Determination of total nitrogen in food by flow injection analysis (FIA) with a potentiometric differential detection system |
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Authors: | José L F C Lima M C B S M Montenegro and Ana P M M O Pinto |
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Institution: | (1) CEQUP / Departamento de Química Física, Faculdade de Farmácia, Rua Aníbal Cunha 164, P-4050 Porto, Portugal, PT |
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Abstract: | A flow injection set-up based on potentiometric detection and gas diffusion device for the determination of total nitrogen
in food is described. The detection system consisted of two ammonium-sensitive electrodes placed sequentially and each alternately
operating as reference electrode. Tubular electrodes without an inner reference solution were prepared with a PVC membrane
composed of nonactin in Tris (2-ethylhexyl) phosphate and potassium tetrakis (4-chlorophenyl) borate to reduce the membrane
resistance. The food sample digests were inserted into the system, and the ammonium present was converted into ammonia gas.
The gas diffused through a gas-permeable membrane to a buffer acceptor stream with a pH that ensured transformation to the
ammonium cation, which was potentiometrically detected. Good agreement between FIA results and those provided by the reference
procedure was obtained, with relative deviation errors below 5%. Using the proposed system, low reagent consumption is possible,
a sampling rate of about 30 samples/h was achieved, as well as a good reproducibility for consecutive injections of the same
sample (variation coefficient < 2%).
Received: 8 October 1998 / Revised: 7 January 1999 / Accepted: 12 January 1999 |
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