ORTHOGONAL ARRAY DESIGN FOR THE OPTIMIZATION OF CLOSED-VESSEL MICROWAVE DIGESTION PARAMETERS FOR DETERMINATION TRACE-METALS IN SEDIMENTS

Orthogonal array design was applied to the optimization of the closed- vessel microwave digestion of sediment samples. Five variables related to the digestion efficiency were studied: the addition of HF in diges tion acid, the ratio between HCl and HNO3, the maximum pressure settin g, the output power and the digestion time. In the experimental assign ment, the digestion time at two levels and other variables at four lev els were tested using an OA(16)(4(4) x 2(3)) matrix. The interactions between the parameters were neglected. From the results, the optimum c onditions for the closed vessel microwave digestion for sediment sampl es were established.