Determinação de chumbo em amostras de corante usando um sensor composto de cortiça e grafite

Abstract

Tha lead is one of the most toxic metals in existence, it has a bioaccumulative character, and it is capable of triggering various pathologies when present in the human body. In view of this, it is important detected and quantified the lead in a way easily, reproducible and cheaply in products for human consumption. The progressive hair dyes are manufactured from metallic salts, mainly based on lead, silver or bismuth. Among these salts, the most common is lead acetate, so that the pigmentation of white wires occurs from the formation of lead (II) sulfide, that is generated through the reaction between lead and sulfur, coming from cystine, which is part of the composition of hair keratin. In this present work, lead was determined in three real samples of progressive hair dyes of different brands. The analyzes were performed using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). For CV the initial potential -0.9 V to -0.3 V was applied with a sweep speed of 100 mV/s, for DPV, the deposition potential -0.9 V was applied for 60 seconds and followed by 10 seconds of equilibrium with final potential -0.3 V, respectively. The electrochemical cell consisted in a working electrode comprised of a composite sensor cork/graphite-70% (m/m) (GrRAC-70%), an Ag/AgCl reference electrode and a platinum wire as counter electrode. This system was placed in front of two different support electrolytes, 0.5 M H2SO4 and 0.1 M acetate buffer solution (pH 4.5). The 0.1 M acetate buffer solution (pH 4.5) showed better results in terms of sensitivity to the analyte using the GrRAC-70% electrode, when compared to the 0.5 M H2SO4 electrolyte. Acetate buffer solution obtained good signals for lead in CV and better peak height in DPV. According to the limits calculated by the calibration curve, the detection limits were 1.25 µM and 1.08 µM, for H2SO4 and acetate buffer, respectively. The limits of quantification were 3.79 µM for H2SO4 and 3.28 µM for acetate buffer. The percentages of lead in the three samples were calculated and the results was compared with the one allowed by ANVISA (RDC 15/2013) which is 0.6% of lead in this type of product. It was found that the three graduates were in accordance with the parameters required by ANVISA.