OPTIMIZATION OF VOLTAMMETRIC METHODOLOGY FOR THE DETERMINATION OF ALUMINIUM IN DRINKING WATER BY COMPLEXATION WITH ALIZARIN RED S

The purpose of this work was to optimize, through experimental design, the differential pulse voltammetry technique using a hanging drop mercury electrode (HMDE) for the determination of Al(III) in drinking water. Since Al(III) is electrochemically inactive in the explored potential range, it cannot be easily determined by conventional voltammetry because it is difficult to reduce it in the electrode in aqueous solution, since its reduction potential is very negative and very close to the reduction potential of hydrogen. However, after the complexation reaction of the Al(III) ion and alizarin red S (ARS), an anodic voltammetric peak is obtained corresponding to the oxidation of the anthraquinone group at -1.07 V (vs Ag/AgCl) using the supporting electrolyte ammonium chloride 1.0 mol L-¹. Instrumental factors and pH were studied using the Plackett-Burman exploratory design to screen the relevant factors and then; to optimize the factor levels, a central composite design (CCD) was performed. The best voltammetric responses were obtained when pH 9,2, pulse time of 15 ms, pulse amplitude of 50 mV and scan rate of 25 mV s-¹ were used. With the optimized parameters, the current relative to the complex was linearly dependent on the Al(III) concentration in a range of 0.82 to 3.67 µg mL-¹. The relative error between the estimated and observed current was 3.97% for the average of 5 independent readings of a 4 µg mL-¹ Al(III) solution in the voltammetric cell. The detection and quantification limits were 0.25 and 0.82 µg mL-¹, respectively.