IJUP08 - Universidade do Porto

Sensor for amperometric determination of ammonia in seawater
C. Peixe 1,2 , C.M. Pereira 1 , F. Silva 1 and M. T. Borges 2,3
1 Department of Chemistry, Faculty of Science, University of Porto, Portugal.
R. Campo Alegre, 687, 4169 – 007 Porto, Portugal
2 Ciimar-University of Porto; Rua dos Bragas 289, 4050-123 Porto, Portugal.
3 Faculty of Sciences (Zoology-Anthropology Dep.)-University of Porto; Praça Gomes Teixeira,
4099-002 Porto, Portugal.
The present work reviews the development of amperometric ammonia determination by
the use of an interface between two immiscible electrolyte solutions (ITIES). Cyclic
voltammetry and square wave voltammetry have been applied to the analysis of the
voltammograms for transfer of ammonium cation facilitated by dibenzo-18-crown-6 [1].
The liquid-liquid interface was supported by use of silicon membrane containing
micropores. The organic solvent used in this work was 2-nitrophenyloctylether (NPOE).
The organic phase was prepared dissolving bis(triphenylphosphoranylidene)-ammonium
tetrakis(4-chlorophenyl)borate (BTPPATPBCl) and 1,3:2,4_dibenzylidene sorbitol (DBS)
(gelling agent) in the organic solvent. NPOE/DBS gels were prepared accordingly to the
literature [2]. The aqueous phase was prepared dissolving lithium chloride and adding
different amounts of ammonium chloride.
Figure 1 shows cyclic voltammograms obtained for microITIES using different aqueous
phases.
I /A
4,0x10 -7 LiCl
LiCl+NH 4 Cl
2,0x10 -7
0,0
-2,0x10 -7
-300 -200 -100 0 100 200 300 400 500 600
Figure 1 – Cyclic voltammograms obtained in different conditions.
In the presence of the ionophore the addition of NH4 + to the aqueous solution results in the
presence of a peak at -200 mV. The peak current intensity increase can be related with the
concentration of ammonium cation in the solution.
Acknowledgements:
CIIMAR for the project EC-CRAFT/016869/2006, “Raceways – A Hypertensive fish farming
concept for lasting competitiveness and superior production” and financial support from FCT.
References:
[1] Liao, Y., Okuwaki, M., Kitamura, F., Ohsaka, T. and Tokuda, K., Electrochimica Acta, 44
(1998), 117-124.
[2] Silva, F., Sousa, M.J., Pereira, C., Electrochimica Acta, 42 (1997), 3095-3103.
φ /mV
127