**3.2 Ethanol**

Budag et al. have used four dyes as solvatochromic probes to study the effect of adding ethanol to pure gasoline. The dye 2,6-di(4-tert-butylphenyl)-4-[2,4,6-tri (4-tert-butylphenyl)pyridinium-1-yl]phenolate (t-Bu5RB), for example, has a greenish blue color in gasoline, is violet in ethanol, and is bluish green in a mixture of 25% ethanol in gasoline, which means ethanol in gasoline can be detected by the naked eye. The development of analytical methods to determine fuel quality based on these promising probes has been discussed. Based on the spectroscopic determination of the maxima on the UV-visible spectra, the respective transition energy can be calculated, which is related to the composition of the fuel, opening up the potential for the development of an analytical method [41].

### **Figure 9.**

*(a) Solid-phase extraction in aminopropyl cartridge to separate and isolate total glycerin, made up of fractions of free glycerin (FG) and combined glycerin, monoacylglycerols (MAGs), diacylglycerols (DAGs), and triacylglycerols (TAGs). Source: Muniz et al. [36]. (b) Solid-phase extraction in silica cartridge to separate and isolate FG from the fractions containing FAME + TAGs, DAGs, and MAGs. For example, for 0.150 mL biodiesel, F1a is eluted with 15 mL petroleum ether, (F1b) with 40 mL of a mixture of 35% ethyl ether and 65% petroleum ether, (F1c) with 40 mL ethyl ether, and (F2) with 12 mL ethanol. Source: Serralvo Neto et al., 2018 (FR 1872032) [40].*

El Seoud et al. have used the same dye in analytical chemical experiments for undergraduates, in the analysis of diesel-ethanol blends, also observing a solvatochromic effect, with colors varying as the composition of the mixture changes, as shown in **Figure 10** [42].
