STUDY OF THE MO(VI) CATALYTIC RESPONSE IN THE OXIDATION OF IODIDE BY HYDROGEN-PEROXIDE USING A MONOSEGMENTED CONTINUOUS-FLOW SYSTEM

Fractional factorial, modified simplex and response surface studies of the Mo(VI)-catalysed and non-catalysed oxidation of iodide by hydrogen peroxide in acidic medium were executed using a monosegmented continuous-flow system (MCFS). As this reaction is commonly used for the spectrophotometric catalytic determination of Mo(VI), the behaviour of the analytically useful response, DELTA-A, the difference of the average absorbance values of the Mo(VI)-catalysed and non-catalysed reactions, was studied over a large range of experimental conditions. The effects of simultaneous changes in the sample flow-rate, the H2SO4, KI and H2O2 concentrations and the reaction time on the signals were measured. The optimum concentrations found using MCFS are 0.0665, 0.1528 and 0.0041 M for H2SO4, KI and H2O2, respectively. Rigorous control of the acid concentration is essential to maintain the sensitivity of the analytical signal for operating conditions close to the optimum values recommended here. On the other hand, the DELTA-A values are much less sensitive to variations in the H2O2 concentration. Increasing KI concentrations can improve the sensitivity but can also cause baseline instability. The response surface is convenient for visualizing the overall behaviour of the system for the experimental control values investigated.