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This paper reports the development of a microwave-assisted procedure for leaching of copper, iron, manganese, and zinc from multivitamin/multimineral supplements by use of dilute acid before determination by flame atomic absorption spectrometry (FAAS). A Doehlert design was used to find optimum conditions for the procedure by use of response-surface methodology. Three variables (acid concentration in the leaching solution, irradiation time, and irradiation power) were used as factors in the optimization study for two acids, HCl and HNO3. Final working conditions were established as a compromise between the optimum values for each analyte, taking into consideration the robustness of the procedure. The best leaching results were obtained with HNO3 and the acid concentration, irradiation time, and irradiation power used were 0.70 mol L−1, 15 min and 360 W, respectively. The accuracy of the optimized procedure was evaluated by comparison with a well-established closed-vessel microwave dissolution technique. [ABSTRACT FROM AUTHOR]

This paper proposes a preconcentration procedure for determination of nickel in saline aqueous waste samples by flame atomic absorption spectrometry (FAAS). It is based on cloud-point extraction of nickel(II) ions as 2-(5-bromo-2-pyridylazo)-5-diethilaminophenol (Br-PADAP) complexes using octylphenoxypolyethoxyethanol (Triton X-114) as surfactant. The optimisation step was performed using a four-variable Doehlert design, involving the factors centrifugation time (CT) of system after addition of surfactant, solution pH, methanol volume (MV) added at micellar phase, and buffer concentration (BC). The analytical response used was absorbance, after volume correction. Using the established experimental conditions in the optimisation step the procedure enables nickel determination with a detection limit (3δ/S) of 0.2 μg L-1, quantification limit (10δ/S) of 0.7 μg L-1, and precision, calculated as relative standard deviation (RSD) of 4.7 (n=8) and 3.5% (n=8) for nickel concentration of 1 and 5 μg L-1, respectively. The preconcentration factor, determined from the ratio of the slopes of the analytical curves with and without preconcentration, is 74. The recovery achieved for nickel determination in the presence of several cations demonstrated that this procedure could be applied for analysis of water samples. The robustness was checked by using saturated fractional factorial designs, centred on the established experimental conditions in the optimisation step. The results of these tests demonstrated that the variables centrifugation time and buffer concentration are robust for modification by 10% and that solution pH and methanol volume are robust for 5%. Accuracy was evaluated by using the certified material reference SLEW-3 estuarine water for trace metals. The procedure was used for determination of nickel in saline effluents from oil refinery samples. Recovery results (95–104%) indicate that the procedure has satisfactory accuracy for nickel determination in these samples. [ABSTRACT FROM AUTHOR]

A system for on-line preconcentration and determination of lead by flame atomic absorption spectrometry (FAAS) was proposed. It was based on the sorption of lead(II) ions on a minicolumn of polyurethane foam loaded with 2-(2-thiazolylazo)-5-dimethylaminophenol (TAM). The optimisation step was carried out using two-level full factorial and Doehlert designs for the determination of the optimum conditions for lead preconcentration. The proposed procedure allowed the determination of lead with a detection limit of 2.2 μg L-1, and a precision, calculated as relative standard deviation (RSD), of 2.4 and 6.8 for a lead concentration of 50.0 and 10.0 μg L-1, respectively. A preconcentration factor of 45 and a sampling frequency of 27 samples per hour were obtained. The recovery achieved for lead determination in the presence of several cations demonstrated that this procedure has enough selectivity for analysis of environmental samples. The validation was carried out by analysis of certified reference material. This procedure was applied to lead determination in natural food. [ABSTRACT FROM AUTHOR]