*3.2.1 Methanol*

The maximum methanol content permitted in ethanol and gasoline in Brazil is 0.5% v/v, and the reference method for its detection uses gas chromatography [44].

**97**

**Figure 12.**

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

ethanol [45–47].

**Figure 11.**

*et al. [43].*

In view of cases of ethanol adulteration with methanol identified in the country, a colorimetric kit has been designed for use in the field to identify this form of adulteration of anhydrous ethanol and hydrous ethanol and in gasoline with

*Range of colors of solutions of the dye in binary mixtures of gasoline-ethanol (pure gasoline, E25, E50, E75, pure ethanol) and binary mixtures of ethanol-water (pure ethanol, W30, W50, W70, W90). Adapted from Galgano* 

The procedure is based on visual detection of a violet blue color as a result of the reaction of aldehydes with Schiff's reagent used in qualitative organic analysis to identify functional aldehyde groups [48, 49]. The color is obtained using the

1.Selective oxidation of the methanol adulterant to formaldehyde in the presence

2.Addition of oxalic acid in an acidic medium to reduce the excess of potassium

The nonappearance of a color indicates the absence of methanol. When the solution turns violet blue, this is a qualitative indication of the presence of methanol in the fuel. A comparison of the intensity of the color with that of a reference solution containing 0.5% v/v methanol (the maximum permitted) enables conformity/non-

**Figure 12** shows the results of the samples of hydrous ethanol containing 0, 0.3, 0.5, and 1.0% methanol, showing the photos of the solutions after the test sequence. The higher the concentration of methanol in the sample, the stronger the blue of the solution. As expected, the blank, containing just ethanol, is colorless.

*Schiff test applied to samples of pure ethanol and ethanol contaminated with 0.3, 0.5, and 1.0% methanol.*

3.Formation of Schiff's reagent by the reaction of *p-*rosaniline with sodium

4.Addition of Schiff's reagent and observation of a violet blue color

aforementioned colorimetric kit by the following reactions:

of potassium permanganate in an acid medium

permanganate, leaving the solution colorless

conformity with specifications to be determined in the field.

metabisulfite in an acid medium

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

**Figure 11.**

*Color Detection*

shown in **Figure 10** [42].

graduates in a chemistry class [43].

*diesel. Adapted from El Seoud et al. [42].*

sition of the mixture, as shown in **Figure 11.**

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

*(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].*

Galgano et al. have also used the solvatochromic dye 2,6-bis[4-(tert-butyl) phenyl]-4-{2,4,6-tris[4-(tert-butyl)phenyl]-pyridinium-1-yl}phenolate (t-Bu)5RB) to make quantitative analyses of bioethanol and mixtures of bioethanol with gasoline and water in an experiment based on a constructivist approach for under-

*Color variation of solutions of t-Bu5RB and pure diesel and ethanol and in solutions of ethanol (%v/v) in* 

Solutions of the dye in ethanol-water and anhydrous ethanol-gasoline mixtures evidenced solvatochromic effects, with the color changing according to the compo-

The maximum methanol content permitted in ethanol and gasoline in Brazil is 0.5% v/v, and the reference method for its detection uses gas chromatography [44].

The results of using solvatochromic effects of different dyes in mixtures, especially involving additized or altered fuels, seem extremely promising for the

development of alternative colorimetric methods with field applications.

**96**

*3.2.1 Methanol*

**Figure 10.**

**Figure 9.**

*Range of colors of solutions of the dye in binary mixtures of gasoline-ethanol (pure gasoline, E25, E50, E75, pure ethanol) and binary mixtures of ethanol-water (pure ethanol, W30, W50, W70, W90). Adapted from Galgano et al. [43].*

In view of cases of ethanol adulteration with methanol identified in the country, a colorimetric kit has been designed for use in the field to identify this form of adulteration of anhydrous ethanol and hydrous ethanol and in gasoline with ethanol [45–47].

The procedure is based on visual detection of a violet blue color as a result of the reaction of aldehydes with Schiff's reagent used in qualitative organic analysis to identify functional aldehyde groups [48, 49]. The color is obtained using the aforementioned colorimetric kit by the following reactions:


The nonappearance of a color indicates the absence of methanol. When the solution turns violet blue, this is a qualitative indication of the presence of methanol in the fuel. A comparison of the intensity of the color with that of a reference solution containing 0.5% v/v methanol (the maximum permitted) enables conformity/nonconformity with specifications to be determined in the field.

**Figure 12** shows the results of the samples of hydrous ethanol containing 0, 0.3, 0.5, and 1.0% methanol, showing the photos of the solutions after the test sequence. The higher the concentration of methanol in the sample, the stronger the blue of the solution. As expected, the blank, containing just ethanol, is colorless.
