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- 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.
- Automatic flow system for sequential determination of ABTS scavenging capacity and Folin-Ciocalteu index: A comparative study in food productsPublication . Magalhães, Luís M.; Segundo, Marcela A.; Reis, Salette; Lima, José L. F. C.; Tóth, Ildikó V.; Rangel, António O. S. S.In the present work, an automatic flow procedure for the sequential spectrophotometric determination of Folin-Ciocalteu reducing capacity (FC assay) and 2,2 -azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS•+) scavenging capacity expressed as the trolox equivalent (TEAC assay) is proposed for a comparative study of antioxidant properties in food products. Exploiting the flexibility of flow management associated to the computer control offered by multisyringe flow injection analysis, both methodologies were carried out in the same manifold using gallic acid and trolox as standard compounds. The proposed system configuration allowed the performance of each method separately or in tandem, providing 24 determinations per hour, which accounts for its application in routine analysis. The present methodology was applied to a large number of beverages (n = 72), namely red and white wines, herbal and tea infusions, juices and beers. The results obtained showed that FC reducing capacity and TEAC values of red wines were significantly different from those obtained for the other beverages, while tea infusions provided significantly higher TEAC values when compared to white wines, herbal infusions, juices and beers. A good correlation was found between TEAC and FC reducing capacity (R > 0.9) for red wines, herbal and tea infusions, and beers. For these beverages, similar slope values were found (106–140 mg L−1 of gallic acid per mM of Trolox), except for beers that showed a higher response for FC assay. These results provided evidence that the correlation between these assays vary according to the type of sample, reinforcing the idea that more than one method should be used for evaluation of antioxidant capacity.
- Multi-syringe flow injection system for the determination of available phosphorus in soil samplesPublication . Almeida, M. Inês G. S.; Segundo, Marcela A.; Lima, José L. F. C.; Rangel, António O. S. S.Considering the importance of monitoring the levels of nutrients present in soils and their availability to plants, an automatic methodology is proposed based on multi-syringe flow injection analysis (MSFIA) for the spectrophotometric determination of available phosphorus in soil extracts. This fully computerized flow technique allowed the development of a flow network where sample and reagents were intercalated and sent further towards the detection system. The colorimetric determination was based on the molybdenum blue method with ascorbic acid as reducing reagent and the Egner–Riehm method was applied to extract phosphorus from soil samples. A linear calibration curve was obtained between 0.75 and 15.0mgL-1. A determination frequency of 15 h-1 was achieved, with good repeatability for 12 consecutive injections of soil extracts (RSD<1.7%). The results obtained from 12 soil samples were statistically comparable to those attained by the usual batch method.
- 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.
- 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.
- Multi-syringe flow injection system with in-line microwave digestion for the determination of phosphorusPublication . Almeida, M. Inês G. S.; Segundo, Marcela A.; Lima, José L. F. C.; Rangel, António O. S. S.A multi-syringe system for spectrophotometric determination of total phosphorus involving in-line digestion is proposed. Sample and digestion solution were dispensed and directed towards a digestion vessel located inside a domestic microwave oven (MWO) where sample digestion took place. Afterwards, the digested sample was merged with the necessary reagents for the colorimetric determination based on the molybdenum blue method. Several digestion conditions were studied regarding composition of digestion solution, digestion time and power set on theMWO. The system was applied to waste water samples and results shown a good agreement with the reference method. Repeatable results (R.S.D. < 2.41%) and determination frequency of 12 h−1 were obtained.
- Automated solid-phase spectrophotometric system for optosensing of bromate in drinking watersPublication . Oliveira, Sara M.; Oliveira, Hugo M.; Segundo, Marcela A.; Rangel, António O. S. S.; Lima, José L. F. C.; Cerdà, VıctorAn automated method based on an optosensor included in a multisyringe flow injection system was developed for the determination of bromate in waters for human consumption. The optosensor was based on the formation of a colored radical cation after oxidation of chlorpromazine by bromate and its selective uptake in a mixed-mode cation exchanger sorbent (Discovery DSC-MCAX), placed on a flow-through spectrophotometric cell. In-line regeneration was attained by methanol + 5% (v/v) ammonia, fostering the application of the same sorbent portion up to 180 determinations. Parameters affecting the reaction development and uptake of the colored compound were studied and optimized, while in-line addition of sulfite ($0.100 g L 1) prevented interference from hypochlorite. The proposed methodology allowed the determination of bromate up to 50.0 mg L 1, with 0.9 mg L 1 as the limit of detection, meeting the requirements of current EU and USA legislation. Application to real drinking water samples was successful, with a mean recovery of 100.2 2.8% for spiked levels of 5.0, 10.0 and 25.0 mg L 1. Repeatability was good (RSD < 3.6%, n ¼ 10) with a determination throughput of 8 h 1, fostering the application to on-line control of water disinfection processes.
- Potentiometric multi-syringe flow injection system for determination of exchangeable potassium in soils with in-line extractionPublication . Almeida, M. Inês G. S.; Segundo, Marcela A.; Lima, José L. F. C.; Rangel, António O. S. S.A multi-syringe flow injection system for the potentiometric determination of exchangeable potassium in soil samples is proposed. Firstly, a manifold was devised to allow determination in soil extracts prepared off-line. It was possible to analyze samples prepared in extractants with different composition (Mehlich or Morgan) without physical or chemical modification of the manifold. A linear dynamic concentration range of 6–391 mg L−1 was obtained, allowing the direct introduction of soil extract without dilution. A determination frequency of 50 h−1 was achieved, with good repeatability for 10 consecutive injections of soil extracts (RSDb3.0%). The in-line preparation of soil extract was implemented by automatic addition of extractant solution to a previously weighed portion of soil, followed by in-line filtration. Good repeatability was attained as the variance of the extraction procedure was not significantly different from the variance obtained in consecutive measurements of the same extract. Furthermore, results comparable to those obtained by off-line extraction and determination by flame emission spectrometry were attained for the two soil samples tested. Using this procedure, a determination frequency of 13 h−1 and a sampling rate of 4 h−1 were achieved.
- 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.
- Sample introduction in multi-syringe flow injection systems: comparison between time-based and volume-based strategiesPublication . Segundo, Marcela A.; Oliveira, Hugo M.; Lima, José L. F. C.; Almeida, M. Inês G. S.; Rangel, António O. S. S.In multi-syringe flowinjection analysis (MSFIA), devices as selection, injection or commutation valves must be incorporated to the manifold to provide access to sample and standard solutions. Therefore, the definition of sample amount can be either volume or time-based. In the present work, four configurations for sample introduction (two for each approach) were tested in order to establish if the different strategies affect the analytical signal in MSFIA systems. The mean absorbance value from ten consecutive injections of a bromothymol blue solution obtained for the time-based strategy was lower than that provided by the volume-based approach as the exact volume delivered by each configuration was different from the “theoretical” volume. For time-based configurations, the exact volume delivered is 2–5% lower than the theoretical value while for volume-based configurations, the volume delivered was between 6 and 46% larger than the theoretical volume. Moreover, for time-based sampling, the order of steps in the analytical cycle was of utmost importance since any alteration in the flow direction affected the volume delivered in the subsequent step in the analytical cycle. The influence of the two sampling approaches was also evaluated in the MSFIA systems for the spectrophotometric determination of phenolic compounds and the potentiometric determination of chloride. There was no evidence that the use of either volume or time-based sampling would improve the analytical features of these determinations when real samples were tested.