Biodiesel water in oil microemulsions: ferrocene as a hydrophobic probe for direct analysis by differential pulse voltammetry at a Pt ultramicroelectrode

Abstract

Aimed at monitoring biodiesel oxidation stability, a reproducible, simple and rapid procedure for the determination of ferrocene (Fc) as a probe in water in oil microemulsions (W/O MEs) has been successfully developed. Electrochemical measurements have been performed in microemulsions, ME1, containing 10% water, 60% biodiesel (B100) and 30% pseudo-phase, and ME2, containing 9% water, 28% biodiesel and 63% pseudo-phase, in mass, using sodium dodecyl sulphate (SDS) and n-pentanol as surfactant and co-surfactant, respectively. The so prepared MEs have been characterized through viscosity, conductivity and small angle X-ray scattering (SAXS) measurements. Ferrocene oxidation at a Pt ultramicroelectrode (ume), both in ME1 and ME2, has been evidenced either by linear and differential pulse voltammetry (DPV). As compared to ME1, the higher conductivity of ME2 favours carrying electrochemical measurements in this medium. The DPV results indicate a linear relationship between i_p and the Fc concentration with a correlation coefficient of 0.999. Thus, the proposed methodology may ultimately be employed for quality control in the biodiesel production line.