An Experimental Study of Membrane Materials and Inner Contacting Layers for Ion-Selective K⁺ Electrodes with a Stable Response and Good Dynamic Range

Abstract

The goal was to identify formulations for use in valinomycin K(+) ion-selective electrodes that could routinely achieve a detection limit of <10(-6) M, even after repeated use and exposure at higher K+ activity (0.1 M) and without the requirement for special pretreatment or conditioning in low K+ activity (10(-3) M). Electrodes that would be characterized by high potential stability were sought in this work. Valinomycin-containing membranes with diffusion coefficient of approximately 10(-11) cm(2) s(-1), formulated from methacrylic/acrylic polymers with or without plasticizer, were compared with plasticized PVC membranes (diffusion coefficient 10(-8) cm(2) s(-1)). The methacrylic/acrylic membranes without plasticizer were shown to give an order of magnitude lower detection limit, when compared with PVC-dioctyl sebacate and o-nitrophenyl octyl ether plasticized methacrylic/acrylic polymers under the same conditions, highlighting the influence of plasticizer on the detection limit. As predicted from current theoretical derivation, the inner contacting layer in the ion-selective electrode construction was shown to be highly influential in maintaining the detection limit below 10(-6) M with use and with poly(pyrrole) providing the inner contact ion-to-electron transduction function, a further order of magnitude improvement in the lower detection limit could be maintained for both chloride and hexacyanoferrate doped poly(pyrrole), when 2% ionophore was employed in the ion-selective membrane. This formulation showed extraordinary stability and reproducibility in terms of measurement range and drift over extended measurement testing, with close to Nernstian slopes. At higher ionophore concentrations (4%), the apparent selectivity of the electrode was improved at the expense of detection limit and the nature of the poly(pyrrole) dopant ion became important in determining the dominant exchange processes at the poly(pyrrole)/ion-selective membrane interface.

A solid-contact Pb2+-selective electrode using poly(2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene) as ion-to-electron transducer

“…CPs represent a large family of synthetic metals, however, the commonly studied subjects of SC-ISEs were mostly confined to polypyrrole [13][14][15], polyaniline [16,17], polythiophene, and their derivatives [18][19][20]. From both the experimental and theoretical points of view, it is of great significance to provide new solid contact materials for fabricating SC-ISEs.…”

A polypyrrole-based solid-contact Pb2+-selective PVC-membrane electrode with a nanomolar detection limit

“…It has recently been demonstrated that fluxes of primary ions also affect the lower detection limit of CP-based SC-ISE [32,33]. When electropolymerized poly(3-methylthiophene) on glassy carbon was used as the internal layer of a solvent-cast Ca 2+ -selective PVC membrane, its lower detection limit was not as good as that of an equivalent ISE with a liquid inner contact (LC).…”

New and low cost plastic membrane electrode with low detection limits for sulfadimethoxine determination in aquaculture waters

“…However, very low concentrations may promote a high flux, associated with a super-Nernstian response at intermediate concentrations and relative insensitivity at very low analyte levels [25]. In the present study, the concentrations of SDM were set at 1 x 10 -7 , 1 x 10 -8 and 1 x 10 -9 mol/L (Table 2, ISES I, II and III).…”