Márcia F. Mesko

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).

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.

Bioaccumulation and oxidative stress parameters in silver catfish (Rhamdia quelen) exposed to different thorium concentrations

The objective of this study was to evaluate the effect of chronic thorium (Th) exposure on bioaccumulation, metabolism (through biochemical parameters of the muscle) and oxidative parameters (lipidic peroxidation levels and antioxidant enzymes in the gills and in the hepatic and muscular tissues) of silver catfish (Rhamdia quelen). Silver catfish juveniles were exposed to different waterborne Th levels (in microg L(-1)): 0 (control), 25.3+/-3.2, 80.6+/-12.0, 242.4+/-35.6, and 747.2+/-59.1 for 30 d. The gills and skin were the organs that accumulated the highest Th levels. The increase in the waterborne Th concentration corresponded to a progressive increase in the Th levels in the gills and kidney. Chronic Th exposure causes alterations in the oxidative parameters of silver catfish gills, which are correlated with the Th accumulation in this organ. The levels of GST decreased in the gills of fish exposed to 747.2 microg L(-1) Th and SOD activity decreased in silver catfish exposed to 242.4 and 747.2 microg L(-1) Th. In addition, the increase in the LPO in the gills exposed to 242.4 and 747.2 microg L(-1) Th suggests that higher oxidative damage occurred in the gills. However, in the liver and muscle, these alterations occurred mainly in the lowest waterborne Th level. Metabolic intermediates in the muscle were altered by Th exposure, but no clear relationship was found.

Biochemistry, cytogenetics and bioaccumulation in silver catfish (Rhamdia quelen) exposed to different thorium concentrations.

The objective of this study was to evaluate the effect of thorium (Th) bioaccumulation on the metabolism of silver catfish (Rhamdia quelen) through biochemical parameters of the muscle (glycogen, glucose, lactate, protein, and ammonia). In addition, lipidic peroxidation levels (TBARS), catalase (CAT) and glutathione-S-transferase (GST) in the gills and in hepatic and muscular tissues were also analyzed. Cytogenetic parameters were studied through the evaluation of nuclear abnormalities in red blood cells. Silver catfish juveniles were exposed to different waterborne Th levels (in microg L(-1)): 0 (control), 25.3+/-3.2, 69.2+/-2.73, 209.5+/-17.6, and 608.7+/-61.1 for 15 days. The organs that accumulated the highest Th levels were the gills and skin. The increase of waterborne Th concentration corresponded to a progressive increase of Th levels in the gills, liver, skin and kidneys, with the highest accumulation in the gills and skin. Metabolic intermediates in the muscle were altered by Th exposure, but no clear relationship was found. CAT and GST activities in the hepatic and muscular tissues of this species suggest that the enzymatic activities can be stimulated at the lowest Th levels and inhibited at the higher levels (mainly in 608.7 microg L(-1)). The results of the cytogenetic assay contribute to this hypothesis because the higher toxicity in blood samples was found in juveniles exposed to 69.2 and 209.5 microg L(-1) Th.

Bromine and Iodine Contents in Raw and Cooked Shrimp and Its Parts

The concentration of bromine and iodine was determined in shrimp and its parts (tissue and shells), and changes in the analyte concentration were evaluated after the cooking procedure. Bromine and iodine concentrations were determined by a method recently developed by our research group based on microwave-induced combustion for sample preparation and inductively coupled plasma mass spectrometry for analyte determination. The accuracy was evaluated using a reference material (NIST 8414) that was digested using the proposed method. No statistical difference was observed between certified and determined values (Students t test, 95% confidence level). Suitable limits of detection (Br, 0.02 μg g(-1) and I, 0.01 μg g(-1)) were obtained for both analytes. Higher concentrations of both analytes were observed in shrimp shells in comparison to shrimp tissue for raw and cooked samples. Moreover, losses of Br and I (between 24 and 43%) were observed after cooking.

Protective effect of high alkalinity against the deleterious effects of chronic waterborne cadmium exposure on the detection of alarm cues by juvenile silver catfish (Rhamdia quelen).

The objective of the present study was to analyze the effect of chronic cadmium (Cd) exposure at two alkalinity levels (63 and 92xa0mgxa0l−1 CaCO3) on the antipredatory behavior of juvenile silver catfish (Rhamdia quelen) exposed to conspecific skin extract and predator odor. At an alkalinity of 63xa0mgxa0l−1 CaCO3, 30xa0days of exposure to either 4.5 or 8.0xa0μgxa0l−1 Cd impaired the catfish’s antipredatory response to alarm cues. However, silver catfish exposed to 4.5xa0μgxa0l−1 Cd at an alkalinity of 92xa0mgxa0l−1 CaCO3 responded to skin extract and predator odor. In catfish exposed to 8.0xa0μgxa0l−1 Cd at the same alkalinity, only the number of feeding bites decreased, and this occurred only for specimens exposed to predator odor. Our results show that higher alkalinity protected against the deleterious effects of Cd on alarm cue detection but only in the larvae exposed to the lowest waterborne Cd level.

Trypanosoma evansi infection on levels of copper, iron, and zinc in the plasma of rats

This study aimed to assess plasma concentrations of copper, iron, and zinc during the course of acute Trypanosoma evansi experimental infection in rats. Fifty male Wistar rats were randomly distributed into seven groups: three trypanosome-infected groups (T2, T4, and T6; nu2009=u200910 animals per group) and four uninfected controls (C0, C2, C4, and C6; nu2009=u20095 animals per group). Animals from trypanosome-infected groups were intraperitoneally injected with 106 trypanosomes/animal. Blood samples were collected by cardiac puncture before infection (day 0; group C0) or on the second (C2 and T2), fourth (C4 and T4), and sixth (C6 and T6) day postinfection. Parasitemia and hematological evaluation were performed to assess the progression of the disease in animals. The difference between groups (control and infected) was evaluated on the same day postinfection. Plasma copper concentration increased in T4 and T6 groups (Pu2009<u20090.001) compared with the control group. Plasma iron concentration decreased only in group T2 (Pu2009<u20090.001). There was no significant difference in the plasma zinc concentration between groups. This study therefore demonstrates that high plasma copper concentration and depression in iron concentration is part of the acute phase response in rats infected with T. evansi.

A Novel and Eco-Friendly Analytical Method for Phosphorus and Sulfur Determination in Animal Feed

An eco-friendly method for indirect determining phosphorus and sulfur in animal feed by ion chromatography was proposed. Using this method, it was possible to digest 500u202fmg of animal feed in a microwave system under oxygen pressure (20u202fbar) using only a diluted acid solution (2u202fmolu202fL-1 HNO3). The accuracy of the proposed method was evaluated by recovery tests, by analysis of reference material (RM) and by comparison of the results with those obtained using conventional microwave-assisted digestion. Moreover, P results were compared with those obtained from the method recommended by AOAC International for animal feed (Method nr. 965.17) and no significant differences were found between the results. Recoveries for P and S were between 94 and 97%, and agreements with the reference values of RM were better than 94%. Phosphorus and S concentrations in animal feeds ranged from 10,026 to 28,357u202fmgu202fkg-1 and 2259 to 4601u202fmgu202fkg-1, respectively.

New adhesive system based in metals cross-linking methacrylate

This study evaluated the anti-antibiofilm potential of silver methacrylate (Ag) or di-n-butyldimethacrylatetin (Sn) in experimental adhesive systems. Ag and Sn methacrylates were incorporated at 0.5mol%, 1mol% and 2mol% in an adhesive resin. The anti-antibiofilm potential, degree of conversion (DC), microtensile bond strength (μTBS), water sorption/solubility (WSR/SL), bonded interfaces pattern (SEM), cytotoxicity and leaching of Ag and Sn ions were evaluated. Data were statistically analyzed considering α = 0.05. Only Ag at 2% affected DC and μTBS. Ag at 1% and 2% and Sn at 1% and 2% showed anti-biofilm potential against Mutans streptococci. Ag at 1% and 2% and Sn at 2% showed a statistically significant difference to the control in WSR/SL (p < 0.05). The additions of metal methacrylate did not affect cell viability, being the adhesive resins statistically similar to controls. Leached metals of Ag were more than 100x higher than for Sn. Between the concentration tested, Ag and Sn methacrylate at 1% presented an anti-biofilm effect without altering the mechanical properties evaluated.