A leitura como um processo cognitivo
Figueiredo, Olívia Maria
1999-01-01
Search results
You search for extraction and 8,991 records were found.
A methodology based on microwave-assisted extraction (MAE) and LC with fluorescence
detection (FLD) was investigated for the efficient determination of 15 polycyclic
aromatic hydrocarbons (PAHs) regarded as priority pollutants by the US Environmental
Protection Agency and dibenzo(a,l)pyrene in atmospheric particulate
samples. PAHs were successfully extracted from real outdoor particulate matter
(PM) samples with recoveries ranging from 81.4±8.8 to 112.0±1.1%, for all the compounds
except for naphthalene (62.3±18.0%) and anthracene (67.3±5.7%), under
the optimum MAE conditions (30.0 mL of ACN for 20 min at 110ºC). No clean-up
steps were necessary prior to LC analysis. LOQs ranging from 0.0054 ng/m3 for benzo(
a)anthracene to 0.089 ng/m3 for naphthalene were reached. The validated MAE
methodology was applied to the determinatio...
Additional apple juice extraction with pulsed electric field pretreated apple cubes towards control samples is evaluated. Monopolar and bipolar shaped pulses are compared and their effect is studied with variation of electric field, pulse width and number of pulses. Variation of electric field strength is ranged from 100 V/cm to 1300 V/cm, pulse width from 20 mu s to 300 mu s and number of pulses from 10 to 200, at frequency of 200Hz. Two pulse trains separated by 1 second are applied to all samples. Bipolar pulses showed higher apple juice yields with all studied parameters. Calculation of specific energies consumed was assessed and a threshold where higher energy inputs do not increase juice yield is found for a number of used parameters. Qualitative parameters of total soluble matter (Brix) and absorbance at 390 nm wavelength were d...
This paper reports the first approach to the antioxidant potential evaluation of traditional stoned table olives ‘‘alcaparras’’. This kind
of olives are largely produced and consumed in Trás-os-Montes region (Northeast of Portugal). Different solvents and temperature
extraction conditions were employed in order to achieve the best method to obtain phenolic compounds and a higher antioxidant
activity. The optimum method (water at boiling temperature) was applied on 10 samples from the traditional market. The total phenol
content ranged between 5.58mg gallic acid equivalents (GAE)/g and 29.88mg GAE/g and effective concentration (EC50) values were in
the range 0.36–1.64 and 0.34–1.72 mg/mL for reducing power and radical scavenging effect, respectively. A significantly negative linear
regression was observed between the total phenol ...
During the last years, considerable attention has been given to different marine organisms, like algae, as
potential sources of valuable materials. The continuous demand for novel materials and technologies is
high and research on the underexploited marine green algae, including its polysaccharidic part—ulvan,
has increased accordingly. In this research work, a novel method for extraction of ulvan from green algae
is proposed and demonstrated successfully. Different characterization techniques were employed to
characterize the isolated algal polysaccharide, namely, on what concerns its thermal trace and crystallinity.
Upon heating, ulvan behaves as a non-meltable polysaccharide that is thermally stable before degradation
at 220 C. Ulvan is semi-crystalline in nature and possesses high hygroscopic features, as revealed
in this ...
Dissertação para obtenção do Grau de Mestre em
Engenharia Biomédica
To explore proper extractive solvents and to design an optimized separation process it is highly imperative to understand the molecular-based phenomena governing the solutes partitioning. Moreover, the development of new techniques for the biomolecules separation and purification, while maintaining their functional characteristics unchanged, is still ongoing. Therefore, in this work, the partition coefficients of vanillin, a compound with well-known organoleptic properties, were determined using improved ionic-liquid-based aqueous two-phase systems (ATPS). Three main parameters were evaluated through the vanillin partitioning process: the ionic liquid (IL) cation and anion structure, the temperature of equilibrium and the available concentration of vanillin in the global system. In all systems and conditions tested, vanillin preferenti...
Offshore sand and gravel extraction for aggregates and beach nourishment is an important economic activity and has been a common practice in various countries worldwide for many years. The evolution of a sandpit, in particular its migration and rate of replenishment, depends strongly on the type of sediments involved, and on the physical and hydrodynamic characteristics of the surrounding area. In order to fully assess the associated impacts on local ecosystems and on the neighboring coastline morphology it is essential to make accurate predictions of the excavation recovery times. For this purpose it is fundamental to investigate areas where there is an adequate observational control of the evolution of the sandpit, prior and after the excavation, to properly calibrate existing numerical models with observations and fully evaluate the...
Extraction of rutin from acerola waste was investigated using alcohol-salt-based aqueous two-phase systems (ATPS). Initially, the partitioning was studied using model systems with pure and commercial rutin. The impact of the ATPS constituents and composition, initial amount of rutin, temperature and addition of electrolytes was evaluated. Rutin can be recovered either in the alcohol-or-salt-rich phase depending on the salt used. To validate the optimization process, rutin extraction from acerola waste was carried out further. The results obtained with the real samples are in close agreement with the model systems and validate the optimization tests and support their applicability in bioresource-related processes.
Fundação para a Ciência e a Tecnologia (FCT)
One of the recognized challenges in chemical extraction of mercury from soil is the diversity of procedures that
are currently available in literature and that differ in terms of the extractant solution used, soil:extractant ratio
and duration of extraction. Therefore, this study focused on establishing the role of operational parameters for
extraction of the available and labile fractions of mercury from soils, considering different soil:extractant ratios
and the kinetics of extraction. The suitability of 1.0 mol L−1 ammonium acetate at pH 7 and 0.1 mol L−1 HCl as
extractants for the available fraction and the extraction of the labile fraction using 0.5 mol L−1 hydrochloric
acid was investigated. No statistical differences were found between ammonium acetate and 0.1 mol L−1 HCl;
therefore both extractants can be used for estimating th...
