Microwave-based strategies for sample preparation and halogen determination in blood using ICP-MS.

In this work, two microwave-assisted sample preparation methods based on combustion and ultraviolet digestion for futher determination of Br, Cl, and I in blood by inductively coupled plasma mass spectrometry were proposed. For microwave-induced combustion (MIC), blood was spotted on square pieces of Munktell TFN paper, and water and diluted NH4OH were evaluated as absorbing solutions. The stability of the analytes in the spotted blood was also evaluated. During 90 days, no changes of halogen content were observed for samples (with and without anticoagulant) on paper stored in a desiccator at 20 ± 5 °C. Whole blood was also digested by microwave-assisted ultraviolet digestion (MAD-UV). Some parameters as the volume of HNO3 solution, the influence of H2O2, and the effect of UV radiation were investigated. The interferences caused by C and K on halogen determination were carefully investigated. The results for MIC and MAD-UV and Br, Cl and I determination by ICP-MS presented no difference. The accuracy of MIC and MAD-UV was also evaluated by analyte spike with reference solutions of Br, Cl and I using inorganic species and also organic I standard (T4-levothyroxine). For both methods, recoveries were 94 and 108% for Br, 96 and 103% for Cl, and 104 and 97% for I. In case of organic I, recoveries were 99 and 111% for MIC and MAD-UV, respectively. The limits of quantification for MIC and MAD-UV after ICP-MS determination were 0.06 and 0.04 µg g-1 for Br, 14 and 30 µg g-1 for Cl and 12 and 8 ng g-1 for I, respectively. The proposed methods provide a suitable digestion approach, assuring safety and high digestion efficiency for further halogen determination in blood, with the possibility to use in clinical analysis.

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.

Microwave-assisted ultraviolet digestion of petroleum coke for the simultaneous determination of nickel, vanadium and sulfur by ICP-OES.

A method for the simultaneous determination of Ni, V and S in petroleum coke by inductively coupled plasma optical emission spectrometry (ICP-OES) after microwave-assisted ultraviolet digestion (MW-UV) in closed vessels was proposed. Digestion was performed using electrodeless discharge lamps positioned inside quartz vessels and turned on by microwave radiation. The following parameters were evaluated: HNO3 concentration (15 mL of 1, 4, 7, 10 or 14.4 mol L(-1)), volume of H2O2 (30%, 1 or 3 mL), sample mass (100, 250 or 500 mg) and heating time (40 or 60 min) with or without the use of UV lamps. Digestion efficiency was evaluated by the determination of the residual carbon content (RCC) in digests. Using UV lamps lower RCC was obtained and the combination of 4 mol L(-1) HNO3 with 3 mL of H2O2 and 60 min of heating allowed a suitable digestion of up to 500 mg of petroleum coke (RCC< 21%). The agreement with the reference values for Ni, V and S (obtained by digestion of petroleum coke by microwave-induced combustion) and with a certified reference material of petroleum coke was between 96 and 101%. The proposed method was considered as advantageous when compared to American Society for Testing and Materials method because it allowed the simultaneous determination of Ni, V and S with lower limit of detection (0.22, 0.12 and 8.7 µg g(-1) for Ni, V and S, respectively) avoiding the use of concentrated nitric acid and providing digests suitable for routine analysis by ICP-OES.