4. Conclusion
The sensitivity for ammonium ion of the PVC-membrane based miniaturized sensor, working in a differential mode is around 30 mVrpNHq and the detection limit is 4 2=10y6 M. The interests of the differential mode was to reduce the interference of Naq and Kq ions and the effect of ionic strength and of temperature. Nevertheless, the repeatability of the measurements is limited by the behaviour of the non sensitive FET. The detection limit obtained allows to detect up to the maximal allowable concentrations, for the control of the pollution in river waters.