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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%.
- Determination of mercury in fish by cold vapor atomic absorption spectrophotometry using a multicommuted flow Injection analysis systemPublication . Silva, M. Fátima; Tóth, Ildikó V.; Rangel, António O. S. S.A flow system was developed for the determination of total mercury concentration in fish samples by cold vapor atomic absorption spectrophotometry (CVAAS), based on the multicommuted flow injection analysis (MCFIA) approach. The system uses independently controlled solenoid valves for the introduction of reagents and samples. When not injected, solutions were recirculating to the reservoir bottles, in this way reducing the waste produced by the analytical system and also the sample consumption. Results were compared to those obtained by the reference flow injection procedure. Accuracy was also assessed by recovery studies using a certified reference material as well as spiked samples; recovery percentages in the range of 90.7% to 99.8% were found. The repeatability of the method was better than 6.0% (RSD, n = 10). A limit of detection of 4.8 μg of mercury per kg of fresh fish sample was achieved. The total waste produced was reduced to 30% of that from the reference flow injection CVAAS procedure.
- A multicommuted flow injection system with a multi-channel propulsion unit: spectrophotometric determination of N-NH4+Publication . Oliveira, Sara M.; Lopes, Teresa I. M. S.; Tóth, Ildikó V.; Rangel, António O. S. S.
- Sequential determination of titratable acidity and tartaric acid in wines by flow injection spectrophotometryPublication . Rangel, António O. S. S.; Tóth, Ildikó V.A flow injection manifold is proposed for the sequential determination of titratable (total) acidity based on a pseudotitration and of tartaric acid based on the formation of a coloured vanadate complex. The method involves in-line dialysis prior to injection to avoid interference from the sample background absorption in the spectrophotometric detection. The changes in the colour of both reactions were monitored using two flow cells aligned in the optical path of a single spectrophotometer. Wine samples were analysed without any sample pre-treatment; table wines in the range 1–10 g l21 (total acidity) and 0.5–4 g l21 (tartaric acid) and port wines in the range 1–8 g l21 (total acidity) and 0.5–5 g l21 (tartaric acid). Sixteen samples can be measured per hour, and the results were comparable to those obtained by reference procedures for both determinations. RSDs (n = 10) generally lower than 3% were obtained
- Novas tendências na automatização das técnicas de geração de hidretos e vapor frio em espectrofotometria de absorção atómicaPublication . Silva, Fátima M.; Tóth, Ildikó V.; Rangel, António O. S. S.
- Miniaturization of enzymatic assay based on the LOV-sequential injection system: application to the determination of ethanol in alcoholic beveragesPublication . Vidigal, Susana S. M. P.; Tóth, Ildikó V.; Rangel, António O. S. S.
- Sistema de fluxo com célula de percurso óptico longo para a determinação de ferro em águasPublication . Páscoa, Ricardo N. M. J.; Tóth, Ildikó V.; Rangel, António O. S. S.
- Review on recent applications of the liquid waveguide capillary cell in flow based analysis techniques to enhance the sensitivity of spectroscopic detection methodsPublication . Páscoa, Ricardo N.M.J.; Tóth, Ildikó V.; Rangel, António O.S.S.Incorporation of long path length liquid waveguide capillary cell (LWCC or LCW) into spectrometric detection systems can increase the sensitivity of these by orders of magnitude (up to 500 times), and consequently can reduce the detection limits. The combination of the long path length spectrophotometry with flow methodologies can provide analytical solutions for various challenges in the field of environmental, biochemical and food chemistry. In this present work, the analytical applications of the long capillary cells are summarised and critically discussed. A historical overview of the cell development is given; applications in different areas are presented and grouped by analyte type. Major improvements achieved based on the use of the LWCC in the analytical characteristics (like sensitivity and detection limit) are emphasised while some of the limitations are also discussed.
- 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.
- Development of a flow method for monitoring cell membrane damage: application to the study of phosphate release from wine lactic acid bacteriaPublication . Torres, André F.; Mesquita, Paulo A. R.; Tóth, Ildikó V.; Campos, Francisco M.; Couto, José A.; Hogg, Tim; Rangel, António O. S. S.