A multi-commuted flow injection system with a multi-channel propulsion unit pla...

• Author(s): Oliveira, Sara M. ; Lopes, Teresa I.M.S. ; Tóth, Ildikó V. ; Rangel, António O.S.S.
• Date: 2007
• Persistent ID: http://hdl.handle.net/10400.14/2819
• Origin: Veritati - Repositório Institucional da Universidade Católica Portuguesa
• Subject(s): Multi-commuted flow system; Gas diffusion; Waters; Trace levels of ammo; Spectrophotometry
• Document Type: Article
• Language: English

Description

A flow system with a multi-channel peristaltic pump placed before the solenoid valves is proposedto 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 useof 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(42ugL−1) and a linear dynamic range of 50–1000ugL−1 with a determination rate of 20h−1.