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- Polymer inclusion membranes (PIMs) as an alternative solid phase extraction (SPE) material: Comparison studies between batch and flow procedurePublication . Ribas, Tânia C. F.; Croft, Charles; Mesquita, Raquel B. R.; Almeida, M. Inês G. S.; Kolev, Spas D.; Rangel, António O. S. S.
- Specially designed hydrophilic 3,4-HPO chelators to be used as chromogenic reagents for iron in a microfluidic paper-based analytical devicePublication . Moniz, Tânia; Bassett, Chelsea R.; Almeida, M. Inês G. S.; Kolev, Spas D.; Rangel, Maria; Rangel, António O. S. S.; Mesquita, Raquel B. R.
- Polymer inclusion membranes (PIMs) as an alternative for on-line solid phase extraction (SPE) in flow analysisPublication . Ribas, Tânia C. F.; Croft, Charles F.; Mesquita, Raquel B. R.; Almeida, M. Inês G. S.; Kolev, Spas D.; Rangel, António O. S. S.
- 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.
- 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.
- Use of a polymer inclusion membrane and a chelating resin for the flow-based sequential determination of copper(II) and zinc(II) in natural waters and soil leachatesPublication . Ribas, Tânia C. F.; Croft, Charles F.; Almeida, M. Inês G. S.; Mesquita, Raquel B. R.; Kolev, Spas D.; Rangel, António O. S. S.A bi-parametric sequential injection method for the determination of copper(II) and zinc(II) when present together in aqueous samples was developed. This was achieved by using a non-specific colorimetric reagent (4-(2-pyridylazo)resorcinol, PAR) together with two ion-exchange polymeric materials to discriminate between the two metal ions. A polymer inclusion membrane (PIM) and a chelating resin (Chelex 100) were the chosen materials to retain zinc(II) and copper(II), respectively. The influence of the flow system parameters, such as composition of the reagent solutions, flow rates and standard/sample volume, on the method sensitivity were studied. The interference of several common metal ions was assessed, and no significant interferences were observed (<10% signal deviation). The limits of detection were 3.1 and 5.6 µg L−1 for copper(II) and zinc(II), respectively; the dynamic working range was from 10 to 40 µg L−1 for both analytes. The newly developed sequential injection analysis (SIA) system was applied to natural waters and soil leachates, and the results were in agreement with those obtained with the reference procedure.
- 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.
- 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.
- Interfacing multisyringe flow injection analysis to flame atomic emission spectrometry: an intelligent system for automatic sample dilution and determination of potassiumPublication . Almeida, M. Inês G. S.; Segundo, Marcela A.; Lima, José L. F. C.; Rangel, António O. S. S.Interfacing automatic flow systems to atomic emission/absorption spectrometry based on flame atomisation techniques may present some difficulties, especially when there are flow interruptions inherent to the technique of automation applied. Therefore, in the present work, different configurations for interfacing multisyringe flow injection analysis (MSFIA) systems to flame-based detectors (flame emission spectrometer in this case) are proposed and compared. To illustrate the feasibility of the selected approach, an intelligent flow system was implemented for in-line dilution of samples prior to determination of potassium content. By selecting the injection volume and the number of dilution channels activated, a dynamic concentration range (1–2000 mg L 1) was established, allowing direct introduction of soil extracts (1–20 mg L 1), parenteral solutions (20–600 mg L 1) and table wines (200–2000 mg L 1). The sampling frequency (three replicates per sample) was about 14 h 1.
- Direct introduction of slurry samples in multi-syringe flow injection analysis: determination of potassium in plant samplesPublication . Almeida, M. Inês G. S.; Segndo, Marcela A.; Lima, José L. F. C.; Rangel, António O. S. S.The present work explores the slurry sampling approach for automatic, flow-based plant analysis. For this purpose, pinch valves were introduced into a multi-syringe flow injection analysis manifold to provide the repeatable aspiration of a few microliters of plant suspension before the material was further processed through the flow system. For validation of the proposed approach, the determination of potassium by flame emission spectrometry was implemented. Several parameters were studied: the concentration of plant particles in the sample suspension and the utilization of matrix modifiers. Microwave digestion was also implemented; no significant difference was found when certified reference material was analyzed with or without the in-line digestion step. The system was successfully applied to 13 samples within a concentration range of 2.5 to 100 mg gˉ¹. A determination frequency of 28 hˉ¹ was achieved and the precision was better than 4.0% (n = 12).