LAUSR

Abstract A practical and environmentally friendly volumetric procedure, which requires only water and ethanol and generates low waste volumes, is proposed for determining the amount of biodiesel in diesel blends or mixtures with vegetable oils. These applications are relevant for the quality control of commercial fuels, to estimate transesterification reaction yields and to detect product adulteration. The proposed method is based on the differences in solubility of biodiesel and either diesel or vegetable oils in an aqueous-ethanol medium. From samples dissolved in ethanol, the volumes of the aqueous-ethanol solution required to achieve a cloudy suspension are taken as analytical signals and directly correlated to the biodiesel amount in the samples. For biodiesel:diesel samples, a linear response was obtained from 7.0 to 25.0% (v/v), whereas two linear ranges, 20.0–50.0% (v/v) and 50.0–80.0% (v/v), were established for biodiesel:vegetable oil samples, depending on the water content in the titrant. For biodiesel:diesel blends, the coefficient of variation (n = 10) and the detection limit (99.7% confidence level) were estimated at 6.8% and 2.5% (v/v), respectively, and the corresponding values for the biodiesel:vegetable oil mixtures were 5.8% and 7.0% (v/v). The procedure takes 5 min and generates 10 mL of waste per determination. Results agreed with those attained by a flow-based spectrophotometric reference procedure at the 95% confidence level, as evaluated by a paired t-test and the elliptical joint confidence region test. The proposed method is a fast, practical, cost-effective, and environmentally friendly alternative for routine analysis, including point-of-care determinations.