This work presents the use of a smart electronic tongue for discriminating adulterated milk samples with various concentrations of sucrose. The smart electronic tongue was integrated by a voltammetric sensor array from polypyrrole doped with various doping agents, a portable multi-potentiostat controlled by a smartphone with an Android application. Sucrose concentrations ranging from 1% to 20% were used to adulterate the tested samples. The sensor array was optimized to perform measurements on milk while maintaining good performance in terms of stability and signal quality. The sensor array was prepared by chronoamperometric electropolymerization of pyrrole with different doping agents, varying polymerization time (from 50 to 300 s), and concentration of monomer (from 0.10 to 0.40 M) and doping agent (from 0.05 to 0.30 M). The optimization process results demonstrated that the parameters polymerization time, monomer concentration, and doping agent concentration affect the stability of the signals in the sensors, allowing for the establishment of adequate conditions to guarantee maximum stability through an experimental design. Thus, values of 0.10 M for monomer concentration, 0.05 to 0.10 M for doping agent concentration, and 50 to 70 s for polymerization time were established. The measurements taken with the smart electronic tongue on the milk samples allowed a principal component analysis to classify the samples in the plane of the first two principal components. Principal components 1 and 2 registered a variance of 93.39% (78.68% and 14.71%, respectively), indicating a high degree of information registered by the sensor array. It could be concluded that the array of optimized polypyrrole sensors allows sufficient information to be recorded through measurements made with the smart electronic tongue to discriminate adulterated milk samples with different sucrose concentrations.
This paper approaches the study of pH's effect on elaborate films of solid biopolymer electrolyte from cassava starch and its impedantiometric response. The films of solid biopolymer electrolyte were elaborated by thermochemical synthesis while varying the pH (2, 4, 5, 7, 9, 10, and 12). Starch was extracted from cassava tubers by a traditional method (disintegrated, washed, decanted, filtered, and dried). Solid biopolymer electrolyte films were processed by thermochemical synthesis by adding plasticizers (glycerol, glutaraldehyde, and polyethylene glycol) and lithium salt (lithium perchlorate). The impedance behavior was studied using the electrochemical impedance spectroscopy technique. The Nyquist and Bode's diagrams registered presented a similar trend in all the films; therefore, they were described by the same equivalent circuit model. However, the equivalent circuit components presented different values in each case. The conductivity and capacitance showed a quadratic polynomial tendency in relation to the pH, obtaining the highest conductivity in the films elaborated at acidic pH and the highest capacitance in the films elaborated at basic pH. The degree of basicity or acids allowed conductivity to be modulated or capacitance of the solid biopolymer electrolyte as required. It could be concluded that the production pH has a marked effect on impedantiometric behavior of films of solid biopolymer electrolyte from cassava starch, which may be useful to modulate the electrochemical properties of this type of material in future Applications.
Corrosion is one of the great problems that many industries face and that generates losses of millions of dollars worldwide. The aim of this work was to evaluate the capacity of polyaniline to increase the anticorrosive capacity of a commercial epoxy paint. Polyaniline was chemically synthesized by oxidation with ammonium persulfate and doped with oleic acid. Polyaniline was added to the paint in various concentrations to evaluate its behavior as an additive to improve the anticorrosion capacity on stainless steel samples. An electrochemical characterization by polarization curves and visual observation was carried out to evaluate the anticorrosive behavior of the modified paints. The results showed that the corrosion rate determined from the tafel plot was lower in the steel samples covered with paint and polyaniline. The concentration of 0.8% of polyaniline in the paint showed a corrosion rate 12 times lower than that of the polyaniline-free paint. Additionally, visual observations and measurements of failed area carried out by applying an accelerated corrosion process by immersion in a 3.5% NaCl aqueous solution, allowed determining that, at a time of exposure of 300 h, corrosion inhibition can be achieved 26 times greater with the addition of 0.8% polyaniline. These results allowed to conclude that the addition of polyaniline by means of a simple mixture, significantly improved the anticorrosive protection capacity of a commercial epoxy paint.
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