VOLTAMMETRIC DETERMINATION OF AL(III) WITH ADSORPTIVE PRECONCENTRATION OF THE PYROCATECHOL VIOLET COMPLEX

A method is described for the determination of aluminum in aqueous samples by linear scan voltammetry after adsorptive accumulation of the pyrocatechol violet (PCV) complex. A pH 6.5 triethanolamine/perchloric acid electrolyte is used for the determination with adsorption onto a mercury drop electrode at -0.50 V (vs a Ag/AgCl/satd KCl reference). Scanning cathodically after adsorption gave a current peak at -0.70 V for reduction of adsorbed PCV and a peak at -0.90 V for reduction of the adsorbed Al-PCV complex. The peaks were well resolved. Using 1.0-mu-M PCV and a 60 s adsorption period gave linear calibration curves for Al in the range 1 to 25 ng mL-1 Al. The detection limit was 0.1 ng mL-1 Al. For analysis, calibration by the method of standard additions is required. Most other metal species do not interfere, but vanadium (V(IV) and V(V)) forms a complex with PCV that is adsorbed and reduced at the same potential as Al-PCV. The interference may be eliminated by complexation of the V with citrate. Al and V present together may be determined by analysis in the absence of citrate (total: Al + V) and in the presence of citrate (Al); V is determined as the difference in the two values. The analysis of a range of samples with Al concentrations from 6 ng mL-1 to 3-mu-g mL-1 gave results which were in good agreement with those obtained by other methods.