Juliano Smanioto Barin

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).

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.

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.

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.

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.

Determination of antimony(III) and total antimony by hydride generation atomic absorption spectrometry in samples of injectable drugs used for leishmaniasis treatment

A procedure for the determination of Sb(III) and total Sb in commercial samples of injectable drugs based on pentavalent antimony was proposed. The drugs studied in this work are currently used for leishmaniasis treatment in many countries. Determination of Sb was performed by hydride generation atomic absorption spectrometry under controlled conditions for the reaction medium. The following parameters were investigated: type and concentration of acid, sodium tetrahydroborate concentration and purge time. The chosen conditions for Sb(III) were: 4% (m/v) citric acid, 1% (m/v) sodium tetrahydroborate and 10 s (a pre-reduction step was performed using 10% m/v KI in 0.2% m/v ascorbic acid solution). The same parameters for total Sb determination were: 0.5 mol l−1 sulfuric acid, 4% (m/v) sodium tetrahydroborate and 10 s. Interference from As, Ni, Cu and Pb on the analytical signal for Sb(III) was also investigated. Two kinds of commercial drugs were analyzed. The trivalent Sb concentration varied from 1.7 to 3.1 mg l−1, corresponding to 1.6 to 2.8% for the total Sb. Recovery tests for Sb(III) showed values varying from 98.9 to 101.9%. The characteristic mass for Sb(III) was 0.22 ng and the detection limit (3s) was about 1.5 ng (absolute). The main advantage of the proposed procedure is to allow the determination of Sb(III) in the presence of a large excess of pentavalent Sb (about 2000 ng).

Mercury determination in soil by CVG-ICP-MS after volatilization using microwave-induced combustion

Microwave-induced combustion (MIC) was applied for mercury volatilization from soil with subsequent determination by cold vapor generation coupled with inductively coupled plasma mass spectrometry (CVG-ICP-MS). Samples of soil were mixed with microcrystalline cellulose (300 mg), pressed as pellets and combusted in closed quartz vessels pressurized with 20 bar of oxygen. Mercury was volatilized from the sample matrix during combustion and quantitatively absorbed in a suitable solution. The type and concentration of absorbing solution (diluted or concentrated nitric or hydrochloric acids, or even water) as well as the use of a reflux step after combustion were studied. Accuracy was evaluated using soil certified reference materials. Using 0.25 mol L−1 HNO3 as absorbing solution with a reflux step of 5 min the agreement with reference values was better than 95%. The limit of detection was 0.006 μg g−1 Hg (using 300 mg of sample mass) and the residual carbon content for MIC digests was always below 1%. The main advantage of the proposed method is related to the complete separation of the analyte from the sample matrix. Up to eight samples could be simultaneously combusted in only 25 min. Taking into account that only 6 ml of very diluted nitric acid solution (0.25 mol L−1) were used, the proposed MIC method coupled with CVG-ICP-MS can be considered in good agreement with green analytical chemistry recommendations.

Determination of Bromide, Chloride, and Fluoride in Cigarette Tobacco by Ion Chromatography after Microwave-Induced Combustion

A microwave-induced combustion (MIC) method was applied for cigarette tobacco digestion and further determination of bromide (Br), chloride (Cl), and fluoride (F) by ion chromatography (IC). Samples (up to 500 mg) were combusted at 20 bar of oxygen. Combustion was complete in less than 30 s, and analytes were absorbed in (NH4)2CO3 solutions. A reflux step, not available in other systems, was applied to improve analyte absorption. Absorbing solution with 50 mmol L−1(NH4)2CO3 was selected because it showed recovery close to 100% for samples containing spikes of halogens. Accuracy of the proposed procedure was evaluated by analysis of certified reference materials and the agreement was better than 97% for all analytes using 50 mmol L−1 (NH4)2CO3 as absorbing solution and 5 min of reflux. Temperature during combustion was higher than 1400°C and the residual carbon content was always lower than 1%. With the use of the MIC system, up to eight samples could be processed simultaneously, and a single absorbing solution was suitable for all analytes. Limits of quantification by MIC and further IC determination were 0.50, 0.20, and 0.10 µg g−1 for Br, Cl, and F, respectively.

Effect of simultaneous cooling on microwave-assisted wet digestion of biological samples with diluted nitric acid and O2 pressure

The present work evaluates the influence of vessel cooling simultaneously to microwave-assisted digestion performed in a closed system with diluted HNO3 under O2 pressure. The effect of outside air flow-rates (60-190 m(3) h(-1)) used for cooling of digestion vessels was evaluated. An improvement in digestion efficiency caused by the reduction of HNO3 partial pressure was observed when using higher air flow-rate (190 m(3) h(-1)), decreasing the residual carbon content for whole milk powder from 21.7 to 9.3% (lowest and highest air flow-rate, respectively). The use of high air flow-rate outside the digestion vessel resulted in a higher temperature gradient between liquid and gas phases inside the digestion vessel and improved the efficiency of sample digestion. Since a more pronounced temperature gradient was obtained, it contributed for increasing the condensation rate and thus allowed a reduction in the HNO3 partial pressure of the digestion vessel, which improved the regeneration of HNO3. An air flow-rate of 190 m(3) h(-1) was selected for digestion of animal fat, bovine liver, ground soybean, non fat milk powder, oregano leaves, potato starch and whole milk powder samples, and a standard reference material of apple leaves (NIST 1515), bovine liver (NIST 1577) and whole milk powder (NIST 8435) for further metals determination by inductively coupled plasma atomic emission spectroscopy (ICP-OES). Results were in agreement with certified values and no interferences caused by matrix effects during the determination step were observed.

Focused microwave-induced combustion for digestion of botanical samples and metals determination by ICP OES and ICP-MS.

The advantages and shortcomings of focused microwave-induced combustion (FMIC) for digestion of plant samples were studied. The effects of sample mass, absorbing solution, oxygen gas flow-rate, and time of reflux step on recoveries of major, minor and trace metals were systematically evaluated. Afterwards, Al, Ba, Ca, Co, Cr, Cu, Mg, Mn, Ni, Sr, V, and Zn were determined by inductively coupled plasma optical emission spectrometry (ICP OES) and by inductively coupled plasma mass spectrometry (ICP-MS). The main advantages of FMIC when compared to microwave-assisted wet digestion (MAWD) and focused-microwave-assisted wet digestion (FMAWD) are the possibility to digest larger masses of samples (up to 3g) using shorter heating times and diluted nitric acid solution for absorbing all analytes. Using the selected experimental conditions for FMIC, residual carbon content was lower than 0.7% for all samples and relative standard deviation (RSD) varied from 1.5 to 14.1%. Certified reference materials (NIST 1515 apple leaves and NIST 1547 peach leaves) were used for checking accuracy and determined values for all metals were in agreement with certified values at a 95% confidence level. No statistical difference (ANOVA, 95% of confidence level) was observed for results obtained by FMIC, FMAWD, and MAWD. Limits of detection were lower when using FMIC in the range of 0.02-0.15 μg g(-1) for ICP OES and 0.001-0.01 μg g(-1) for ICP-MS, which were about 3 and 6 times lower than the values obtained by FMAWD and MAWD, respectively. It is important to point out that FMIC was a suitable sample preparation method for major, minor and trace metals by both determination techniques (ICP OES and ICP-MS). Additionally, since it allows lower LODs (because up to 3g of sample can be digested) and diluted acid solutions are used (without any further dilution), the use of ICP-MS is not mandatory.