This experiment describes a quantitative UV-Vis analysis of mixtures of diesel/ethanol and diesel/biofuel based on the absorption of a solvochromatic probe dye. Students first synthesize the dye and then monitor the change in the dye’s λmax for different known mixtures, creating an empirical scale of solvent polarity. Mixtures containing unknown (to the student) mixtures of diesel/ethanol and diesel/biofuel are then analyzed using calibration curves of solvent polarity as a function of the concentration of ethanol or biofuel.
The full citation is here: El Seoud, O. A., Loffredo, C., Galgano, P. D., Sato, B. M., Reichardt, C. J. Chem. Educ. 2011, 88, 1293–1297 and a link to the article is provided below (subscription to the journal required).