Bi-parametric data analysis

Combination of selected pairs of variables in two-dimensional (2D) diagrams enables a separation between different electroactive materials. This can be seen in Fig. 3.5, where a representation of (E3/4 -Ej/q) vs. (Eg j gj - Eonset) measured in 

This can be seen in Fig. 3.6, where square-wave voltammograms for synthetic pictorial specimens contain recommended dosages [177] of lead white, plus (a) casein and (b) sunflower oil. As depicted in Fig. 3.3, the response of the pristine pigment consisted of a unique peak at -0.56 V. The pictorial specimens 

The above voltammetric responses can be rationalized by assuming that the response of the grains of pristine pigments is superimposed to that of the ionomeric layer containing lead-binder compounds [178, 179]. For lead carbonate, this can be represented as [126, 177] 

In these equations, represents species confined in the ionomeric layer surrounding the grains of pigment. In the case of proteinaceous binders, Pb + ions are probably coordinated to any extent to donor sites of the binder, so that Eq. 3.3 should be replaced by 

Additionally, the ionomeric layer can form a barrier for charge diffusion surrounding the particles of pigment. As a result, the rate of the overall electrochemical process described by Eqs. 3.3, 3.4 and 3.5 is modified. Our data suggest that the peak at ca. -0.45 V is attributable to the reduction of free (Eq. 3.5) or binder-coordinated (Eq. 3.6) Pb + ions, while peaks at ca. -0.65 V must correspond to the reduction scheme described by Eqs. 3.3 and 3.4. 

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