The invention relates to a potentiometric probe for measuring a measurement variable of a medium to be measured contained in a tank, in particular a disposable
bioreactor, comprising: a housing (1) comprising a first chamber (5) in which a reference
half cell is formed, said
cell being connected to a medium surrounding the housing (1) by means of an electrolytic contact point (7) disposed in a wall of the housing (1), wherein the housing (1) comprises a second chamber (9) in which a measurement
half cell is formed, wherein the second chamber (9) is closed on one side by a measurement membrane (11), so that a surface of the measurement membrane facing away from the second chamber (9) is in contact with the medium surrounding the housing (1), and wherein the measurement
half cell comprises a longitudinal extension between the measurement membrane (11) and a closure element (18); bounding the measurement half
cell on a side opposite the measurement membrane (11), characterized in that a quotient of a distance (h) of the measurement membrane (11) from the closure element (18) and an outer
diameter (rA) of the housing (1) is less than 5, in particular less than 2.