Diogo P. Moraes

Determination of Halogens in Coal after Digestion Using the Microwave-Induced Combustion Technique

The microwave-induced combustion (MIC) technique was applied for coal digestion and further determination of bromide, chloride, fluoride, and iodide by ion chromatography (IC). Samples (up to 500 mg) were combusted at 2 MPa of oxygen. Combustion was complete in less than 50 s, and analytes were absorbed in water or (NH(4))(2)CO(3) solution. A reflux step was applied to improve analyte absorption. Accuracy was evaluated for Br, Cl, and F using certified reference coal and spiked samples for I. For Br, Cl, and F, the agreement was between 96 and 103% using 50 mmol L(-1) (NH(4))(2)CO(3) as the absorbing solution and 5 min of reflux. With the use of the same conditions, the recoveries for I were better than 97%. Br, Cl, and I were also determined in MIC digests by inductively coupled plasma mass spectrometry, inductively coupled plasma optical emission spectrometry, and F was determined by an ion-selective electrode with agreement better than 95% to the values obtained using IC. Temperature during combustion was higher than 1350 degrees C, and the residual carbon content was lower than 1%. With the use of the MIC technique, up to eight samples could be processed simultaneously, and a single absorbing solution was suitable for all analytes and determination techniques (limit of detection by IC was better than 3 microg g(-1) for all halogens).

Nickel, vanadium and sulfur determination by inductively coupled plasma optical emission spectrometry in crude oil distillation residues after microwave-induced combustion

Microwave-induced combustion (MIC) was applied for digestion of crude oil distillation residues for further total nickel, vanadium and sulfur determination by inductively coupled plasma optical emission spectrometry (ICP OES). Sample masses up to 500 mg of atmospheric distillation residue (AR) and vacuum distillation residue (VR) were completely combusted using the MIC system. A polyethylene film was used to wrap the samples allowing a feasible combustion process. Ammonium nitrate (6 mol l−1 solution, 50 µl) was used as an aid for ignition. Parameters related to the combustion process, as sample mass and oxygen pressure for MIC were investigated. The type and concentration of absorbing solution (H2O, 5% v/v H2O2 and 1 to 14 mol l−1 HNO3) used to absorb gaseous combustion products as well as the use of an additional reflux step were studied. Diluted nitric acid (2 mol l−1) was selected as absorbing solution resulting in a suitable medium for simultaneous Ni, V and S determination by ICP OES in both AR and VR samples. The agreement to certified values for Ni, V and S was from 99 to 101% for MIC using 2 mol l−1 HNO3 as absorbing solution with a reflux step. Results obtained by MIC for AR and VR samples were also in agreement with results obtained using high pressure microwave-assisted wet digestion. Limits of detection by MIC and further ICP OES determination were 0.2, 0.1 and 2 µg g−1 for Ni, V and S, respectively. It was possible to digest up to eight samples each run. Digestion time was reduced twice when compared to high-pressure microwave-assisted wet digestion.

Focused microwave-induced combustion: a new technique for sample digestion.

A procedure for sample digestion based on focused microwave-induced combustion (FMIC) is proposed. This system was developed using a commercial focused microwave oven with a lab-made quartz sample holder and a modified glass vessel. Oxygen flow was used to start and support the combustion. A botanical sample was used to evaluate the operational conditions for further Al, Ba, Ca, Fe, Mg, Mn, Sr, and Zn determination by inductively coupled plasma optical emission spectrometry. Pelletized samples were positioned on the quartz holder, and 50 microL of 6 mol L(-1) NH(4)NO(3) solution was added as igniter. Combustion was completed in less than 2 min, and the temperature was higher than 950 degrees C. The use of a reflux step, the position of sample holder inside the vessel, sample mass, ignition and combustion time, oxygen flow rate, and condenser type were evaluated. Results were compared with those obtained by focused microwave-assisted wet digestion and by high pressure microwave-assisted wet digestion. Agreement of 95-103% was obtained for certified reference materials digested by FMIC (reflux step with 10 mL of 4 mol L(-1) HNO(3)). With the proposed procedure, a complete sample decomposition (residual carbon content lower than 0.5%) was achieved with low consumption of reagents as only 10 mL of diluted nitric acid was necessary. Low relative standard deviation (lower than 3.8%) was observed and high amount of sample (up to 1500 mg) could be digested that allowed lower limits of detection.

Evaluation of sample preparation methods for elastomer digestion for further halogens determination

In this work, three sample preparation methods were evaluated for further halogen determination in elastomers containing high concentrations of carbon black. Samples of nitrile-butadiene rubber, styrene-butadiene rubber, and ethylene-propylene-diene monomer elastomers were decomposed using oxygen flask combustion and microwave-induced combustion (MIC) for further Br and Cl determination by ion chromatography (IC), inductively coupled plasma optical emission spectrometry (ICP OES), and inductively coupled plasma mass spectrometry (ICP-MS). Extraction assisted by microwave radiation in closed vessels was also evaluated using water or alkaline solution. Digestion by MIC was carried out using 50xa0mmolxa0l−1 (NH4)2CO3 as the absorbing solution. The effect of the reflux step was also evaluated. Accuracy was evaluated using certified reference materials with polymeric matrix composition and by comparison of results using neutron activation analysis. Agreement for Br and Cl was better than 95% by MIC using 5xa0min of reflux, and no statistical difference was found using IC, ICP OES, and ICP-MS for determination of both analytes. For MIC, the relative standard deviation (RSD) was lower than 5%. Using extraction in closed vessels, a high amount of residues was observed, and recoveries were lower than 45% for both analytes. For oxygen flask combustion, the agreement was similar using MIC but RSD was higher (20%). The residual carbon content, an important parameter used to evaluate the digestion efficiency, was always below 1% for MIC. Using MIC, it was possible to digest elastomers with high efficiency, resulting in a single solution suitable for halogen determination by different techniques.

Trypanosoma evansi: levels of copper, iron and zinc in the bloodstream of infected cats.

The aim of this study was to evaluate the concentrations of copper, iron and zinc in blood serum of cats experimentally infected with Trypanosoma evansi. Animals were divided into two groups: control and infected with T. evansi. The animals were infected with 10(8) trypomastigotes each and parasitemia was estimated daily for 56 days by microscopic examination of smears. Hematological and biochemical parameters were evaluated for monitoring of the disease. Serum metal levels were determined in blood samples collected at days 7, 28 and 56 of the experiment. Inductively coupled plasma optical emission spectrometry was used to measure the levels of copper, iron and zinc. Significant differences were observed among groups (P<0.05). Increased levels of copper and decreased iron and zinc levels were observed. A decrease in the number of red blood cells was also observed 7 days after inoculation. Biochemical parameters were not altered. Therefore, the infection by T. evansi might alter the serum metal levels, causing metabolic disturbances in cats.

Separation of Heavy Crude Oil Emulsions Using Microwave Radiation for Further Crude Oil Analysis

Microwave radiation in closed vessels was used for the separation of heavy crude oil emulsions for further oil characterization. Operational conditions were studied and the following parameters were evaluated: water content, density, viscosity, N, S, V, Ni, and Cl. Using the proposed procedure it was possible to reduce the water and Cl content in crude oil to values lower than 1% and 300 µg g−1, respectively. It was possible to determine important crude oil properties without interferences caused by excessive water and salt concentrations. The proposed procedure is relatively fast and it was possible to obtain a suitable condition for water and salt removal from heavy crude oil emulsions without using demulsifiers or toxic reagents.

Influence of extraction method on antibacterial activity of ethanolic extracts of Ocimum gratissimum L.

The aim of this study was to define whether novel extraction methods such as microwave and ultrasound could obtain the most effective ethanolic extracts of Ocimum gratissimum as antibacterial agents. These extracts were compared with respect to extractive yield, eugenol content, antibacterial activity and brine-shrimp (Artemia salina) toxicity with extracts obtained by the classical procedures of maceration and Soxhlet. Significant differences among the extracts were observed in all analyses. Soxhlet extraction gave the highest yield (19.5%). Maceration and microwave extracts yielded the highest eugenol contents (11.6 and 11.8%, respectively). The bactericidal activity of the extracts was correlated with eugenol content (rs = 0.894). Maceration gave the extract with the broadest spectrum of activity. Ultrasound methods yielded an efficient extract for use as a topical antiseptic (minimum inhibitory concentration (MIC) = 0.66 to 1.32 mg/ml for Staphylococcus aureus and Methicillin-resistant Staphylococcus aureus (MRSA)). The most active extracts to treat vancomycin-resistant enterococcixa0(VRE) infections were obtained by Soxhlet xa0and microwave (MIC = 5.28 mg/ml). The extract obtained by maceration was the most toxic for brine shrimp, followed by the extracts obtained by ultrasonic horn, ultrasonic cleaning bath and Soxhlet /microwave. In conclusion, the antibacterial results showed that the extractive methodology can be chosen according to the intended use. n n xa0 n n Key words: Ocimum gratissimum, microwave-assisted extraction (MAE), ultrasonic cleaning bath (UCB), ultrasonic horn (UH), antibacterial activity, toxicity, Artemia salina.