The present work describes the direct quantification of EDTA by
means of formation of the colored complex containing the Mn(III) ion.
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].