Emprego da voltametria de onda quadrada para a determinação e estudo da extração de metais de amostras de sombra para olhos

Abstract

In this work, a voltammetric method was developed for the determination of Bi3+ in eye shadow samples. The technique used was square wave anodic stripping voltammetry, with glassy carbon electrode, in 1.0 mol L-1 NaOH. In this supporting electrolyte, the limit of detection obtained for Bi3+ was 8 nmol L-1 (1.7 ppb). Among the different procedures studied for sample pretreatment, the best performance for Bi3+ extraction was obtained with ASTM D335-85a method, reference method for ink sample treatment; and with a proposed alternative method, based on the sample treatment with concentrated HCl solution, 30 % (v / v) H2O2, combined with ultrasonic radiation bath. Bi3+ contents found in the samples that presented this metal in their original composition were in good agreement with those obtained with atomic absorption spectroscopy using either ASTM or the proposed method with HCl, H2O2 and ultrasound radiation as sample pretreatment procedure. For the samples without Bi3+ in their original composition, addition recovery experiments were conducted and recovery percentages close to 100 % were always obtained. These results indicate that both the sample pretreatment procedure and the voltammetric method developed are efficient for the determination of Bi3+ in eye shadow samples. The square wave anodic stripping voltammetry was also employed to evaluate the efficiency of different sample pretreatment procedures for Bi3+ extraction. This evaluation was performed using an CPE with friction-immobilized particles. Particles of the untreated original samples and the solid residues from different sample pretreatment procedures were immobilized onto CPE. The absence of Bi3+ voltammetric peak in the solid residues was the indicative for quantitative extraction of this metal. The toxic metals Cd2+ and Pb2+ were not detected in the analyzed samples, suggesting these metals are absent or they are present at concentrations bellow the limit of detection of the proposed method. Pb2+ addition-recovery experiments were conducted with four eye shadow samples and recovery percentages close to 100 % were obtained. This result suggests that the methods proposed for sample pretreatment and voltammetric determination could also be used for Pb2+ determination in eye shadow samples. Thus, this work demonstrated that the voltammetry has a great and almost unexplored potential to contribute to the quality control of cosmetics regarding their heavy metal contents.