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  • Title: A multi-commuted flow injection system with a multi-channel propulsion unit placed before detection: Spectrophotometric determination of ammonium.
    Author: Oliveira SM, Lopes TI, Tóth IV, Rangel AO.
    Journal: Anal Chim Acta; 2007 Sep 26; 600(1-2):29-34. PubMed ID: 17903461.
    Abstract:
    A flow system with a multi-channel peristaltic pump placed before the solenoid valves is proposed to overcome some limitations attributed to multi-commuted flow injection systems: the negative pressure can lead to the formation of unwanted air bubbles and limits the use of devices for separation processes (gas diffusion, dialysis or ion-exchange). The proposed approach was applied to the colorimetric determination of ammonium nitrogen. In alkaline medium, ammonium is converted into ammonia, which diffuses over the membrane, causing a pH change and subsequently a colour change in the acceptor stream (bromothymol blue solution). The system allowed the re-circulation of the acceptor solution and was applied to ammonium determination in surface and tap water, providing relative standard deviations lower than 1.5%. A stopped flow approach in the acceptor stream was adopted to attain a low quantification limit (42 microgL(-1)) and a linear dynamic range of 50-1000 microgL(-1) with a determination rate of 20 h(-1).
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