Percorrer por autor "Mesquita, Raquel B.R."
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- Exploring newly synthesized iron chelators as colorimetric/fluorescent sensors in polymer inclusion membranesPublication . Mesquita, Raquel B.R.; Leite, Andreia; Rangel, Maria; Rangel, António O.S.S.
- Greener sequential injection method for iron spectrophotometric determination in fresh and marine watersPublication . Ribas, Tânia C.F.; Mesquita, Raquel B.R.; Moniz, Tânia; Rangel, Maria; Rangel, António O.S.S.
- Improved sequential injection method for phosphate quantification within a wide dynamic range with in-line pre-concentration to monitor soil leachatesPublication . Ferreira, Francisca T.S.M.; Mesquita, Letícia S.; Mesquita, Raquel B.R.; Rangel, António O.S.S.Phosphate is a well-known contaminant and its content is an indicator of water quality, so it is important to have an efficient monitoring of the soil leaching process. In this work, an automatic, low cost flow analysis method, capable of real-time monitoring of the soil leaching processes using spectrophotometric detection, based on the molybdenum blue reaction, was developed. The developed methodology for phosphate determination was based on the molybdenum blue reaction and includes an on-line solid phase extraction (SPE) step, involving an AG1-X8 anionic exchange sorbent. The described SI method enabled phosphate determination within a wide range, 1–80 µM, with a detection limit of 0.52 µM. It was successfully applied to leachates from laboratory scale soil columns (LSSC) and one sample analysis was carried out in triplicate, in less than 10 minutes.
- New hydrophilic 3-hydroxy-4-pyridinone chelators with ether-derived substituents: synthesis and evaluation of analytical performance in the determination of iron in watersPublication . Moniz, Tânia; Cunha-Silva, Luís; Mesquita, Raquel B.R.; Miranda, Joana L.A.; Silva, André M.N.; Silva, Ana M.G.; Rangel, António O.S.S.; Castro, Baltazar de; Rangel, MariaThree new hydrophilic 3-hydroxy-4-pyridinone chelators containing ether-derived substituents were prepared by a more sustainable synthetic protocol that involves the use of microwave heating and commercially available amines, allowing the successful production of highly water soluble chelators with improved reaction yields and reaction times. Compared with parent 3-hydroxy-4-pyridinone ligands, the new compounds were obtained faster and in higher amounts, facilitating the scale up of the synthesis, which is crucial to produce these ligands and their respective iron(III) complexes for many biological, analytical and agricultural applications. Ligands were fully characterized by 1H and 13C Nuclear Magnetic Resonance, High Resolution Mass Spectrometry and Single Crystal X-Ray Diffraction and their performance in the analytical determination of iron(III) in water samples was evaluated by sequential injection methods. The results obtained are scientifically relevant, pointing out the potential of the new and straightforwardly synthesized ligands as analytical reagents for determination of iron(III).
- Recent developments on waterborne bacteria strategies for environmental assessementPublication . Machado, Ana; Sá, Adriano A. Bordalo e; Rangel, António O.S.S.; Mesquita, Raquel B.R.
- Use of solid phase extraction for the sequential injection determination of alkaline phosphatase activity in dynamic water systemsPublication . Santos, Inês C.; Mesquita, Raquel B.R.; Bordalo, Adriano A.; Rangel, António O.S.S.In this work, a solid phase extraction sequential injection methodology for the determination of alkaline phosphatase activity in dynamic water systems was developed. The determination of the enzymatic activity was based on the spectrophotometric detection of a coloured product, p-nitrophenol, at 405 nm. The p-nitrophenol is the product of the catalytic decomposition of p-nitrophenyl phosphate, a noncoloured substrate. Considering the low levels expected in natural waters and exploiting the fact of alkaline phosphatase being a metalloprotein, the enzyme was pre-concentrated in-line using a NTA Superflow resin charged with Zn2þ ions. The developed sequential injection method enabled a quantification range of 0.044–0.441 unit mL 1 of enzyme activity with a detection limit of 0.0082 unit mL 1 enzyme activity (1.9 mmol L 1 of pNP) and a determination rate of 17 h 1. Recovery tests confirmed the accuracy of the developed sequential injection method and it was effectively applied to different natural waters and to plant root extracts.