Erico M.M. Flores

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).

Cadmium and mineral nutrient accumulation in potato plantlets grown under cadmium stress in two different experimental culture conditions

In order to evaluate the effect of cadmium (Cd(2+)) toxicity on mineral nutrient accumulation in potato (Solanum tuberosum L.), two cultivars named Asterix and Macaca were cultivated both in vitro and in hydroponic experiments under increasing levels of Cd(2+) (0, 100, 200, 300, 400 and 500 microM in vitro and 0, 50, 100, 150 and 200 microM in hydroponic culture). At 22 and 7 days of exposure to Cd(2+), for the in vitro and hydroponic experiment, respectively, the plantlets were separated into roots and shoot, which were analyzed for biomass as well as Cd(2+), and macro (Ca(2+), K(+) and Mg(2+)) and micronutrient (Cu(2+), Fe(2+), Mn(2+) and Zn(2+)) contents. In the hydroponic experiment, there was no reduction in shoot and root dry weight for any Cd(2+) level, regardless of the potato cultivar. In contrast, in the in vitro experiment, there was an increase in biomass at low Cd(2+) levels, while higher Cd(2+) levels caused a decrease. In general, Cd(2+) decreased the macronutrient and micronutrient contents in the in vitro cultured plantlets in both roots and shoot of cultivars. In contrast, the macronutrient and micronutrient contents in the hydroponically grown plantlets were generally not affected by Cd(2+). Our data suggest that the influence of Cd(2+) on nutrient content in potato was related to the level of Cd(2+) in the substrate, potato cultivar, plant organ, essential element, growth medium and exposure time.

Ultrasound-assisted oxidative process for sulfur removal from petroleum product feedstock

A procedure using ultrasonic irradiation is proposed for sulfur removal of a petroleum product feedstock. The procedure involves the combination of a peroxyacid and ultrasound-assisted treatment in order to comply with the required sulfur content recommended by the current regulations for fuels. The ultrasound-assisted oxidative desulfurization (UAOD) process was applied to a petroleum product feedstock using dibenzothiophene as a model sulfur compound. The influence of ultrasonic irradiation time, oxidizing reagents amount, kind of solvent for the extraction step and kind of organic acid were investigated. The use of ultrasonic irradiation allowed higher efficiency for sulfur removal in comparison to experiments performed without its application, under the same reactional conditions. Using the optimized conditions for UAOD, the sulfur removal was about 95% after 9min of ultrasonic irradiation (20kHz, 750W, run at 40%), using hydrogen peroxide and acetic acid, followed by extraction with methanol.

Sample preparation methods for subsequent determination of metals and non-metals in crude oil--a review.

In this review sample preparation strategies used for crude oil digestion in last ten years are discussed focusing on further metals and non-metals determination. One of the main challenges of proposed methods has been to overcome the difficulty to bring crude oil samples into solution, which should be compatible with analytical techniques used for element determination. On this aspect, this review summarizes the sample preparation methods for metals and non metals determination in crude oil including those based on wet digestion, combustion, emulsification, extraction, sample dilution with organic solvents, among others. Conventional methods related to wet digestion with concentrated acids or combustion are also covered, with special emphasis to closed systems. Trends in sample digestion, such as microwave-assisted digestion using diluted acids combined with high-efficiency decomposition systems are discussed. On the other hand, strategies based on sample dilution in organic solvents and procedures recommended for speciation analysis are reported as well as the use of direct analysis in view of the recent importance for crude oil field. A compilation concerning sample preparation for crude oil provided by official methods as well as certified reference materials available for accuracy evaluation is also presented and discussed.

Determination of mercury in mineral coal using cold vapor generation directly from slurries, trapping in a graphite tube, and electrothermal atomization☆

Abstract A rugged and reliable method for the determination of mercury in coal without sample digestion, based on chemical vapor generation (cold vapor technique) from slurried coal samples has been developed. It involves collection of the mercury vapor in a graphite tube, treated with gold or rhodium as permanent modifier, and determination by electrothermal atomic absorption spectrometry. Mercury quantitatively leached out of the investigated coal reference materials into 1 mol l −1 nitric acid within 48 h when the coal was ground to a particle size of ≤50 μm, except for one sample (BCR 180), which had to be ground to ≤30 μm, or a leaching time of 72 h had to be used. No detectable quantity of mercury was generated directly from the slurry particles, but it was not necessary to filter the solution. The greatest advantage of the method is that only a minimum of reagents and sample handling steps are required, a prerequisite for accurate results in routine analysis. The results were well within the 95% confidence level of the certificate or close to the information value of the reference materials investigated. The characteristic mass of 110 pg obtained with gold as the permanent modifier is close to values reported for direct analysis of solutions, showing close to 100% trapping efficiency for mercury. A limit of detection (LOD) of 90 pg absolute was obtained with this modifier, which corresponds to an LOD of 0.009 μg g −1 Hg in coal. This is based on 1 ml of slurry containing 10 mg of coal, and is an order of magnitude lower than the lowest mercury content in the investigated reference materials.

Determination of toxic elements in coal by ICP-MS after digestion using microwave-induced combustion.

A microwave-induced combustion (MIC) procedure was applied for coal digestion for subsequent determination of As, Cd and Pb by inductively coupled plasma mass spectrometry (ICP-MS) and Hg using cold vapor (CV) generation coupled to ICP-MS. Pellets of coal (500 mg) were combusted using 20 bar of oxygen and ammonium nitrate as aid for ignition. The use of nitric acid as absorbing solution (1.7, 3.5, 5.0, 7.0 and 14 mol L(-1)) was evaluated. For coal samples with higher ash content, better results were found using 7.0 mol L(-1) HNO(3) and an additional reflux step of 5 min after combustion step. For coal samples with ash content lower than 8%, 5.0 mol L(-1) nitric acid was suitable to the absorption of all analytes. Accuracy was evaluated using certified reference material (CRM) of coal and spikes. Agreement with certified values and recoveries was better than 95 and 97%, respectively, for all the analytes. For comparison of results, a procedure recommended by the American Society of Testing and Materials (ASTM) was used. Additionally, a conventional microwave-assisted digestion (MAD) in pressurized vessels was also performed. Using ASTM procedure, analyte losses were observed and a relatively long time was necessary for digestion (>6h). By comparison with MAD procedure, higher sample mass can be digested using MIC allowing better limits of detection. Additionally, the use of concentrated acids was not necessary that is an important aspect in order to obtain low blank levels and lower limits of detection, respectively. The residual carbon content in digests obtained by MAD and MIC was about 15% and <1%, respectively, showing the better digestion efficiency of MIC procedure. Using MIC it was possible to digest completely and simultaneously up to eight samples in only 25 min with relatively lower generation of laboratory effluents.

Microwave-assisted digestion in closed vessels: effect of pressurization with oxygen on digestion process with diluted nitric acid

The efficiency of diluted nitric acid solutions under oxygen pressure for decomposition of bovine liver was evaluated using microwave-assisted wet digestion. Calcium, Cu, Fe, Mg, Mn and Zn were determined by inductively coupled plasma optical emission spectrometry (ICP OES). Efficiency was evaluated by determining the residual carbon content (RCC) by ICP OES and residual acidity in digests. Samples (up to 500 mg) were digested using nitric acid solutions (0.1, 0.5, 1, 2, 3, 7, and 14 mol L−1 HNO3) and the effect of oxygen pressure was evaluated using pressures of 0.5, 1, 1.5 and 2 MPa. It was demonstrated that 2 and 0.5 mol L−1 nitric acid solutions may be used for efficient digestion of 500 and 100 mg of bovine liver, respectively, with oxygen pressures ranging from 0.5 to 2 MPa. Using these conditions, less than 0.86 and 0.21 mL of concentrated nitric acid were necessary to digest 500 and 100 mg of sample, respectively. Similar digestion efficiencies for both conditions were obtained under pressures of O2 ranging from 0.5 to 2 MPa. The residual acidities in final digests were lower than 24% when compared to the initial amount of acid used for digestion. The accuracy of the proposed procedure was evaluated using certified reference materials of bovine liver and bovine muscle. Using a solution of 2 mol L−1 with oxygen pressure of 0.5 MPa for 500 mg of sample, the agreement with certified values ranged from 96 to 105% (n = 5). Using the proposed procedure with diluted nitric acid it was possible to obtain RCC values lower than 15% that is important for minimizing the generation of laboratory residues and improving limits of detection.

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.

Evaluation of oxygen pressurized microwave-assisted digestion of botanical materials using diluted nitric acid.

The feasibility of diluted nitric acid solutions for microwave-assisted decomposition of botanical samples in closed vessels was evaluated. Oxygen pressurized atmosphere was used to improve the digestion efficiency and Al, Ca, K, Fe, Mg and Na were determined in digests by inductively coupled plasma optical emission spectrometry (ICP OES). Efficiency of digestion was evaluated taking into account the residual carbon content (RCC) and residual acidity in digests. Samples were digested using nitric acid solutions (2, 3, 7, and 14 mol L(-1) HNO(3)) and the effect of gas phase composition inside the reaction vessels by purging the vessel with Ar (inert atmosphere, 1 bar), air (20% of oxygen, 1 bar) and pure O(2) (100% of oxygen, 1 bar) was evaluated. The influence of oxygen pressure was studied using pressures of 5, 10, 15 and 20 bar. It was demonstrated that a diluted nitric acid solution as low as 3 mol L(-1) was suitable for an efficient digestion of sample masses up to 500 mg of botanical samples using 5 bar of oxygen pressure. The residual acidities in final digests were lower than 45% in relation to the initial amount of acid used for digestion (equivalent to 1.3 mol L(-1) HNO(3)). The accuracy of the proposed procedure was evaluated using certified reference materials of olive leaves, apple leaves, peach leaves and pine needles. Using the optimized conditions for sample digestion, the results obtained were in agreement with certified values. The limit of quantification was improved up to a factor of 14.5 times for the analytes evaluated. In addition, the proposed procedure was in agreement with the recommendations of the green chemistry once it was possible to obtain relatively high digestion efficiency (RCC<5%) using only diluted HNO(3), which is important to minimize the generation of laboratory residues.

Evaluation of sample preparation methods for polymer digestion and trace elements determination by ICPMS and ICPOES

In this work, sample preparation methods for polymer digestion based on microwave-induced combustion (MIC) and microwave-assisted acid digestion (MW-AD) were evaluated for further As, Bi, Cd, Co, Cu, Hg, Mn, Mo, Ni, Pb, Sb, Sr, Ti, V and Zn determination by inductively coupled plasma mass spectrometry (ICPMS) and inductively coupled plasma optical emission spectrometry (ICPOES). Samples of low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET, colorless and green), polyetheretherketone (PEEK) and nylon 6,6 were digested using MIC and MW-AD in closed quartz vessels. The type and concentration of acids used for MIC were investigated and better results were achieved using a 4 mol l−1 HNO3 + 4 mol l−1 HCl solution. Microwave-assisted acid digestion was also evaluated for polymer digestion using concentrated acids. Both sample preparation methods were considered suitable for polymer digestion but MIC was preferable in view of the possibility of using diluted acids as absorbing solution and allowing higher sample mass to be digested and consequently better limits of detection. Residual carbon content in digests of polymers obtained by MIC was lower in comparison with the values obtained after MW-AD. Accuracy for all the analytes determined by ICPOES and ICPMS after MIC digestion was better than 95% (analysis of certified reference materials and by neutron activation analysis). It was possible to digest up to 8 samples by MIC in less time (in 25 min) in comparison with MW-AD (more than 50 min) and also using diluted acids (4 mol l−1 HNO3 and HCl) instead of concentrated acids.