Effect of flow injection parameters on the selectivity of an iodide-selective electrode

Abstract

A study has been carried out on the influence of several experimental parameters on the selectivity of a homogeneous membrance iodide-selective electrode operating under flow injection conditions. Selectivity coefficients were measured for bromide, thiocyanate and thiosulfate by use of a mixed-solution technique, with the effects of sample loop volume, flow rate, carrier iodide concentration, interferent activity, solution pH and temperature being investigated in turn. When the flow system was optimized, it proved possible to double the selectivity of the electrode towards iodide. Facets of the observed behaviour were found to correlate well with existing theories on the time-dependent response of solid-state ion-selective electrodes. Peak profiles were also examined, with particular attention being given to the potential excursions or ‘overshoots’ recorded when mixed solutions of low iodide activity were injected into the flow stream.