Extração em fase sólida e voltametria de redissolução anódica: uma estratégia para quantificação de chumbo em nível traço

Abstract

Considering the environmental pollution and damage caused to living beings due to heavy metal contamination, especially lead, it was developed an extraction method for this metal in aqueous samples by using the ion exchange resin Amberlite IR-120. It is known that the anodic stripping voltammetry is widely used for the quantification of trace levels of elements due to their high sensitivity, being used together with bismuth-film chemically modified electrodes for the determination of lead. Studies involving the optimization of the supporting electrolyte were conducted in order to evaluate which one would provide the best peak intensity relative to lead. Still in the optimization studies, it was confirmed the advantage of the using the bismuth film by adding Bi3+ to the supporting electrolyte, it was observed a significant increase in the voltammetric peak of lead. Thus, the studies showed that the most suitable supporting electrolyte was 0.1 mol L-1 acetate buffer in the presence of 10 µmol L-1 Bi3+. Subsequently, it was carried out a treatment/activation of the resin-active sites with HCl 1 mol L-1. Ca(NO3)2 solutions at different concentrations were added to the electrochemical cell aiming to improve the kinetics of the releasing of the adsorbed Pb2+. However, it was not observed a significant improvement, therefore, the Pb2+ releasing was studied in the supporting electrolyte containing only Bi3+. Different concentrations of Pb2+, 10 and 50 nmol L-1, were used in order to evaluate the percentage of metal extraction and recovery, and both concentrations provided almost the same percentages (33 ± 8) % and (32 ± 11) %, respectively. Despite the low recovery percentage, some results showed that the proposed method brought a significant enhancement of detectability when comparing the analytical signal of 10 nmol L-1of Pb2+ in the electrochemical cell with and without the extraction procedure. Thus, the cationic resin used in the proposed method has the potential to extract and pre-concentrate lead, as well as the use of the bismuth film chemically modified electrodes coupled to anodic stripping voltammetry technique brought sensitivity enhancement to the proposed method, in view of the objective of detection at trace level of lead. Future perspectives involve the application of the method developed in several aqueous and non-aqueous samples.