Development of Solid State Membrane Fluoride Ion Selective Electrode

Abstract

This research presents a development of a solid state fluoride ion selective electrode (ISE). The solid state membranes were prepared from the mixture of 70% Ag2S, 10% Cu2S and 20% CaF2 and then pressed in a stainless steel die (normally used for KBr disc preparation) with a 13 mm diameter plunger under a pressure of 1940 atm. The membrane disc was then polished to sharp shape for making the electrode smaller than the commercial electrodes, using small amounts of chemicals and samples, and using low production costs for applying in the field. The change of electrical potential of the developed ISE in the range of 10-7 – 10-1 mol/L fluoride ion was analyzed in order to study the response of the fabricated electrode. Nernstian slope, detection limit, and lifetime of electrodes were determined. The test of electrode efficiency gave a linear response with Nernstian slope of 30.9 mV per decade within the concentration range 10-4 to 10-1 mol/L of fluoride ion. The detection limit was 10-4 mol/L, and response time was less than one minute. The lifetime of the electrodes was found to be one week. The developed fluoride ISE was applied for determination of fluoride ion in tap water of Pathumwan Institute of Technology and the results showed that the electric potential value is not constant.