SENSITIVE MEMBRANE ISFETS FOR NITRATE ANALYSIS IN WATERS

We have fabricated and characterized two new nitrate-sensitive ISFET devices employing two different kinds of field-effect transistors (FETs), one supplied by Academia Sinica, Beijing (China), the other purchased from HEDCO Lab., Utah University (USA), and both based on a poly(vinyl chloride) (PVC)-sebacate membrane, containing tetradodecylammonium nitrate as exchanger. A comparison with a classical nitrate ISE fabricated using the same PVC-sebacate membrane and the same exchanger is also reported. The two nitrate ISFETs display fast response (less than 25 s), a minimum detection limit of 1.0x10(-5) mol/l and a linearity range extending over more than three decades, from about 10(-5) to 10(-2) mol/l, with a slope of about 52 and 54 mV per decade. Lastly, tests were performed on an ISFET with a membrane containing PVC and a copolymer (PVC-poly(vinyl alcohol) (PVA)-poly(vinyl acetate) (PVAc)) as base polymer. The application of these sensors to the nitrate determination in real matrices (river or lake water and aqueous soil extracts) has also been evaluated.