Paola A. Mello

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).

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.

Bromine and iodine determination in active pharmaceutical ingredients by ICP-MS

A method based on microwave-induced combustion (MIC) was applied for digestion of active pharmaceutical ingredients (APIs) and subsequent determination of bromine and iodine by inductively coupled plasma mass spectrometry (ICP-MS). Ten APIs including amoxicillin, atenolol, clavulanic acid, clonazepan, diltiazem, haloperidol, imipramine, nimesulide, propranolol and sodium diclofenac were decomposed by MIC. Combustion of 500 mg of each API was possible in less than 30 s using 20 bars of oxygen as initial pressure. A single and diluted solution (50 mmol L−1 (NH4)2CO3) was used for the absorption of both analytes and a reflux step of 5 min was applied to improve analyte recoveries. Final digests were suitable to Br and I determination by ICP-MS. Accuracy was evaluated using certified reference materials and agreement better than 95 and 97% for Br and I was obtained, respectively. Results were also compared with those obtained by ion chromatography (IC). The carbon content in digests obtained after decomposition was lower than 500 mg L−1 avoiding interferences in the determination step for both techniques. With the use of MIC, up to eight samples could be processed simultaneously and only diluted solutions are required, minimizing reagent consumption and waste generation. The limits of detection for Br and I by ICP-MS were 0.02 and 0.001 μg g−1, respectively, that were considered suitable for the determination of these elements in the investigated active pharmaceutical ingredients.

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 Sulfur in Petroleum Coke Combining Closed Vessel Microwave-Induced Combustion and Inductively Coupled Plasma-Optical Emission Spectrometry

Abstract A new procedure based on closed vessel Microwave-Induced Combustion (MIC) technique is proposed for the decomposition of petroleum coke and further determination of sulfur by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). The procedure is based on sample ignition by microwave radiation using closed quartz vessels pressurized with oxygen and use of NH4NO3 as an ignition aid. The nature and concentration of absorbing/refluxing solution were studied, as well as the operational parameters related to MIC technique. Results were compared with those obtained by conventional wet digestion in closed vessels, certified reference materials (agreement was better than 98%), and also using ion chromatography for S determination.

Study and determination of elemental impurities by ICP-MS in active pharmaceutical ingredients using single reaction chamber digestion in compliance with USP requirements

In this work a method for active pharmaceutical ingredients (APIs) digestion using the single reaction chamber (SRC-UltraWave™) system was proposed following the new recommendations of United States Pharmacopeia (USP). Levodope (LEVO), primaquine diphosphate (PRIM), propranolol hydrochloride (PROP) and sulfamethoxazole (SULF) were used to evaluate the digestion efficiency of the proposed method. A comparison of digestion efficiency was performed by measuring the carbon content and residual acidity in digests obtained using SRC and in digests obtained using conventional microwave-assisted digestion system (Multiwave(TM)). Three digestion solutions (concentrated HNO3, aqua regia or inverse aqua regia) were evaluated for digestion of APIs. The determination of Cd, Ir, Mn, Mo, Ni, Os, Pb, Pd, Pt, Rh, Ru was performed using inductively coupled plasma mass spectrometry (ICP-MS) in standard mode. Dynamic reaction cell (DRC) mode was used for the determination of (51)V, (52)Cr, (53)Cr, (63)Cu and (65)Cu in order to solve polyatomic ion interferences. Arsenic and Hg were determined using chemical vapor generation coupled to ICP-MS (FI-CVG-ICP-MS). Masses of 500mg of APIs were efficiently digested in a SRC-UltraWave™ system using only HNO3 and allowing a carbon content lower than 250mg L(-1) in final digests. Inverse aqua regia was suitable for digestion of sample masses up to 250mg allowing the determination of Ir, Pd, Pt, Rh and Ru. By using HNO3 or inverse aqua regia, suitable recoveries were obtained (between 91 and 109%) for all analytes (exception for Os). Limits of quantification were in agreement with USP requirements and they ranged from 0.001 to 0.015µg g(-1) for all elemental impurities (exception for Os). The proposed method was suitable for elemental impurities determination in APIs and it can be used in routine analysis for quality control in pharmaceutical industries.

Halogen determination in food and biological materials using plasma-based techniques: challenges and trends of sample preparation

Halogens are a group of reactive elements, which are capable of making stable bonds with metals and nonmetals. Due to their properties, they play an important biochemical role in living organisms; some, such as F, Cl and I, are essential for humans, whereas others, such as Br, are non-essential and can cause key toxicological effects. This is probably the main reason why this group of elements has been extensively studied in food and biological materials, especially in recent years. The determination of halogens at trace levels requires suitable instrumentation, and plasma-based techniques, such as inductively coupled plasma optical emission spectrometry (ICP-OES) and especially inductively coupled plasma mass spectrometry (ICP-MS), are particularly well suited for this purpose. Although they are very versatile for performing multielemental determination, halogens present high ionization potentials and low wavelength emission lines, and they are prone to interferences due to matrix effects. Such drawbacks are difficult to overcome without changing instrumental features, such as mass or optical resolution. On the other hand, some interferences due to the presence of dissolved carbon in solution, enhancement or suppression of ionization, and related matrix effects can be minimized by applying an appropriate sample preparation step. In this sense, the present review covers the main sample preparation methods applied for halogen determination in food and biological materials by using ICP-OES and ICP-MS. Methods based on dilution, solubilization, extraction or those involving matrix decomposition (e.g., acid digestion and combustion) are discussed based on key applications selected in the last 20 years.

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.