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

Ion-selective Liquid membrane electrodes for Ca2+, CO32-, NH4+, NO3-, NO2-, and pH have been miniaturized and their characteristics evaluated in view of their application in sediment pore water of lakes. PVC membranes were pr e pared in polyethylene pipette tips with an end diameter of 0.6 mm. This i s a simple method to produce inexpensive disposable ion-selective electrode s for various applications. Detection limits were 1 mu M for Ca2+, CO32-, N H4+, and NO3-, and 10 mu M for NO2-. The pH sensor was Linear in the pH ran ge of 4-11. Selectivities for Ca2+, CO32-, and pH are high enough for the a pplication in seawater. The sensors for NH4+, NO3-, and NO2- in their low c oncentration range experience interferences from K+, SO42-, and HCO3-, resp ectively, in lake pore water. Reproducibility in pure solutions is between +/-0.2 and +/-0.6 mV. The applicability of the miniaturized sensors are dem onstrated in measurements of concentration gradients across the sediment-wa ter interface in sediment cores of several lakes.