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- Development of a sequential injection gas diffusion system for the determination of ammonium in transitional and coastal watersPublication . Segundo, Ricardo Alves; Mesquita, Raquel B. R.; Ferreira, Maria Teresa Soares Oliveira Barbosa; Teixeira, Catarina Fernanda Carvalho Pinheiro; Bordalo, Adriano Agostinho; Rangel, António O. S. S.This work describes the development of a sequential injection system for the ammonium determination in transitional and coastal waters with a wide salinity range. Estuarine waters are rather complex matrices as their characteristics change considerably along the salinity gradient, as well as the ammonium levels. The developed system effectively solves these issues by converting ammonium into ammonia and using a gas diffusion unit (GDU) for matrix removal. The ammonium determination in a wide quantification range (0.1–5.0 mg L−1) was obtained with small changes in the protocol sequence and was applied, not only to estuarine samples, but also well water samples (low salinity) and coastal waters (higher salinity). Spectrophotometry was the chosen detection system to measure the absorbance change in the bromothymol blue acid base indicator caused by the diffusion of ammonia through the GDU. Additionally, the developed system used a green chemistry approach, as there was no indicator reagent consumption per determination, still maintaining a good precision (relative standard deviation lower than 2%) and a low detection limit, 27 μg L−1 (1.5 μM).
- Development of a flow method for the determination of phosphate in estuarine and freshwaters - Comparison of flow cells in spectrophotometric sequential injection analysisPublication . Mesquita, Raquel B. R.; Ferreira, M. Teresa S. O. B.; Tóth, Ildikó V.; Bordalo, Adriano A.; McKelvied, Ian D.; Rangel, António O. S. S.A sequential injection system with dual analytical line was developed and applied in the comparison of two different detection systems viz; a conventional spectrophotometer with a commercial flow cell, and a multi-reflective flow cell coupled with a photometric detector under the same experimental conditions. The study was based on the spectrophotometric determination of phosphate using the molybdenum-blue chemistry. The two alternative flow cells were compared in terms of their response to variation of sample salinity, susceptibility to interferences and to refractive index changes. The developed method was applied to the determination of phosphate in natural waters (estuarine, river, well and ground waters). The achieved detection limit (0.007 mu M PO43-) is consistent with the requirement of the target water samples, and a wide quantification range (0.024-9.5 mu M) was achieved using both detection systems.
- Distribution and diversity of anammox bacteria in NW Portuguese coastal environmentsPublication . Teixeira, Catarina; Bordalo, Adriano
- Sequential injection system exploring the standard addition method for phosphate determination in high salinity samples: interstitial, transitional and coastal watersPublication . Mesquita, Raquel Beatriz Ribeiro; Santos, Inês Carvalho; Bordalo, Adriano Agostinho; Rangel, António Osmaro Santos SilvaA sequential injection system for phosphate determination within a wide concentration range was developed for water samples with high salinity levels. The determination is based on molybdenum blue chemistry using the standard addition quantification method. The detection system included a multireflective flow cell coupled to a light emitting diode, enabling the minimization of the schlieren effect. The developed system gave a LOD of 0.3 mmol P L 1 and LOQ of 1.1 mmol P L 1 with a sample consumption of 125 mL. A determination rate of about 30 h 1 was obtained, and the developed method was effectively applied to interstitial, transitional and coastal waters.
- Development of a sequential injection system for the determination of nitrite and nitrate in waters with different salinity: Application to estuaries in NW PortugalPublication . Mesquita, Raquel B. R.; Ferreira, Maria Teresa Soares Oliveira Barbosa; Segundo, Ricardo Luiz Alves; Teixeira, Catarina Fernanda Carvalho Pinheiro; Bordalo, Adriano Agostinho; Rangel, António O. S. S.In this work, a sequential injection methodology for monitoring nitrite and nitrate in estuarine waters without any previous treatment is described. The developed system was applied to the measurement of nitrite and nitrate in estuarine waters of three rivers in the NW Portugal, allowing an automatic, fast (ca 60 h 1) and precise method (relative standard deviation lower than 2%). The procedure was based on the reaction between nitrite, sulfanilamide and N-(1-naphthyl)-ethylenediamine dihydrochloride (N1NED), whereas the determination of nitrate resulted from its reduction to nitrite, using an in-line cadmium column, followed by the same reaction. The samples were collected in three locations for each river (Douro, C avado and Ave) covering the lower, middle and upper section of the estuaries. Despite the presence of a salinity gradient, this parameter showed no interference in the accuracy of the determinations. The results obtained for the described method for nitrite were statistically comparable to those obtained by the reference procedure. For the determination of nitrate, recovery tests confirmed that the sequential injection methodology provided good quality results.
- Seasonal monitoring of inland bathing waters using a sequential injection method as a fast and effective tool for nutrient quantification (N : P)Publication . Mesquita, Raquel B. R.; Machado, Ana; Santos, Inês C.; Bordalo, Adriano A.; Rangel, António O. S. S.In this work, an expedite flow method for the combined determination of major nutrients, nitrogen base ions (nitrate, nitrite and ammonium) and phosphate, is described for seasonal monitoring of inland bathing waters. Individual determinations were adapted and comprised within the same manifold to attain a comprehensive assessment of the environmental status of natural waters. The multiparametric determination was performed to explore the features of a sequential injection analysis technique yielding a real-time assessment of various parameters and effective in-line sample handling. The sequential injection multiparametric method enabled the determination within the ranges: 15.0-150 mu M nitrate; 0.15-5.00 mu M nitrite; 1.00-60 mu M ammonium; and 0.2-30 mu M phosphate. The determination rates provided a full nutrient analysis within 7 minutes, an overwhelming improvement in relation to the individual determination of each parameter. The described method was successfully applied to seasonal monitoring of six inland bathing waters dealing in-line with sample variability.
- A greener alternative for inline nitrate reduction in the sequential injection determination of NOx in natural waters: replacement of cadmium reduction by UV radiationPublication . Machado, Ana; Marshall, Graham; Bordalo, Adriano A.; Mesquita, Raquel B. R.The use of sequential injection analysis (SIA) for key nutrient determination in water has been previously described using a copperised cadmium column to attain nitrate reduction to nitrite prior to determination, yielding hazardous waste. Here, a greener alternative is proposed for nitrate reduction using a UV lamp, aiming to avoid the use of cadmium. This method was based on the colorimetric Griess reaction for nitrite determination, after the UV reduction of nitrate. The reduction was performed inline during the determination of nitrite, minimizing both effluent production and the overall determination rate. Its application to natural waters, namely river water, proved to be effective as the results were comparable to those obtained with the reference procedure. Furthermore, certified reference samples were analysed, and an average of 3% relative deviation was observed. A limit of detection of 5.30 mM was achieved, enabling the nitrate determination in the dynamic range of 25-500 mM with a determination rate of 24 h(-1), and with a recovery percentage rate around 100%.
- Iodine speciation in coastal and inland bathing waters and seaweeds extracts using a sequential injection standard addition flow-batch methodPublication . Santos, Inês C.; Mesquita, Raquel B. R.; Bordalo, Adriano A.; Rangel, António O. S. S.The present work describes the development of a sequential injection standard addition method for iodine speciation in bathing waters and seaweeds extracts without prior sample treatment. Iodine speciation was obtained by assessing the iodide and iodate content, the two inorganic forms of iodine in waters. For the determination of iodide, an iodide ion selective electrode (ISE) was used. The indirect determination of iodate was based on the spectrophotometric determination of nitrite (Griess reaction). For the iodate measurement, a mixing chamber was employed (flow batch approach) to explore the inherent efficient mixing, essential for the indirect determination of iodate. The application of the standard addition method enabled detection limits of 0.14 µM for iodide and 0.02 µM for iodate, together with the direct introduction of the target water samples, coastal and inland bathing waters. The results obtained were in agreement with those obtained by ICP-MS and a colorimetric reference procedure. Recovery tests also confirmed the accuracy of the developed method which was effectively applied to bathing waters and seaweed extracts.
- Sequential injection methodology for carbon speciation in bathing watersPublication . Santos, Inês C.; Mesquita, Raquel B. R.; Machado, Ana; Bordalo, Adriano A.; Rangel, António O. S. S.A sequential injection method (SIA) for carbon speciation in inland bathing waters was developed comprising, in a single manifold, the determination of dissolved inorganic carbon (DIC), free dissolved carbon dioxide (CO2), total carbon (TC), dissolved organic carbon and alkalinity. The determination of DIC, CO2 and TC was based on colour change of bromothymol blue (660 nm) after CO2 diffusion through a hydrophobic membrane placed in a gas diffusion unit (GDU). For the DIC determination, an in-line acidification prior to the GDU was performed and, for the TC determination, an in-line UV photo-oxidation of the sample prior to GDU ensured the conversion of all carbon forms into CO2. Dissolved organic carbon (DOC) was determined by subtracting the obtained DIC value from the TC obtained value. The determination of alkalinity was based on the spectrophotometric measurement of bromocresol green colour change (611 nm) after reaction with acetic acid. The developed SIA method enabled the determination of DIC (0.24-3.5 mg C L-1), CO2 (1.0-10 mg C L-1), TC (0.50-4.0 mg C L-1) and alkalinity (1.2-4.7 mg C L-1 and 4.7-19 mgC L-1) with limits of detection of: 9.5 mu g C L-1, 20 mu g C L-1, 0.21 mg C L-1, 0.32 mg C L-1, respectively. The SIA system was effectively applied to inland bathing waters and the results showed good agreement with reference procedures.
- Improvement of the Sandell-Kolthoff reaction method (ammonium persulfate digestion) for the determination of iodine in urine samplesPublication . Machado, Ana; Lima, Lurdes; Mesquita, Raquel B. R.; Bordalo, Adriano A.