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

Abstract

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 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+, CO32−, NH4+, and NO3−, and 10 µM for NO2−. The pH sensor was linear in the pH range of 4–11. Selectivities for Ca2+, CO32− 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+, SO42+, and HCO3−, 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.

Mineralization pathways in lake sediments with different oxygen and organic carbon supply

“…Miniaturized polyvinylchloride (PVC)-based liquid membrane ISEs for NH were prepared according to the method of Mü ller et al (1998). Pipette tips of 10 mL volume with a tip diameter of about 0.6 mm were used as electrode bodies, and approximately 1 mL of membrane solution was drawn up, resulting in a 0.5-mm- thick membrane after evaporation.…”

“…Lander for ion-selective analysis (LISA)-In situ measurements were conducted at the lake bottom using a submersible profiling lander system (LISA; Mü ller et al 2002) equipped with two to three miniaturized ion-selective electrodes (ISEs) each for NH z 4 and NO { 3 and two O 2 microelectrodes (OX-25, Unisense). Briefly, the lander consists of two pressure cases containing power supply, stepping motor control, and data logger units.…”

“…As a result of the low concentration of interfering ions, freshwater systems allow the application of ion-selective sensors for, for example, NH (Sweerts et al 1991;Mü ller et al 2002;Maerki et al 2006). …”

“…Among various methods tested (Tengberg et al 1995;Viollier et al 2003), one of the most promising tools is in situ profiling with microelectrodes (Sweerts and De Beer 1989;Mü ller et al 2002), a method providing penetration depths, vertical concentration gradients, and production or consumption rates of substrates and metabolites at submillimeter resolution. However, the in situ applications of microsensors may affect the vertical velocities of the bottom water , reduce the thickness of the diffusive boundary layer, and thus influence the interstitial O 2 pore-water profile (Glud et al 1994(Glud et al , 2007.…”

In situ speciation measurements. Using diffusive gradients in thin films (DGT) to determine inorganically and organically complexed metals

“…However, as reagents are still added and the samples degassed, composition is inevitably changed from the in situ condition in the 2-3 min that elapses from sample removal to measurement. While ion-selective electrodes are in principle an ideal tool for in situ measurement and have been used in certain special conditions as microelectrodes [11], they generally lack the required sensitivity for trace metals. Voltammetry, however, has the correct attributes for in situ measurement of metals, as it minimally perturbs the sample and in stripping mode is extremely sensitive.…”