The choice of an experimental design based on the Doehlert matrix,
rather than other experimental designs, was more suitable in the present
work, permitting the use of fewer experiments. As pH influences
both the deprotonation of EDTA4−, as well as the formation of hydroxo
complexes of Mn(II) and Mn(III), possible non-linear behavior justified
the use of a greater number of levels for this variable. On the other hand,
in the case of the ratio between the concentrations of EDTA andMn(II),
it was important to ensure that complex formation showed linearity
with the concentration of the analyte and followed a monotonic trend,
enabling the use of a smaller number of levels. The analytical sensitivity
(corresponding to the slope of the analytical curve) ranged from2266 to
7762 L mol−1, demonstrating the importance of the optimization and
the use of suitable ranges of values for the variables studied.