Search

In the past few years, microwave induced plasma optical emission spectrometry (MIP-OES) has generated great interest as an alternative technique to inductively coupled plasma-based techniques due to its lower operational cost. Since MIP-OES suffers from severe matrix effects due to easily ionizable elements (EIEs) (Na, Ca, etc.), it is unclear whether this technique could be employed for elemental bioavailability studies in soils and sediments since the main extractant solutions employed in such works may contain high levels of these elements. Thus, the aim of this work was to evaluate the feasibility of MIP-OES as a detector for such applications. To this end, the influence of different extractant solutions (0.25 mol L−1 MgCl2, 0.25 mol L−1 CaCl2, 0.10 mol L−1 acetic acid, 0.05 mol L−1 Na2EDTA, 0.25 mol L−1 NaNO3, 0.25 mol L−1 NaOAc/HOAc and 0.10 mol L−1 NH2OH·HCl) on the analyte emission of several elements (As, Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Pb, Rh, Se, Sr and Zn) was investigated. Results were compared to those obtained using a reference solution made of 5% w w−1 HNO3 solution. For saline extractant solutions, both the optimum nebulizer gas flow rate (Qg) and analyte emission were modified with regard to the reference solution. In general, the optimum Qg was reduced by between 0.1 and 0.2 L min−1 for both ionic and atomic lines. Under optimum Qg conditions, analyte emission was supressed by saline solutions except for atomic lines with an upper electronic state below 4 eV, which were enhanced. The magnitude of matrix effects was strongly dependent on EIE ionization energy. The lower the ionization energy, the greater the matrix effects were registered. No measurable matrix effects were registered on both Qg and analyte emission within experimental uncertainties for NH2OH·HCl and acetic acid extractant solutions. Experimental data suggest that matrix effects were related to changes in plasma characteristics and the analyte excitation/ionization mechanism. To mitigate matrix effects and improve long-term MIP-OES performance, internal standardization using either Rh (343.489 nm and 369.236 nm) or OH molecular emission band (308.958 nm) was required. This calibration methodology was successfully applied to the study of the elemental bioavailability in soil samples from a vineyard affected by copper-based fungicides and sediment samples from an area affected by mining waste. This research was funded by the Ministerio de Ciencia, Innovación y Universidades (MCIU) through research project PID2019-107033GB-C22 / AEI / 10.13039/501100011033 and the University of Alicante through research projects VIGROB-050 and UADIF17-42.

Microwave-induced plasma under atmospheric pressure is an effective technique for catalyst preparation. A Pd/Al2O3 catalyst was prepared using a fixed bed with microwave plasma irradiation. The activity of the catalyst was compared with that of catalysts made using the plasma spouted bed and the conventional furnace. From the results of X-ray powder diffraction (XRD) spectra and transmission electron microscopy (TEM) images, plasma treatment induced a rapid reduction process (PdO&rarr, Pd). Moreover, the plasma treatment derived the growth of a different facet from Pd (111) to Pd (100). A different kind of phase transition behavior was observed with plasma-treated alumina. H2 chemisorption analysis confirmed that the plasma treatment had a positive effect on the dispersion of Pd metal on the support. These improvements to the properties of the catalyst resulted in excellent performance in hydrogenation of acetylene.

Made available in DSpace on 2018-12-11T16:40:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-02-25 In this work, standard dilution analysis (SDA) is combined with microwave-induced plasma optical emission spectrometry (MIP OES) to determine seven elements in coffee, green tea, energy drink, beer, whiskey and cachaça (Brazilian hard liquor). No sample preparation other than simple dilution in HNO3 1% v v-1 is required. Due to relatively low plasma temperatures, matrix effects may compromise accuracies in MIP OES analyzes of complex samples. The method of standard additions (SA) offers enhanced accuracies, but is time-consuming and labor intensive. SDA offers a simpler, faster approach, with improved accuracies for complex matrices. In this work, SDA's efficiency is evaluated by spike experiments, and the results are compared to the traditional methods of external calibration (EC), internal standard (IS), and standard additions (SA). SDA is comparable to the traditional calibration methods, and it provides superior accuracies for applications involving ethanol-containing beverage samples. The SDA-MIP OES procedure is effective. Using only two calibration solutions, it may be easily automated for accurate and high sample throughput routine applications. Department of Physics and Chemistry UNESP-Univ Estadual Paulista, Av. Brasil, 56 Agilent Technologies, 2500 Regency Parkway Department of Analytical Chemistry UNESP-Univ Estadual Paulista, R. Prof. Francisco Degni, 55 Department of Chemistry Wake Forest University, Salem Hall, Box 7486 Department of Physics and Chemistry UNESP-Univ Estadual Paulista, Av. Brasil, 56 Department of Analytical Chemistry UNESP-Univ Estadual Paulista, R. Prof. Francisco Degni, 55

International audience; A semi-automated flow-injection system was developed for on-line sample preparation for the determination of mono-, di- and tributyl- and phenyltin compounds in water. The procedure is based on the preconcentration of ionic organotin compounds by sorption on bonded silica with octadecyl functional groups followed by on-column ethylation using sodium tetraethylborate. The derivatized species are eluted with 250 ?l of methanol, separated by gas chromatography and detected with a microwave-induced plasma atomic emission detector. Aliquots of 25 ?l of the eluate are introduced on to a capillary column using the cool injection technique. The solvent is vented off in the liner before the temperature of the latter is raised to release the analytes. A 10-50-ml water sample is sufficient for the analysis and a detection limit of 0.1 ng l-1 can be obtained. The developed procedure was applied to the determination of organotin compounds in a number of river water samples which were analyzed in parallel using a manual liquid-liquid extraction procedure. The results agreed within 10-15% for concentration of a few ng l-1.