Abstract: In an ionic-activity sensor, an osmotic pump drives a reference-cell electrolyte to flow through an interface with the solution to be measured. This minimizes contamination of the reference cell by that solution. The driving force results from expansion of an electrolytic-agent reservoir into which solvent from a solvent reservoir diffuses through a semi-permeable membrane. The electrolytic-agent reservoir contains an electrolytic-agent solution in which a quantity of undissolved is disposed to keep the electrolytic-agent solution saturated as solvent diffuses into it.

Abstract: A reference half-cell and method includes a reference electrode and a reference electrolyte disposed in mutual electrolytic contact, and a reference junction including a porous member configured to provide controlled flow of the reference electrolyte therein to form a primary electrical pathway extending through the member. A secondary electrical pathway is disposed electrically in parallel with the primary electrical pathway.