Teresa Cristina Oliveira da Fonseca

Microwave-induced combustion of crude oil for further rare earth elements determination by USN–ICP-MS

A procedure for light and heavy crude oils digestion by microwave-induced combustion (MIC) is proposed for the first time for further rare earth elements (REE) determination by inductively coupled plasma mass spectrometry (ICP-MS) equipped with an ultrasonic nebulizer (USN). Samples of crude oil (API density of 10.8-23.5, up to 250 mg) were inserted in polycarbonate capsules and combusted using 20 bar of oxygen and 50 μL of 6 mol L(-1) ammonium nitrate as igniter. Nitric acid solutions (1-14.4 mol L(-1)) were evaluated for analyte absorption and a reflux step was applied after combustion (5 min of microwave irradiation at 1400 W) in order to achieve better analyte recoveries. Accuracy was evaluated using a spiked sample and also by comparison of results obtained by microwave-assisted digestion combined to ultraviolet radiation (MW-UV) and by neutron activation analysis (NAA). Using 3 mol L(-1) HNO3, quantitative recoveries (better than 97%) were obtained for all analytes. Blank values were always negligible. Agreement was higher than 96% for La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y by comparison of results with those obtained by MW-UV and by NAA (only for La, Ce, Nd, Sm, and Yb). Residual carbon content in digests using MIC was always below 1%. As an advantage over conventional procedures for crude oil digestion, using MIC, it was possible to use diluted acid as absorbing solution, obtaining better limits of detection and avoiding interferences in REE determination by USN-ICP-MS.

Multielemental determination in oil matrices diluted in xylene by ICP-MS with a dynamic reaction cell employing methane as reaction gas for solving specific interferences

The analysis of organic samples by ICP-MS is still a challenge due to the occurrence of non-spectral and spectral interferences, which usually requires time-consuming sample preparation procedures for their minimization. In this work, results are presented on the direct multielemental determination in oil samples after simple dilution in xylene. The solutions were introduced into the plasma by a sample introduction system especially suited for organics, and the operational conditions of the plasma and the dynamic reaction cell were optimized. A central composite design showed that the nebulizer and the auxiliary gas flow rates had a significant influence on interference formation, monitored by Ba++ and LaO+ intensities. The compromised plasma conditions were: RF power of 1300 W and gas flow rates of 0.42 L min−1 for the nebulizer (Ar), 1.1 L min−1 for the auxiliary gas (Ar), and 0.1 L min−1 of O2 used as an additional gas. In order to minimize spectral interferences on Ca, Cr, Fe and Mg, the operational conditions of the dynamic reaction cell, working with methane as reaction gas, were optimized for 56Fe, 52Cr, 40Ca and 24Mg. Two certified reference materials, NIST 1634c (used fuel oil) and NIST 1085b (lubricating oil), were analyzed and the recoveries were in the range of 90% to 110% for most elements, being the sample detection limits between 0.2 μg kg−1 (Cr) and 40 μg kg−1 (Zn). Reliability of the data was also tested by comparing the results for a set of biodiesel samples with those determined by ICP OES and good agreement was obtained for most elements. Differences in the elemental compositions of biodiesel samples produced from different raw materials were observed, suggesting that elemental fingerprinting may be used for source identification.

Trace element distributions in biodegraded crude oils and fractions from the Potiguar Basin, Brazil

Trace element distribution patterns were determined in crude oils from onshore biodegraded reservoirs along a secondary migration trend (Potiguar Basin, Brazil). Samples were fractionated into asphaltenes, paraffins, aromatics and polars and resins for the determination of 22 trace elements by ICP-MS. Most of them are strongly enriched in the resin and asphaltene fractions, but V and Ni are also associated with the aromatic and polar fractions. V, Co, Ni and Mo were influenced by biodegrading processes and accumulate in the most affected and migrated samples. Variations of the Ni/V ratio in aromatics and polars, matching those of homohopane and gammacerane indexes in paraffin, evidenced also the influence of biodegradation. Very similar elemental distribution patterns in oil and corresponding asphaltenes were observed, suggesting that the latter fraction, more refractory than the original oil, can be used as a robust inorganic geochemical fingerprint for oil characterization.

Mantle-like Trace Element Composition of Petroleum – Contributions from Serpentinizing Peridotites

The origin of trace metals in petroleum is intimately connected with the origin of petroleum itself, one of the most exciting topics in chemistry and geology for the past 150 years. Because of its fluidity and consequent migration, the origin of petroleum is more difficult to interpret than that of most rocks. Biogenic and abiogenic models developed side by side, each championed by some of the greatest names in chemistry and geology. According to biogenic models, petroleum forms by thermal breakdown, in the presence of water, of complex, ultimately biogenic organic polymers (kerogen) (Tissot & Welte, 1984; Lewan, 1997). Conversely, according to abiogenic models, petroleum forms by reductive polymerization of simple carbon compounds such as CO and CO2. Experiments and calculations indicate that such polymerization is thermodynamically stable only at high temperatures and pressures (above 1300°C and 30 kbar; Kenney et al., 2002) but it takes place also at low temperatures (<400°C) and low pressures in the presence of metallic hydrogenation catalysts in the Fischer-Tropsch-type synthesis, FTTS (Fischer, 1926; Szatmari, 1989). Although the biogenic, organic model has been the one generally accepted by the petroleum industry almost since its birth, abiogenic, inorganic models recurrently emerge, proposed by geologists and, more often, chemists. Major contribution to oil deposits of hydrogen and hydrocarbon liquids formed by FTTS during serpentinization was suggested by Szatmari (1989). The process was demonstrated by the discoveries of the Rainbow (Holm and Charlou, 2001) and Lost City (Kelley et al., 2001; Fruh-Green et al, 2003; Kelley, 2005; Proskurowski et al., 2008; Bach and Fruh-Green, 2010) hydrothermal fields at the Mid-Atlantic ridge, where hydrothermal plumes rising over serpentinizing peridotites contain abundant hydrogen, methane, and aliphatic hydrocarbons in the C16-C29 range, formed by FTTS. This finding, together with the discovery of aliphatic and cyclic hydrocarbons in the Orgueuil meteorite and, more recently, in the pristine Tagish Lake meteorite (Pizzarello et al., 2001; Nakamura et al., 2003), as well as new studies on hydrocarbon stability at high P-T conditions (Kenney et al., 2002), gave renewed stimulus to the abiogenic models. The Tagish Lake meteorite is a new type of water and carbon-rich Type 2 carbonaceous chondrite that contains about 5% total carbon, of

Models to Implement a Sustainable Forest Management - An Overview of the ModisPinaster Model

For a long period, practical recommendations for forest management were based upon experience gained through trial and error experimentation, observation and an understanding of density effects on tree growth within the stand. As stated by Zeide (2008), the limitations of the traditional empirical approach coupled with improvements on modelling efforts led to a change of procedures from forestry to forest science, this being defined by the author, as a new development relying on reasoning to produce the optimal system of forest management aimed at satisfying human needs and preserving nature at the same time (though not at the same place). Nowadays, the use of mathematical models for tree and stand growth dynamics is the recommended scientific approach to test for alternative management options under a Sustainable Forest Management (SFM) concept and to help solve practical problems such as the appropriate range of stand densities, the thinning prescriptions and rotation ages that allow for a given goal. Assessment of volume and biomass growth, for a given period, or of yield and carbon stock at a point in time becomes a straightforward procedure as long as there are proper equations available, for the species and region of study. Central to the successful implementation of research findings of sustainable forest management is their efficient transfer from the researcher to the manager (Farrell et al., 2000). In this context, there is a strong need for easily accessible programs to run various and numerous simulations in a convenient and flexible way. There are different possible approaches to build a simulation system, each having advantages and drawbacks. One is to build a specific tool for each model. Development can be fast when the objectives of the model are well defined, its structure remains simple and there is no need for complex outputs and interfaces. This approach nevertheless results in building many prototypes

New Pb2+ carbon paste electrode based on organically modified silicate and its square wave anodic stripping voltammetric response for pretreated gasoline samples

An analytical procedure for determining Pb2+ by square wave anodic stripping voltammetry in pretreated gasoline sample is described and a carbon paste electrode modified with a inorganic-organic hybrid material (aminopropyl linked to the silica network (APSil) obtained by the sol-gel method) was evaluated as an electrochemical sensor. The optimum conditions for the analysis of Pb2+ ions were presented as follows: composition of APSil on the carbon paste electrode 40% (wt.%); deposition solution of pH 1.8; accumulation potential of -0.7 V vs. Ag/AgCl and deposition time of 600 s. Interference studies indicated that only Cu2+, at a 5-fold excess, interfered drastically on the stripping response of Pb2+.