2.2.4. Aqueous solubility at different pH values

Aqueous solubility determination of granules, related mixtures and plain IBU was executed by classical shake flask method in the same aqueous mediums used for the IDR test.

Saturated solutions were prepared by adding 50 ml of selected media into each flask which contained an excess quantity of drug. The sparingly soluble drugs need to be stirred or shaken for longer time to reach equilibrium (Baka et al., 2008). Hence, the solutions were shaken for seven days (Stuart and Box, 2005) under constant shaking rate of 50 agitations per minute and temperature (25 ± 1 °C) using a shaking bath (GFL 1083 Burgwedel, Germany). The solutions were then filtered using cellulose filters with 0.45 μm pore size. The amount of dissolved IBU was determined in triplicate by an Agilent 8453 UV–Vis Spectrophotometer at 220 and 264 nm for pH 1.0 and pH 5.5 respectively.