title: A multi-commuted flow injection system with a multi-channel propulsion unit placed before detection: Spectrophotometric determination of ammonium.
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).
authors: Escola Superior de Biotecnologia, Universidade Católica Portuguesa, Rua Dr. António Bernardino de Almeida, 4200-072 Porto, Portugal.
authors: Sara M
authors: SM
authors: Oliveira
authors: Teresa I M S
authors: TI
authors: Lopes
authors: Ildikó V
authors: IV
authors: Tóth
authors: António O S S
authors: AO
authors: Rangel
mesh_terms: D000641:Ammonia / Q000032:analysis*; D017022:Flow Injection Analysis / Q000295:instrumentation* / Q000379:methods*; D005740:Gases / Q000737:chemistry; D013053:Spectrophotometry / Q000295:instrumentation* / Q000379:methods*; D014867:Water / Q000032:analysis
chemical_list: D005740:Gases; D014867:Water; D000641:Ammonia