The HI4000-54 replacement pH reference assembly is for use with Hanna’s HI4105 carbon dioxide gas sensing ion selective electrode (ISE). This internal glass pH assembly provides the sensing and reference components for the carbon dioxide combination ISE.

Theory of Operation

A gas sensor works due to the partial pressure of the measured gas in solution. The dissolved gas in the sample diŽffuses into the membrane and changes the pH in a thin Ÿfilm of unbuffŽered electrolyte on the surface of the internal pH sensor. DiŽffusion continues until the partial pressure of the sample and the thin film of electrolyte are the same. The pH change is proportional to the concentration of dissolved gas in the sample solution.