Loading...
8 results
Search Results
Now showing 1 - 8 of 8
- Multisyringe flow system: determination of sulfur dioxide in winesPublication . Segundo, Marcela A.; Rangel, António O. S. S.; Claderab, Andreu; Cerdà, VíctorA multisyringe flow system for the spectrophotometric determination of sulfur dioxide in wines is described. The methodology is based on the well-known reaction among SO2, formaldehyde and pararosaniline. The proposed manifold also includes a gas diffusion unit in order to prevent the colour interference of red wines in the spectrophotometric measurement. The proposed method was successfully applied to the determination of free SO2 (2–75 mg l21) and total SO2 (10–250 mg l21) in wines, just by changing a few operating parameters in the controlling software. A sampling-rate of 25–30 samples per hour was achieved with good repeatability for 10 consecutive injections of wine samples (RSD < 3.2%). The results obtained from 10 wine samples for each determination were statistically comparable to those obtained by the recommended procedure.
- Spectrophotometric determination of bromate in drinking water using a multi-syringe flow injection systemPublication . Oliveira, Sara M.; Segundo, Marcela A.; Lima, José L. F. C.; Cerdà, Victor; Rangel, António O. S. S.
- Multi-pumping flow system for the determination of dissolved orthophosphate and dissolved organic phosphorus in wastewater samplesPublication . Pons, Carmen; Tóth, Ildikó V.; Rangel, António O. S. S.; Forteza, Rafael; Cerdà, VíctorA multi-pumping flow system (MPFS) for the spectrophotometric determination of dissolved orthophosphate and dissolved organic phosphorus in wastewater samples is proposed. The determination of orthophosphate is based on the vanadomolybdate method. In-line ultraviolet photooxidation is employed to mineralise organic phosphorus to orthophosphate prior to detection. A solenoid valve allows the deviation of the flow towards the UV-lamp to carry out the determination of organic phosphorus. Calibration was found to be linear up to 20 mg P L−1, with a detection limit (3sb/S) of 0.08 mg P L−1, an injection throughput of 75 injections h−1 and a repeatability (R.S.D.) of 0.6% for the direct determination of orthophosphate. On the other hand, calibration graphs were linear up to 40 mg P L−1, with a detection limit (3sb/S) of 0.5 mg P L−1, an injection throughput of 11 injections h−1 and a repeatability (R.S.D.) inferior to 2.3% for the procedures involving UV photo-oxidation.
- Avaliação comparativa da utilização de compostos da família das fenotiazinas para a determinação do ião bromatoPublication . Oliveira, Sara M.; Segundo, Marcela A.; Lima, José L. F. C.; Cerdà, Victor; Rangel, António O. S. S.
- The application of multicommutated flow techniques to the determination of ironPublication . Pons, Carmen; Forteza, Rafael; Rangel, António O.S.S.; Cerdà, VíctorNew flow techniques such as multicommutated flow-injection analysis (MCFIA), multi-syringe FIA (MSFIA) and multi-pumping flow systems (MPFSs) have been developed. The low reagent consumption achieved by these techniques should be highlighted, as they can be regarded as environmentally friendly alternatives to conventional FIA. We present several applications of these novel flow techniques to the determination of iron.
- Flow-through solid-phase based optical sensor for the multisyringe flow injection trace determination of orthophosphate in waters with chemiluminescence detectionPublication . Morais, Inês P.A.; Miró, Manuel; Manera, Matias; Estela, José Manuel; Cerdà, Víctor; Souto, M. Renata S.; Rangel, António O.S.S.In this work, a novel flow-through solid-phase based chemiluminescence (CL) optical sensor is described for the trace determination of orthophosphate in waters exploiting the multisyringe flow injection analysis (MSFIA) concept with multicommutation. The proposed time-based injection flow system relies upon the in-line derivatisation of the analyte with ammonium molybdate in the presence of vanadate, and the transient immobilisation of the resulting heteropolyacid in a N-vinylpyrrolidone/divinylbenzene copolymer packed spiral shape flow-through cell located in front of the window of a photomultiplier tube. The simultaneous injection of well-defined slugs of luminol in alkaline medium and methanol solution towards the packed reactor is afterwards performed by proper switching of the solenoid valves. Then, the light emission from the luminol oxidation by the oxidant species retained onto the sorbent material is readily detected. At the same time, the generated molybdenum-blue compound is eluted by the minute amount of injected methanol, rendering the system prepared for a new measuring cycle. Therefore, the devised sensor enables the integration of the solid-phase CL reaction with elution and detection of the emitted light without the typical drawbacks of the molybdenum-blue based spectrophotometric procedures regarding the excess of molybdate anion, which causes high background signals due to its self-reduction. The noteworthy features of the developed CL–MSFIA system are the feasibility to accommodate reactions with different pH requirements and the ability to determine trace levels of orthophosphate in high silicate content samples (Si/P ratios up to 500). Under the optimised conditions, a dynamic linear range from 5 to 50 g P l−1 for a 1.8 ml sample, repeatability better than 3.0% and a quantification limit of 4 g P l−1 were attained. The flowing stream system handles 11 analysis h−1 and has been successfully applied to the determination of trace levels of orthophosphate in environmental samples such as mineral, ground, tap and pond waters as well as samples from a water-steam cycle of an incineration plant. The t-test comparison of the means for the developed optical sensor and the molybdenum-blue spectrophotometric APHA/AWWA/WPCF reference method revealed that there is no evidence of significant differences between the obtained results at the 95% confidence level.
- Spectrophotometric determination of bromate in drinking water using a multi-syringe flow injection systemPublication . Oliveira, Sara M.; Segundo, Marcela A.; Lima, José L. F. C.; Cerdà, Victor; Rangel, António O. S. S.
- Avaliação comparativa da utilização de compostos da família das fenotiazinas para a determinação do ião bromatoPublication . Oliveira, Sara M.; Segundo, Marcela A.; Lima, José L. F. C.; Cerdà, Victor; Rangel, António O. S. S.