Delmo Santiago Vaitsman

A simplified version of the total kjeldahl nitrogen method using an ammonia extraction ultrasound-assisted purge-and-trap system and ion chromatography for analyses of geological samples

The total Kjeldahl nitrogen (TKN) method was simplified by using a manifold connected to a purge-and-trap system immersed into an ultrasonic (US) bath for simultaneous ammonia (NH(3)) extraction from many previously digested samples. Then, ammonia was collected in an acidic solution, converted to ammonium (NH(4)(+)), and finally determined by ion chromatography method. Some variables were optimized, such as ultrasonic irradiation power and frequency, ultrasound-assisted NH(3) extraction time, NH(4)(+) mass and sulfuric acid concentration added to the NH(3) collector flask. Recovery tests revealed no changes in the pH values and no conversion of NH(4)(+) into other nitrogen species during the irradiation of NH(4)Cl solutions with 25 or 40 kHz ultrasonic waves for up to 20 min. Sediment and oil free sandstone samples and soil certified reference materials (NCS DC 73319, NCS DC 73321 and NCS DC 73326) with different total nitrogen concentrations were analysed. The proposed method is faster, simpler and more sensitive than the classical Kjeldahl steam distillation method. The time for NH(3) extraction by the US-assisted purge-and-trap system (20 min) was half of that by the Kjeldahl steam distillation (40 min) for 10 previously digested samples. The detection limit was 9 microg g(-1)N, while for the Kjeldahl classical/indophenol method was 58 microg g(-1)N. Precision was always better than 13%. In the proposed method, carcinogenic reagents are not used, contrarily to the indophenol method. Furthermore, the proposed method can be adapted for fixed-NH(4)(+) determination.

Long-term fluoride release from resin-reinforced orthodontic cements following recharge with fluoride solution

The aim of this study was to test the hypothesis that there is no difference in the fluoride release behavior of resin-reinforced glass ionomer cements before or after fluoride recharge. The materials were divided into 5 groups: 2 resin-reinforced glass ionomer cements used for attaching orthodontic bands, that is, group FOB (Fuji Ortho Band) and group MCB (Multi-Cure Glass Ionomer Orthodontic Band Cement); 2 resin-reinforced glass ionomer cements and a composite used for bonding orthodontic brackets, that is, group OGLC (Ortho Glass LC), group FOLC (Fuji Ortho LC), and group TXT (Transbond XT), respectively. Fluoride release was measured during a 60-day period by using selective ion electrodes connected to an ionic analyser. After 4 weeks, the samples were exposed to 0.221% sodium fluoride solution. The results showed that cements achieved a maximum fluoride release 24 h after initial setting. No statistically significant differences were observed between groups FOB and OGLC regarding the amount of released fluoride following fluoride recharge from day 31 to day 36 (p>0.05). In conclusion, FOB and OGLC cements showed a higher capacity of capturing and releasing fluoride compared to the other cements studied.

Determination of metals in coal fly ashes using ultrasound-assisted digestion followed by inductively coupled plasma optical emission spectrometry

A method for determination of Co, Cr, Cu, Fe, Mn, Ni, Ti, V and Zn in coal fly ash samples using ultrasound-assisted digestion followed by inductively coupled plasma optical emission spectrometry (ICP-OES) is proposed. The digestion procedure consisted in the sonication of the previously dried sample with hydrofluoric acid and aqua regia at 80 degrees C for 30 min, elimination of fluorides by heating until dryness for about 1h and dissolution of the residue with nitric acid solution. A classical digestion method, used as comparative method, consisted in the addition of HCl, HNO(3) and HF to 1 g of sample, and heating on a hot plate until dryness for about 6h. The proposed method presents several advantages: it requires lower amounts of sample and reagents, and it is faster. It is also advantageous when compared to the published methods, which also use ultrasound-assisted digestion procedure: lower detection limits for Co, Cu, Ni, V and Zn, and it does not require shaking during the digestion. The detection limits (microg g(-1)) for Co, Cr, Cu, Fe, Mn, Ni, Ti, V and Zn were 0.06, 0.37, 1.0, 25, 0.93, 0.45, 4.0, 1.7 and 4.3, respectively. The results were in good agreement with those obtained by the classical method and reference values. The exception was Cr, which presented low recoveries in classical and proposed methods (83 and 87%, respectively). Also, the concentration for Cu obtained by the proposed method was significantly different from the reference value, in spite of the good recovery (91+/-1%).

A preliminary study on the magnetic treatment of fluids

ABSTRACT Although the influence of magnetic fields on paraffin deposition is still dimly understood, magnetic devices have been exploited by the petroleum industry to mitigate this problem. In this study, a series of experiments were carried out using a lab-scale magnetic conditioner and two kind of samples: paraffin mixture and crude oil. The investigated parameters were: exposition time, temperature, magnetic field intensity. paraffin type and content in the fluid and the reversibility of the observed alterations. The results indicate that magnetic fields, up to 1 Tesla applied at a temperature close to the Wax Appearance Temperature (WAT), reduce the apparent viscosity of the samples. This effect has been ascribed to changes in the paraffin crystal morphology promoted by the magnetic field. Scanning Electronic Microscopy (SEM) was fundamental to confirm this hypothesis.

The role of the yeast ATP-binding cassette Ycf1p in glutathione and cadmium ion homeostasis during respiratory metabolism

Cadmium (Cd2+) is a toxic environmental contaminant for biological systems, which can form complexes with reduced glutathione (GSH), and thus alter the intracellular redox state. In Saccharomyces (S.) cerevisiae, bis(glutathionato)cadmium (Cd-[GS]2) complexes can be removed from the cytosol and transported into the vacuole by a glutathione-conjugated pump, Ycf1p. In this study, we investigated the role of Ycf1p in Cd2+ detoxification during respiratory metabolism of S. cerevisiae, and the correlation of Ycf1p with GSH intracellular homeostasis. The results showed that in respiratory condition the mutant ycf1Delta is more tolerant to Cd2+ and to the oxidants t-BOOH and H2O2 than wild-type strain. This tolerance is probably related to the high content of GSH present in ycf1Delta mutant. The expression of YCF1 promoter in the wild-type strain is naturally down-regulated after the transition from fermentative to respiratory metabolism (diauxic shift), and its induction in response to Cd2+ is dependent on GSH availability. Our data suggest that Ycf1p is involved in the maintenance of intracellular GSH homeostasis and it can interfere with the oxidative tolerance of yeast. Moreover, the detoxification of Cd2+ is dependent on GSH availability and on cellular metabolic status.

Leite e alguns de seus derivados: da antiguidade à atualidade

This work presents a little of the history which marked the development of the dairy industry in Brazil and in the world. It shows problems and solutions related to the preservation of milk. In general, it also describes the traditional manufacture of cheese and applications of membrane technology as an auxiliary tool in the processing of some types of cheese.

Fluoride Release/Uptake from Different Orthodontic Adhesives: A 30-Month Longitudinal Study

The aim of this study was to test the null hypothesis that there is no difference in fluoride release between resin-modified glass ionomer cements (RMGICs) and composites in the long term. The materials were divided into 5 groups: a nonfluoride-releasing composite - Group TXT (Transbond XT), a fluoride-releasing composite - Group QC (Quick-Cure), and three RMGICs - Groups FOLC, FOB and MC (Fuji Ortho LC, Fuji Ortho Band, and Multi-Cure). Fluoride release was measured at time intervals of 1 h, 1, 7, 14, 21 and 29 days, followed by further evaluations performed at 6, 12, 18, 24 and 30 months using selective ion electrodes connected to an ionic analyzer. Fluoride releasing and re-releasing experiments were analyzed using the Kruskal-Wallis test and Mann-Whitney test with the Bonferroni correction. The amount of fluoride released by FOB was larger in comparison with the other adhesives (p=0.01). In the long-term, FOLC and MC had a similar performance (p>0.05). The composites presented a low fluoride release, but fluoride ion uptake and re-release capacity of QC was statistically significant (p<0.05) during the experiment. In conclusion, the null hypothesis was rejected, the RMGIC Fuji Ortho Band and the composite Quick-Cure presented greater fluoride release and re-release capacity when recharged.

Uso da poeira e do ar como indicadores de contaminação ambiental em áreas circunvizinhas a uma fonte de emissão estacionária de chumbo

This study measured lead concentrations in both the outdoor air and household dust from houses located around a lead-acid battery repair shop. Such installations are one of the largest sources of lead exposure, since outdated technology is still used, coupled with the lack of strict air-quality control programs. Measurements of the air lead concentration around the repair shop were carried out at 6 points, approximately 25 and 500 m from the shop. Over 50% of the air samples exceeded the limit of 1.5 microg Pb.m-3 (range 0.03 - 183.3 microg Pb.m-3). House dust samples were collected from 6 places in houses located at approximately 25, 50, and 500 m from the repair shop, and the concentration of 1,500 microg Pb.m-2 for lead in house dust was exceeded in 44% of the samples, with results varying from 2.2 to 54,338.9 microg Pb.m-2.

Antimicrobial and fluoride release capacity of orthodontic bonding materials

OBJECTIVE The aim of this study was to evaluate the antimicrobial and fluoride releasing capacity of 3 bonding materials. MATERIAL AND METHODS Thirty nine specimens with standardized surface smoothness and dimensions were prepared. The antimicrobial capacity of the materials against S. mutans, L. casei and C. albicans was evaluated by determining the percentage of growth inhibition of these microorganisms in an inoculated medium, obtained by optical density readouts on a spectrophotometer. The potential to interfere in microbial growth on the surface of the studied materials was observed by means of scanning electron microscopy (SEM). The fluoride release capacity in ultrapure water for 14 days was analyzed by means of ion chromatography. RESULTS The PLUS group presented the highest percentage of microbial inhibition and the most contamination-free surface. The FUJI group presented the best fluoride release capacity. CONCLUSIONS The TransbondTM Plus Color Change was the one that presented the best general behavior considering the evaluated aspects.

Magnetic field effect on paraffin deposition

In the oil industry, the paraffination phenomenon is a major problem during oil production, displacement and treatment. Paraffin deposition in subsea flowlines, surface equipment, production string or even in the reservoir, can cause significant and increasing oil losses. To minimize paraffin precipitation, the application of magnetic field in the petroleum path has been suggested based on empiric studies. In this study, we assembled a labscale magnetic conditioner to determine the influence of magnetic field on the physical-chemical properties of two fluids : oil and a paraffin mixture. We observed that magnetic field reduce sample aparent viscosity due to crystal morphology alteration.