High spatial resolution measurements in lake sediments with PVC based liquid membrane ion‐selective electrodes

Ion‐selective liquid membrane electrodes for Ca 2+ , CO 3 2− , NH 4 + , NO 3 − , NO 2 − , and pH have been miniaturized and their characteristics evaluated in view of their application in sediment pore water of lakes. PVC membranes were prepared in polyethylene pipette tips with an end diameter of 0.6 mm. This is a simple method to produce inexpensive disposable ion‐selective electrodes for various applications. Detection limits were 1 µM for Ca 2+ , CO 3 2− , NH 4 + , and NO 3 − , and 10 µM for NO 2 − . The pH sensor was linear in the pH range of 4–11. Selectivities for Ca 2+ , CO 3 2− and pH are high enough for the application in seawater. The sensors for NH 4 + , NO 3 − , and NO 2 − in their low concentration range experience interferences from K + , SO 4 2+ , and HCO 3 − , respectively, in lake pore water. Reproducibility in pure solutions is between 20.2 and 20.6 mV, The applicability of the miniaturized sensors are demonstrated in measurements of concentration gradients across the sediment‐water interface in sediment cores of several lakes.