APPLICATION OF THE SPLIT-PLOT EXPERIMENTAL-DESIGN FOR THE OPTIMIZATION OF A CATALYTIC PROCEDURE FOR THE DETERMINATION OF CR(VI)

A kinetic catalytic procedure for the determination of Cr(VI), based o n the o-dianisidine oxidation reaction with hydrogen peroxide in a wea kly acid medium was optimized with respect to both reactants [HCl, o-d ianisidine and H2O2] and solvent composition [mixtures of water, aceto ne and N, N-dimethylformamide], in order to achieve higher sensitiviti es. This was accomplished by making use of a split-plot experimental d esign which permitted simultaneous variations in both mixture and proc ess variables, using a response surface approach. Ten mixture experime nts were randomized at each one of the 23 factorial levels and error a nalysis was performed using a split-plot approach. The optimal mixture [water-acetone 70-30% m/m] and process variables [HCl: 6.0 x 10(-4) m ol/l, o-dianisidine: 1.9 x 10(-2) mol/l and H2O2: 0.79 mol/l] values r esulted in a significant sensitivity increase compared with a similar procedure described in the literature. (C) 1998 Elsevier Science B.V. All rights reserved.