Mariana A. Vieira

A New, Simple and Efficient Method of Steglich Esterification of Juglone with Long-Chain Fatty Acids: Synthesis of a New Class of Non-Polymeric Wax Deposition Inhibitors for Crude Oil

A esterificacao direta de naftoquinonas mostrou-se uma tarefa dificil. Metodologias mais comuns envolvem a aplicacao de cloretos de acila em piridina ou anidridos, entretanto, quando acidos de cadeia longa sao utilizados tais metodologias se mostram ineficientes devido aos baixos rendimentos obtidos. Apresentamos uma nova sintese de esteres de cadeia longa de juglona baseado na esterificacao de Steglich utilizando um acido de Lewis barato como cocatalisador. Rendimentos obtidos sao consideravelmente maiores do que os reportados previamente. Quimica computacional foi utilizada para avaliar os efeitos do CeCl3 como cocatalisador. Os compostos preparados foram testados como inibidores de deposicao de parafinas em petroleo. Ester palmitico da juglona foi capaz de reduzir 4 oC na temperatura de inicio de aparecimento de cristais (WAT) do oleo estudado, representando uma reducao de 1,5% m/m de parafinas normais precipitadas. Direct esterification on naphthoquinone presented itself as a hard task. Usual methodologies apply acyl chloride in pyridine or anhydrides but with long-chain esters this procedure proved to be ineffective because of the low yields obtained. We present a new synthesis of long-chain esters of juglone based on Steglich esterification using a cheap Lewis acid as cocatalyst. Yields obtained are considerably better than those found previously. Computational chemistry was used to evaluate the effects of CeCl 3 as cocatalyst. Prepared compounds were tested as wax deposition inhibitors in crude oil. Palmitic ester of juglone was able to lower 4 oC on the wax appearance temperature (WAT) of the studied oil, representing a reduction of precipitated normal paraffin of 1.5% m/m.

Avaliação da Concentração de Mercúrio em Amostras de Biodiesel por Geração Fotoquímica de Vapor

In this paper, the photochemical vapor generation coupled with atomic absorption spectrometry was used to assess the concentration of Hg in biodiesel samples. The main parameters to assess the best conditions for the photochemical vapor generation of Hg were investigated (sample mass, formic acid concentration, irradiation time and gas flow rate). Volatile species of Hg were generated in biodiesel samples prepared in 20% (v/v) formic acid and 76% (v/v) ethanol. Analytical curves were generated using inorganic (Hg 2+ ) and organic standards (CH3Hg + e C2H5Hg + ) in ethanol and showed correlation coefficients higher than 0.99. The limits of detection and quantification, in μg L -1 , were 0.01 and 0.05, respectively. Due to the lack of biodiesel samples with a certified concentration of Hg, the accuracy was evaluated by assessing the recoveries of species of Hg added to the samples, obtaining values ranged from 101.0 to 111.9% of recoveries. The relative standard deviation values were lower than 0.1%, indicating an excellent precision of the method. No Hg was detected in the biodiesel samples, considering the obtained limit of detection. The proposed method is sensitive and the sample pre-treatment is simple and practical.

Recovery of latent fingermarks from brass cartridge cases: Evaluation of developers, analysis of surfaces and internal ballistic effects

A study was undertaken wherein different fingermark developers were evaluated for the recovery of fingermarks from brass cartridge cases, besides the evaluation of factors such as firing effects and surface characterization of the cases. The latent fingermarks on α-brass plates, fired and unfired cartridge cases were deposited and aged for 1-14days before development with different developers. In order to mimic the fired cartridge case conditions, the brass plates were heated and examined at room temperature (RT), at 63 and at 200°C. The sequential treatment with cyanoacrylate, gun blue and fluorescent dye has been found to be the best among other developers for the recovery of latent fingermarks on brass surfaces including fired and unfired cartridge cases. Cartridge cases and other brass surfaces were also analyzed by surface characterization methods, including X-ray diffraction, scanning electronic microscopy, energy dispersive X-ray spectroscopy and metallographic examination. The tested surfaces correspond to α-phase brass Cu0.7Zn0.3 composition and have shown different surface morphologies (such as grain structure) and different levels of oxidation, even for cartridge cases obtained from the same batch. Due to this, the effectiveness of a given reagent for a specific brass surface is uncertain. Therefore, the application of the entire tested sequence of developers is strongly recommended. Further, the effects of firing on fingermarks on cartridge cases were examined, and the results indicated that the blowback of hot gases through the looseness between cartridge case and chamber wall of the firearm is the main cause responsible for deterioration of fingermarks during firing. Despite the recognized damage caused to fingermarks by the firing effects, good quality fingermarks were recovered from fired cartridge cases in which full fingermarks were intentionally deposited prior to firing. This indicates that the handling of the cartridges before and during the loading of the gun may have a strong influence on the quantity and quality of fingermarks, and that the firing itself is not the main responsible factor for the absence or low quality of fingermarks, as frequently reported in fired cartridge cases studies.

New Design of Mini PTFE Vessels for Sample Preparation in Micro Scale: Determination of Cd, K, Mg and Na in Biological Sample

This paper presents a study involving the development of a new mini polytetrafluoroethylene (PTFE) vessel project for biological sample preparation in micro scale in closed system with microwave radiation for subsequent determination of Cd, K, Mg and Na by atomic spectrometry techniques. All experiments were carried out in micro quantities of samples (up to 20 mg) and reagents (300 μL of HNO3) for 5 min at 350 W. Certified reference materials of biological samples (bovine muscle and liver) were used to evaluate the accuracy of the proposed system and the results obtained were in agreement with the certified value at 95% of confidence (t-test). Relative standard deviations (RSD) were lower than 8.0% for all elements. The proposed method is not only easy and fast, but it is also based on the use of an inexpensive system for sample digestion.

Evaluation of the Concentration of Cu, Zn, Pb and Cr in Different Fish Species from the São Gonçalo Channel in Pelotas-RS, Brazil

The objective of this study was to evaluate the concentration of Cu, Zn, Cr and Pb in different species of fish collected in the estuarine and limnic regions of the São Gonçalo channel, located in the Patos-Mirim lagoon complex in the coastal plain of Rio Grande do Sul State (Southern Brazil) during 2013 (autumn, winter and spring) and 2014 (summer). Fish samples were decomposed in a digester block with a reflux system under conditions optimized using a central composite design as it follows: 250 mg of fish sample, 5 mL HNO3, 2 mL H2O2 during 2 h at 150 °C. The concentrations obtained ranged from 6.7 to 12.0 mg kg for Cu; 1.8 to 23.6 mg kg for Zn; 37 to 487 μg kg for Pb; and 40 to 1268 μg kg for Cr. The highest concentrations of Cu, Zn and Pb, were observed in fishes collected at locations in the estuarine region and Cr showed high levels, especially in the limnic region. The samples of the species Loricariichthys anus (viola) showed the highest concentrations of all analytes investigated.

Determination of Hg in Biological Samples and Ethanol Fuel by Photochemical Vapor Generation after Pre-Concentration in a Gold Trap

In this work, the photochemical vapor generation (PVG) coupled with atomic absorption spectrometry and a pre-concentration step with an Au column was used for the determination of Hg in biological samples and ethanol fuel. PVG with pre-concentration showed an up to 250-fold higher sensitivity compared to the approach without pre-concentration. The accuracy of analysis of biological samples was evaluated using certified reference materials (fish tissues), while for ethanol fuel samples, recovery tests were employed (91%). Analytical curves were linear (R > 0.99) in the studied range of 2.5 to 10 μg L for conventional PVG and 0.2 to 0.5 μg L for PVG with the pre-concentration step. For the last, the limits of detection reached for biological samples and ethanol fuel were 0.02 and 0.01 μg L, respectively. The systems presented are simple, sensitive and safe for the control of low Hg concentrations in different samples. However, only the system using pre-concentration with an Au column was capable of obtaining the reproduced signals of Hg in low concentrations of the order of 0.2 μg L.