Here at Hanna we have a wide variety of both combination ISEs and half-cell ISEs.
Half-cell ion-selective electrodes contain the sensing material of the ion you wish to measure, however, they require a second reference electrode to function. When submerged in a sample, the ions in the sample cause a voltage change that is measured by the sensing electrode. The reference electrode provides a stable voltage for the meter to compare to. The overall reading is based on BOTH the sensing and reference electrodes.
Combination ion-selective electrodes have both the sensing portion and reference portion of an ISE all in one electrode. This can make testing more convenient.
Hanna Instruments Ion Selective Electrodes (ISEs)