In the same way that in factorial experimental design, it is considered
advisable to transform natural variables into coded variables, usually
defined as dimensionless with mean zero and the same spread or
standard deviation (29), in mixture experimental design, the pseudocomponents
are defined as combinations of the original components;
the reason for introducing pseudo-components is that usually both the
construction of designs and the fitting of models are much easier when
done in the pseudo-component system than when done in the original
component system (28). Thus, for each reagent included in the extraction
mixture (hexane, acetone, and ethanol), one pseudo-component
was considered, i.e., X1, X2, and X3, respectively