Percorrer por autor "Lopes, Teresa I. M. S."
A mostrar 1 - 10 de 18
Resultados por página
Opções de ordenação
- Construction and use of a tubular picrate ion-selective electrode for reducing sugar determination in Port wine by flow-injection analysisPublication . Lopes, Teresa I. M. S.; Rangel, António O. S. S.; Lima, José L. F. C.; Montenegro, M. Conceição B. S. M.A picrate ion-selective electrode without inner reference solution and based on bis(triphenylphosphoranylidene)ammonium picrate dissolved in 2-nitrophenyloctyl ether was constructed and its characteristics assessed. With respect to reducing sugar determination in Port wine, a tubular electrode based on the same sensor system was developed and incorporated into a flow-injection manifold devised for this determination. The methodology involves a reaction between the reducing sugar and picric acid, the decrease in the picrate concentration being monitored with the tubular electrode. A linear dependence between peak width, at a fixed potential and the logarithm of sugar concentration in the range 25–200 g l−1 was obtained. The proposed system allows wine samples to be injected with no previous treatment and allows a sample throughput of 50 determinations per hour, a relative standard deviation less than 4%, and the results are comparable to the reference procedures.
- Desenvolvimento de um sistema de análise por injecção sequencial para a determinação espectrofotométrica de nitratos e nitritos em carnes curadasPublication . Oliveira, Sara M.; Lopes, Teresa I. M. S.; Rangel, António O. S. S.
- Desenvolvimento de um sistema multi-comutado para a determinação de SO2 livre e totalPublication . Oliveira, Sara M.; Lopes, Teresa I. M. S.; Tóth, Ildikó V.; Rangel, António O. S. S.
- Desenvolvimento de um sistema multi-comutado para a determinação de SO2 livre e totalPublication . Oliveira, Sara M.; Lopes, Teresa I. M. S.; Tóth, Ildikó V.; Rangel, António O. S. S.
- Determinação espectrofotométrica de N-NH4 + em águas salinas utilizando um sistema de fluxo multicomutadoPublication . Oliveira, Sara M.; Lopes, Teresa I. M. S.; Tóth, Ildikó V.; Rangel, António O. S. S.
- Determinação espectrofotométrica de N-NH4 + em águas salinas utilizando um sistema de fluxo multicomutadoPublication . Oliveira, Sara M.; Lopes, Teresa I. M. S.; Tóth, Ildikó V.; Rangel, António O. S. S.
- Development of a gas diffusion multicommuted flow injection system for the determination of sulfur dioxide in wines, comparing malachite green and pararosaniline chemistriesPublication . Oliveira, Sara M.; Lopes, Teresa I. M. S.; Tóth, Ildikó V.; Rangel, António O. S. S.A flow system based on the multicommutation concept was developed for the determination of free and total sulfur dioxide in table wines, exploiting gas diffusion separation and spectrophotometric detection. The system allowed the comparison of malachite green and pararosaniline chemistries, using the same manifold configuration. Free and total SO2 were determined within the ranges 1.00-40.0 and 25.0-250 mg L-1, at determination throughputs of 25 and 23 h-1, respectively. Employing the malachite green reaction, detection limits of 0.3 and 0.8mgL-1 were attained for free and totalSO2, respectively. Pararosaniline chemistry provided detection limits of 0.6 mg L-1 for free SO2 and 0.8 mg L-1 for total SO2. Relative standard deviations better than 1.8 and 1.4% were obtained by the malachite green and pararosaniline reactions, respectively. With regard to the two tested chemistries, 18 wines were analyzed and the results achieved by the pararosaniline reaction compared better with those furnished by the recommended procedure.
- Enzymatic determination of L(+) lactic and L(-) malic acids in wines by flow-injection spectrophotometryPublication . Lima, José L. F. C.; Lopes, Teresa I. M. S.; Rangel, António O. S. S.A flow-injection system for the enzymatic determination of L( ) lactic acid and L(ÿ) malic acid in wines with spectrophotometric detection is described. The samples are dialysed in-line, and the enzymes in solution (malate dehydrogenase and lactate dehydrogenase) are injected as a train of plugs in the acceptor stream of the dialysis unit, yielding two peaks corresponding to the NADH formed for each determination. This methodology enables the determination of both acids with a single detector with a sampling rate of 20 h ÿ1 (0.4±3 g l ÿ1). The results are comparable to those obtained by the reference procedure, the repeatability is better than 5% (rsd), with low enzyme consumption (1.3 ml of suspension per sample).
- A multi-commuted flow injection system with a multi-channel propulsion unit placed before detection: Spectrophotometric determination of ammoniumPublication . Oliveira, Sara M.; Lopes, Teresa I. M. S.; Tóth, Ildikó V.; Rangel, António O. S. S.A flow system with a multi-channel peristaltic pump placed before the solenoid valves is proposedto overcome some limitations attributed to multi-commuted flow injection systems:the negative pressure can lead to the formation of unwanted air bubbles and limits the useof devices for separation processes (gas diffusion,dialysis or ion-exchange). The proposed approach was applied to the colorimetric determination of ammonium nitrogen. In alkaline medium, ammonium is converted into ammonia, which diffuses over the membrane,causing a pH change and subsequently a colour change in the acceptor stream (bromothymol blue solution). The system allowed the re-circulation of the acceptor solution and was applied to ammonium determination in surface and tap water, providing relative standard deviations lower than 1.5%. A stopped flow approach in the acceptor stream was adopted to attain a low quantification limit(42ugL−1) and a linear dynamic range of 50–1000ugL−1 with a determination rate of 20h−1.
- 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.