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DE CARVALHO PINHEIRO TEIXEIRA, CATARINA FERNANDA
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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).
- Distribution and diversity of anammox bacteria in NW Portuguese coastal environmentsPublication . Teixeira, Catarina; Bordalo, Adriano
- 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.