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- Validation of a method for the analysis of volatile organic compounds in waterPublication . Karmacharya, Amresh Prasad; Cardoso, Vitor Vale; Cavaco, IsabelMany of the volatile organic compounds (VOCs) which can be harmful to humans have their origin in petroleum products. The VOCs have been found in water sources and leakage from storage tank and accidental spills have been regarded as the main causes of contamination from VOCs. The main objective of this study was to validate detection method of some 15 VOCs by solid-phase microextraction – gas chromatography – mass spectrometry. SPME-GC-MS has been a widely accepted method for analysis of VOCs. The compounds analyzed in this study are; MTBE, 3-ethyltoluene, 4-ethyltoluene, 2-ethyltoluene, 1,2,4-trimethylbenzene, 4-isopropyltoluene, 1,3-diethylbenzene, Indane, 1,4-diethylbenzne, 1,3-dimethyl-5-ethylbenzene, 1,2-diethylbenzene, 1,4-dimethyl-2-ethylbenzenene, 1,3-dimethyl-4-ethylbenzene, 1,2-dimethyl-4-ethylbenzene, 1,2-dimethyl-3-ethylbenzene and hexachlorobutadiene. After separation by the gas chromatograph the compounds were detected in full scan mode and later further studies were carried out in selected ion monitoring (SIM) mode of mass spectrometer. Method validation parameters for the detection of these compounds included selectivity, linear working range, limit of detection (LOD), limit of quantification (LOQ) precision, accuracy and measurement uncertainty. Various statistical tools like regression analysis, residual analysis, Mandel’s test of linearity, RIKILT, and normalized area test were applied to derive and ascertain the results and arrive at a conclusion. The retention time and representative mass fragments were identified for each compound. A linear curve (regression analysis) in the working range was also identified for each of these compounds after suitable dilution of the pure compounds. Working range was between less than 0.1 μg/L and 0.5 μg/L (the minimum and maximum calibration standards) for all the compounds except for MTBE and indane. Linearity was confirmed by residual analysis and Mandel’s test for linearity. Two of the compounds 1,4-diethylbenzene and 1,3-dimethyl-5-ethylbenzene coelute and appear as a single peak in the chromatogram and therefore, their quantity is expressed as the combined quantity of the two. LODs are well above the baseline and LOQs are either equal to or lower than the lowest calibration standards. LOD and LOQ were also quantified from precision data. Precision was studied by determining repeatability and intermediate precision and was expressed as relative standard deviation (RSD %). Council Directive 98/83/EC has prescribed a limit value of 25% for precision. None of the values of repeatability and intermediate precision exceeded the limit of 25%. Accuracy was determined by recovery study of three types of spiked water matrices; tap water, river water and groundwater. Recovery was expressed by comparing the spiked results with the theoretical value (a value provided by the commercial supplier) of a compound in terms of percentage of recovery. Also 10 replicate analysis of the spiked sample gave its precision. Most of the recovery results have been found between 90 and 115%. All the recovery values meet the criterion of 25% recovery set by the Council Directive 98/83/EC. ISO 17025 requires that the laboratories express the results accompanied by the estimated uncertainty. Expanded uncertainty of the method was determined for each compound by combining the component uncertainty of precision, calibration standards and regression interpolation and then multiplying the combined uncertainty by a coverage factor of two for a 95% confidence level. Uncertainty values ranged from 8.2% to 23%. It has been found that for the same compound the uncertainty values for the three different matrices are similar. VOCs targeted in this study can be used as possible indicators of petroleum product contamination of water sources. Each compound has its own retention time and mass spectra which can be used for its detection. Linearity of the working range has been confirmed by various statistical tests. LOD, LOQ and recovery results meet European regulation requirement and this indicates validity of the method and can be applied to detect the compounds in water. HS-SPME sampling is solvent free and less time consuming and therefore is preferable. There has been only limited research in method validation of many target VOCs. So this study contributes to methods of analysis used to detect the target VOCs in different water matrices.
- A influência da batimetria no regime de impacte de tempestades. Estudo de um caso prático com recurso a SIGPublication . Almeida, Sílvia Maria Ferreira de; Matias, Ana; Madeira, SaraO galgamento representa um fenómeno natural modelador da geomorfologia das zonas costeiras e áreas adjacentes. Os sistemas de ilhas-barreira são os mais expostos e vulneráveis aos efeitos da atuação do galgamento. Desta forma, é fundamental a realização de estudos que permitam conhecer e prever a vulnerabilidade das ilhas-barreira ao galgamento. A possibilidade de traçar mapas de vulnerabilidade representa um instrumento que contribui para o planeamento e ordenamento do território através do conhecimento das principais zonas suscetíveis à ocorrência do galgamento. Este relatório de projeto descreve o desenvolvimento de uma caixa de ferramentas de geoprocessamento para obtenção de mapas do potencial de vulnerabilidade ao galgamento denominada por Geoprocessamento do Potencial de Vulnerabilidade ao Galgamento (GeoGal). Esta tem como objetivo principal o estudo do Potencial de Galgamento (Overwash Potential - OP), tendo como informação de base a influência das morfologias submersas sobre a propagação e incidência da agitação marítima sobre as ilhas-barreira, através do cálculo de onze fórmulas de runup (R). A ferramenta GeoGal foi testada e validada para uma área de estudo na Ilha Barreta pertencente ao sistema de ilhas-barreira da Ria Formosa, a sul de Portugal. Os dados cedidos e processados são oriundos do Projeto de Investigação RUSH (From runup to overwash. PTDC/CTE-GIX/116814/2010. CIMA/FCT/UAlg), onde se enquadra o tema de trabalho do presente relatório. O dia 29 de Setembro de 2012 foi selecionado como teste. Para a criação da informação de entrada a fornecer à ferramenta GeoGal, foi desenvolvida uma metodologia de pré-processamento de dados em ambiente ArcMap (software ArcGIS v.10 - ESRI) que potencia a qualidade dos resultados obtidos em GeoGal. O Pré-processamento é principalmente focalizado na seleção do método de interpolação que melhor descreve a superfície em estudo e as condições de propagação da agitação marítima do largo até à costa (modelo numérico SWAN – Simulating WAves Nearshore). A qualidade dos Modelos Digitais de Elevação (MDE) é de extrema importância uma vez que são a base sobre a qual se gera a informação do modelo numérico SWAN e da ferramenta. Para o caso de estudo, Ordinary Kriging demonstrou ser o melhor método de interpolação. GeoGal foi desenvolvida segundo uma metodologia em ambiente de Sistema de Informação Geográfica (SIG) com recurso ao ModelBuilder (ArcMap – software ArcGIS v.10 – ESRI) auxiliado com a linguagem de programação Python. É composta por dois módulos, o Módulo 1 – Runup_GIS e o Módulo 2 – OP_GIS. GeoGal permite, de modo eficaz, a identificação da fórmula empírica de runup que melhor descreve a suscetibilidade de um dado ponto da costa à ocorrência do galgamento, tendo em conta a geomorfologia e a agitação marítima junto à costa.
- DRIFT and DRUV spectroscopy methods for studying the interaction of metal compounds with native cellulosePublication . Visekruna, Jovana; Garcia, Ana Rosa; Cavaco, IsabelCellulose, the most abundant organic polymer on earth, has numerous applications including the application in pharmacy as excipient in different kinds of pharmaceutical formulations where it comes in contact with metal compounds used in therapeutic purposes. Chemically, is composed of hundreds to thousands of β 1→4 linked D glucopyranose units. It is insoluble in water and most organic solvents and its structure cannot be loosened by heat or with solvents without causing irreversible chemical decomposition. However it can be broken down chemically into glucose units by treatment with concentrated acids at high temperatures. Aqueous solutions of several metals are also known to dissolve cellulose by deprotonating and coordinative binding the hydroxyl groups in the C2 and C3 position of the anxydroglucose. In this work, different metal complexes of copper, iron, vanadium and zinc, and native cellulose were used to a better understanding on the interactions established upon adsorption. Those metals are long used as components of dietary supplements, food additives and different kinds of drugs. It is also known from previous research that the metals complexes can react with cellulose, changing its structure or even cause its decomposition under certain conditions. In general, cellulose fibers have very few functional groups that are capable of bonding with metals and interaction between cellulose and metals and their compounds can occur in one of four ways: adsorption on the fibers, forming chemical bonds with the reactive groups of cellulose, incorporation into cellulose matrix, and formation of complexes with dissolved degradation products of cellulose. The objective of this work was to study the interaction of cellulose fibers with these four metals complexes, evaluating the changes induced by the matrix on the metal complex, specially by the identification of different metal adsorbed species, and assessing the changes in the cellulose structure namely in its crystallinity degree, upon the metal complex adsorption. For the analysis two spectroscopic techniques were used: diffuse reflectance infrared spectroscopy (DRIFTS) and diffuse reflectance ultraviolet-visible spectroscopy (DRUVS). One of the effects that the adsorption of the metal can have in cellulose is by altering its chain spatial arrangement changing its crystallinity degree. The cellulose crystallinity of the samples estimated by DRIFTS, using the region between 1300 and 1180 cm-1 and bands at 898 and 1430 cm-1, showed that in the case of vanadium (V) and zinc (II) there has been increase in the degree of crystallinity while for the other metals crystallinity was not influenced by the presence of metal complexes. However, quantification of this change was only possible in the case of vanadium (V) where it was clear that in the acidic environment at pH 3 and 5 and concentrations higher than 1mM / g cellulose, crystallinity increased from approximately 44 to 76% with the increase of vanadium complex concentration from 1 to 10 mM / g cellulose. The influence of the matrix on the metal complex structure, in the case of vanadium (IV) was analyzed by the alterations observed in the infrared bands, in particular in the regions 1000 -1200 cm-1 and 600 – 670 cm-1, showed that there has been a change in crystalline structure of the initial compound from water soluble α to insoluble β form. The shift of the bands at 1200 cm-1 in all three sets of samples (three different pH) indicated entrapment of the SO42- ion into cellulose and shift in the band at approximately 980 cm-1 indicates entrapment of different vanadium species in the cellulose chains but only in the high range of concentrations. The ultraviolet-visible absorption spectra (DRUVS) shown low intensity of d-d transition bands in the region after 500 nm for the samples with pH 3 and non-adjusted pH, which can be related with the oxidation from V(IV) to V(V). However, considering the blue color of these samples, characteristic for V(IV), the low intensity of the d-d bands in diluted samples appear weak only because they are so in comparison with the stronger CT bands at ~240nm. On the other hand, the high intensity of the CT relative to the d-d bands in samples with cellulose compared to the control may be indicative of binding of cellulose groups to the metal. In the set of samples with pH 5 there are indications of the formation of a new complex and also partial oxidation of V(IV) to V(V). For vanadium (V) adsorbed onto cellulose, the analysis of the new appearing bands present at wavenumbers 960, 971 and 965 cm-1; 836, 829 and 829 cm-1 703, 750 and 747 cm-1 for the non-adjusted pH set of samples, pH 3 and pH 5 sets of samples, respectively, revealed deposition of different polymeric vanadium species onto cellulose when vanadium is present in higher concentrations. Since the equilibrium of vanadium species greatly depends on the pH value it was expected that different species deposited onto cellulose will be observed in the sets of samples with different pH values. At low pH values such as pH 3 it is found that decavanadates are dominant species. At pH 5 dominant species seemed to be mixture of tri and decavanadates and at pH 6-7 we can expect to have mixture of tri and tetravanadates deposited on cellulose. These conclusions are also confirmed after analysis of the DRUV spectra which showed that there hasn’t been any reduction from V (V) to V (IV) and that only different polyoxovanadates are formed in the samples. The DRIFT spectra of iron (II) indicated very weak interaction between the metal complex and the matrix, which means a deposition of the complex on the cellulose surface or on the amorphous phase. Analysis of DRUV spectra showed that it is possible that Fe (III) ions were formed in the samples during oxidation of Fe (II) under aerobic conditions. A different behavior was proposed to iron (III), since in the DRIFT spectra of Fe(III) complex samples (at all preparation pH values) strong bands are appearing at 1384 cm-1 but they are probably just the result of the high complex concentration leading to deposition onto the cellulose exterior surface with low interaction. However, the shifted bands at 1360, 830 and 802 cm-1 indicate deposition of different species or more probably an adsorption onto the cellulose chains with stronger interactions. In the case of zinc and copper metal complexes no significant effect is present in any of the spectra. In fact, neither the bands of the metal complex or those of cellulose are affected by the deposition of the metal complex onto cellulose. Moreover, no new bands are observed, pointing to a poor interaction between the complex and the matrix upon deposition. Since zinc has very low absorptivity in the UV/Vis region no additional information were obtained from the analysis of DRUV spectra. However, the absence of expected d-d bands at around 800 nm in the DRUV spectra of Cu (II) samples, confirmed that the deposition of octahedral copper species onto cellulose did not occurred. Quantitative analysis is performed, for all the metals except zinc, using the Kubelka-Munk equation, or reemission function which gives the correlation between the intensity of the diffuse reflected radiation and concentration for solid samples, similarly to the lambert-Beer law for liquid samples. In all metal complex/cellulose pairs studied the increase of F(R) with increase of concentration was evident. In the full range of concentrations only regression models for V(V) set of samples with pH 5 and V(IV) set with pH 3 showed good fit for the data while in all the other cases only regression models in the lower range of the concentrations from 0.20 up to 1.00, 3.00 or 5.00 mM/g of cellulose (depending of the sample set) showed good fit. These results point to the necessity of optimizing the sample preparation, with a very low repeatability, reducing and replacing the steps involved that leads to a huge possibility of loss of analyte.
- Evaluation of the binding of vanadium-based anticancer drugs to human serum proteinsPublication . Chorna, Ielyzaveta; Pessoa, João da Costa; Cavaco, IsabelOxidovanadium(IV) complexes, namely those containing organic polydentade ligands, often designated by VO8carrier)n compounds, have attracted a great interest due to their prospective therapeutic effects, particularly in the treatment of diabetes, cancer and diseases caused by parasites.