Figure 4.1 Solubility as a function of temperature for paracetamol in three solvents (data from Granberg and Rasmuson (1999)).

Figure 4.2 A schematic plot showing the change in solubility with temperature for drugs with endothermic and exothermic enthalpies of solution.

Figure 4.3 A plot of ln x 2 versus 1/T for three drugs in water (solubility data from Mota et al. (2009)).

Figure 4.4 Concentration versus time profile for dissolution of a metastable (ms) form of a drug. The system is in equilibrium until excess drug is removed by filtration, after which the solution is supersaturated with respect to the stable (s) form. Subsequently the stable form precipitates and a new position of equilibrium is reached.

Figure 4.5 Phase–solubility diagram for a pure compound.

Figure 4.6 Phase–solubility diagram for a compound with one impurity.

Figure 4.7 Effect of the drug:solvent phase ratio when the drug is impure (redrawn from Wells, 1988, with permission from John Wiley & Sons, Inc.).

Figure 4.8 DSC thermal traces for benzoic acid of varying purity.

Figure 4.9 Melting endotherm for indomethacin recorded by DSC and the integration of partial areas to allow calculation of sample purity.

Figure 4.10 van’t Hoff plot for melting of indomethacin.

Figure 4.11 van’t Hoff plot for melting of indomethacin, corrected using Sondack’s method.