Ion Selective Electrodes (ISEs) detect ions using a potentiometric method. The selectivity of each ISE is established by an ion selective membrane. Oroboros Instruments has developed the O2k-TPP+_ISE-Module, consisting of separate reference and measuring electrodes, available as sets of two or one electrodes.
The membrane of the electrode can be exchanged, therefore the ISE system may be used to do detect different analytes. Currently Oroboros Instruments is selling membranes for the detection of TPP+ and of Ca2+ ions (scientific support for Ca2+ limited to Calcium electrode). With TPP membranes the ISE system is a TPP electrode. TPP electrodes are used to measure Mitochondrial membrane potential.