RESUMO
In this paper, a fast, simple and new alternative method for determination of water content (moisture) in biodiesel using electrochemical impedance spectroscopy (EIS) is developed. The method is based on the sensitive variation of the charge transfer resistance (Rct) of the biodiesel medium in the presence of different quantities of water. To obtain an accurate analytical measurement, a pre-treatment based on a simple dilution by acetonitrile is employed. The two identical Pt electrodes are used in the measurement cell filled with sample solution. The experiment conditions are also optimized for the measurements. The obtained analytical linear curve between the water content and EIS impedance is the basis for the water content analysis in biodesiel fuel. The EIS method is then successfully applied to both real and certified samples, and the results confirm that the method is reliable with high sensitivity, precision and accuracy. The comparison of EIS method with the official standard method is also made through the Student test t, demonstrating that both methods are statistically consistent and similars. The validation of such an EIS method confirms that the method presented for the fist time in this paper can be succesessfully applied to determining the water content of biodiesel fuel.
RESUMO
Microemulsions are thermodynamically stable systems of two immiscible liquids, one aqueous and the other of organic nature, with a surfactant and/or co-surfactant adsorbed in the interface between the two phases. Biodiesel-based microemulsions, consisting of alkyl esters of fatty acids, open a new means of analysis for the application of electroanalytical techniques, and is advantageous as it eliminates the required pre-treatment of a sample. In this work, the phase behaviours of biodiesel-based microemulsions were investigated through the electrochemical impedance spectroscopy (EIS) technique. We observed thatan increase in the amount of biodiesel in the microemulsion formulation increases the resistance to charge transfer at the interface. Also, the electrical conductivity measurements revealed that a decrease or increase in electrical properties depends on the amount of biodiesel. EIS studies of the biodiesel-based microemulsion samples showed the presence of two capacitive arcs: one high-frequency and the other low-frequency. Thus, the formulation of microemulsions plays an important role in estimating the electrical properties through the electrochemical impedance spectroscopy technique.