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Abstract

A membrane-enclosed amperometric cell (MEAC) for use in determining the concentration of an electroactive species of interest (EASI) in an ambient medium comprises: a working electrode defined by a periphery; a liquid electrolyte covering the sensing area in a film of uniform thickness and being in electrolytic contact with a counter eletrode; a flexible polymer membrane of generally uniform thickness that is substantially impermeable to the electrolyte but permeable to the EASI; the membrane extends in a substantially conforming manner over the sensing area and the electrolyte film thereon; the cell of the invention has a physical permeation barrier that (1) consists of a layer of a substantially inert solid material which is substantially impermeable to the electrolyte and to the EASI; (2) extends between the ambient medium and the sensing area; (3) is disposed in a parallel configuration and in physical contact with the membrane; (4) has at least one opening permitting access of the EASI through the membrane to the sensing area yet phsyically restricting such access to a limited portion of the sensing area; (5) the limited portion is enclosed by a circumjacent margin that has an outer periphery defined by the periphery of the sensing area, an inner periphery, and a width defined by the smallest distance between the outer and the inner periphery; and (6) the width of the circumjacent margin is at least three times greater than the thickness of the electrolyte layer, or at least three times greater than the thickness of the membrane, depending upon the position of the barrier.

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First Claim