Determination of Fluoride in Tap Water by FISE - DETERMINING FLUORIDE IN TAP WATER USING THE FLUORIDE ION SELECTIVE ELECTRODE Background Reading Harris

1 DETERMINING FLUORIDE IN TAP WATER USING THE FLUORIDE ION SELECTIVE ELECTRODE Background Reading: Harris, 7 th ed., Chap. 15. Skoog, West, Holler and Crouch, 7 th ed., Chap. 19. Introduction The fluoride electrode based on a solid LaF 3 membrane is one of the few ion "selective" electrodes that is truly selective for a particular ion, in this case F - . A potentiometric technique, it is routinely used in analytical laboratories and in the field as a cost-effective, reliable method for F- determination. The electrode itself is made from a single crystal of LaF 3 sealed into a plastic tube. The LaF 3 acts as a membrane which selectively exchanges and transports F - ions. The cavity inside the electrode is filled with a solution containing F - and Cl - ions, and an AgCl coated Ag wire dips into this to make an internal reference electrode, just as in the pH electrode. A separate reference electrode completes the cell. The response of the electrode to F - under the right conditions is very close to ideal E(volts) = constant – 0.059