1989 Volume 35 Pages 44-48
The freezing and thawing behaviour of the phosphate buffer mixtures was investigated by differential scanning calorimetry (DSC) in view of its practical importance in the cryopreservation and freeze-drying of biological materials. Salt precipitation from the freeze-concentrated phosphate solutions, ie., eutectic formation, depended on the kind of phosphates, cooling rate and the initial concentration of the solution. The amount of salt precipitated decreased with decreasing concentration when it comes to ca. 1M. In the case of the ternary phosphate buffers, the amount of salt precipitated depended also on the initial salt composition. It decreases especially near the composition where monobasic and dibasic salts are mixed in the molar ratio 1 : 1, or near the composition of the ternary eutectic. From these results, it was concluded that the potassium phosphate buffer is more stable at sub-zero temperatures than the sodium phosphate buffer not only under the equilibrium freezing condition but also under the non-equilibrium freezing condition.
