CHEMICALLY-MODIFIED FIELD-EFFECT TRANSISTORS WITH NITRITE OR FLUORIDESELECTIVITY

Polysiloxanes with different types of polar substituents are excellent membrane materials for nitrite and fluoride selective chemically modi fied held effect transistors (CHEMFETs). Nitrite selectivity has been introduced by incorporation of a cobalt porphyrin into the membrane; f luoride selectivity has been obtained with a uranyl salophen derivativ e as the anion receptor. Polysiloxanes with acetylphenoxypropyl or phe nylsulfonylpropyl substituents are the best sensing membranes, The nit rite selective CHEMFETs exhibit Nernstian responses and a high selecti vity over chloride and bromide (log K-NO2,j(Pot)=-2.9 and -2.7 respect ively, based on a phenylsulfonylpropyl functionalized polysiloxane). A lso the sensitivity and selectivity of the fluoride selective CHEMFETs is better with the polysiloxane membranes than with plasticized PVC m embranes. Even in the presence of O.1 M of the more lipophilic chlorid e, bromide, or nitrate ions an almost Nernstian response and a detecti on limit of 0.25 mM is obtained for fluoride(log K-Fj(Pot)=-2.5).