*Fuel Quality Monitoring by Color Detection DOI: http://dx.doi.org/10.5772/intechopen.86531*

*Color Detection*

of mixtures [59–61].

blends [35].

**Figure 6.**

*Costa [34].*

Solvatochromism is the term used to describe the phenomenon of color change of a solute when it is dissolved in different solvents, resulting in a change in the position of absorption or emission of its spectroscopic band. When these changes of position occur in the visible range, they exhibit different colors that can be detected by the naked eye and can be used as sensors to determine the composition

*Schematic representation of procedure for taking pictures of samples (front and perspective views). Source:* 

Fong and Xue have developed an optical sensor to detect biodiesel in dieselbiodiesel blends based on the solvatochromic behavior of the dye called Nile Blue chloride, which turns blue when dissolved in ethanol or methanol and pink when in contact with biodiesel. **Figure 7** illustrates the change in color, enabling the direct, rapid detection of variations from 0.5 ppm to 20% v/v biodiesel in diesel-biodiesel

As Nile Blue chloride is not soluble in nonpolar solvents, like diesel, it was encapsulated in an ethyl cellulose polymer, dissolved in methanol or ethanol in the form of a fine film that turns blue in alcohols, with absorbance at 610 nm, and pink when

*Change in color of Nile Blue chloride from blue (without diesel) to pink (exposed to biodiesel), due to* 

*solvatochromic effects. Adapted from Fong and Xue [35].*

**94**

**Figure 7.**

in contact with biodiesel, with absorbance at around 520 nm. Exposing the sensor containing the Nile Blue chloride to diesel resulted in no change in color or change in its stability. When it was exposed to biodiesel, it changed from blue to pink, which can be attributed to the alcohols surrounding the sensor being replaced by FAMEs from the biodiesel, resulting in a solvatochromic effect. The sensor provides a quick, direct method compared with methods involving gas chromatography or infrared spectrophotometry, presenting a linear response between color intensity and biodiesel concentration for low concentrations, between 0.5 and 30 mg kg<sup>−</sup><sup>1</sup> . For high concentrations of biodiesel (up to 20% v/v), absorbance may be linearly adjusted by a logarithmic function [35].
