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

Abstract

Ion-selective liquid membrane electrodes for Ca2+, CO3/2-, 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 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 Ca2+, CO3/2-, NH4/+, and NO3/-, and 10 μM for NO2/-. The pH sensor was linear in the pH range of 4-11. Selectivities for Ca2+, CO3/2-, and pH are high enough for the application in seawater. The sensors for NH4/+, NO3/-, and NO2/- in their low concentration range experience interferences from K+, SO4/2-, and HCO3/-, respectively, in lake pore water. Reproducibility in pure solutions is between ±0.2 and ±0.6 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.