The pH influenced this system because of the deprotonation of EDTA
aswell as the formation of hydroxo complexes ofMn(II) (and to a lesser
degree, Mn(III)). Optimization of the experimental conditions was performed
using the Doehlert matrix procedure. This is a second order experimental
design that enables evaluation of the most significant
variable (in this case, pH) using a greater number of levels. This multivariable
optimization also has the advantage of only requiring a small
number of additional experiments to expand the evaluation,where necessary
[25,26].