3. Results and discussion
3.1. Sensitivity of the NH q-ISFET for the detection of 4 NH q ions 4
Fig. 2 shows the response of the ammonium ISFET for the two modes of measurement and the non-sensitive FET response, in the range of activity: 10y7 –10y1. The response time of the ISFET is around 30 s. In the normal mode, the curve, in the range 3=10y5 M to 0.1 M, is composed of two sections with slightly different slopes. The slope increases for concentrations higher than 10y3 M. The average slope is 55 mVrpNHq 4 with a regression coefficient rs0.994.
In the differential mode, the curve is quite linear from 2=10y4 M to 0.1 M with a slope of 38 mVr pNHq 4 and rs0.998 and in the range 2=10y4 M to 2=10y6 M theslope is 23 mVr pNHq. The detection limit is 2=10y6 4M.