Comparison of different permanent chemical modifiers for lead determination in Orujo spirits by electrothermal atomic absorption spectrometry

Different analytical methods for the determination of lead in Orujo spirits by electrothermal atomic absorption spectrometry (ETAAS) were developed using permanent modifiers (W, Ir, Ru, W-Ir and W-Ru) thermally deposited on platforms inserted in pyrolitic graphite tubes and Pd-Mg(NO₃)₂ conventional modifier mixture. In all cases, the Pb determination was performed without any sample pretreatment or preconcentration steps. The comparison between the chemical modifiers employed has been made in terms of pyrolysis and atomization temperatures, characteristic masses, detection limits, and atomization and background signal shapes. The limits of detection obtained were 0.375, 0.387, 0.109, 0.251 and 0.267 ng mL⁻¹ for W, Ir, Ru, W-Ir and W-Ru, respectively and 0.710 ng mL⁻¹ for Pd-Mg(NO₃)₂. The characteristic masses were 14.1, 11.2, 5.6, 8.3 and 9.3 pg for W, Ir, Ru, W-Ir and W-Ru, respectively and 22.2 pg for Pd-Mg(NO₃)₂. For all the developed procedures using the different modification systems, the relative standard deviations (<10%) and the analytical recoveries (95-103%) were acceptable. The more suitable methods for Pb determination in distillate spirits were those using permanent modifiers in contrast with classical Pd-Mg(NO₃)₂. The best analytical performance was achieved for W, Ir and W-Ir methods, which were applied to lead determination in Orujo spirit samples from Galicia (NW Spain). The Pb concentrations found in the analyzed samples were comprised in the range (<LOD to 1.5 μg mL⁻¹).