A simple and fast method to determine water content in biodiesel by electrochemical impedance spectroscopy

Abstract

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 (R) 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.

Interdigitated Electrode for Electrical Chacarcterization of Commercial Pseudo-Binary Biodiesel-Diesel Blends

“…As shown in Figure 11, the impedance values of biodiesel, diesel, and the B10 mixture are in megaohms, indicating a very high electrical resistance of the liquid. According to [37,38], these values align with the expected values for viscous and non-polar liquids.…”

“…We also see in Figure 11, more precisely in the region of low frequencies, the tendency of forming a second capacitive arc is more evident in samples of B100 than for the media where there is the presence of diesel, indicating a possible interaction of biodiesel with the surface of the electrode. This fact was also observed by [38]. Furthermore, it can be seen that the value of load transfer resistance for B0 is lower when compared to B10, which has 10 % biofuel and B100, demonstrating in principle that the first is a more conductive medium when compared with the last two.…”

Mineral oil moisture measurement with the use of impedance spectroscopy

“…In the IS, it is manifested by significant changes in measured electrical capacity in the function of frequency, while such changes do not occur in a real parallel resistor/capacitor circuit. The CPE models the phenomenon of variable capacitance much better than the capacitor; hence it can be found in oil studies together with at least a resistor [24,25,29]. Impedance of the aforementioned equivalent circuit can be described through the equation below:…”

“…Using the impedance measurement results, it is also possible to calculate permittivity of the test substance and such an approach is often called dielectric spectroscopy. The aforementioned broad applications of IS include measurements, among others, in: material science including studies of metal corrosion [19], environmental science to detect pollution [20], the development of biosensors [21,22], the petroleum [23], fuel [24,25], and pharmaceutic [26] industries to determine water or biocomponent content in oil. In several of these cases, it was successfully used to estimate water content in oil [21,23,25] and W/O/W-type emulsion [26].…”

“…However, these were slightly different approaches than the ones proposed by the authors in this paper. In the determination of water content in biodiesel, the sample was exposed to the solvent prior to measurement [25]. In two other cases, a different type of mixture (W/O/W) [26] and another type of oil was tested [21].…”