The HI4004-51 calcium module is for use with the HI4004 calcium half-cell ion selective electrode (ISE). The liquid membrane sensor contains an organic polymer within the inert PVC matrix that is responsible for exchange of calcium ions across the membrane. A charge imbalance develops between the sample and the internal cell in response to the calcium ion activity. The potential change is proportional to the concentration of ions in solution.

The HI4004-51 calcium half-cell module easily screws onto the HI4004 probe body, allowing for quick assemblage or replacement. Presoaking the calcium sensor in HI4004-45 conditioning solution or a calcium standard (0.01M) without ionic strength adjuster (ISA) for at least one half hour before calibration will help to optimize the sensor response. Refrigeration of the HI4004-51 calcium module will help extend its life.