Different approaches to the determination of ammonium ions at low levels by flow injection analysis |
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Authors: | G Schulze CY Liu M Brodowski O Elsholz W Frenzel J Möller |
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Institution: | Institut für Anorganische und Analytische Chemie, Technische Universität Berlin, Strasse des 17 Juni 135, D-1000 Berlin 12 Federal Republic of Germany;Institut für Technische Umweltschutz, Fachgebiet Luftreinhaltung, Technische Universität Berlin, Strasse des 17 Juni 135, D-1000 Berlin 12 Federal Republic of Germany;Tecator AB, Box 70, S-26301 Höganäs Sweden |
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Abstract: | Several flow-injection methods are examined critically for their suitability for determing submicromolar levels of ammonium ion on a routine basis. Nesslerization and the Berthelot reaction are not sufficiently sensitive. The gas-diffusion separation is more satisfactory. On the basis of a simple diffusion model, the effects of operating parameters on the ammonium concentration in the acceptor line of the gas-diffusion unit are discussed and experimentally verified. With the optimized gas-diffusion conditions, spectrophotometric detection with an acid-base indicator or the application of a liquid-membrane ammonium-sensitive electrode offers detection limits around 10 ?8 mol 1-1. Carbon dioxide interference in the acid-base indicator method causes problems with baseline stability and long-term drift. A severe limitation on futher enhancement of sensitivity by in-valve preconcentration is the contamination levelof ammonium present in water and reagents. Effective preconcentation (20-fold in 1 min) is obtained by using an ion-exchange microcolumn placed in the injection loop of the valve. |
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