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- 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.
- 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.