EMF RESPONSE OF NEUTRAL-CARRIER BASED ION-SENSITIVE FIELD-EFFECT TRANSISTORS WITH MEMBRANES FREE OF IONIC SITES

Response characteristics of field effect transistors covered by membra nes containing neutral carriers and an organic liquid but neither a po lymer nor ionic sites were determined. The commercially available 2-ni trophenyl octyl ether and dioctyl sebacate, both frequently used plast icizers for poly(vinyl chloride) ISE membranes, had impurity concentra tions large enough to lead to small emf responses. Upon removal of the se impurities by HPLC, no emf responses were detectable any more, whic h seems to be due to a negligibly small permselective uptake of primar y ions into the membrane and not the high impedance of the membrane bu lk. The use of membranes of the more polar nitrobenzene and 2-fluoro-2 '-nitrodiphenyl ether resulted in small but transient emf responses. T he absence of ionic sites led however to the failure of permselectivit y and resulted in co-extraction even of the highly hydrophilic chlorid e ions. Liquid membranes containing neutral carriers but no ionic site s are thus not only unsuitable for ISEs due to their high impedance, b ut also because it is very likely that either the failure of permselec tivity occurs or the concentration of primary ions permselectivity ent ering the membrane is too small to determine the phase boundary potent ial.