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- A sequential injection fluorimetric methodology with in-line solid phase extraction for biogenic amines screening in waterPublication . Ribas, Tânia C. F.; Tóth, Ildikó V.; Rangel, António O. S. S.A method for the screening of biogenic amines in waters, whose presence at some concentration levels potentially cause adverse effects on humans, was developed for the first time. A suitable and easy to operate system, with low reagent consumption was devised. The proposed flow-based system was divided into two analytical parts, preconcentration and derivatization of the biogenic amines. Solid phase extraction, using a Chelex 100 resin, was the newly chosen strategy for preconcentration of the analyte and also removal of possible matrix interferences. Fluorescamine was used as derivatization reagent for biogenic amines followed by fluorimetric detection. The influence of different sorbent materials for preconcentration and flow system parameters such as pH of standards and buffer, composition of the eluent solution, flow-rates, standard/sample volume, were studied. The interference of ammonia was assessed, and no interference was observed. The limits of detection and quantification were 1.7 and 5.6 µmol L−1, respectively. The developed system was applied to water samples and the recovery results were 98 ± 7%.
- Interferences minimization using solid phase extraction in a multiparametric sequential injection systemPublication . Ribas, Tânia C. F.; Croft, Charles F.; Moniz, Tânia; Almeida, M. Inês G.S; Mesquita, Raquel B. R.; Rangel, Maria; Kolev, Spas D.; 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.
- A solid phase extraction flow injection spectrophotometric method for the zinc determination in plantsPublication . Ribas, Tânia C. F.; Tóth, Ildikó V.; Rangel, António O. S. S.A solid phase extraction flow injection system for the spectrophotometric determination of total zinc in plant digests was developed. Solid phase extraction was chosen as a strategy for zinc preconcentration and removal of some interferences. The determination of zinc was based on the colorimetric reaction with Zincon. As detection system, a multi-reflection flow cell coupled with a light emitting diode was used. The analytical characteristics of the methodology such as pH of standard/sample solution, nitric acid concentration, the placement of SPE column within the manifold and preconcentration flow rate were studied. The interference of some metals present in plants was also assessed. The limits of detection and quantification achieved were 0.04 mg L−1 and 0.12 mg L−1, respectively. The corresponding Zincon consumption was 0.17 mg for each determination. The developed system was applied to plant digests and the results obtained were in agreement with those obtained with reference procedure.
- Use of a polymer inclusion membrane and a chelating resin for the flow-based sequential determination of copper(II) and zinc(II) in natural waters and soil leachatesPublication . Ribas, Tânia C. F.; Croft, Charles F.; Almeida, M. Inês G. S.; Mesquita, Raquel B. R.; Kolev, Spas D.; Rangel, António O. S. S.A bi-parametric sequential injection method for the determination of copper(II) and zinc(II) when present together in aqueous samples was developed. This was achieved by using a non-specific colorimetric reagent (4-(2-pyridylazo)resorcinol, PAR) together with two ion-exchange polymeric materials to discriminate between the two metal ions. A polymer inclusion membrane (PIM) and a chelating resin (Chelex 100) were the chosen materials to retain zinc(II) and copper(II), respectively. The influence of the flow system parameters, such as composition of the reagent solutions, flow rates and standard/sample volume, on the method sensitivity were studied. The interference of several common metal ions was assessed, and no significant interferences were observed (<10% signal deviation). The limits of detection were 3.1 and 5.6 µg L−1 for copper(II) and zinc(II), respectively; the dynamic working range was from 10 to 40 µg L−1 for both analytes. The newly developed sequential injection analysis (SIA) system was applied to natural waters and soil leachates, and the results were in agreement with those obtained with the reference procedure.
- High throughput microplate assays for the Spectrophotometric study of metal complexes involving Zincon and PARPublication . Ribas, Tânia C. F.; Tóth, Ildikó V.; Rangel, António O. S. S.