Sergio Roberto Mortari

Microwave-induced combustion of carbon nanotubes for further halogen determination

A procedure for single and multi-walled carbon nanotubes digestion by microwave-induced combustion (MIC) is proposed for the first time for further halogens (Cl, Br and I) determination by inductively coupled plasma mass spectrometry (ICPMS) and ion chromatography (F, C, Br and I). Samples of carbon nanotubes (up to 500 mg) were pressed as pellets and combusted using 20 bar of oxygen and 50 μl of 6 mol l−1 of ammonium nitrate as igniter. The following absorbing solutions were evaluated: H2O, (NH4)2CO3, NH4OH, tetramethylammonium hydroxide (TMAH) and water-soluble tertiary amines (CFA-C). A reflux step was applied after combustion (5 min of microwave irradiation at 1400 W) in order to achieve better analyte recoveries. For Cl determination by ICPMS, a dynamic reaction cell was used with ammonia as reaction gas. The accuracy was evaluated using certified reference materials (CRM) of coal, spiked samples and also by comparison of results with neutron activation analysis. In spite of 1% (v/v) of TMAH or CFA-C being used as absorbing solution, 100 mmol l−1 NH4OH was preferred in view of lower blank values and quantitative recoveries (better than 97%). Agreement with CRM values for NIST 1632b, NIST 1632c and SARM 19 was higher than 96% for Cl and Br (ICPMS) and for F (IC). The limit of detection (LOD, 3σ) for Cl, Br and I obtained by ICPMS was 1.3, 0.02 and 0.002 μg g−1, respectively. The LOD for F, Cl, Br and I determined by IC was 0.3, 1.1, 2.4 and 4.2 μg g−1, respectively. The residual carbon content for MIC digests was always below 1%. As an advantage over conventional procedures, using MIC it was possible to digest up to eight samples in only 25 min, obtaining a single solution suitable for determination of all halogens by different techniques. According to the authors’ knowledge this is the first application for halogen determination in this kind of material.

Evaluation of a digestion procedure based on the use of diluted nitric acid solutions and H2O2 for the multielement determination of whole milk powder and bovine liver by ICP-based techniques

Many efforts have been made in order to reduce the amount of reagents and waste produced in analytical laboratories. However, suitable digestion efficiency must be considered, and depending on the sample preparation procedure, incomplete digestion can result in severe matrix effects during analysis by spectrometric techniques such as ICP OES and ICP-MS. In the present work a procedure based on the use of H2O2 was developed in order to minimize the consumption of HNO3 without decreasing the efficiency of digestion. Although H2O2 has been used combined with HNO3 for sample digestion, its role is still not completely elucidated even as its action combined with O2 in pressurized systems. The performance obtained using H2O2 was similar to that observed when adding O2 to the reaction vessel, driving the better understanding of the role of H2O2 in closed digestion procedures. Digestion using H2O2 allowed the use of HNO3 solutions as diluted as 1 mol L−1 to digest sample masses of biological materials as high as 500 mg. The proposed procedure allowed a reduction of up to 14 and 9.3-fold in the HNO3 amount normally used in whole milk powder and bovine liver digestions, respectively, without decreasing the digestion efficiency. Calcium, Cu, Fe, K, Mg, Mn, Mo, Na, and Zn were determined by ICP OES, while Cd, Co, and Pb were determined by ICP-MS. Using diluted HNO3 solution low blank values were obtained resulting in relatively lower limits of detection and relative standard deviations. The accuracy was evaluated by using certified reference materials of milk powder and bovine liver (agreement was better than 95% to certified values for all evaluated analytes).

Fast Digestion Procedure for Determination of Catalyst Residues in La- and Ni-Based Carbon Nanotubes

A procedure based on microwave-induced combustion (MIC) was applied for carbon nanotube (CNT) digestion and further determination of La and Ni by inductively coupled plasma optical emission spectrometry (ICP OES). Samples (up to 400 mg) were completely combusted at 20 bar of oxygen, and a reflux step was applied to improve the analyte absorption. Combustion was finished in less than 50 s, and analytes were absorbed in diluted acid solution. Absorbing solutions ranging from 1 to 12 mol L(-1) for HCl and from 1 to 14 mol L(-1) HNO(3) were tested. Accuracy for both analytes was evaluated using certified reference materials and analyte spikes. Neutron activation analysis was also used to check accuracy for La. Agreement was better than 96% for La and Ni using a 4 mol L(-1) absorbing solution of HNO(3) or HCl and 15 min of reflux. The residual carbon content was lower than 0.5%. Up to eight samples could be digested simultaneously in 36 min, that makes the throughput using MIC more suitable when it is compared to the digestion by dry ashing as recommended by other procedures. The obtained limits of detection using MIC were lower than those using dry ashing, and a single absorbing solution, e.g., diluted HNO(3), can be used for simultaneous determination of La and Ni by ICP OES.

American Tegumentary Leishmaniasis in Older Adults: 44 Cases Treated with an Intermittent Low‐Dose Antimonial Schedule in Rio de Janeiro, Brazil

American tegumentary leishmaniasis (ATL) is a disease affecting the skin and mucosae caused by protozoans of the genus Leishmania transmitted by the bite of female sandflies. Cutaneous leishmaniasis (CL) presents mainly as skin ulcers at exposed body sites. Mucosal leishmaniasis (ML) manifests as chronic and destructive lesions of the nasal, oral, pharyngeal, and laryngeal tissues.1 Pentavalent antimonials are the first-line treatment for ATL. Reports of pentavalent antimonial toxicity include renal tubular dysfunction; cardiac, hepatic, pancreatic, and hematological alterations; and even death.2–6 Adverse effects (AEs) are frequent, and interruption is sometimes needed in patients aged 60 and older, even those receiving low-dose treatment. Observing that lesions continued to heal during withdrawal, it was decided to evaluate the safety and efficacy of an intermittent low-dose meglumine antimonate (MA) regimen for ATL in the elderly.....

A fast microwave-assisted procedure for loss on drying determination in saccharides

A fast procedure for loss on drying (LOD) determination was developed using microwave radiation. Samples of commercial saccharides were dried and the influence of sample position inside the microwave cavity, sample mass and irradiation time were evaluated. Sample mass of 1 g and irradiation time between 15 to 25 min were enough to LOD determination for all saccharides. Results obtained using the proposed microwave-assisted loss on drying (MALOD) procedure were compared with those obtained by conventional LOD determination using an oven and no statistical difference was found among results of these techniques. Using MALOD procedure the relative standard deviation was below 1%. The time for analysis was reduced from 2.4 to 15 times when compared to conventional LOD determination and up to 16 samples could be simultaneously processed making MALOD procedure suitable for routine analysis.

Determination of Br, Cl and I in honey using ICP-based techniques following microwave-assisted wet digestion with alkaline H2O2 in a single reaction chamber

In this work, a sample preparation method using only H2O2 in an alkaline medium in a single reaction chamber system (SRC-UltraWave™) was evaluated for honey digestion and for further determination of Br, Cl and I by inductively coupled plasma (ICP)-based techniques. Some important parameters, such as temperature, volume of H2O2, sample mass and volume of NH4OH, were evaluated to produce digests with the minimum concentration of residual carbon (RC). Determination of RC and Cl was carried out using inductively coupled plasma optical emission spectrometry (ICP-OES), while Br and I were determined by inductively coupled plasma mass spectrometry (ICP-MS). Digestion was performed using up to 500 mg of honey, 8 mL of H2O2, 500 μL of NH4OH and a maximum temperature and pressure of 270 °C and 199 bar, respectively. The digests obtained by the proposed method presented a concentration of RC lower than 220 mg L−1 combined with an alkaline pH that minimized memory effects during ICP-based technique analysis. The accuracy of the proposed method was evaluated by analysis of certified reference materials NIST 8433 (corn bran) and NIST 1568a (rice flour), and by comparison between the results obtained using the proposed method and those obtained by microwave-induced combustion (MIC). Significant differences were not observed on comparing the results of the proposed method with reference values of CRMs and MIC. Limits of detection obtained by the proposed method were 10 μg g−1 for Cl using ICP-OES and 0.03 and 0.005 μg g−1 for Br and I (ICP-MS), respectively.