Enhanced performance of ion-selective electrodes in flow injection analysis: non-nernstian response, indirect determination, differential detection and modified reverse flow injection analysis

Abstract

Some general aspects concerning the measuring device, cell design, flow manifold and sensor requirements for the incorporation of ion-selective electrodes (ISEs) in flow injection systems are outlined. The main aim of this paper is to demonstrate how the control of sample dispersion and timing in flow injection analysis (FIA) can be used to attain unique potentialities. The detection limits of ISEs can be decreased, even below the intrinsic solubility of the sensor membrane. The integration of sample processing steps within the manifold improves the reliability of the electrode for reaction products which are unstable or volatile. The series differential detection method is shown to increase the sensitivity (slope of the calibration graph) and to simplify data evaluation. The indirect determination of trace amounts of aluminium with a fluoride ISE can be performed with a simple experimental set-up and high sample throughput. Finally, the modified reverse FIA technique is shown to be a novel method for process analysis, continuous monitoring purposes and high precision calibration.