Development of a Novel and Simple Electroanalytical Procedure for the Determination of Copper in Biofuel Employing a Sensor Based on Vulcan Functionalized with Carbazone

Abstract

A novel and simple electroanalytical method for the determination of Cu 2+ in biodiesel samples by stripping voltammetric analysis was developed. The method employs a carbon paste electrode (CPE) modified with Vulcan carbon, previouly functionalized with carbazone (CBZ). The CPE/Vulcan-CBZ sensor promoted a significant increase in the analytical signal obtained from copper as compared to unmodified CPE, and the CPE modified with Vulcan carbon (CPE/ Vulcan). Vulcan-CBZ, Vulcan and CBZ materials were characterized by Fourier transform infrared spectroscopy (FTIR) technique. The electrochemical behavior of the sensor was evaluated using cyclic voltammetry (CV) and square-wave anodic stripping voltammetric (SWASV) techniques. The CPE/Vulcan-CBZ modified electrode showed excellent response and was able to detect Cu 2+ at nanomolar levels. The electrochemical method is based on preconcentration of Cu 2+ ions on the CPE/Vulcan-CBZ at 0.35 V vs. Ag/AgCl(sat) in 0.2 mol L -1 ammonium sulfate solution ((NH 4 ) 2 SO 4 ), pH 3.5, during 120 s, followed by subsequent chemical stripping. The analytical signal showed a linear response for Cu 2+ concentrations in the range from 6 to 190 nmol L -1 (r = 0.998), with a detection limit of 1.2 nmol L -1 . The sensor was successfully applied for the determination of Cu 2+ in biodiesel and the average recovery varied between 97.0 and 102.8% for the soybean biodiesel samples and between 109.6 and 111.0% for the babassu biodiesel samples showing a good accuracy for the proposed method.Keywords: biofuel, copper, voltammetric sensor, Vulcan carbon, carbazone IntroductionThe pursuit of alternative fuels has been acquiring prominence in the last decades. The replacement of fossil fuels has been motivated by environmental, economical and social factors, since society itself depends on its use. In this context, one alternative that has stood out is the use of biofuels, such as charcoal, alcohol, biogas and biodiesel. 1,2 Biodiesel is a renewable fuel produced either from vegetable sources (soybean, castor oil, palm oil, sunflower, among others) or from ethanol (from sugarcane) or methanol (which can be obtained from wood biomass). 3 It is, therefore, a biodegradable, sustainable and environmentally friendly fuel. However, some metals, such as Cu, Fe, and Ni, can be inserted in the production process with the catalysts, during transportation and storage. Furthermore, the presence of these metals, even at trace levels, can promote the formation of gums and sediments that damage vehicle engines and promote the oxidation of biodiesel. 4,5 Copper, iron and the effect of nickel on biodiesel's stability has been widely evaluated. Among these metals, copper is the most powerful catalyst in biodiesel's oxidation process. 5 Therefore, the monitoring of the amount of copper is extremely important in this fuel for preventing undesirable variations in its physical state and properties, during its use or storage. 5 In this context, it is opportune and necessary to develop novel sensitive and selective anal...

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