Monolithic capillary-based ion-selective electrodes

Poly(styrene-co-divinylbenzene)-based monolithic capillaries of an inner diameter of 200 [micro]m and a length of 2-5 mm have been used to construct C[a.sup.2+]-, A[g.sup.+]-, and N[a.sup.+]selective electrodes. The membranes consist of a solution of ionophore and ion exchanger in bis(2-ethylhexyl) sebacate or 2-nitrophenyl octyl ether, which are used as plasticizers in conventional PVC-based membranes. With capillaries of low porosity, the potentiometdc responses down to [10.sup.-8]-[10.sup.-9] M solutions do not depend on the composition of the internal solution, which indicates a strong suppression of transmembrane ion fluxes. Thus, no tedious optimization of the inner solution is required with monolith ISEs. The lower detection limits of A[g.sup.+]- and C[a.sup.2]- ISEs are comparable to the best ones obtained earlier with optimized inner solutions. Additionally, a monolithic N[a.sup.+]-selective ISE has been obtained exhibiting a lower detection limit of 3 X [10.sup.-8] M N[a.sup.+]. With monolithic capillaries of higher porosity and fused-silica GC caprilades, the transmembrane flux effects are noticeable but still significantly smaller than with conventional PVC membranes.