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- Iron specification in bathing waters using sequential labe-on-valve (si-Lov) solid-phase spectrophotometryPublication . Suárez, Ruth; Rangel, Maria; Bordalo, Adriano A.; Cerdà, Víctor; Rangel, António O. S. S.; Mesquita, Raquel B. R.
- 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.
- Spectrofluorimetric determination of iodide in urine samples without pretreatment using a miniaturized analyzer chip in a multi-syringe flow systemPublication . Miranda, Joana L. A.; Mesquita, Raquel B. R.; Estrela, José M.; Cerdà, Victor M.; Palacio, Edwin; 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.
- Microsequential injection lab-on-valve system for the spectrophotometric bi-parametric determination of iron and copper in natural watersPublication . González, Alba; Mesquita, Raquel B. R.; Avivar, Jessica; Moniz, Tânia; Rangel, Maria; Cerdà, Víctor; Rangel, António O. S. S.The determination of iron and copper exploiting a microsequential injection lab-on-valve system with online spectrophotometric detection is described. A new, environmental friendly 3-hydroxy-4-pyridinone chelator, functionalized with a polyethylene glycol chain (MRB12) to improve water solubility, was used for iron determination. For copper determination, 1-(2-pyridylazo)-2-naphthol (PAN) was used. Different parameters affecting the formation of the complexes were studied, namely sample volume, reagent concentration, and buffer composition and concentration. The optimized conditions, 150 mu L of sample volume and 250 mg L-1 of MRB12 for iron determination, and 200 mu L of sample and 120 mg L-1 of PAN for copper determination, enabled an LOD of 15 and 18 mu g L-1 for iron and copper, respectively. The robustness of the developed procedure was assessed by the calculation of the relative standard deviation (RSD), 5% for iron determination and 2% for copper determination. The accuracy of the method was assessed comparing the results with two certified samples (RD < 7.5%) and calculating recovery percentages with five river water samples (average < 107%).
- Sequential injection system with in-line solid phase extraction and soil minicolumn for determination of zinc and copper in soil leachatesPublication . Paluch, Justyna; Mesquita, Raquel B. R.; Cerdà, Victor; Kozak, Joanna; Wieczorek, Marcin; Rangel, António O. S. S.A sequential injection (SI) system equipped with in-line solid phase extraction column and in-line soil minicolumn is proposed for determination of zinc and copper in soil leachates. The spectrophotometric determination (560 nm) is based on the reaction of both analytes with 1-(2-Pyridylazo)-2-naphthol (PAN). Zinc is determined after retaining copper on a cationic resin (Chelex100) whereas copper is determined from the difference of the absorbance measured for both analytes, introduced into the system with the use of a different channel, and zinc absorbance. The influence of several potential interferences was studied. Using the developed method, zinc and copper were determined within the concentration ranges of 0.005–0.300 and 0.011–0.200 mg L−1, and with a relative standard deviation lower than 6.0% and 5.1%, respectively. The detection limits are 1.4 and 3.0 μg/L for determination of zinc and copper, respectively. The developed SI method was verified by the determination of both analytes in synthetic and certified reference materials of water samples, and applied to the determination of the analytes in rain water and soil leachates from laboratory scale soil core column and in-line soil mini-column.
- Exploiting the use of 3,4-HP Oligands as non toxic reagents for the determination of iron in natural waters with a sequential injection approachPublication . Mesquita, Raquel B. R.; Suárez, Ruth; Cerdà, Víctor; Rangel, Maria; Rangel, António O.S.S.In this paper, the use of 3-hydroxy-4-pyridinone (3,4-HPO) chelators as nontoxic chromogenic reagents for iron determination is proposed. The potential application of these compounds was studied in a sequential injection system. The 3,4-HPO ligands used in this work were specially designed to complex iron(III) at physiologic pH for clinical applications. The developed sequential injection method enabled to study the reaction conditions, such as buffering and interferences. Then, to further improve the low consumption levels, a microsequential injection method was developed and effectively applied to iron determination in bathing waters using 3,4-HPO ligands. The formed iron complex has a maximum absorbance at 460 nm. The advantage of using minimal consumption values associated with sequential injection, together with the lack of toxicity of 3,4-HPO ligands, enabled to present a greener chemistry approach for iron determination in environmental samples within the range 0.10-2.00 mg Fe/L with a LOD of 7 mu g/L. The overall effluent production was 350 mu L corresponding to the consumption of 0.48 mg of 3,4-HPO ligand, 0.11 mg of NaHCO3, 0.16 mg of HNO3 and 50 mu L. of sample. Three reference samples were assessed for accuracy studies and a relative deviation < 5% was obtained. The results obtained for the assessment of iron in inland bathing waters were statistically comparable to those obtained by the reference procedure.
- Spectrophotometric determination of Bromate in water using multisyringe flow injection analysisPublication . Oliveira, Sara M.; Segundo, Marcela A.; Rangel, António O. S. S.; Lima, José L. F. C.; Cerdà, VíctorA multisyringe flow injection system for the spectrophotometric determination of bromate in water is proposed, based on the oxidation of phenothiazine compounds by bromate in acidic medium. Several phenothiazines were tested, including chlorpromazine, trifluoperazine, and thioridazine. Higher sensitivity and lower LOD were attained for chlorpromazine. Interference from nitrite, hypochlorite, and chlorite was eliminated in-line, without any changes in the manifold. The automatic methodology using chlorpromazine allowed the determination of bromate between 25 and 750 lgL 1, with LOD of 6 lgL 1, good precision (RSD<1.6%, n¼10), and determination frequency of 35 h 1.