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- Sequential injection system for the spectrophotometric determination of ammonium in Portuguese estuarine watersPublication . Segundo, Ricardo L. A.; Mesquita, Raquel B. R.; Ferreira, M. Teresa S. O. B.; Teixeira, Catarina F. C. P.; Bordalo, Adriano A.; Rangel, António O. S. S.
- Determinação de diversos parâmetros em águas por análise por injecção sequencialPublication . Mesquita, Raquel B. R.; Rangel, António O. S. S.
- Use of tetramethylbenzidine for the spectrophotometric sequential injection determination of free chlorine in watersPublication . Mesquita, Raquel B. R.; Noronha, M. Lúcia F.O. B.; Pereira, Ana I. L.; Santos, Arménia C. F.; Torres, André F.; Víctor, Cerdà; Rangel, António O. S. S.A sequential injection (SI) method was developed for the spectrophotometric determination of chlorine based on the reaction between tetramethylbenzidine (TMB) and free chlorine. The advantages resulting from the use of TMB are considerable: TMB is highly selective for chlorine, it enables a fairly low quantification limit and represents a less toxic alternative to reagents such as tolidine. The use of this reaction in SI adds other advantages as it enhances the degree of automation, minimisation of reagent consumption (6.8 g TMB/assay) and low effluent production (2.5 mL/determination). The developed method allowed a quantification limit of 90 g/L with a working range of 0.09–1.30 mg OCl−/L and a determination rate of 60 det./h. Based on these features, the system was applied to tap-water and surface water samples with no previous treatment required. The results obtained with the developed system were compared to the reference method, diethyl-p-phenylelediamine (DPD) colorimetric method, and proved not to be statistically different.
- Turbidimetric determination of chloride in different types of water using a single sequential injection analysis systemPublication . Mesquita, Raquel B. R.; Fernandes, Sílvia M. V.; Rangel, António O. S. S.A sequential injection analysis system for the turbidimetric determination of chloride in different types of water is proposed. The determination is based on the reaction of chloride with silver ions and the subsequent measurement of the turbidity caused by silver chloride precipitation. In this method, the use of toxic reagents, such as mercury thiocyanate, commonly employed in most spectrophotometric techniques for chloride determination, is avoided. The main feature of the developed system is the use of a single configuration to carry out the determination over a wide concentration range (2–400 mg L21) by changing only the aspirated sample volume. This characteristic allows the determination of chloride in ground, surface and wastewaters using the same manifold. In addition, a considerable saving of precipitating reagent is achieved due to noncontinuous consumption. The results obtained with the developed system were statistically indistinguishable from those of the potentiometric titration reference method. Relative standard deviations for ten consecutive injections were lower than 3.7%, with a sampling frequency of between 55 and 57 determinations per hour.
- A flow system for the spectrophotometric determination of lead in different types of waters using ion-exchange for pre-concentration and elimination of interferencesPublication . Mesquita, Raquel B. R.; Fernandes, Sílvia M.V.; Rangel, António O.S.S.A flow system for the spectrophotometric determination of lead in natural and waste waters is proposed. The determination is based on the colorimetric reaction between malachite green and iodide, followed by the formation of a ternary complex between those reagents and lead cations. The developed flow system includes a lead pre-concentration step in a column packed with a cationic resin (Chelex 100) operating in a sequential injection mode. To improve the mixture of sample and reagents, a flow injection approach was adopted for the colorimetric determination. This way a hybrid flow system, involving both sequential and flow injection concepts was designed. Another feature of the proposed system is the efficient elimination of major interferent species, such as cadmium and copper. The elimination of cadmium interference is obtained by complexing Cd2+ with chloride and retaining the formed negatively charged complexes in an anionic resin, AG1 X-8. As for copper, with the presence of both ionic resins as well as the conditions for cadmium elimination, it no longer acts as an interferent. Different ranges of lead concentration (50–300 and 300–1000 g l−1) can be determined with minor changes in the controlling software, useful for application to both natural and waste waters. Therefore, a detection limit of 25 g l−1 was achieved. Repeatability was evaluated from 10 consecutive determinations being the results better than 4%. The recoveries of lead spikes added to the samples ranged from 93 to 102%. The sampling frequency was 17 and 24 determinations per hour, for 50–300 and 300–1000 g l−1 ranges, respectively.
- Flow injection determination of fluoride for monitoring the biodegradation of fluorophenol in a bioreactorPublication . Mesquita, Raquel B. R.; Inés C., Santos; Pedrosa, Marta F.F.; Anouk F., Duque; Carvalho, Maria F.; Castro, Paula M.L.; Rangel, António O.S.S.
- Use of flow injection multisite detection as a novel approach for blank signal correction in a spectrophotometric determinationPublication . Oliveira, Teresa A.C.; Mesquita, Raquel B. R.; Lima, José L. F. C.; Rangel, António O. S. S.A flow injection multisite detection system was developed for correction of the sample blank in a colorimetric determination. By using detector relocation, a single spectrophotometer is used for the sequential reading of the sample blank and of the colored product; the sample crosses the flow cell to measure intrinsic absorption, the color reagent is subsequently added, and the flow cell is relocated to provide the reading of the resulting plug. The subsequent detector relocation immediately after peak maximum increases the determination frequency. This strategy was tested in the colorimetric determination of iron in soil samples based on the reaction of Fe (II) with 1,10-phenanthroline after reduction of Fe (III) to Fe (II) by ascorbic acid. The results obtained for 15 soil extracts were in good agreement with those obtained by the reference procedure. Relative standard deviations better than 4% were obtained, with a sampling rate of 30/h.
- 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.
- Development of a sequential injection system for the determination of nitrite and nitrate in estuarine watersPublication . Mesquita, Raquel B. R.; Ferreira, M. Teresa S. O. B.; Rangel, António O. S. S.
- Desenvolvimento de uma metodologia de análise em fluxo para monitorizar a eficácia de um biorreactor na degradação de 2-fluorfenolPublication . Santos, Inés C.; Pedrosa, Marta F.F.; Mesquita, Raquel B. R.; Duque, Anouk F.; Carvalho, Maria F.; Castro, Paula M.L.; Rangel, António O.S.S.
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