Common use of Solubility Clause in Contracts

Solubility. In a previous study one of the major limitations in the iontophoretic transport of rotigotine.HCl was its low solubility. The maximum solubility of rotigotine.HCl was only 7.1 ± 0.4 mM at pH 5.0. In that study the iontophoretic transport at varying rotigotine.HCl concentrations between 1.4 and 3.9 mM showed a linear relationship between the Fluxss and the donor concentration [2]. This demonstrated that the maximum iontophoretic flux of rotigotine was not yet achieved, but the low solubility of rotigotine.HCl was the limiting factor for further increasing the iontophoretic flux. Higher donor concentrations could be achieved by replacing HCl by another salt [20-21]. As shown in Table 1, in the presence of 68 mM NaCl, the solubility of rotigotine increased substantially when HCl was replaced by H3PO4. Compared to rotigotine.HCl the solubility of rotigotine.H3PO4 is 2, 6, 10 fold higher at pH 6.0, 5.0 and 4.0, respectively. Furthermore in contrast to the solubility of the HCl-salt the presence of NaCl did not affect the solubility of rotigotine.H3PO4. This can be explained by an absence of the common ion effect. The next step was to investigate the transdermal delivery of rotigotine as H3PO4 salt.