Browsing by Author "Calisto, Sandra C."
Now showing 1 - 10 of 11
Results Per Page
Sort Options
- Analytical protocol for the characterization of solid organic fractions: contribution for the biochemical and thermochemical potential assessment of biomass [Poster]Publication . Trancoso, Maria Ascensão; Crujeira, Teresa; Sousa, R.; Calisto, Sandra C.; Branco, J.; Oliveira, Ana Cristina; Passarinho, Paula; Abreu, Mariana; Moura, Patrícia; Gírio, FranciscoABSTRACT: In the scope of the CONVERTE project an optimised and uniformed methodology was developed in order to better evaluate the use of endogenous biomasses for energy production by biochemical or thermochemical processes. A protocol for preparation and characterization was designed and validated by the use of biomass certified reference materials and quality control actions. Extensive analytical work was performed and the results were summarized in accordance with their relevance for either biochemical or thermochemical processes.
- Avaliação da conformidade do teor em enxofre em gasóleo e biodieselPublication . Crujeira, Teresa; Calisto, Sandra C.; Trancoso, Maria AscensãoRESUMO: Os transportes rodoviários que utilizam combustíveis de origem fóssil são uma das principais fontes de emissão de poluentes para a atmosfera, conduzindo à degradação da qualidade do ar, em particular nos grandes centros urbanos. A necessidade de utilização de combustíveis de origem renovável levou ao desenvolvimento de combustíveis alternativos, que permitem a redução significativa de emissões de CO2, ou a adição de produtos de origem renovável ao gasóleo. No caso dos óxidos de enxofre, a redução dessas emissões tem sido conseguida como resultado da progressiva diminuição do teor máximo de enxofre permitido nos combustíveis rodoviários.
- Contributo dos ensaios interlaboratoriais para laboratórios de ensaioPublication . Calisto, Sandra C.
- Controlo analítico de impurezas em misturas de sais fundidos usadas em tecnologias de solar concentrado: adequabilidade de métodosPublication . Sousa, Ana R.; Calisto, Sandra C.; Crujeira, Teresa; Trancoso, Maria AscensãoRESUMO: Apresentam-se métodos de ensaio para quantificar impurezas em misturas de sais fundidos que combina a cromatografia iónica para cloreto e sulfato, a análise de fluxo segmentado para nitrito, a espectrometria de absorção atómica com chama para cálcio, magnésio e sódio. As impurezas metálicas são identificadas por análise qualitativa de fluorescência de raios X. Os métodos selecionados foram adaptados dos incluídos no âmbito de acreditação do Laboratório de Biocombustíveis e Biomassa com validação do modelo matemático das funções de calibração, controlo da sua estabilidade no tempo, limites de quantificação, precisão e veracidade. Com base nos dados obtidos calculou-se a incerteza de medição. A declaração da adequabilidade dos métodos de ensaio para quantificar impurezas em sais fundidos teve por base a avaliação da conformidade do limite de quantificação em relação a limites de decisão. Estes foram calculados a partir dos valores máximos de níveis de impurezas, tendo em conta a incerteza de medição e uma regra de decisão que estabelece uma confiança elevada na aceitação correta.
- Environmentally friendly matrix effect matching evaluation for the major elements in solid biofuel characterization by atomic absorption spectrometryPublication . Trancoso, Maria Ascensão; Lopes, Helena; Teixeira, P. Alexandra; Calisto, Sandra C.The thermo-chemical conversion of biomass has become increasingly important, from the last decade, due to the need to reduce CO2 emissions and to increase renewable energy sources. Currently, the use of biomass already has a strong economic environmental and social impact. The biomass source can be very different where by biomass characterization is a crucial task allowing the prediction and prevention of problemas associated with biofuel burning.
- Evaluation of acid matrix effects in the determination of major elements in biomass by atomic absorption spectrometry from an environmentally friendly point of viewPublication . Teixeira, P. Alexandra; Calisto, Sandra C.; Lopes, Helena; Trancoso, Maria AscensãoThe estimation of major element content in solid biofuels is required for prediction and prevention of eventual ash-related problems during combustion. These analyses have to be achieved with minimum impact on the environment. The quantitation of Al, Ca, Mg, Na, K, Fe, Si and Mn in biofuels was carried out according to EN 15290 using acid decomposition of solid samples followed by atomic absorption spectrometry (AAS). A microwave-assisted acid digestion with a HNO3/H2O2/HF mixture was used, followed by HF complexation using H3BO3. Due to the presence of tetrafluoroboric acid complex in the digestion solution, matrix effects were noticed during elemental quantification by AAS. Standard addition calibration methods did not compensate for this matrix effect. Matrix effects that constrain an analytical response may be overcome by applying the procedure used for samples to the calibration standards using the same reagents. However, this entails using large amounts of toxic reagents. In this work, the fluoric–boric acid matrix matching was assessed statistically using one-way ANOVA tests. For the seven groups of nitric acid and reagent blank (HNO3/H2O2/HF/H3BO3) mixtures used, ranging from 0 to 1 volume ratios, no significant differences were observed for Si, Al, Fe and Mn. The calculated F values were lower than the critical value, F 6,14 = 2.85 (p = 0.05). However, for Ca, Mg, Na and K, significant differences were observed. Tenfold dilution was used for samples where the mass fraction exceeded the analytical dynamic range of the AAS instrument. The calibration solutions were prepared using the reagent blanks in the same proportion thus decreasing the amount of acids used. The procedure was validated using SRM 1573a—tomato leaves—purchased from the National Institute of Standards and Technology. Target recoveries of (1 ± 0.1) were achieved.
- Evaluation of measurements uncertainty for the moisture and dry matter mass fraction in industrial residues and sludgesPublication . Mouro, Filomena C.; Calisto, Sandra C.; Trancoso, Maria AscensãoMoisture mass fraction, , and dry matter mass fraction, wOH2wDM,, are analytical parameters required by environmental European regulations. The metrological quality, namely measurement uncertainty, comply the fitness for purpose and enhances the comparability of analytical results. In this work, the component by component approach for measurement uncertainty estimation of and wOH2wDM is reported and the input quantities assessed. The measurement uncertainty of method’s precision, under within-laboratory reproducibility conditions, f(precision)Rw, was the only significant influence quantity when > 0,10 g gOH2w-1 for both ranges. In case of ≤ 0,10 g gOH2w-1, the mass of the capsule containing sample after the drying step, m(C+S)dry, has also a relevant contribution. Simplified models are proposed.
- Monitoring laboratory performance over time from proficiency testing by interlaboratory comparisonsPublication . Trancoso, Maria Ascensão; Sousa, Ana R.; Calisto, Sandra C.Proficiency testing by interlaboratory comparisons is used to determine the individual performance of a laboratory for a specific test or measurement and to monitor the continuing performance of laboratories. Monitoring PT performance over time allows to identify potential problems related to random and systematics errors. Participation in interlaboratory comparison tests (IEC), is a requirement of the accreditation bodies either for granting laboratory accreditation by EN ISO/IEC 17025:2005 as external quality control.
- Procedure validation and laboratory performance monitoring for the measurement of moisture, ash and volatile matter mass fractions in solid biofuelsPublication . Trancoso, Maria Ascensão; Sousa, Ana R.; Calisto, Sandra C.Participation in interlaboratory comparisons is a requirement of the accreditation bodies for granting laboratory accreditation by EN ISO/IEC 17025:2005 as external quality control. Proficiency testing (PT) is used to demonstrate the individual performance of a laboratory for a specific test or measurement. Monitoring PT performance over time shows the continuing performance and allows the identification of potential problems related to random and systematic errors. In this study, it is shown that the procedures applied to measure mass fractions of moisture, ash and volatile matter in solid fuels fulfill the conditions stated in the European standards EN 14774-3, EN 14775 and EN 15148:2009 regarding target uncertainty, repeatability and reproducibility. Repeatability was assessed from sample duplicate analysis and combined standard uncertainty. Limits of detection and quantification were also estimated although no target values are stated. The obtained values fulfill the requirements for specifications and classes of solid biofuels. Laboratory performance over the time from 2011 to 2013 regarding such measurements was evaluated with 18 materials provided by WEPAL within the BIMEP program. Apart from monitoring the individual z-scores, their sequence was checked with summarizing parameters including the ‘rescaled sum z-scores’, RSZ, the ‘sum squared z-scores’, SSZ, and J-scores. For none of the analytes, the parameters indicated a trend over time and therefore it was not necessary to trigger any investigation or correcting procedure.
- Validation and setting up quality control for characterization of aluminum alloys in non‑ferrous fraction of auto‑shreddersPublication . Trancoso, Maria Ascensão; Nogueira, Carlos; Calisto, Sandra C.ABSTRACT: The improvement of recycling rates of metal waste, namely those of end-of life vehicles, is nowadays becoming imperative. Aluminum and its alloys are the main metal components in non-ferrous fraction of auto-shredders separated out after sampling. Silicon, Mg, Cu, Zn, Mn, Ti, Fe and Cr are alloying elements, which allowed the identification and differentiation of Al alloys. Flame Atomic Absorption Spectrometry was used for quantification after HCl-HNO3 digestion, with the exception of Si, where HCl–HNO3–HF–H3BO3 digestion was used. Performance characteristics of measurement procedures, namely analytical dynamic ranges, limits of detection and quantification, precision and trueness were evaluated and measurement uncertainty estimated by applying an approach based on precision and trueness validation studies and quality control data. Target values, for repeatability, intermediate precision, trueness (recovery) and measurement uncertainty, were specified to differentiate Al alloys based on their own fit-for-purpose. Metrological traceability of the measurements results of the alloying elements was established by using certified values of British Chemical Standard (BCS) of Al alloys, BCS nº 181/1, BCS Nº 268. BCS Nº 300 and Standard Reference Material of Al-base alloy, SRM 87. The quantification of Si, Mg, Cu, Zn, Mn, Ti, Fe and Cr in aluminum alloys from the non-ferrous fraction of automatic crushers was determined successfully through the validated procedures.