973 resultados para Plasma. Dielectric barrier discharge. Lissajous figures. Optical emission spectroscopy
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The historical development of atomic spectrometry techniques based on chemical vapor generation by both batch and flow injection sampling formats is presented. Detection via atomic absorption spectrometry (AAS), microwave induced plasma optical emission spectrometry (MIP-OES), inductively coupled plasma optical emission spectrometry (ICP-OES) , inductively coupled plasma mass spectrometry (ICP-MS) and furnace atomic nonthermal excitation spectrometry (FANES) are considered. Hydride generation is separately considered in contrast to other methods of generation of volatile derivatives. Hg ¾ CVAAS (cold vapor atomic absorption spectrometry) is not considered here. The current state-of-the-art, including extension, advantages and limitations of this approach is discussed.
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In this work a micro-heater device to be used as an integral part of the flow analysis manifold is described. The usefulness of the device was demonstrated using it in the development of a multicommutated flow analysis procedure for the spectrophotometric determination of manganese in plant digest. The method was based on the manganese oxidation by periodate in phosphoric acid medium to form the permanganate anion. The reaction development is dependent on the temperature and it was observed that at 25 °C a time interval of ca. 15 min was necessary for the reaction to attain equilibrium. Setting the temperature to 70 ºC, this time interval could be decreased to ca. 30 s. This condition was easily attained employing the proposed micro-heater device coupled to the manifold. The procedure was applied to manganese determination in soybean digests and results compared with those obtained by inductively coupled argon plasma optical emission spectrometry (ICP-OES). No significant difference at 90% confidence level was observed. A linear response for sample concentrations ranging from 5.0 to 30.00 mg L-1 Mn2+; a relative standard deviation of 1.3% (n = 6) for a typical sample containing 6.3 mg L-1 Mn2+; a sampling rate of 22 determinations per hour; a low reagent consumption, of 12.0 mg NaIO4 per determination; and a detection limit of 1.2 mg L-1 were achieved.
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The use of an internal standard (IS) in ET AAS can be considered a new trend after the commercial introduction of a simultaneous spectrometer. The evaluation of experimental data to choose the most appropriate IS can be done by comparing correlation graphs. They were used to verify the resemblance among the simultaneous measurements obtained for the analyte(s) and the IS by inductively coupled plasma optical emission spectrometry (ICPOES). The judicious selection of IS by using correlation graphs for determinations by ET AAS can be exploited to improve the precision and accuracy of the analytical results. Therefore, a new approach for studying the use of IS in ET AAS is presented.
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Inductively Coupled Plasma Optical Emission Spectrometry was used to determine Ca, Mg, Mn, Fe, Zn and Cu in samples of processed and natural coconut water. The sample preparation consisted in a filtration step followed by a dilution. The analysis was made employing optimized instrumental parameters and the results were evaluated using methods of Pattern Recognition. The data showed common concentration values for the analytes present in processed and natural samples. Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) indicated that the samples of different kinds were statistically different when the concentrations of all the analytes were considered simultaneously.
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The applicability of the recently proposed procedure based on gradual sample addition to microwave-assisted pre-heated concentrated acid is limited by the sample viscosity. In this work, lubricating oil samples with high viscosity were encapsulated and manually added to the microwave-assisted pre-heated concentrated digestion mixture. The procedure was applied for determination of Al, Ca, Cr, Cu, Fe, Mg, Ni, P, Pb, Si, Sn, Sr, V, W, and Zn in lubricating oil by inductively coupled plasma optical emission spectrometry (ICP OES). Determined and certified values for Ca, Mg, P, and Zn in lubricating oil were in agreement at a 95% confidence level.
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One hundred fifteen cachaça samples derived from distillation in copper stills (73) or in stainless steels (42) were analyzed for thirty five itens by chromatography and inductively coupled plasma optical emission spectrometry. The analytical data were treated through Factor Analysis (FA), Partial Least Square Discriminant Analysis (PLS-DA) and Quadratic Discriminant Analysis (QDA). The FA explained 66.0% of the database variance. PLS-DA showed that it is possible to distinguish between the two groups of cachaças with 52.8% of the database variance. QDA was used to build up a classification model using acetaldehyde, ethyl carbamate, isobutyl alcohol, benzaldehyde, acetic acid and formaldehyde as chemical descriptors. The model presented 91.7% of accuracy on predicting the apparatus in which unknown samples were distilled.
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This work deals with paint decomposition methods for major, minor and trace elements determination. Three methods were investigated: (1) decomposition in closed quartz vessel and heating in microwave oven; (2) decomposition in open vessel using HNO3 and ashing, following the ASTM D 3335-85a method; and (3) decomposition in open vessel using HNO3 + HF and ashing. Paints of different types and colours were analyzed, in which several elements were determined using inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP OES). It was observed that method (1) is appropriate for trace, minor and major elements determination, while method (3) is appropriate for Ti.
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A method for selective determination of tributyltin in the presence of Sn(IV) by combining hydride generation inductively coupled plasma optical emission spectrometry (HG-ICP OES) and solid phase extraction (SPE) using baker's yeast is proposed. The procedure is based on selective retention of TBT by the yeast at pH = 6. Detection limit of 1.9 µg L-1 and quantification limit of 6.3 µg L-1 were obtained. TBT and San(IV) were determined in the range of 0-25 µg L-1 and the proposed approach was applied to analyze river water, sea water and biological extracts, with recoveries of 114, 101 and 86%, respectively.
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The performance of inductively-coupled plasma optical emission spectrometers with axial and radial views for determination of iodine in table salt was evaluated. Interference and memory effects in nitric acid and water-soluble tertiary amines (CFA-C) media were studied. Based on a factorial experiment, one optimum instrument operational condition for axial configuration, and two optima conditions for radial configuration was established. The ICP OES with axial view was 5-fold more sensitive than the radial view. Both matrix matching and standard addition methods were used for iodine quantification and for most samples, both strategies of calibration led to similar results. Recoveries ranged from 104 to 114%.
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The present study utilized thermogravimetry (TG) and optical emission spectrometry with inductively coupled plasma (ICP/OES) to determine the amount of calcium in calcium lactate tablets used in the treatment of osteoporosis. Thermogravimetry results indicated that the decomposition temperature of CaCO3 occurred at 603.9 and 609.4 ºC in the samples of calcium lactate and tablets, respectively. The calcium content obtained by TG for the tablets sample showed a similar result to that disclosed by ICP-OES, indicating a value of 8.93% for both techniques.
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In this study, dispersive liquid-liquid microextraction based on the solidification of floating organic droplets was used for the preconcentration and determination of thorium in the water samples. In this method, acetone and 1-undecanol were used as disperser and extraction solvents, respectively, and the ligand 1-(2-thenoyl)-3,3,3-trifluoracetone reagent (TTA) and Aliquat 336 was used as a chelating agent and an ion-paring reagent, for the extraction of thorium, respectively. Inductively coupled plasma-optical emission spectrometry was applied for the quantitation of the analyte after preconcentration. The effect of various factors, such as the extraction and disperser solvent, sample pH, concentration of TTA and concentration of aliquat336 were investigated. Under the optimum conditions, the calibration graph was linear within the thorium content range of 1.0-250 µg L-1 with a detection limit of 0.2 µg L-1. The method was also successfully applied for the determination of thorium in the different water samples.
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Glass is a unique material with a long history. Several glass products are used daily in our everyday life, often unnoticed. Glass can be found not only in obvious applications such as tableware, windows, and light bulbs, but also in tennis rackets, windmill turbine blades, optical devices, and medical implants. The glasses used at present as implants are inorganic silica-based melt-derived compositions mainly for hard-tissue repair as bone graft substitute in dentistry and orthopedics. The degree of glass reactivity desired varies according to implantation situation and it is vital that the ion release from any glasses used in medical applications is controlled. Understanding the in vitro dissolution rate of glasses provides a first approximation of their behavior in vivo. Specific studies concerning dissolution properties of bioactive glasses have been relatively scarce and mostly concentrated to static condition studies. The motivation behind this work was to develop a simple and accurate method for quantifying the in vitro dissolution rate of highly different types of glass compositions with interest for future clinical applications. By combining information from various experimental conditions, a better knowledge of glass dissolution and the suitability of different glasses for different medical applications can be obtained. Thus, two traditional and one novel approach were utilized in this thesis to study glass dissolution. The chemical durability of silicate glasses was tested in water and TRIS-buffered solution at static and dynamic conditions. The traditional in vitro testing with a TRISbuffered solution under static conditions works well with bioactive or with readily dissolving glasses, and it is easy to follow the ion dissolution reactions. However, in the buffered solution no marked differences between the more durable glasses were observed. The hydrolytic resistance of the glasses was studied using the standard procedure ISO 719. The relative scale given by the standard failed to provide any relevant information when bioactive glasses were studied. However, the clear differences in the hydrolytic resistance values imply that the method could be used as a rapid test to get an overall idea of the biodegradability of glasses. The standard method combined with the ion concentration and pH measurements gives a better estimate of the hydrolytic resistance because of the high silicon amount released from a glass. A sensitive on-line analysis method utilizing inductively coupled plasma optical emission spectrometer and a flow-through micro-volume pH electrode was developed to study the initial dissolution of biocompatible glasses. This approach was found suitable for compositions within a large range of chemical durability. With this approach, the initial dissolution of all ions could be measured simultaneously and quantitatively, which gave a good overall idea of the initial dissolution rates for the individual ions and the dissolution mechanism. These types of results with glass dissolution were presented for the first time during the course of writing this thesis. Based on the initial dissolution patterns obtained with the novel approach using TRIS, the experimental glasses could be divided into four distinct categories. The initial dissolution patterns of glasses correlated well with the anticipated bioactivity. Moreover, the normalized surface-specific mass loss rates and the different in vivo models and the actual in vivo data correlated well. The results suggest that this type of approach can be used for prescreening the suitability of novel glass compositions for future clinical applications. Furthermore, the results shed light on the possible bioactivity of glasses. An additional goal in this thesis was to gain insight into the phase changes occurring during various heat treatments of glasses with three selected compositions. Engineering-type T-T-T curves for glasses 1-98 and 13-93 were stablished. The information gained is essential in manufacturing amorphous porous implants or for drawing of continuous fibers of the glasses. Although both glasses can be hot worked to amorphous products at carefully controlled conditions, 1-98 showed one magnitude greater nucleation and crystal growth rate than 13-93. Thus, 13-93 is better suited than 1-98 for working processes which require long residence times at high temperatures. It was also shown that amorphous and partially crystalline porous implants can be sintered from bioactive glass S53P4. Surface crystallization of S53P4, forming Na2O∙CaO∙2SiO2, was observed to start at 650°C. The secondary crystals of Na2Ca4(PO4)2SiO4, reported for the first time in this thesis, were detected at higher temperatures, from 850°C to 1000°C. The crystal phases formed affected the dissolution behavior of the implants in simulated body fluid. This study opens up new possibilities for using S53P4 to manufacture various structures, while tailoring their bioactivity by controlling the proportions of the different phases. The results obtained in this thesis give valuable additional information and tools to the state of the art for designing glasses with respect to future clinical applications. With the knowledge gained we can identify different dissolution patters and use this information to improve the tuning of glass compositions. In addition, the novel online analysis approach provides an excellent opportunity to further enhance our knowledge of glass behavior in simulated body conditions.
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In this thesis, stepwise titration with hydrochloric acid was used to obtain chemical reactivities and dissolution rates of ground limestones and dolostones of varying geological backgrounds (sedimentary, metamorphic or magmatic). Two different ways of conducting the calculations were used: 1) a first order mathematical model was used to calculate extrapolated initial reactivities (and dissolution rates) at pH 4, and 2) a second order mathematical model was used to acquire integrated mean specific chemical reaction constants (and dissolution rates) at pH 5. The calculations of the reactivities and dissolution rates were based on rate of change of pH and particle size distributions of the sample powders obtained by laser diffraction. The initial dissolution rates at pH 4 were repeatedly higher than previously reported literature values, whereas the dissolution rates at pH 5 were consistent with former observations. Reactivities and dissolution rates varied substantially for dolostones, whereas for limestones and calcareous rocks, the variation can be primarily explained by relatively large sample standard deviations. A list of the dolostone samples in a decreasing order of initial reactivity at pH 4 is: 1) metamorphic dolostones with calcite/dolomite ratio higher than about 6% 2) sedimentary dolostones without calcite 3) metamorphic dolostones with calcite/dolomite ratio lower than about 6% The reactivities and dissolution rates were accompanied by a wide range of experimental techniques to characterise the samples, to reveal how different rocks changed during the dissolution process, and to find out which factors had an influence on their chemical reactivities. An emphasis was put on chemical and morphological changes taking place at the surfaces of the particles via X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy (SEM). Supporting chemical information was obtained with X-Ray Fluorescence (XRF) measurements of the samples, and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) measurements of the solutions used in the reactivity experiments. Information on mineral (modal) compositions and their occurrence was provided by X-Ray Diffraction (XRD), Energy Dispersive X-ray analysis (EDX) and studying thin sections with a petrographic microscope. BET (Brunauer, Emmet, Teller) surface areas were determined from nitrogen physisorption data. Factors increasing chemical reactivity of dolostones and calcareous rocks were found to be sedimentary origin, higher calcite concentration and smaller quartz concentration. Also, it is assumed that finer grain size and larger BET surface areas increase the reactivity although no certain correlation was found in this thesis. Atomic concentrations did not correlate with the reactivities. Sedimentary dolostones, unlike metamorphic ones, were found to have porous surface structures after dissolution. In addition, conventional (XPS) and synchrotron based (HRXPS) X-ray Photoelectron Spectroscopy were used to study bonding environments on calcite and dolomite surfaces. Both samples are insulators, which is why neutralisation measures such as electron flood gun and a conductive mask were used. Surface core level shifts of 0.7 ± 0.1 eV for Ca 2p spectrum of calcite and 0.75 ± 0.05 eV for Mg 2p and Ca 3s spectra of dolomite were obtained. Some satellite features of Ca 2p, C 1s and O 1s spectra have been suggested to be bulk plasmons. The origin of carbide bonds was suggested to be beam assisted interaction with hydrocarbons found on the surface. The results presented in this thesis are of particular importance for choosing raw materials for wet Flue Gas Desulphurisation (FGD) and construction industry. Wet FGD benefits from high reactivity, whereas construction industry can take advantage of slow reactivity of carbonate rocks often used in the facades of fine buildings. Information on chemical bonding environments may help to create more accurate models for water-rock interactions of carbonates.
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Although the greatest variety of Brazilian flora is in the Amazon region, the Southern region of Brazil also has an estimated number of at least 5,000 species of vascular native plants. These species have been neglected as potential food sources, remaining unknown and under-utilized and limiting the potential variety in the diet of Brazilians and other peoples. Therefore the aim of this study was to characterize the mineral composition and content present in seven native fruit species of Southern Brazil using inductively coupled plasma optical emission spectrometry (ICP-OES). The essential element concentrations in the fruit samples were higher or similar to the values reported for traditional fruits. The araticum-do-mato fruit samples had high concentrations of the elements Ca, K, and Cu, and trace elements such as Pb and Sr. Mandacaru-de-três-quinas had predominance of Ba, Bi, and Ga, and the essential elements Mg and Mn. Uvaia and guabiroba had the highest levels of Al and Cr, but uvaia had high levels of Fe and Zn. The pindo palm had high amounts of Cd and Ni, and the yellow guava had high concentrations of Na, while red guava had high levels of Co.
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Demand for organic products is intensified in many countries each year. Following this trend, Brazil produces increasing volumes of organic grape juice. In this way, a survey of organic grape juices made from grapes produced according to this system was carried out where physicochemical composition, minerals, trace elements, and pesticide residues were determined. Variables related to grape juice composition were performed by physicochemical procedures; minerals and trace elements, by inductively plasma optical emission spectrometry; pesticide residues, by liquid chromatography-mass spectrometry. Main results show that the physicochemical composition of organic grape juices was in general in accordance to the Brazilian legislation. The mean concentrations of trace elements were very low, varying from 0.002 (Cd) to 0.970 (Ba) mg L–1. Pesticide residues were not detected in any sample analyzed (MRL= 10 µg L–1). These results show that the Serra Gaúcha viticultural region present conditions to produce organic grape juices, despite the adverse climate factors that occurs in some years. Nevertheless, these products should be made with grape varieties, such as the labrusca ones, less susceptibles to the main grapevine pathogens.