Abstract: Difficulties occur in finding an electrode which responds reliably to the concentration of some ions.The concentration of a required ion in an electrolyte is measured by measuring the potential between first and second electrodes when the electrolyte is passed from the first electrode to the second electrode through a material which changes the concentration of another ion by an amount which depends on the concentration of the required ion. The first and second electrodes are reliable electrodes for measuring the concentration of the other ion.

Abstract: A metal sulphide ionic membrane for use in monitoring heavy metal ions in solution comprises a mixture of at least four metal sulphides in relative proportions such that the membrane is capable of responding electrochemically to all of the corresponding metal ions when said ions are contained in solution, e.g. at concentrations in the range from 10.sup.-5 up to 1M. A preferred embodiment of the ionic membrane consists of a mixture of silver 15 to 65% by weight, cadmium 15 to 65% by weight, lead 30 to 65% by weight and copper 3 to 9% by weight sulphides. The ionic membranes are preferably prepared by co-precipitation of sulphides followed by hot pressing and may be detachably mounted in suitable electrodes, internal electrical connections made either by way of filling solutions or by direct connection, preferably biassed connection, of an internal conductor to the internal surface of the electrode pellet.

Abstract: An ion selective potentiometric electrode component consisting essentially of a solid, plate-like interface element prepared by simultaneously co-precipitating Ag.sub.2 S, Ag.sub.2 Se, CdS and CdSe followed by compressing the precipitated material at an elevated temperature to provide a substantially impervious agglomerate having an X-ray diffraction pattern distinct from a composite pattern of the individual four components and characterized by improved response properties and enhanced sensitivity to cadmium ion concentration in solution.

Abstract: An ion selective electrode having a silicon wafer substrate secured to one end of a tube made of insulating material by an adhesive agent and an ion sensitive film applied on the outer surface of silicon wafer substrate is disclosed. In order to prevent a portion of a side edge of silicon wafer substrate from being exposed to a sample liquid to be measured, the side edge of silicon wafer substrate is tapered and the ion sensitive film is applied on the tapered side edge as well as on the outer surface of silicon wafer substrate. The tapered side edge may be simply formed by effecting an anisotropic etching for a silicon wafer.