDA-61). Extraction recoveries for the CRM and spiked model solutions were in the range of 92–101 %. Finally, the method was applied to the separation/preconcentration and determination of trace Pb in different kinds of waters.