Claudio F. Lima

Determination of Eucalyptus spp lignin S/G ratio: A comparison between methods

The syringyl/guaiacyl ratio was determined for six different Eucalyptus spp. wood clones cultivated in four regions in Brazil. The determinants were made by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and the results were compared with those obtained by alkaline nitrobenzene oxidation method. The S/G ratios were obtained considering all the identified lignin derivatives in the pyrograms and also using two groups of markers. The first group of markers consisted of guaiacol, 4-methylguaiacol, 4-vinylguaiacol, trans-isoeugenol, syringol, 4-methylsyringol, 4-vinylsyringol and trans-4-propenylsyringol compounds as markers. The second group included guaiacol, 4-methylguaiacol, 4-vinylguaiacol, vanillin, 4-ethylsyringol, 4-vinylsyringol, syringaldehyde, syringylacetone and trans-4-propenylsyringol. It was observed from the statistical analysis that the values of S/G obtained by Py-GC-MS using the two groups of markers did not differ significantly from those obtained by nitrobenzene oxidation method.

Extraction induced by emulsion breaking: a novel strategy for the trace metals determination in diesel oil samples by electrothermal atomic absorption spectrometry

This present work reports a novel strategy for the extraction of metals (Cu, Fe, Ni and Pb) from diesel oil and their determination by Electrothermal Atomic Absorption Spectrometry (ETAAS). The method is based on the formation of water-in-oil emulsions by vigorous mixing of the samples with a Triton X-114 solution containing HNO3 and posterior breaking of the emulsion by heating. After the emulsion breaking, three well separated phases were obtained: (i) the upper phase, which is an organic phase containing only the diesel oil, (ii) an acidic aqueous phase containing the extracted metals and (iii) the lower phase, which is a surfactant-rich phase. The metals were concentrated in the aqueous phase, as a result of their acidic extraction from diesel oil. Several parameters that could influence the extraction efficiency and the time required to break the emulsions were evaluated such as the concentration and nature of the surfactant (Triton X-100 and Triton X-114), the HNO3 concentration and the temperature. At best conditions, the emulsions were prepared by mixing 10 mL of diesel oil with 2 mL of a solution containing 7% w/v Triton X-114 and 10% v/v HNO3. Afterwards, the emulsions were broken by heating at 80 °C for 15 min and then, the aqueous phase was collected and the metals were determined by ETAAS using external calibration with aqueous standard solutions. The limits of detection for Cu, Fe, Ni and Pb were equal to 114, 183, 145 and 294 ng L−1 and the limits of quantification were 380, 609, 484 and 980 ng L−1, respectively. These limits were estimated for the original sample taking into account the preconcentration factor obtained due to the Extraction Induced by Emulsion Breaking (EIEB) application. The novel strategy was applied in the analysis of five samples of diesel oil and the obtained results fitted well with those obtained by the reference method. Also, a recovery test was performed by spiking the samples with known amounts of the metals in the form of organometallic standards and thus applying the proposed procedure. The recoveries were in the range of 85.2–109%.

Multivariate optimization of the determination of zinc in diesel oil employing a novel extraction strategy based on emulsion breaking.

This paper describes the extraction/pre-concentration of Zn from diesel oil and its determination by Flame Atomic Absorption Spectrometry (FAAS), proposed as a novel approach for these kinds of analyses and the multivariate optimization of the proposed procedure. The extraction of Zn is based on the emulsification of an aqueous solution containing Triton X-114 and HNO(3) with diesel oil samples followed by breaking of the emulsion by heating. The aqueous phase obtained after the emulsion breaking was collected and used for Zn quantification by FAAS. The methodology was optimized using a Doehlert design and the system variables were the concentrations of surfactant and HNO(3) in the solution employed in the emulsification and the temperature used in the emulsion breaking. The ratio between absorbance and the time required to break the emulsions was taken as response. Two sets of experiments, using different emulsifier agents, were run: the first one using Triton X-100 and the second one using Triton X-114. At optimized conditions, the emulsions were prepared by mixing 10 mL of diesel oil with 2 mL of a solution containing 5% w/v of Triton X-114 and 15% v/v of HNO(3) and broken by heating at 80 °C. The proposed analytical procedure was applied in the analysis of six real samples of diesel oil and a recovery test was carried out by spiking the samples with known amounts of Zn (25 and 50 μg L(-1)), added as organometallic oiled standard. Recovery percentages achieved in this test were between 92 and 109%.

Extraction induced by emulsion breaking for metals determination in diesel oil by ICP-MS

This present work proposes a new approach for diesel oil preparation for metals determination by ICP-MS. The proposed methodology is based on the extraction of the elements of interest into an aqueous phase employing the extraction induced by emulsion breaking procedure. In this approach, the diesel oil was emulsified with an acid surfactant (Triton X-114) solution in order to form a stable water-in-oil emulsion. Further, the emulsion was broken by centrifugation for 60 min at 3200 rpm, yielding two separated phases: (i) the upper organic phase, containing the diesel oil mixed with the surfactant and (ii) the lower acidic aqueous phase, containing the elements of interest that were extracted from oil. Then, the lower phase was collected, diluted and the analytes were determined by ICP-MS using the internal standardization method. The optimization of the methodology was carried out by analyzing the effect of several parameters that could affect the extraction efficiency such as the concentrations of HNO3 and Triton X-114 in the solution used for emulsification (and extraction), the extraction and collection times and the calibration strategy. The limits of detection and quantification for the elements of interest (Al, Cu, Mn, Ni, Sn and V) were in the range of 26–88 ng L−1 and 86–295 ng L−1, respectively. The accuracy of the methodology was tested by the analysis of spiked samples, since there are no certified samples of diesel oil available in the market. The recovery percentages were in the range of 84–113%. The developed methodology was successfully applied in the metals determination in five commercial diesel oils of different brands.

Determination of disulfoton in surface water samples by cloud-point extraction and gas chromatography

This article proposes an alternative method, using cloud-point extraction and gas chromatography, for extraction and determination of disulfoton in water samples. For cloud-point extraction, the nonionic surfactant Triton X-114 was used. Before gas chromatography, a cleanup stage for surfactant removal from the extracts was optimized. Cleanup used two columns, in series, containing silica gel and Florisil, with methanol:hexane (1 : 1) as eluent, resulting in the removal of more than 95% of the Triton X-114. Factors such as ionic strength (>0.5 mol L−1) and surfactant concentration (1.0% w/v) increased the extraction efficiency of the cloud-point methodology, yielding disulfoton recoveries of almost 100%. Compared with liquid–liquid extraction, the cloud-point methodology was more efficient, with a better detectability, and resulted in a significant reduction in solvent volume.

Sorption and desorption of sulfentrazone in Brazilian soils

This study was undertaken to obtain information about the behavior of sulfentrazone in soil by evaluating the sorption and desorption of the herbicide in different Brazilian soils. Batch equilibrium method was used and the samples were analyzed by high performance liquid chromatography. Based on the results obtained from the values of Freundlich constants (Kf), we determined the order of sorption (Haplic Planosol < Red-Yellow Latosol < Red Argisol < Humic Cambisol < Regolitic Neosol) and desorption (Regolitic Neosol < Red Argisol < Humic Cambisol < Haplic Planosol < Red-Yellow Latosol) of sulfentrazone in the soils. The process of pesticide sorption in soils was dependent on the levels of organic matter and clay, while desorption was influenced by the organic matter content and soil pH. Thus, the use of sulfentrazone in soils with low clay content and organic matter (low sorption) increases the probability of contaminating future crops.

Polyurethane foam loaded with sodium dodecylsulfate for the extraction of 'quat' pesticides from aqueous medium: Optimization of loading conditions

The cationic herbicides paraquat, diquat and difenzoquat are largely used in different cultures worldwide. With this, there is an intrinsic risk of environmental contamination when these herbicides achieve natural waters. The goal of this work was to propose a novel and low-cost sorbent for the removal of the cited herbicides from aqueous medium. The proposed sorbent was prepared by loading polyurethane foam with sodium dodecylsulfate. The influence of several parameters (SDS concentration, HCl concentration and shaking time) on the loading process was investigated. The results obtained in this work demonstrated that all studied variables influenced the loading process, having significant effect on the extraction efficiency of the resulted PUF-SDS. At optimized conditions, the PUF was loaded by shaking 200mg of crushed foam with 200mL of a solution containing 5.0×10(-3)molL(-1) SDS and 0.25molL(-1) HCl, for 30min. The obtained PUF-SDS was efficient for removing the three herbicides from aqueous medium, achieving extraction percentages higher than 90%. The sorption process followed a pseudo second-order kinetics, which presented excellent predictive capacity of the amount of herbicide retained with time.

Determinação de constituintes químicos em madeira de eucalipto por Pi-CG/EM e calibração multivariada: comparação entre redes neurais artificiais e máquinas de vetor suporte

Multivariate models were developed using Artificial Neural Network (ANN) and Least Square - Support Vector Machines (LS-SVM) for estimating lignin siringyl/guaiacyl ratio and the contents of cellulose, hemicelluloses and lignin in eucalyptus wood by pyrolysis associated to gaseous chromatography and mass spectrometry (Py-GC/MS). The results obtained by two calibration methods were in agreement with those of reference methods. However a comparison indicated that the LS-SVM model presented better predictive capacity for the cellulose and lignin contents, while the ANN model presented was more adequate for estimating the hemicelluloses content and lignin siringyl/guaiacyl ratio.

Sorption of the herbicides diquat and difenzoquat from aqueous medium by polymeric resins in the presence of sodium dodecylsulfate: Kinetic and mechanistic study

ABSTRACT The goal of this work was to propose a novel method for the solid-phase extraction of the herbicides diquat (DQT2+) and difenzoquat (DFQT+) from aqueous medium using polymeric Amberlite XAD-2 and XAD-4 resins in the presence of sodium dodecylsulfate (SDS). The addition of SDS to the medium was of fundamental importance in order to allow the formation of a negatively charged surface able to sorb the cationic solutes. Several factors that could influence the sorption process, such as SDS concentration in the medium, sorbent mass, pH, ionic strength, and initial concentration of the solutes were investigated. Kinetic studies were also performed to model the system and to identify the mechanisms that operate the sorption process of the herbicides. SDS concentration in the medium presented remarkable influence on the extraction efficiency, achieving maximum values when the ratios [SDS]/[herbicide] were approximately 90, for XAD-2, and 22 and 11 for DQT2+ and DFQT+, respectively, for XAD-4. The sorption process followed a pseudo second-order kinetic in all cases studied. It was also found that an intraparticle diffusion process controlled exclusively the sorption of the herbicides by the Amberlite XAD-2 and XAD-4 resins in the first 15 min, becoming less active with time.

Sulfentrazone dechlorination by iron-nickel bimetallic nanoparticles ☆

The sulfentrazone dechlorination using bimetallic nanoparticles of Fe/Ni was studied. Different variables that could influence the sulfentrazone conversion were investigated, such as nitrogen atmosphere, pH and dosage of the nanoparticles and initial concentration of sulfentrazone. The best results were obtained using controlled pH (pH 4.0) and 1.0 g L(-1) of nanomaterials, resulting in 100 % conversion in only 30 min. Kinetic studies were also conducted, evaluating the influence of different nanoparticle dosages (1.0 to 4.0 g L(-1)), system temperatures (20 to 35 °C) and nickel levels in the composition of the nanomaterials (0.025 to 0.10 gNi/gFe). The mechanism of sulfentrazone conversion has changed due a direct reduction on the catalytic activity sites and indirect reduction by atomic hydrogen. Both mechanisms have followed pseudo-first order models. The conversion rate improved when the dosage of the nanomaterials, system temperature and nickel content in the composition of the nanocomposites were increased. Finally, the conversion products were elucidated by mass spectrometry and toxicity assays were performed using Daphnia Similis. The results showed that the dechlorination product is less toxic than sulfentrazone.