Cloud point extraction for the determination of lead and cadmium in urine by graphite furnace atomic absorption spectrometry with multivariate optimization using Box-Behnken design

Cloud point extraction (CPE) is proposed as a pre-concentration procedure for the determination of Pb and Cd in undigested urine by graphite furnace atomic absorption spectrometry (GF AAS). Aliquots of 0.5 mL urine were acidified with HCl and the chelating agent ammonium O,O-diethyl dithiophosphate (DDTP) was added along with the non-ionic surfactant Triton X-1 14 at the optimized concentrations. Phase separation was achieved by heating the mixture to 50 degrees C for 15 min. The surfactant-rich phase was analyzed by GF AAS, employing the optimized pyrolysis temperatures of 900 degrees C for Ph and 800 degrees C for Cd, using a graphite tube with a platform treated with 500 mu g Ru as permanent triodifier. The reagent concentrations for CPE (HCl, DDTP and Triton X-114) were optimized using a Box-Belinken design. The response surfaces and the optimum values were very similar for aqueous solutions and for the urine samples, demonstrating that aqueous standards submitted to CPE could be used for calibration. Detection limits of 40 and 2 ng L-1 for Ph and Cd, respectively, were obtained along with an enhancement factor of 16 for both analytes. Three control urine samples were analyzed using this approach, and good agreement was obtained at a 95% statistical confidence level between the certified and determined values. Five real samples have also been analyzed before and after spiking with Ph and Cd, resulting in recoveries ranging from 97 to 118% (C) 2007 Elsevier B.V All rights reserved.