an electrochemical sensing cell includes a planar sensing electrode clamped between a manifold cap and a cover for a container housing the counterelectrode and electrolyte . in the manifold cap , the gas being analyzed flows through a shallow recess into contact with one side of the sensing electrode . the cover includes an opening across which is supported a porous disc saturated with electrolyte . when the cap is secured to the cover , the disc presses against the other side of the sensing electrode to ensure good electrolyte contact therewith . a vent hole in the cover also permits replenishing of the electrolyte without major disassembly of the cell .