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- Determination of urinary iron by colorimetric detection with a novel microfluidic paper-based analytical devicePublication . Ferreira, Francisca T.S.M.; Catalão, Karina A.; Mesquita, Raquel; 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.
- Greener and wide applicability range flow-based spectrophotometric method for iron determinationPublication . Ribas, Tânia; Mesquita, Raquel; Moniz, Tânia; Rangel, Maria; Rangel, António O. S. S.A flow-based method for the spectrophotometric determination of iron in recreational waters, both fresh and marine (variable salinity content), was developed. For that purpose, 3-hydroxy-4-pyrydinone ligand functionalized with an ether function was synthetized and used as chromogenic chelator (1-(3′-methoxypropyl)-2-methyl-3-benzyloxy-4-(1H)pyridinone - MRB13) for iron quantification. This water-soluble reagent was previously reported as a greener alternative to quantify iron, due to its low toxicity and a more environmental friendly synthesis. Furthermore, it also displayed a high affinity and specificity for iron. With the main objective of quantifying iron in a variety of water types (different matrices and iron content), two strategies were developed, one of them including on-line solid-phase extraction (SPE), and the other without resorting to a SPE process. Water matrix clean-up and iron enrichment was achieved using a nitrilotriacetic acid resin column. The potential interference of metal ions usually present in water samples was assessed and no significant interference (<10%) was observed. The limits of detection were 11 and 2.9 μg L−1 without and with SPE, respectively. For one determination (three replicates), the corresponding consumption of MRB13 is 90 μg, sodium hydroxide is 1.4 mg, and boric acid is 5.6 mg. The method was applied to certified water samples and the results were in agreement with certified values. The developed method was also applied to fresh and marine water, and recovery ratios of 103 ± 4 and 101 ± 7 without and with SPE, respectively, were achieved.
- Design and functionalization of a µpad for the enzymatic determination of nitrate in urinePublication . Ferreira, Francisca T. S. M.; Mesquita, Raquel B. R.; Rangel, António O. S. S.In this work, the design of a microfluidic paper-based analytical device (µPAD) for the quantification of nitrate in urine samples was described. Nitrate monitoring is highly relevant due to its association to some diseases and health conditions. The nitrate determination was achieved by combining the selectivity of the nitrate reductase enzymatic reaction with the colorimetric detection of nitrite by the well-known Griess reagent. For the optimization of the nitrate determination µPAD, several variables associated with the design and construction of the device were studied. Furthermore, the interference of the urine matrix was evaluated, and stability studies were performed, under different conditions. The developed µPAD enabled us to obtain a limit of detection of 0.04 mM, a limit of quantification of 0.14 mM and a dynamic concentration range of 0.14–1.0 mM. The designed µPAD proved to be stable for 24 h when stored at room temperature in air or vacuum atmosphere, and 60 days when stored in vacuum at −20◦C. The accuracy of the nitrate µPAD measurements was confirmed by analyzing four certified samples (prepared in synthetic urine) and performing recovery studies using urine samples.
- Micro-PAD card for measuring total ammonia nitrogen in salivaPublication . Thepchuay, Yanisa; Mesquita, Raquel; Nacapricha, Duangjai; Rangel, António O. S. S.This work presents a portable microfluidic paper-based analytical device (micro-PAD) card for the quantification of total ammonia nitrogen in human saliva. The amount of total ammonia nitrogen in saliva can be an indicator of the status of the oral microbiome with potential correlation to kidney health problems. The developed micro-PAD card comprises twenty units consisting of three stacked layers of circular discs: the sample layer, paper discs impregnated with sodium hydroxide solution, the PTFE membrane layer, and the detection layer, paper discs impregnated with bromothymol blue. The twenty units were aligned on transparent laminating pouches laminated to form the micro-PAD card (7.5 cm × 10.5 cm). Saliva samples can be directly dispensed onto the micro-PAD card and the detection was achieved by the BTB indicator color change, from yellow to blue, after conversion of ammonium into ammonia and diffusion of the ammonia gas through a hydrophobic layer. The determination of total ammonia nitrogen in saliva using the developed micro-PAD card intended to be very simple method and operated without the need of laboratory equipment. A quantification limit of 11.3 NH4+mg L-1 and linear application range from up to 150 NH4+mg L-1 were obtained making it suitable for the expected concentrations of total ammonia nitrogen in human saliva. It was successfully applied to saliva samples and its validation obtained by comparison against a potentiometric method. The card is stable for at least 1 month making it ideal as a portable device for point-of-care diagnosis.
- 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.
- 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.
- Exploring flow analysis tools for monitoring calcium and magnesium in soil leachates from laboratory scale soil columns (LSSCs)Publication . Costa, C. F. F. A.; Mesquita, L. S.; Rocha, F. V.; Mesquita, R. B. R.; Rangel, A. O. S. S.Monitoring the soil/water interface has become fundamental for both environmental and agricultural studies. This work aimed to set up and monitor laboratory scale soil columns (LSSCs) for assessing nutrient levels and characterizing soil leachates using flow analysis methods. A flow analysis method was developed to determine calcium and magnesium concentrations, overcoming the disadvantages of conventional methods in terms of time consumption, waste production and cost. The LSSCs were set up with soil cores from distinct locations and with burned soil to verify if soil type or forest fires affect leaching behaviour. Leachates were obtained through rain simulations with rainwater. In order to establish valid comparisons, simulated rain was assessed before and after going through the LSSCs. The accommodation of both metals in the same sequential injection manifold was successfully attained, as well as the determination of ranges of calcium of 0.160–35.0 mg L-1, and a range of magnesium of 0.160–8.00 mg L-1. The developed method was successfully used to monitor different soil leachates, allowing for the assessment of both metal ions before and after going through the LSSCs. The limits of detection obtained for calcium and magnesium determinations were 7 and 8 mg L-1, respectively. Effluent production equalled 1.8 mL for the assessment of magnesium and the smaller range of calcium and 2.0 mL for the larger range.
- Novel microfluidic paper-based analytical devices (μPADs) for the determination of nitrate and nitrite in human salivaPublication . Ferreira, Francisca T.S.M.; Mesquita, Raquel; Rangel, António O. S. S.In this work, two different microfluidic paper-based analytical devices (μPADs) were developed for the quantification of nitrite and nitrate in human saliva samples, in order to aid in the diagnosis of some diseases and health conditions associated with these ions. The development of these nitrite and nitrate μPADs involved several studies to optimize their design and construction, including an interference assessment and stability studies. These μPADs allowed a nitrite determination in a range of 5–250 μM with limits of detection and quantification of 0.05 μM and 0.17 μM, respectively, and a nitrate determination in the range 0.2–1.2 mM with limits of detection and quantification of 0.08 mM and 0.27 mM, respectively. As for the stability, both of the μPADs were stable when stored in vacuum at 4 °C (the nitrite μPAD for at least 60 days and the nitrate μPAD for at least of 14 days) and, after the sample placement, the nitrite and nitrate μPADs could be scanned within the first 4 and 2 h, respectively. The nitrite μPAD measurements were compared with the ones obtained from the standard colorimetric method and there were no statistically significant differences between these two methods. To evaluate the accuracy of nitrate μPAD measurements, 4 certified water samples were used and recovery studies using saliva samples were performed.
- Use of an ether-derived 3-hydroxy-4-pyridinone chelator as a new chromogenic reagent in the development of a microfluidic paper-based analytical device for Fe(III) determination in natural watersPublication . Moniz, Tânia; Bassett, Chelsea R.; Almeida, M. Ines G. S.; Kolev, Spas; Rangel, Maria; Mesquita, Raquel B. R.This article reports on the development and validation of a disposable microfluidic paper-based analytical device (μPAD) for on-hand. in-situ, and cheap Fe(III) determination in natural waters complying with World Health Organization guidelines. The developed μPAD used 3-hydroxy-4-pyridinone (3,4-HPO) as a colour reagent due to its considerably lower toxicity than traditionally used iron analytical reagents. It was selected among a group of hydrophilic 3,4-HPO chelators containing ether-derived chains in their structure which were prepared using green methods. The relatively high water solubility of these chelators improved the detection limit and applicability as μPAD reagents. Under optimal conditions, the μPAD is characterised by a quantification range between 0.25-2.0 mg/L, a detection limit of 55 μg/L and 15 min of analysis time. The signal stability extends up to 4 hours and the device is stable for at least one month. The reagent consumption is below 0.2 mg per analysis and the μPAD method was validated by analysis certified reference materials and by comparison with atomic absorption results (RD < 10%). The newly developed μPAD was successfully applied to the determination of iron in river, well and tap waters with no need of any prior sample pre-treatment.