A new high pressure (40 bar) continuous flow system with a large volume reactor (13.5 mL heated volume inside the microwave cavity) has been developed. The microwave-assisted digestion of the samples occurred in a coiled perfluoroalkoxy (PFA) tube reactor. As the mechanical stability of the PFA-tube is insufficient at the used digestion conditions (40 bar, >200 C), it was placed inside an autoclave constructed from a thick-walled borosilicate tube and pressurized by nitrogen. Nitric acid and mixtures of HNO 3 with HCl and/or HF were used for sample digestion and no elevated blank levels caused by contamination with corrosion products from the flow digestion system were encountered. For glucose, glycine and phenylalanine a residual carbon content (RCC) of 2.3 AE 0.5, 37 AE 3 and 77.9 AE 0.7% (mean AE standard deviation, n ¼ 5), respectively, was obtained under optimized digestion conditions (500 W microwave power and 5.0 mL min À1 carrier flow rate). The accuracy of the method was evaluated using certified reference materials (NIST SRM 1577b, SRM 1515). The determined values were in good agreement with the certified ones using inductively coupled plasma optical emission spectrometry (ICP-OES) for analyte quantification. Moreover, a comparison between closed vessel microwave-assisted digestion and high pressure flow digestion was performed using several plant-and animal tissue samples. These materials were less finely ground than CRM's making slurry generation more difficult.Nevertheless, the element concentrations obtained by ICP-OES after flow digestion were in good agreement with those from closed vessel batch digestion.
Moringa oleifera seeds were investigated for the removal of manganese ions from aqueous solutions. The seeds utilized were obtained from plants grown in Uberlândia, Brazil. After being dried and pulverized, the seeds were treated with 0.1 mol L -1 NaOH. Using the optimized methodology (50 mL of 4.0 mg L -1 Mn(II), pH range of 4.0-6.0, contact time of 5 min, and biosorbent mass of 0.5 g) it was found that 100% of Mn(II) could be removed from water samples. In order to remove up to 95% of Mn ions in 50 mL of a laboratory residue produced during biochemical oxygen demand determinations with 112.0 mg L -1 of manganese, the contact time and pH were maintained, but a mass of 3.0 g was used. The kinetic data were fitted to a pseudo-second-order kinetic model. The sorption data were fitted satisfactorily to the Langmuir and Freundlich isotherm models. Evaluation applying the Langmuir equation gave the monolayer sorption capacity as 5.61 mg/g. In this application the method was found to be efficient, fast, simple, and economical.
Metal contaminants are generally removed from effluents by chemical and physical processes which are often associated with disadvantages such as the use of toxic reagents, generation of toxic waste and high costs. Hence, new techniques have been developed, among them the study of natural adsorbents, for instance, the use of Moringa oleifera seeds. The potential of M. oleifera seeds for nickel removal in aqueous systems was investigated. The seeds utilized were obtained from plants grown in Uberlândia/Brazil. After being dried and pulverized, the seeds were treated with 0.1 mol/L NaOH. Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analyses were used for the characterization of the material. Using the optimized methodology (50 mL of 4.0 mg/L Ni(II), pH range of 4.0-6.0, agitation time of 5 min and adsorption mass of 2.0 g) more than 90% of Ni(II) could be removed from water samples. The sorption data were fitted satisfactorily by the Langmuir adsorption model. Evaluation applying the Langmuir equation gave the monolayer sorption capacity as 29.6 mg/g. The results indicate that this material could be employed in the extraction of nickel, considering its ease of use, low cost and environmental viability, which make it highly attractive for application in developing countries.
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