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

*Color Detection*

The standard test method for the ASTM color of petroleum products (ASTM 1500:2012) is used on samples of diesel S10 (which contains no dye). The test involves transferring a sample of the product to a test tube and comparing its color with the color of standard colored glass disks, which represent a range of values from 0.5 to 8.0. A standard light source is used in this test [22]. Corgozinho et al. have developed a method using partial least squared regression with molecular absorption spectrophotometry to determine the ASTM color of diesel in the 0–6.5

range, offering greater precision than the standard colorimetry test [23].

corrosion, classified from 1 to 4 [24–26].

**use in the field**

*3.1.1 In a diesel-biodiesel blend*

triglycerides also have C〓O bonds.

shows the reaction by which this complex is formed.

*of biodiesel in fossil diesel. Adapted from Silva et al. [29].*

**3.1 Biodiesel**

with Fe3+

Corrosiveness is determined using the copper strip test in Brazil (ABNT NBR 14359), the USA (ASTM D130), and Europe (EN ISO 2160). It consists of immersing a standard copper strip in a sample of biodiesel in a corrosion bath for 3 hours at 50°C. The strip is then rinsed in solvent and compared with an ASTM copper strip corrosion standard, which has different colors that correspond to different levels of

**3. Colorimetric methods for monitoring fuel quality with potential for** 

The level of biodiesel in a diesel-biodiesel blend is determined in a laboratory by observing the mid-infrared absorption of the C〓O bond present in the fatty acid methyl esters (FAMEs) that constitute the biodiesel. Although this test gives satisfactory results, it cannot be used in the field, which is a major drawback, as fuel distributors need to test the fuel when they are adding biodiesel to diesel on a commercial scale. Furthermore, the accuracy of the results will be compromised if the biodiesel itself is adulterated with vegetable oil or animal fat, whose constituent

The conversion of esters into hydroxamates by their reaction with hydroxylamine [27–29], forming complexes of a red to violet color caused by the reaction

*Chemical reactions involved in the test for esters known as the hydroxamic acid test, used to test for the presence* 

, has been used to confirm esters in organic analysis procedures. **Figure 1**

**90**

**Figure 1.**

Silva et al. used this test to develop a new spectrophotometric method to determine biodiesel levels in diesel-biodiesel blends ranging from B0 (pure fossil diesel) to B5 (fossil diesel containing 5% biodiesel), in which the esters from the biodiesel present in the mixtures react with hydroxylamine chlorhydrate in an alkaline solution, forming alkaline salts from the hydroxamic acid, followed by acidification, to form hydroxamic acid, followed by a reaction with Fe3+ ions. The complex formed, the intensity of whose color is proportional to the biodiesel content, is extracted with *n*-hexane/*n*heptane, forming an upper phase with a yellow, orange, or red color, depending on the biodiesel concentration, as shown in **Figure 2**. Absorbance can be measured using spectrophotometry at 420–440 nm. The linearity, limit of detection, limit of quantification, accuracy, selectivity, and specificity results indicate that the proposed method is adequate for analyses of biodiesel in diesel-biodiesel blends. A simplified method was proposed for qualitative analyses for use at filling stations [29, 31].

## **Figure 2.**

*Color scale of samples of fossil diesel containing biodiesel at 0–6% v/v, showing intensities proportional to the concentrations of biodiesel in the diesel, for semiquantitative analysis observable by the naked eye. Source: Santos [30].*

Using the same reaction, Santos developed a simple, practical, rapid method that could be used in the field for semiquantitative identification by the naked eye of biodiesel in diesel-biodiesel blends ranging from 0% to 6% v/v biodiesel [30]. A similar method was developed by Leite and Fernandes for the 0–7% range [32]. What sets these methods apart from their predecessors is the separation of the biodiesel from the blend before the hydroxamic acid test. To do this, solid-phase extraction is conducted using a chromatographic column adapted from a 3mL disposable plastic syringe into which around 0.4 g silica gel is inserted, supported by a cotton plug (see **Figure 3a**). The diesel-biodiesel blend is introduced as if in frontal chromatography, pushed by a plunger, generating a less polar diesel fraction (F1) followed by a more polar fraction containing biodiesel (F2), displaced by the addition of ethanol (see **Figure 3b**).

By using seven reference samples of the diesel-biodiesel blend containing 0, 1, 2, 3, 4, 5, and 6% (v/v) biodiesel, the concentrations of which were confirmed by the laboratory reference method [33], a standard table of colors was prepared that could be used for the semiquantitative analysis of the percentage of biodiesel, as in **Figure 2**, since the intensity of the color formed by the ferric hydroxamate complex is proportional to the level of biodiesel present in the sample. By comparing the observed colors with the standard color table, it was possible to determine the

**Figure 3.**

*(a) Chromatographic column adapted from a disposable plastic syringe; (b) solid-phase extraction of the biodiesel from the diesel-biodiesel blend before undergoing the hydroxamic acid test.*

biodiesel concentration semiquantitatively with the naked eye, with a relative error of around 1%. This could be done in the field to find out whether samples are off spec. The proposed method was used on 33 samples of diesel containing different biodiesel concentrations and was found to be equivalent to the laboratory reference method (EN14078) by Student's t-test, with 95% confidence [30].

Another method—also adaptable for use in the field—has been developed for determining biodiesel in a diesel-biodiesel blend and for identifying the presence of vegetable oil in this blend. After solid-phase extraction using a silica stationary phase (EFS1), the fraction composed of biodiesel and potentially vegetable oil is then put through another solid-phase extraction with an aminopropyl stationary phase (EFS2) to separate the biodiesel from any vegetable oil (**Figure 4a**). For use in the field, the stages involving a manifold for solid-phase extraction and nitrogen-supported solvent evaporation are replaced by the manual use of plungers in the solid-phase extraction cartridges, which has yielded viable preliminary results. **Figure 4b** illustrates the procedures that can be done in the field to obtain the complexes. **Figure 5** also illustrates the use of the hydroxamic acid test on both fractions to confirm the presence of esters, which has also proven satisfactory for indicating adulteration with 1% or more vegetable oil in diesel containing 5% biodiesel [32].

Any sample identified in the field as potentially adulterated with vegetable oil could be sent to a laboratory for confirmation via more precise analytical techniques, like high-performance liquid chromatography. As such, both methods (semiquantitative identification of the percentage of biodiesel in diesel and the identification of any vegetable oil in the blend) are potentially effective for field analyses not only for their ease of use but also for their speed. Furthermore, the fact that the methods use low-cost, low-toxicity materials and reagents makes them even more attractive.

The sequence of operations for the hydroxamic acid test, illustrated in **Figure 5**, is easily adapted for field analysis.

Costa has also developed an alternative method for determining the level of biodiesel in fossil diesel using the hydroxamic acid test in association with image processing and a colorimeter and compared it with the standard method (EN 14078). After the hydroxamic acid test, the images were photographed, and the

**93**

**Figure 5.**

**Figure 4.**

Colorsys program was used to create calibration curves based on color vs. biodiesel concentration, enabling the determination of biodiesel content by the intensity of the color. It was found that the hydroxamic acid test associated with image processing was adequate for detecting and quantifying the biodiesel content of dieselbiodiesel blends because the results given by the method were statistically similar to those given by the reference method using infrared spectroscopy (EN 14078).

*(a) Sequence of operations for solid-phase extraction to separate biodiesel from diesel-biodiesel blends in a silica column (EFS1) and to separate any vegetable oil or animal fat contaminating the biodiesel in an aminopropyl column (EFS2). (b) Field test made up of solid-phase extraction followed by hydroxamic acid test.*

Furthermore, it is easily adapted for field analysis (**Figure 6**) [34].

*Schematic representation of hydroxamic acid colorimetric test. Adapted from Costa [34].*

*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*

### **Figure 4.**

*Color Detection*

**Figure 3.**

biodiesel concentration semiquantitatively with the naked eye, with a relative error of around 1%. This could be done in the field to find out whether samples are off spec. The proposed method was used on 33 samples of diesel containing different biodiesel concentrations and was found to be equivalent to the laboratory reference

*(a) Chromatographic column adapted from a disposable plastic syringe; (b) solid-phase extraction of the* 

Another method—also adaptable for use in the field—has been developed for determining biodiesel in a diesel-biodiesel blend and for identifying the presence of vegetable oil in this blend. After solid-phase extraction using a silica stationary phase (EFS1), the fraction composed of biodiesel and potentially vegetable oil is then put through another solid-phase extraction with an aminopropyl stationary phase (EFS2) to separate the biodiesel from any vegetable oil (**Figure 4a**). For use in the field, the stages involving a manifold for solid-phase extraction and nitrogen-supported solvent evaporation are replaced by the manual use of plungers in the solid-phase extraction cartridges, which has yielded viable preliminary results. **Figure 4b** illustrates the procedures that can be done in the field to obtain the complexes. **Figure 5** also illustrates the use of the hydroxamic acid test on both fractions to confirm the presence of esters, which has also proven satisfactory for indicating adulteration with 1% or more vegetable oil in diesel containing 5%

Any sample identified in the field as potentially adulterated with vegetable oil could be sent to a laboratory for confirmation via more precise analytical techniques, like high-performance liquid chromatography. As such, both methods (semiquantitative identification of the percentage of biodiesel in diesel and the identification of any vegetable oil in the blend) are potentially effective for field analyses not only for their ease of use but also for their speed. Furthermore, the fact that the methods use low-cost, low-toxicity materials and reagents makes them even

The sequence of operations for the hydroxamic acid test, illustrated in **Figure 5**,

Costa has also developed an alternative method for determining the level of biodiesel in fossil diesel using the hydroxamic acid test in association with image processing and a colorimeter and compared it with the standard method (EN 14078). After the hydroxamic acid test, the images were photographed, and the

method (EN14078) by Student's t-test, with 95% confidence [30].

*biodiesel from the diesel-biodiesel blend before undergoing the hydroxamic acid test.*

**92**

biodiesel [32].

more attractive.

is easily adapted for field analysis.

*(a) Sequence of operations for solid-phase extraction to separate biodiesel from diesel-biodiesel blends in a silica column (EFS1) and to separate any vegetable oil or animal fat contaminating the biodiesel in an aminopropyl column (EFS2). (b) Field test made up of solid-phase extraction followed by hydroxamic acid test.*

**Figure 5.**

*Schematic representation of hydroxamic acid colorimetric test. Adapted from Costa [34].*

Colorsys program was used to create calibration curves based on color vs. biodiesel concentration, enabling the determination of biodiesel content by the intensity of the color. It was found that the hydroxamic acid test associated with image processing was adequate for detecting and quantifying the biodiesel content of dieselbiodiesel blends because the results given by the method were statistically similar to those given by the reference method using infrared spectroscopy (EN 14078). Furthermore, it is easily adapted for field analysis (**Figure 6**) [34].
