**4. Conclusions**

The quality and adulteration of fuels have been the object of several publications, especially with the use of modern analytical techniques, such as chromatography, spectroscopy, and chemometric methods, but with very few examples of colorimetric techniques. Among the colorimetric techniques shown here, developed for fuel quality and adulteration monitoring, especially those that are based on simple, rapid, low-cost procedures with potential for application in the field, we highlight those traditionally used for the qualitative identification of functional groups in organic analysis. The colorimetric methods for detecting biodiesel and vegetable oil adulterants in diesel-biodiesel blends are based on the qualitative analysis of carboxylic esters using the hydroxamic acid test, which produces a colored ferric hydroxamate complex. The colorimetric detection of methanol in ethanol and in gasoline was also based on a reaction for identifying aldehydes by the reaction for the formation of a Schiff base, which is colored. These assays are based on spot tests developed and described by Fritz Feigl and colleagues, whose publications [27, 48, 58] describe an incommensurable archive of spot tests used in organic and inorganic analyses, which could serve as inspiration for the development of other colorimetric assays. Likewise, the solvatochromic effect of dyes and fibers, used as probes or sensors, has been used to detect biodiesel in diesel-biodiesel blends and water or ethanol in gasoline and even for detecting adulterants in gasoline. Publications that use solvatochromic effects for the analysis of fuels based on undergraduate experiments—showing their operational simplicity—are also highlighted [43]. The solvatochromic effect has been the target of several studies by Christian Reichardt and colleagues and also represents an opportunity for the development of new colorimetric techniques [59–61].

**101**

**Author details**

Amanda Pereira Franco dos Santos1

and Luiz Antonio d'Avila1,2

\*, Kissya Kropf da Silva1

1 Petroleum Products and Fuels Laboratory (LABCOM), School of Chemistry,

2 Chemical and Biochemical Process Engineering Program, School of Chemistry,

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Federal University of Rio de Janeiro, Rio de Janeiro, Brazil

Federal University of Rio de Janeiro, Rio de Janeiro, Brazil

\*Address all correspondence to: apfranco@eq.ufrj.br

provided the original work is properly cited.

, Gisele Alves Borges1,2

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

*Color Detection*

*3.3.3 Adulteration*

**4. Conclusions**

**Figure 16.**

ner, methanol, and toluene (see **Figure 16**) [57].

Lee et al. (2011) have developed a sensor to detect gasoline adulteration based on the solvatochromic behavior of a polydiacetylene (PDA) conjugated polymer embedded in matrix polymers of polystyrene and polyacrylic acid in the form of fibers. When exposed to pure and adulterated gasoline, they change to different colors and also change color in the presence of potential adulterants like paint thin-

The quality and adulteration of fuels have been the object of several publications, especially with the use of modern analytical techniques, such as chromatography, spectroscopy, and chemometric methods, but with very few examples of colorimetric techniques. Among the colorimetric techniques shown here, developed for fuel quality and adulteration monitoring, especially those that are based on simple, rapid, low-cost procedures with potential for application in the field, we highlight those traditionally used for the qualitative identification of functional groups in organic analysis. The colorimetric methods for detecting biodiesel and vegetable oil adulterants in diesel-biodiesel blends are based on the qualitative analysis of carboxylic esters using the hydroxamic acid test, which produces a colored ferric hydroxamate complex. The colorimetric detection of methanol in ethanol and in gasoline was also based on a reaction for identifying aldehydes by the reaction for the formation of a Schiff base, which is colored. These assays are based on spot tests developed and described by Fritz Feigl and colleagues, whose publications [27, 48, 58] describe an incommensurable archive of spot tests used in organic and inorganic analyses, which could serve as inspiration for the development of other colorimetric assays. Likewise, the solvatochromic effect of dyes and fibers, used as probes or sensors, has been used to detect biodiesel in diesel-biodiesel blends and water or ethanol in gasoline and even for detecting adulterants in gasoline. Publications that use solvatochromic effects for the analysis of fuels based on undergraduate experiments—showing their operational simplicity—are also highlighted [43]. The solvatochromic effect has been the target of several studies by Christian Reichardt and colleagues and also represents an opportunity for the development of new

*Photos after the exposure of the PDA fibers in polystyrene to commercial and adulterated gasoline, thinner,* 

*methanol, and toluene on glass (a) and on silica TLC plate (b). Adapted from Lee et al. [57].*

**100**

colorimetric techniques [59–61].
