A.R.L. Caires

Determination of the biodiesel content in diesel/biodiesel blends: a method based on fluorescence spectroscopy.

Blends of biodiesel and diesel are being used increasingly worldwide because of environmental, economic, and social considerations. Several countries use biodiesel blends with different blending limits. Therefore, it is necessary to develop or improve methods to quantify the biodiesel level in a diesel/biodiesel blend, to ensure compliance with legislation. The optical technique based on the absorption of light in the mid-infrared has been successful for this application. However, this method presents some challenges that must be overcome. In this paper, we propose a novel method, based on fluorescence spectroscopy, to determine the biodiesel content in the diesel/biodiesel blend, which allows in loco measurements by using portable systems. The results showed that this method is both practical and more sensitive than the standard optical method.

Effects of residue and antioxidant on thermo-optical properties of biodiesel

Thermal lens (TL) spectrometry was applied to soybean biodiesel samples, in order to assess the behavior of their thermo-optical properties during the preparation before and after the washing process. The study was based on the thermal diffusivity parameter, which is highly sensitive and is related to the chemical composition of the sample. The results showed a difference of approximately 20% between the initial (unwashed) and the final (washed) steps of biodiesel production. This behavior indicates that the residue of the biodiesel production influences the thermal diffusivity value. Consequently, TL spectrometry can be a useful methodology for certifying the quality of biodiesel during production.

Fluorescence as an Analytical Tool for Assessing the Conversion of Oil into Biodiesel

In this work fluorescence–based method to assess the biodiesel production from different refined vegetable oils is presented. Four different refined oils (soybean, sunflower, canola, and corn) and their respective biodiesel were used and the fluorescence of the compounds contained in their compositions was taken as a probe. The results show that the fluorescence intensity of the biodiesel is lower than one verified in the vegetable oil. The data achieved point out that the ratio between the fluorescence intensity of biodiesel and oil is about 0.6 regardless of the vegetable oil feedstock investigated. Reduced content of fluorophores as well as low viscosity of the biodiesel regarding the oil have been raised as hypotheses to explain the low fluorescence intensity of the biodiesel. The results obtained may provide the basis for the development of an alternative method able to give fast and accurate information about the conversion of oil into biodiesel without the requirement of dilution or pre-treatment of the biodiesel.

A close analysis of metal-enhanced fluorescence of tryptophan induced by silver nanoparticles: wavelength emission dependence

In the last few years, silver nanoparticles have been proposed as a promising alternative for the label-free detection of proteins via metal-enhanced fluorescence. Generally, the aromatic amino acid tryptophan is most frequently used in this type of studies, because the intrinsic fluorescence of proteins is usually dominated by tryptophan emissions. In the present study, we evaluated the fluorescence behavior of tryptophan in the presence of a silver colloid with nanoparticles of 100 nm in diameter. The results showed that a nanoparticles concentration of 32 mg L−1 induced maximum fluorescence enhancement. However, the metal-enhanced fluorescence was dependent on the emission wavelength of tryptophan, and this phenomenon was closely related to the metal surface reabsorption process (inner filter effect), suggesting that the plasmon resonance reabsorption effect should be taken into account in analyses involving protein studies by metal-enhanced fluorescence.

Fluorescence analysis of iodinated acetophenone derivatives

In the present paper the synthesis and optical characterization of iodinated acetophenone, 4-hydroxy-3-iodoacetophenone and 4-hydroxy-3,5-diiodoacetophenone obtained from 4-hydroxyacetophenone, were carried out. The optical features of iodinated molecules were determined by performing the UV-Vis absorption, fluorescence and thermal lens spectroscopies. The results showed that the optical properties of the 4-hydroxyacetophenone is altered when the iodine atom is inserted, as substituent, in the aromatic ring. Although it was determined that the optical feature was changed when one iodine atom was inserted in the aromatic ring (4-hydroxy-3-iodoacetophenone), the results revealed that emission behavior was strongly altered when two iodine atoms (4-hydroxy-3,5-diiodoacetophenone) were acting as substituents: the fluorescence quantum efficiency increases approximately 60%.

Changes in chlorophyll a fluorescence of glyphosate-tolerant soybean plants induced by glyphosate: in vivo analysis by laser-induced fluorescence spectroscopy

A significant increase in the use of the herbicide glyphosate has generated many questions about its residual accumulation in the environment and possible damage to crops. In this study, changes in chlorophyll a (chl-a) fluorescence induced by glyphosate in three varieties of glyphosate-resistant soybean plants were determined with an in vivo analysis based on a portable laser-induced fluorescence system. Strong suppression of chl-a fluorescence was observed for all plants treated with the herbicide. Moreover, the ratio of the emission bands in the red and far-red regions (685 nm/735 nm) indicates that the application of glyphosate led to chlorophyll degradation. The results also indicated that the use of glyphosate, even at concentrations recommended by the manufacturer, suppressed chl-a fluorescence. In summary, this study shows that fluorescence spectroscopy can detect, in vivo, very early changes in the photosynthetic status of transgenic soybeans treated with this herbicide.

Size-Dependent Interaction of Gold Nanoparticles with Tryptophan: A Spectroscopic Analysis

In the present study, we evaluated the optical behavior of tryptophan in the presence of gold nanoparticles with different diameters and concentrations. The results showed that both absorption and fluorescence of tryptophan were strongly dependent on the nanoparticle size and concentration.

A Espectroscopia de Fluorescência Sincronizada Aplicada na Análise Qualitativa e Quantitativa de Hidrocarbonetos Policíclicos Aromáticos em Amostras D’água

Polycyclic Aromatic Hydrocarbons (PAHs) are known to then high toxicity. Different methods are used to identify these compounds in environmental samples. However, often the methods involve high complexity experiments and high costs for operations. However, the Synchronous Fluorescence Spectroscopy (SFS) shows to be a highly simple and effective experimental technique in the identification of these substances. In this context, this study aimed to conduct a qualitative and quantitative study of PAHs present in aqueous in order to propose this technique as a tool for environmental monitoring arrays. After statistical analyzes, was identified the limit of detection below 0.7 × 10 -9 g.mL - 1 for the eight PAHs identified by the SFS. This is a value recommended by the Ministry of Health in Brazil, demonstrating that the technique is highly sensitive and applicable to analysis in water samples.