ON THE ADSORPTION VOLTAMMETRY OF THE LANTHANUM(III)-ALIZARIN COMPLEXONE-FLUORIDE SYSTEM

A very sensitive electrochemical voltammetric procedure for trace measurement of fluoride in water is described. The complex of lathanum(III) with alizarin complexone (ALC) and fluoride ion is adsorbed on the surface of a hanging mercury drop electrode. The reduction current of the accumulated complex is determined by linear sweep voltammetry. In order to form the ternary complex, it is necesary that the solution stands for 7 h at room temperature. The adsorptive and voltammetric behaviours of the ternary complex are described. The peak potential of adsorption reduction of the ternary complex is -0.62 V at pH = 4.6. Optimum experimental conditions include 0.02 M (CH26N4 + HNO3 (pH = 4.6), 10% actone, 4 × 10-6 M La(III), 1 × lO-6 M ALC and a pre-concentration potential of -0.25 V (vs. SCE). At optimum experimental conditions, the linear rangeis 4.8 × 10-9 -1 × 10-7 M. The relative standard error of the method is 3.3% for 4 × 10-8 M fluoride. © 1990.