Characterization of Phosphate Buffered Saline (PBS) in Frozen State and after Freeze-Drying.

Freezing of PBS solution caused a pronounced pH shift due to selective crystallization of Na2HPO4•12H2O. The addition of trehalose or mannitol suppressed the buffer salt crystallization and attenuated the magnitude of pH shift. The potential instability of biologics due to pH shift in PBS, can be potentially mitigated with the cosolutes.