Many environmental applications are difficult due to a lack of ions in the sample. The IONOTRODE pH electrode solves this problem with the new TK inner buffer design. A low membrane resistance is achieved through the special membrane shape, resulting in simple and reliable measurements of ion-weak samples. Equipped with a liquid electrolyte, this electrode shows excellent signal stability, even at low temperatures. These features, combined with the sidearm design with the electrolyte tube connector, make this the ideal on-line electrode for drinking water applications.