The reproducibility for different ISFETs is also better in normal measurement mode: the response fluctuates between 50 to 58 mVrpNHq. In the differential mode, the 4 fluctuation is bigger: 25 to 45 mVrpNHq. In fact, this 4 parameter epends essentially on the non-sensitive FET behaviour. The response of the ammonium sensitive membrane is quite reproducible but the non sensitive FET one exhibits great dispersion.