Yara Patricia da Silva

Role of the co-surfactant nature in soybean w/o microemulsions.

The influence of the co-surfactant on physicochemical properties of w/o soybean oil microemulsions (MEs) has been studied. In spite of the similarity in phase diagrams, the MEs display remarkable differences when examined by electrical conductivity, dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and linear voltammetry. When different short-chain alcohols were employed as co-surfactants, together with sodium dodecyl sulfate (SDS) as surfactant, the DLS results indicated the systems to be monodisperse. Both the electrical conductivity of the MEs and the hydrodynamic radii of the droplets (R(H)) increased with water content while R(H) diminished as temperature increased, no aggregation or percolation of the droplets being observed. In comparison to w/o MEs prepared with 3-methyl-1-butanol, those prepared with 1-pentanol presented higher electrical conductivity and larger limiting currents at a Pt ultramicroelectrode for oxidation of the water occluded into the particles. Finally, from the electrochemical viewpoint the use of 1-pentanol is recommended, no advantage being gained by using any of the other tested alcohols.

Direct determination of oleic acid in soybean oil by capacitively coupled contactless conductivity detection capillary electrophoresis in an oil-miscible KOH/1-propanol/methanol medium

The aim of this work was to develop a quick direct analytical technique for the determination of oleic acid content in soybean oil by non-aqueous capillary electrophoresis with capacitively coupled contactless conductivity detection. The oil-miscible background electrolyte was a mixture of methanol/1-propanol (1:6 v/v) containing 4 × 10-2 mol L-1 KOH and 10% (v/v) ethylene glycol. Samples of 50 g L-1 soybean oil were prepared directly in the background electrolyte added with 1.33 × 10-3 g L-1 of salicylic acid as internal standard. Quantitative tests were performed by adding to the samples pure oleic acid in the range from 0.53 to 2.13 × 10-3 mol L-1. Under negative polarity anionic solutes moved faster than the electro-osmotic flow so that oleic acid was detected in 16 minutes. The limits of detection and quantification were, respectively, 24 and 81 µmol L-1. Such results demonstrate that, unlike required by other methods, low levels of oleic acid can be quantitatively determined in soybean oil without prior extraction.

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

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 ip 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.