Kinetic determination of EDTA and citrate by the displacement of fluoride from Al(3+)F(-) complexes and use of a fluoride ion-selective electrode

The displacement of fluoride from its aluminium complexes by the action of EDTA, citrate and other ligands is a relatively slow process which can be monitored potentiometrically with a fluoride ion-selective electrode. Some characteristics of these reactions are presented. There is evidence that [AlF](2+) reacts with the competitive ligand faster than the simple free (hydrated) Al(3+) species does. The relative rates of release of fluoride by the action of various aminopolycarboxylic acids have been determined. Potentiometric reaction-rate methods have been developed for the determination of 0.2-1.5 mumole of EDTA and 0.1-1.0 mumole of citric acid, with average relative errors of approximately 3%.