Abstract
A novel and simple electroanalytical method for the determination of Cu2+ 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 Cu2+ at nanomolar levels. The electrochemical method is based on preconcentration of Cu2+ ions on the CPE/Vulcan-CBZ at 0.35 V vs. Ag/AgCl(sat) in 0.2 mol L-1 ammonium sulfate solution ((NH4)2SO4), pH 3.5, during 120 s, followed by subsequent chemical stripping. The analytical signal showed a linear response for Cu2+ 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 Cu2+ 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.
Highlights
The pursuit of alternative fuels has been acquiring prominence in the last decades
Optimization of the experimental and operational conditions of the square-wave anodic stripping voltammetric (SWASV) technique In order to verify the effect of the carbon paste composition in the voltammetric response of the electrodes, analytical curves were constructed by SWASV using the following composition of Vulcan-CBZ:graphite powder (% m/m): 2.5:72.5; 5:70; 7.5:67.5; 10:65; 12.5:62.5; 15:60, and 25% m/m of mineral oil, on electrodes
There is a small variation of the sensitivity for the determination of the copper, the shift of the sensitivity for determination of the analyte of interest in presence of foreign species was lower than 7% when compared to sensitivity of the sensor for the determination of the analyte in the absence of each interfering species. These results suggest that these ions do not significantly interfere in the determination of copper
Summary
The 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. This work describes the synthesis and application of the Vulcan-cabarzone composite (Vulcan-CBZ) for the determination of copper ions (Cu2+) in complex samples, such as biodiesel, aiming to the development of a stable, sensitive and selective voltammetric sensor.
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