Acrodisc 4mm syringe filter

Suspensions were prepared by adding sufficient solids to 1ml of aqueous buffer. They were tumbled end to end for 3 days in a water bath at 25°C. After equilibration, the samples were filtered (Acrodisc 4mm syringe filter, 0.45 μm polytetrafluoroethylene membrane; Pall Life Sciences), diluted, and analyzed by HPLC. The solid residue was examined by powder X‐ray diffractometry to ensure no phase change. Different aqueous buffers were used to achieve the range of pH values for the profile.

Approximately 2g of solids was added to 5ml of aqueous solution in a 20ml scintillation vial. The suspension was kept in a 25°C water bath while stirring for 2 hours after pH stabilization. The suspension was filtered (Acrodisc 4mm syringe filter, 0.45μm polytetrafluoroethylene membrane; Pall Life Sciences, Cortland, NY, USA). The filtrate was diluted appropriately and analyzed by high‐performance liquid chromatography (HPLC). The solid residue was examined by powder X‐ray diffractometry to ensure no phase change. Water, aqueous solutions with different concentrations of acid or base were used to achieve different values of pH.