Simple flow system for the rapid pre-concentration and potentiometric determination of fluoride using a micro-column and a wall-jet electrode

Abstract

A flow system for the selective pre-concentration and determination of p.p.b. levels of fluoride has been developed. The system consisted of two micro-columns (150 × 0.5 mm i.d.) packed with an anion-exchange resin loaded with alizarin fluorine blue sulphonate-lanthanum complex and a fluoride ion-selective electrode in a wall-jet type cell. The fluoride present in 1 ml of sample was adsorbed on the resin and eluted with 1 M sodium hydroxide containing 0.5 M sodium chloride. This system allowed 24 samples to be treated in 1 h. Interference by the ubiquitous foreign ions Ca²⁺, Mg²⁺ and H₂PO₄^– at levels 300 times higher than that of fluoride was not observed but Al³⁺ and Fe³⁺ interfered seriously at much lower levels; this interference could be eliminated by application of a previously reported method.