ORTHOGONAL ARRAY DESIGN AS A CHEMOMETRIC METHOD FOR THE OPTIMIZATION OF ANALYTICAL PROCEDURES .3. 5-LEVEL DESIGN AND ITS APPLICATION IN A POLAROGRAPHIC REACTION SYSTEM FOR SELENIUM DETERMINATION

The theory and methodology of a five-level orthogonal array design for the optimization of analytical procedures were developed. In the theoretical section, the construction and characteristics: of the OA(25)(5(6)) matrix are described in detail while orthogonality is proved by means of a fourth-order polynomial model. Next, the assignment of experiments in the OA(25)(5(6)) matrix is illustrated, followed by the data analysis strategy, in which significant/non-significant influence for each factor is quantitatively evaluated by the analysis of variance (ANOVA) technique including the percentage contribution, and the differences among five levels for each factor that has a significant influence are determined by Duncan's multiple F-test, Finally, the response surface methodology for the OA(25)(5(6)) matrix is developed by using the equations obtained from the proof on orthogonality. In the application section, the reaction system for selenium determination by differential-pulse polarography, as a practical example, is employed to demonstrate the application of the OA(25)(5(6)) matrix in the area of analytical chemistry.