Figure 6.1 Solution pH as a function of concentration for a basic salt.

Figure 6.2 Solution pH as a function of concentration for an acidic salt.

Figure 6.3 Percentage of salt formed as a function of acid pKa when reacted with a basic drug of pKa 7.5.

Figure 6.4 A decision tree for salt selection based on characterisation of physicochemical properties (data from Morris et al. (1994)).

Figure 6.5 Solubility profile for a basic salt as a function of pH (pKa 6.7).

Figure 6.6 Solubility profile for an acidic salt as a function of pH (pKa 5.6).

Figure 6. 7 Solubility profiles for a basic drug (pKa 6 Figure 6.7 Solubility profiles for a basic drug (pKa 6.7) in three salt forms (solubilities 5, 2 and 0.5 mg mL−1).

Figure 6.8 Effect of a change in pKa on the solubility profile of a basic salt (original pKa 6.7).

Figure 6.9 Effect of free base solubility on the solubility profile of a basic salt (St 0.01 mg mL−1).

Figure 6.10 Effect of salt solubility on pHmax for a basic salt.

Figure 6.11 Schematic representation of the boundary layer surrounding the surface of a dissolving solid and (inset graph) the change in pH with distance from the surface of the dissolving solid.

Figure 6.12 pH across the diffusion layer as a function of dissolution medium for haloperidol (redrawn from Serajuddin. Copyright (2007), with permission from Elsevier).