Flow-through units for solid-state, liquid and PVC matrix membrane ion-selective electrodes to minimise streaming potentials

Abstract

When making measurements with ion-selective electrodes in continuous flow systems, potential oscillations are observed which are due to changes in the flow-rate and consequently to changes in streaming potentials. Three different flow-through units suitable for potentiometric measurements with solid-state, liquid and PVC matrix membrane electrodes have been constructed. In all the units, streaming potential oscillations were reduced to ⩽0.2 mV by minimising the distance between the sensing membrane and the external reference electrolyte-sample solution contact zone. Air-segmented streams were used to evaluate the units at flow-rates of 1.74, 3.64 and 6.70 ml min^–1. Sampling rates as high as 60, 120 and 240 h^–1, respectively, were achieved.