Iara Messerschmidt

Determination of phenol and o-cresol in soil extracts by flow injection analysis with spectrophotometric detection

Phenol and o-cresol determination by flow injection analysis (FIA) with spectrophotometric detection, employing the 4-aminoantipyrine reaction, is proposed in this work in order to quantify these species in soil extracts. The method was improved by a factorial planning, being verified a higher sampling rate in comparison with the conventional method, and recovery values, limits of detection and quantification similar for both methods. These aspects suggest this method as a feasible alternative for phenolic compound determinations in soil extracts.

Preconcentration of polar phenolic compounds from water samples and soil extract by liquid-phase microextraction and determination via liquid chromatography with ultraviolet detection

This work proposes a liquid-phase microextraction (LPME) method to extract the highly polar compounds phenol (Ph), o-cresol (o-Cr), m-cresol (m-Cr), p-cresol (p-Cr), and 2,4-dimethylphenol (2,4-DMP) from aqueous matrices. The first extraction step of the LPME method employed a common volumetric flask and n-octanol, and the second extraction step used NaOH as the acceptor phase. The optimized extraction conditions were 900 μL of n-octanol as the extraction solvent, NaOH at 0.60 mol L(-1) as the acceptor phase, an extraction time of 5.0 min, HCl at 0.01 mol L(-1) and NaCl at 20.0% as the donor phase, and an extraction temperature of 20.0°C. The analysis of 50.0 mL of aqueous sample, pretreated under the optimized LPME conditions, afforded a limit of detection (LOD) between 0.3 and 3.5 μg L(-1), a limit of quantification (LOQ) between 1.2 and 11.6 μg L(-1), and a linear range from 2.50 to 50.0 μg L(-1) for Ph, o-Cr, m-Cr and p-Cr and from 12.5 to 250 μg L(-1) for 2,4-DMP. The proposed LPME method was a successful sample preparation strategy, and allowed for precise and accurate quantification of polar phenolic compounds in aqueous matrices such as tap water, river water, groundwater, and seawater, and also in a soil extract. The recovery values ranged from 72.5% to 126.0%, and the relative standard deviation was between 0.3 and 11.5%.

Caracterização espectroscópica multivariada do potencial antioxidante de vinhos

In this work the antioxidant capacity of red wine samples was characterized by conventional spectroscopic and chromatographic methodologies, regarding chemical parameters like color, total polyphenolic and resveratrol content, and antioxidant activity. Additionally, multivariate calibration models were developed to predict the antioxidant activity, using partial least square regression and the spectral data registered between 400 and 800 nm. Even when a close correlation between the evaluated parameters has been expected many inconsistencies were observed, probably on account of the low selectivity of the conventional methodologies. Models developed from mean-centered spectra and using 4 latent variables allowed high prevision capacity of the antioxidant activity, permitting relative errors lower than 3%.

Use of Fe3+ ion probe to study intensively weathered soils utilizing electron paramagnetic resonance and optical spectroscopy

Analises por espectroscopias de ressonância paramagnetica eletronica (EPR) e de ultravioleta-visivel por refletância difusa (DRUV-VIS) de solos intensamente intemperizados contendo altos niveis de oxidos- hidroxidos de ferro, a partir de um projeto-piloto de agricultura de precisao, incluindo 13 fazendas no sudoeste do estado do Parana, Brasil, foram realizadas, visando definir parâmetros de fertilidade dos solos. Os resultados dos estudos espectroscopicos no laboratorio foram comparados com aqueles obtidos atraves da utilizacao de um espectrorradiometro portatil, em condicoes de campo. Os solos estudados apresentaram como constituintes inorgânicos, principalmente minerais de argila 1:1, oxidos e hidroxidos de ferro (principalmente goetita e hematita) e de aluminio (principalmente gibbsita), caracteristicas de solos altamente intemperizados, como por exemplo, Latossolos. Os espectros de EPR, tipicos de agregados de ions Fe 3+ com interacao magnetica, apresentaram aumento na largura da linha do sinal em g ca. 2 quando obtidos em temperatura de nitrogenio liquido, em comparacao com os obtidos a temperatura ambiente. Este fenomeno pode ter sido causado por mudancas no ambiente do campo cristalino dos ions Fe 3+ ou pelo mecanismo de relaxacao spin-spin, o que provoca aumento da largura de linha quando a temperatura diminui. As curvas espectrais eletronicas obtidas com o espectrorradiometro portatil apresentaram-se menos detalhadas, porem mais especificas de cada amostra de solo analisada. Os resultados indicam que o uso do espectrorradiometro portatil juntamente com ferramentas matematicas, como a segunda derivada da funcao Kubelka-Munk, e uma boa alternativa para analisar solos argilosos ricos em oxidos-hidroxidos metalicos. Foram feitas atribuicoes das absorcoes espectrais, principalmente para as transicoes eletronicas d-d entre niveis de energia de pares de ions Fe3+-Fe3+. Electron paramagnetic resonance (EPR) spectroscopy and optical analyses of intensively weathered soils containing high levels of oxide-hydroxide of iron from a pilot project on precision agriculture, including 13 farms in the southwest of Parana state, Brazil, were carried out, aiming at defining parameters of soil fertility. The results of the optical studies in the laboratory were compared with those obtained by the use of a portable spectroradiometer in field conditions. The studied soils were mainly composed of 1:1 clay minerals, oxides and oxide hydroxides of iron (mainly goethite and hematite) and aluminum (mainly gibbsite), characteristics of highly weathered soils, as for example Ferralsols. The EPR spectra, typical of mutual magnetic interaction of aggregated Fe 3+ ions, showed a signal linewidth increase at g ca. 2 upon cooling. This phenomenon can be caused by changing the crystal field environment of Fe 3+ ions or by the spin-spin relaxation mechanism, which causes an increase of linewith when the temperature decreases. The optical spectral curves obtained from the portable spectroradiometer presented less detailed but more specific features for each soil sample analyzed. The results indicate that use of the portable spectroradiometer along with mathematical tools such as the second derivative mode of the Kubelka-Munk function is a good alternative to analyze clay soils rich in metallic oxide and oxide hydroxides. A full attribution of the spectra features was made, mainly for the electronic transitions between energy levels into Fe 3+ -Fe 3+ couples.

Interaction of phenol, o-cresol, and p-cresol with a clay-rich soil sample.

The present paper describes an interaction study of phenol, o-cresol, and p-cresol with a rich-clay soil sample (clay content of 62.3%). Experiments performed using long contact times, in concentrations of 50.0 mg L(-1) showed practically no signal of phenol, o-cresol, and p-cresol after 48, 72, and 120 h, respectively, suggesting a sorption process. Sorption experiments in the period of 24 h were carried out with the phenolic compounds in concentrations between 5.00 and 500.0 mg L(-1), and negligible interaction between the phenolic species and the soil was observed. Additional experiments were carried out using HgCl(2) or NaN(3) solution as biodegradation inhibitors. After 10 days of contact time in the presence of inhibitors, no alterations in the concentrations of the three compounds studied were observed, and the results suggest no sorption process, with the compounds being almost entirely biodegraded by the soil sample, or possibly the formation of nonextractable residues could occur.

Proposal of an EPR based method for pollution level monitoring in mangrove sediments.

The objective of this study was the monitoring of the pollution level of underwater mangrove sediments using electron paramagnetic resonance (EPR), near-infrared (NIR) spectroscopy and chemical analyses. EPR spectroscopy was useful to determine the presence of organic free radical semiquinone, as well as, to provide information about the presence of trivalent iron in diluted and concentrated or clustered dominion in the sediment samples spectra. It was concluded that by using EPR and NIR spectroscopy measurement, in the appropriate spectral range, it was possible to nondestructively assess the environmental pollution level of coastline underwater mangrove sediments. Though, in a relatively small period of time, the authorities can take the necessary decisions to avoid environmental damages.

Multivariate spectroscopic determination of the lamivudine-zidovudine association

The multivariate spectroscopic determination of lamivudine-zidovudine associations was carried out by partial least square regression (PLS). This model was developed from 20 synthetic mixtures using mean-centered spectral data acquired from 190 to 350 nm and with 3 latent variables. External validation was performed with 6 synthetic mixtures providing prediction errors close to 1%. Moreover, the analysis of commercial drugs showed good results with prediction errors lower than 10%. The multivariate methodology was validated according to International Conference on Harmonization (ICH) criteria, demonstrating precision, accuracy and robustness within legal requirements.

EFEITO DA ATIVAÇÃO QUÍMICA NAS PROPRIEDADES DE SUPERFÍCIE DE XISTO RETORTADO

A pyrolyzed oil shale by-product known as retorted shale was functionalized with HCl, HNO3, H2SO4, H3PO4, HNO3/H2SO4 (3:1), Fentons reagent, (NH4)2S2O7, NaOH, and KMnO4 using either ultrasound (Route 1) or reflux (Route 2). The products obtained were evaluated in terms of cation exchange capacity (CEC). Structural characterization was performed using X-ray diffraction, X-ray fluorescence, and infrared spectroscopy to identify the functional groups present. The best results were achieved using Route 2 with solutions of either H3PO4 or HNO3/H2SO4 (3:1), giving CEC values of 315 and 316 mmolc kg-1, respectively. The pyrolyzed oil shale functionalized using Route 2 (reflux) with NaOH as the activating agent showed the highest sorption of methylene blue (35.6 mg g-1). The main mechanisms observed for oil shale by-product functionalization were oxidation, nitration, and CaO leaching.