Solución de sistemas de ecuaciones lineales mediante el método de Gauss-Jordan : problemario

1 archivo PDF (55 páginas)Ejercicios y problemas de sistemas de ecuaciones lineales mediante el método de Gauss-Jordan, con respuestas al final del libro

Magnetic graphene oxide as a valuable material for the speciation of trace elements

Magnetic solid phase extraction (MSPE) has been explored for the application in preconcentration processes to achieve highly sensible analytical methods. Attending to the different magnetic adsorbent materials used in this field, functionalized magnetic graphene oxide (MGO) has proven to be effective for selective analysis and speciation of metals, metalloids, and derivatives in combination with several analytical techniques. Despite the increasing number of articles on speciation of trace elements using functionalized MGO as solid phase adsorbent, there are no dedicated reviews that cover the application of this novel nanomaterial, being this work pioneer in this area. This article provides a comprehensive review of the relevant literature related to the speciation of Al, Cr, As, Se, Ag, Cd, Hg, Tl and Pb, with special focus on species determined, toxicity, MGO functionalization, analytical performance, and applications, mainly to environmental and food samples. Finally, future challenges and trends related to this topic are shown.This work has been partially supported by the University of Malaga (I Plan Propio de Investigación y Transferencia, Proyecto Puente UMA and fellowship A.2.-2021 predoctoral contracts), FEDER funds, Junta de Andalucia, Project UMA18-FEDERJA-060 and the Spanish Ministerio de Ciencia y Tecnologia (fellowship FPU18/05371). Funding for open access charge: Universidad de Málaga / CBUA

Semiautomatic method for the ultra-trace arsenic speciation in environmental and biological samples via magnetic solid phase extraction prior to HPLC-ICP-MS determination

A novel magnetic functionalized material based on graphene oxide and magnetic nanoparticles (MGO) was used to develop a magnetic solid phase extraction method (MSPE) to enrich both, inorganic and organic arsenic species in environmental waters and biological samples. An automatic flow injection (FI) system was used to preconcentrate the arsenic species simultaneously, while the ultra-trace separation and determination of arsenobetaine (AsBet), cacodylate, AsIII and AsV species were achieved by high performance liquid chromatog raphy combined with inductively coupled plasma mass spectrometry (HPLC-ICP-MS). The sample was introduced in the FI system where the MSPE was performed, then 1 mL of eluent was collected in a chromatographic vial, which was introduced in the autosampler of HPLC-ICP-MS. Therefore, preconcentration and separation/deter mination processes were automatic and conducted separately. To the best of our knowledge, this is the first method combining an automatic MSPE with HPLC-ICP-MS for arsenic speciation, using a magnetic nanomaterial based on MGO for automatic MSPE. Under the optimized conditions, the LODs for the arsenic species were 3.8 ng L− 1 AsBet, 0.5 ng L− 1 cacodylate, 1.1 ng L− 1 AsIII and 0.2 ng L− 1 AsV with RSDs <5%. The developed method was validated by analyzing Certified Reference Materials for total As concentration (fortified lake water TMDA 64.3 and seawater CASS-6 NRC) and also by recovery analysis of the arsenic species in urine, well-water and seawater samples collected in Malaga. ´ The developed method has shown promise for routine monitoring of arsenic species in environmental waters and biological fluids.This work has been partially supported by the University of Malaga (Proyecto Puente UMA), FEDER funds, Junta de Andalucia, Project UMA18FEDERJA060 and the Spanish Ministerio de Ciencia y Tecnologia (fellowship FPU18/05371). Funding for open access charge: Universidad de Málaga / CBU

New magnetic chelating sorbent for chromium speciation by magnetic solid phase extraction on-line with inductively coupled plasma optical emission spectrometry

A novel sorbent material employing magnetic nanoparticles (MNPs) coupled to graphene oxide (GO) functionalized with 4-aminobenzenesulfonic acid (M@GO-ABS) has been synthesized and applied to develop an inexpensive and automatic method for Cr(III) and Cr(VI) speciation in environmental samples; the developed method combines inductively coupled plasma optical emission spectrometry (ICP-OES) with on-line magnetic solid phase extraction (MSPE). Two magnetic-knotted reactors containing M@GO-ABS were installed in the eight-port injection valve of a flow injection (FI) manifold. Two different eluents were used, one for Cr(VI) (the most toxic chromium species) and one for total Cr concentration. Cr(III) concentration was calculated by the difference between Cr(VI) concentration and total Cr concentration. The optimized method presented detection limits (LOD, peak height) of 0.1 μg LFunding for open access charge: Universidad de Málaga / CBU

Development of an on-line MSPE-ICP-OES method for the preconcentration and speciation of Cr(III)/Cr(VI) in aqueous samples

SHOTGUN PRESENTATIONIn this work, a new double-reactor method for the analysis and speciation of trace amounts of Cr(III)/Cr(VI) ions in environmental samples has been developed combining on-line magnetic solid phase extraction (MSPE) with inductively coupled plasma optical emission spectrometry (ICP OES). For the preconcentration and speciation of Cr, a new magnetic graphene oxide (MGO) functionalized with p-sulfanilic acid has been syhthesized. This material presents good capacity of adsorption towards Cr(III) and Cr(VI) species. The FI manifold used for on-line preconcentration and elution is shown in Fig.1. The eight-port valve (V) was changed from position A-B, and vice versa allowing the load of sample of the two reactors (R1 and R2) followed of the elution of Cr(VI) with NH3 3.2 % in R1 and total Cr with HNO3 2.3 % in R2 to ICP-OES. Subtracting the signal of Cr (VI) to the signal of Cr(III)+Cr(VI), both ions can be determined. Moreover, several flow and chemical variables were optimized by two multivariate central composite designs (CCD). The optimized method offers good sensitivity and precision. The accuracy of the proposed method was verified using certified reference materials. The obtained results were in good agreement with the certified values and high recoveries were achieved for the spiked samples. Thus, the new adsorbent has demonstrated to be useful for the preconcentration and speciation of Cr(III)/Cr(VI).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Fondos FEDER y Junta de Andalucía Proyecto UMA18-FEDERJA-060. Plan Propio. Proyecto Puente. Universidad de Málag

A novel material for Sb speciation in aqueous samples.

In this work, a new double-reactor method for the analysis and speciation of trace amounts of SbIII/SbV in environmental samples has been developed combining online magnetic solid phase extraction (MSPE) with graphite furnace atomic adsorption spectroscopy (GFAAS). Two novel materials have been developed for the Sb speciation, both based on magnetic graphene oxide (M@GO), one functionalized with PSTH (M@GOPS) and another one functionalized with MeI (M@GONIO). These materials present different behaviours towards the Sb species; M@GONIO presents good adsorption capacity for both SbIII and SbV meanwhile M@GOPS is selective for SbIII. The materials are confined in a knotted reactor. Reactors are coupled to a FI manifold connected to a hydride generator which is the last step before the sample introduction in the GFAAS. The eight-port valve allows the sample load in both reactors at the position A, and the elution of the reactors is developed in position B. Moreover, several flow and chemical variables were optimized by multivariate central composite designs (CCD). The optimized method offers good sensitivity and precision. Thus, new adsorbents have demonstrated to be useful for the preconcentration and speciation of SbIII/SbV.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

New methodologies to characterize ZnO nanoparticles in cosmetic samples

In recent years, based on their good properties as solar radiation filters and antibacterial agent, the use of zinc nanoparticles (ZnO NPs) in cosmetic industry has been increased. According to the literature, the potential toxicity of these NPs could be size-dependent and also by the amount of solubilized metal from the NPs in solution. This work investigates new reliable and straightforward methodologies that enables the determination of ZnO NPs, discriminating them from ionic zinc in cosmetic samples. Two different strategies of analysis have been applied in this study: solid sampling high-resolution continuum source electrothermal atomic absorption spectrometry (SS-HR-CS-GFAAS), and “single particle” inductively coupled plasma mass spectrometry (sp-ICP-MS). Triton X-100 has been used as a surfactant, for the formation of homogeneous and stable slurries, which allowed the determination of the concentration and sizes of ZnO NPs in baby creams and eyeshadows. To achieve stable suspensions of the samples, two compound central design experiments (CCD) were performed to optimize the concentration of Triton X-100 and sonication time. The concentration of each sample in the slurry was adjusted considering the customer % ZnO content. The results of Zn 2+ and ZnO NPs contents achieved by the two techniques were compared, and the total Zn content was analyzed by acid digestion of the samples. A size comparison was also carried out with the data obtained with transmission electron microscopy (TEM).The authors thank “Plan Propio, Universidad de Málaga” for supporting this study and also FEDER funds and Junta de Andalucia (Project UMA18-FEDERJA-060) for financial support of this work. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Optimization of the mechanochemical synthesis of graphene oxide and its characterization. Application to the synthesis of magnetic graphene oxide.

Nowadays, the use of materials derived from graphene oxide (GO) is extended in the technologycal industry and research due to their excellent physico-chemical properties. This fact invites us to investigate a sustainable synthesis of GO and its derivatives according to the postulates of the so-called “green chemistry”. Recently, the mechanochemical synthesis of graphene oxide (GO) has been postulated as a sustainable alternative for the preparation of GO using graphite as starting material and a planetary ball mill (Fig. 1). In this work, an optimization has been carried out based on the comparative study of the use of balls of different diameters as well as different operating protocols of the mill. The obtained GO obtained have been adequately characterized by elemental analysis, SEM and TEM images, XPS spectra and the nitrogen adsorption-desorption isotherms. The results obtained from the characterization have allowed us to verify the goodness of the method used, confirming that the synthesis is possible not only on a laboratory scale but also on an industrial level. This “dry” synthesis complies with the recommendations included in the 2019 IUPAC report, which indicated the chemical techniques that would make our planet a more sustainable place. Finally, magnetic graphene oxide (M@GO) has been obtained by coupling magnetic nanoparticles with GO synthesized by the optimized mechanochemical protocol, demonstrating an excellent capacity of adsorption towards several contaminant.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Synthesis of a novel magnetic nanomaterial for the development of a multielemental speciation method of lead, mercury, and vanadium via HPLC‑ICP MS

A new magnetic functionalized material based on graphene oxide magnetic nanoparticles named by us, M@GO-TS, was designed and characterized in order to develop a magnetic solid-phase extraction method (MSPE) to enrich inorganic and organic species of lead, mercury, and vanadium. A flow injection (FI) system was used to preconcentrate the metallic and organometallic species simultaneously, while the ultra-trace separation and determination of the selected species were achieved by high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC-ICP MS). Therefore, preconcentration and separation/determination processes were automated and conducted separately. To the best of our knowledge, this is the first method combining an online MSPE and HPLC-ICP MS for multielemental speciation. Under the optimized conditions, the enrichment factor obtained for PbII, trimethyllead (TML), HgII, methylmercury (MetHg), and VV was 27. The calculated LOD for all studied species were as follows: 5 ng L−1, 20 ng L−1, 2 ng L−1, 10 ng L−1, and 0.4 ng L−1, respectively. The RSD values calculated with a solution containing 0.5 μg L−1 of all species were between 2.5 and 4.5%. The developed method was validated by analyzing Certified Reference Materials TMDA 64.3 for total concentration and also by recovery analysis of the species in human urine from volunteers and a seawater sample collected in Málaga. The t statistical test showed no significant differences between the certified and found values for TMDA 64.3. All the recoveries obtained from spiked human urine and seawater samples were close to 100%. All samples were analyzed using external calibration. The developed method is sensitive and promising for routine monitoring of the selected species in environmental waters and biological samples.Funding for open access charge: Universidad de Málaga/CBU

Síntesis y aplicación de un nuevo nanomaterial magnético para la especiación online de cromo en muestras acuosas

En este trabajo, se ha desarrollado un nuevo método de doble reactor para el análisis y especiación de cantidades traza de iones Cr (III)/Cr (VI) en muestras ambientales que combina la extracción magnética en fase sólida (MSPE) en línea con espectrometría de emisión óptica de plasma de acoplamiento inductivo (ICP-OES). Para la preconcentración y especiación de Cr se ha sintetizado un nuevo óxido de grafeno magnético (MGO) funcionalizado con ácido p-sulfanílico. Este material presenta buena capacidad de adsorción para las especies Cr (III) y Cr (VI). El colector FI utilizado para la preconcentración y elución en línea se muestra en la Fig. 1Con la variación entre las posiciones 1 y 2 de la válvula de ocho puertos, se consigue la carga de muestra de los dos reactores (R1 y R2) seguida de la elución de Cr (VI) con NH3 3.2% en R1 y Cr total con HNO3 2.3% en R2 para ICP-OES. Restando la señal de Cr (VI) a la señal de Cr (III) + Cr (VI), se pueden determinar ambos iones. Además, se optimizaron las variables químicas y de flujo mediante dos diseños centrales compuestos multivariantes (CCD). El método optimizado ofrece buena sensibilidad y precisión. La precisión del método propuesto se verificó utilizando materiales de referencia certificados. Los resultados obtenidos estuvieron en buen acuerdo con los valores certificados y se lograron altas recuperaciones para las muestras enriquecidas. Así, el nuevo adsorbente ha demostrado ser útil para la preconcentración y especiación de Cr (III)/Cr (VI). Los autores agradecen al “Plan Propio, Universidad de Málaga” por apoyar este estudio y también a los fondos FEDER y a la Junta de Andalucía (Proyecto UMA18-FEDERJA-060) por el apoyo financiero de este trabajo.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec