OF EXPERIMENTAL PLANNING FOR OPTIMIZATION OF A PROCEDURE FOR SIMULTANEOUS VOLTAMMETRIC DETERMINATION OF METALS Zn, Cd, Pb AND Cu FREE IN COCONUT WATER

Optimization of the main parameters of SWASV using boron-doped diamond electrode was described for the simultaneous determination of Zn, Cd, Pb and Cu free in coconut water. The values of electroanalytical parameters studied were optimized with the factorial design and center composite design. The optimized parameters for the preconcentration of metals were -1.50 V for potential, and 240 s for deposition time. For SWV, the optimized value was 11.56 mV for step potential. In addition, frequency and pulse height were defined at 100 Hz and 55 mV, respectively. Furthermore, the concentration of the supporting electrolyte (acetate buffer, pH 4.7) was optimized in 0.206 mol L-1. The optimized procedure was applied in two samples of coconut water: natural and processed. The limits of detection (LOD) obtained for Zn, Cd, Pb and Cu were 7.2; 4.4; 3.3 and 1.5 mu g L-1, respectively. The concentrations of Cd and Pb were not detected. On the other hand, the values found for the concentrations of Zn and Cu were: < LOD (29 mu g L-1) and (6.8 +/- 0.9) mu g L-1 for the natural sample; and (85.8 +/- 4.2) mu g L-1 and (7.7 +/- 0.6) mu g L-1 for the processed sample, respectively.