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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.
- 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.