Tratamento de amostras de cosméticos faciais para análise eletroquímica de cobre, chumbo e zinco

Abstract

Cosmetic products such as eye shadow, compact powder and lipstick are used too much by the feminine society in search of a better appearance. However, it is important to note that not all products are free from impurities such as metals, which can be toxic to humans. The objective of this work was to optimize a suitable procedure for the treatment of facial cosmetic samples (lipstick, compact powder and eye shadow), employing experiment planning (Box Behnken and factorial 32 with triplicate at the central point), With digestion in heating plate and microwave oven using concentrated nitric and hydrochloric acid mixtures, for the electrochemical determination of copper, lead and zinc. For analysis of these metals we worked with a set of three electrodes: mercury modified glass carbon electrode (work), Ag / AgCl (reference) and platinum (auxiliary).The modification of the glassy carbon electrode with mercury was done in situ, that is, simultaneously with the deposition of the analytes, being necessary the time of 300 s for deposition. Parameters involved with the step of redissolution of the square wave voltammetry frequency, amplitude and potential increase were optimized univariate. being the conditions optimized respectively (60 Hz, 45 mV and 7 mV). Copper and lead analyzes were performed simultaneously using 0.1 M hydrochloric acid as the electrolyte, While the zinc was analyzed separately using the 0.1 M acetate buffer (pH = 4.6) as the electrolyte. The microwave oven was the method chosen for digestion of all samples of facial cosmetics, where recoveries varied from 83-108%, 67-76% and 75-103% respectively for copper, lead and zinc. Limits of detection of the method for copper, lead and zinc varied from 0,05-0,36 μg g -1, and the limits of quantification of 0,36-1,16 μg g -1. Nine samples were analyzed, with concentrations of Cu, Pb and Zn varying respectively in 14-26.68 μg g-1; 1.319.74 μg g-1 and 7.1-42064 μg g -1. For the validation of the results obtained electrochemically, an F AAS (Cu and Zn) and GF AAS (Pb) were used. From statistical tests it was verified that there was no evidence of significant differences between the electrochemically developed method and F AAS, GF AAS with 95% confidence. The concentration levels found for metals are below the level established by the European company and do not pose a risk to human health as regards the metals analyzed.