A potentiometric sensor apparatus, comprising: a measuring half-cell having a measuring membrane; a reference half-cell; and a measurement circuit for registering a potential difference between the measuring half-cell and the reference half-cell. The measuring membrane has, covering at least one portion of the measuring membrane during dry storage of the sensor apparatus, a coating, which is embodied, upon immersion of at least one immersion region of the sensor apparatus (which region comprises the measuring membrane and is intended for immersion in a measured medium) in a liquid, especially a water containing liquid, in the case of continued contact with the liquid, to dissolve, at least partially, off of the measuring membrane.