Rodrigo M. Pereira

Feasibility of halogen determination in noncombustible inorganic matrices by ion chromatography after a novel volatilization method using microwave-induced combustion.

A microwave-induced combustion (MIC) system based on the volatilization process was applied for subsequent halogen determination from noncombustible inorganic matrices. Portland cement samples were selected to demonstrate the feasibility of the proposed method, allowing the subsequent determination of Cl and F by ion chromatography (IC). Samples were mixed with high-purity microcrystalline cellulose, wrapped with a polyethylene film and combusted in quartz closed vessels pressurized with oxygen (20bar). Water and NH4OH (10, 25 or 50m mol L(-1)) were evaluated for Cl and F absorption, but water was selected, using 5min of reflux after volatilization. Final solutions were also suitable for analysis by pontentiometry with ion-selective electrode (ISE) for both analytes, and no difference was found when comparing the results with IC. The accuracy of the proposed method for Cl was evaluated by analysis of certified reference materials (CRMs), and agreement with certified values ranged from 98% to 103%. Results were also compared to those using the procedure recommended by the American Society of Testing and Materials (ASTM) for the determination of total chlorides (C114-13), and no difference was found. Volatilization by MIC using a mixture of cement, cellulose and a biological CRM was carried out in order to evaluate the accuracy for F, and recovery was about 96%. The proposed method allowed suitable limits of detection for Cl and F by IC (99 and 18mg kg(-1), respectively) for routine analysis of cement. Using the proposed method, a relatively low standard deviation (<7%), high throughput (up to eight samples can be processed in less than 30min) and lower generation of laboratory effluents, when compared to the ASTM method, were obtained. Therefore, the method for volatilization of Cl and F by MIC and subsequent determination by IC can be proposed as a suitable alternative for cement analysis.

The synergic effect of microwave and ultraviolet radiation for chocolate digestion and further determination of As, Cd, Ni and Pb by ICP-MS

The synergic effect between microwave and ultraviolet radiation was proposed for chocolate digestion and further toxic element determination by inductively coupled plasma mass spectrometry (ICP-MS). As, Cd, Ni and Pb were chosen to show the applicability of the proposed method. Ultraviolet radiation was generated in situ using a low-pressure Cd discharge microwave lamp inside each digestion vessel. HNO3 solutions of several concentrations (2, 4, 7 and 14.4 mol L−1) were evaluated as digestion media. Parameters such as sample mass and microwave irradiation time were also evaluated in order to provide the best conditions for chocolate digestion. A relatively high sample mass, up to 600 mg of chocolate (white and milk), was digested using a diluted acid solution (10 mL of 4 mol L−1 HNO3), allowing for a final solution with dissolved carbon content lower than 100 mg L−1, which was suitable for ICP-MS measurements. The accuracy of the proposed method was evaluated by the digestion of a certified reference material (CRM, BCR 414), and the agreement with the certified values for all analytes was between 95 and 98%. Recovery tests were also performed and results between 95 and 104% for all analytes were obtained. The limits of detection for As, Cd, Ni and Pb by the proposed method were 0.87, 0.98, 29.7 and 7.85 ng g−1, respectively. Thus, for the first time, chocolate was efficiently digested using only a diluted acid solution (digestion efficiency was higher than 90%). Moreover, the digests were suitable for subsequent ICP-MS analysis without any filtration and/or extra-dilution step, as generally reported in the literature.

Green and efficient sample preparation method for the determination of catalyst residues in margarine by ICP-MS

Responding to the need for green and efficient methods to determine catalyst residues with suitable precision and accuracy in samples with high fat content, the present work evaluates a microwave-assisted ultraviolet digestion (MW-UV) system for margarines and subsequent determination of Ni, Pd and Pt using inductively coupled plasma mass spectrometry (ICP-MS). It was possible to digest up to 500mg of margarine using only 10mL of 4molL-1 HNO3 with a digestion efficiency higher than 98%. This allowed the determination of catalyst residues using the ICP-MS and free of interferences. For this purpose, the following experimental parameters were evaluated: concentration of digestion solution, sample mass and microwave irradiation program. The residual carbon content was used as a parameter to evaluate the efficiency of digestion and to select the most suitable experimental conditions. The accuracy evaluation was performed by recovery tests using a standard solution and certified reference material, and recoveries ranging from 94% to 99% were obtained for all analytes. The limits of detection for Ni, Pd and Pt using the proposed method were 35.6, 0.264 and 0.302ngg-1, respectively. When compared to microwave-assisted digestion (MW-AD) in closed vessels using concentrated HNO3 (used as a reference method for sample digestion), the proposed MW-UV could be considered an excellent alternative for the digestion of margarine, as this method requires only a diluted nitric acid solution for efficient digestion. In addition, MW-UV provides appropriate solutions for further ICP-MS determination with suitable precision (relative standard deviation < 7%) and accuracy for all evaluated analytes. The proposed method was applied to margarines from different brands produced in Brazil, and the concentration of catalyst residues was in agreement with the current legislation or recommendations.

A Novel and Eco-Friendly Analytical Method for Phosphorus and Sulfur Determination in Animal Feed

An eco-friendly method for indirect determining phosphorus and sulfur in animal feed by ion chromatography was proposed. Using this method, it was possible to digest 500 mg of animal feed in a microwave system under oxygen pressure (20 bar) using only a diluted acid solution (2 mol L-1 HNO3). The accuracy of the proposed method was evaluated by recovery tests, by analysis of reference material (RM) and by comparison of the results with those obtained using conventional microwave-assisted digestion. Moreover, P results were compared with those obtained from the method recommended by AOAC International for animal feed (Method nr. 965.17) and no significant differences were found between the results. Recoveries for P and S were between 94 and 97%, and agreements with the reference values of RM were better than 94%. Phosphorus and S concentrations in animal feeds ranged from 10,026 to 28,357 mg kg-1 and 2259 to 4601 mg kg-1, respectively.

A selective volatilization method for determination of chloride and sulfate in calcium carbonate pharmaceutical raw material and commercial tablets

In this work a feasible method for chloride and sulfate determination in calcium carbonate pharmaceutical raw material and commercial tablets by ion chromatography after microwave-induced combustion was developed. The analytes were released from matrix by combustion in closed system pressurized with oxygen. Starch as volatilization aid, 100mmolL-1 HNO3 as absorbing solution and 5min of microwave irradiation time were used. Recovery tests using standard solutions were performed for the accuracy evaluation. A mixture of calcium carbonate pharmaceutical raw material or commercial tablets, starch and a certified reference material was also used as a type of recovery test. Recoveries ranging from 88% to 103% were obtained in both spike tests. Limits of detection (Cl-: 40µgg-1 and SO42-: 140µgg-1) were up to eighteen times lower than the maximum limits established for the analytes by Brazilian, British, European and Indian Pharmacopoeias. The limit tests recommended by the European Pharmacopoeia for Cl- and SO42- in CaCO3 were carried out to compare the results. Chloride and SO42- concentrations in the samples analyzed by proposed method were in agreement with those results obtained using the tests recommended by the European Pharmacopoeia. However, the proposed method presents several advantages for the routine analysis when compared to pharmacopoeial methods, such as the quantitative simultaneous determination, high sample preparation throughput (up to eight samples per run in less than 30min), reduced volume of reagents and waste generation. Thus, the proposed method is indicated as an excellent alternative for Cl- and SO42- determination in CaCO3 pharmaceutical raw material and commercial tablets.

Determinação de Cl e S em Algas Marinhas Comestíveis por Cromatografia de Íons após Decomposição por Combustão Iniciada por Micro-ondas

A determinacao de Cl e S nas algas marinhas comestiveis (Hidaka-Kombu, Hijiki, Kombu, Nori e Wakame) foi realizada por cromatografia de ions (IC) apos a decomposicao por combustao iniciada por micro-ondas (MIC). A concentracao de Cl nas algas foi mais elevada (6 a 10 vezes) que a de S, exceto para as algas Hijiki e Nori. O lixiviamento dos analitos apos lavagem das algas foi avaliado, sendo observada uma reducao nas concentracoes de Cl (de ate 75%) e um aumento da concentracao de S (de ate 58%). Usando a MIC-IC foi possivel obter boa exatidao (> 95%) para ambos os analitos e adequados limites de deteccao (Cl: 11 mg kg -1 e S: 9,1 mg kg -1 ).