Ion-selective layered sensor and methods of making and using the same

Claim 1

A sensor for the potentiometric measurement of an ion in a liquid sample, comprising: a dimensionally stable, chemically inert, electrically insulating, substantially planar substrate layer having disposed thereon a sensing half-cell and a reference half-cell. the sensing half-cell comprising: (a) a terminated layer of electroconductive material in intimate contact with the substrate layer, the electroconductivity being at least 1×10 2 (ohm·cm) -1 , the electroconductive material layer having coated thereon (b) a carbon layer of finely divided particles of carbon uniformly dispersed in a matrix of organic polymeric binder having coated thereon (c) an ion-selective membrane layer comprising an ionophoric material dispersed in a matrix of dielectric organic polymer, the layer having an electrical impedance at least two orders of magnitude greater than the impedance of the carbon layer, the interface between the ion-selective membrane layer and the dispersed carbon layer comprising a zone in which the layers are partially interdiffused, layers (a) and (b) being shielded from both chemical and electroconductive contact with the liquid sample; the reference half-cell comprising: (a) a terminated layer of electroconductive material in intimate contact with the substrate layer, the electroconductivity being at least 1×10 2 (ohm·cm) -1 , the electroconductive material layer having coated thereon (b) a carbon layer of finely divided particles of carbon uniformly dispersed in a matrix of organic polymeric binder having coated thereon (c) an ion-selective membrane layer comprising an ionophoric material dispersed in a matrix of dielectric organic polymer, the layer having an electrical impedance at least two orders of magnitude greater than the impedance of the carbon layer, the interface between the ion-selective membrane layer and the dispersed carbon layer comprising a zone in which the layers are partially interdiffused, layers (a) and (b) being shielded from both chemical and electroconductive sample, the ion-selective membrane having coated thereon (d) a salt bridge layer comprising a predetermined concentration of an ion capable of interacting with the ionophoric material, the ion being dissolved in a solid hydrophilic polymer, the salt bridge layer being substantially, but incompletely, shielded from ionic contact with the liquid sample by an overlying layer of an inert liquid-impermeable electrically insulating layer to define a shielded and an unshielded surface area of the salt bridge layer. the sensing half-cell and the reference half-cell being spaced apart on the substrate layer to define a liquid sample receiving zone adapted to allow the liquid sample to make ionic contact with both the ion-selective membrane layer of the sensing half-cell and the unshielded surface area of the salt bridge layer of the reference half-cell, such that application of the liquid sample to the sensor does not substantially change the predetermined ion concentration in the salt bridge layer of the reference half-cell thereby establishing a stable reference potential.