Lead (II) is considered a potentially toxic metal ion and causes various health hazards to human health. Therefore, the development of sensitive and inexpensive techniques for monitoring these metals is necessary. In the Amazon region, the guarana fruit (Paullinia cupana) is widely used by the industry; however, the residues from the grinding process are discarded into nature. In this context, a carbon paste electrode was developed using a biochar (CPE/G) obtained from the pyrolysis at 400 ºC/2h of the guarana husk biomass. The electrode was composed of biomass, graphite powder, and mineral oil (25:50:25), and the structure was assembled in a plastic syringe, with a copper wire used for electrical contact. To evaluate the formation of biochar, XRD and SEM analyses were used. The working range, reversibility kinetics, and active area of the electrode were determined from electrochemical characterization. SWASV parameters were optimized, including effects of pH, accumulation potential, accumulation time, and pulse amplitude. The calibration curve was constructed with an excellent linearity coefficient (R2 = 0.99887) with a linear range from 10 to 30 µg/L, a detection limit of 4.98 µg/L, and a quantification limit of 15.09 µg/L. The applicability was verified using CPE/G in spring water samples, where no voltammetric peak corresponding to Pb2+ was observed. Analysis using Inductively Coupled Plasma Atomic Emission Spectrometer was used as a confirmation method.
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