Probing Chemical Equilibrium in Frozen Sodium Phosphate Buffer Solution by ³¹P Solid-State NMR

Area of Science:

• Analytical Chemistry
• Physical Chemistry
• Biophysical Chemistry

Background:

• Phosphate buffers are vital for cryopreservation across pharmaceuticals, food, and biomedical fields.
• Quantitative characterization of phosphate buffer freeze concentrates at subzero temperatures remains limited.
• Understanding physicochemical properties of phosphate species in frozen solutions is critical for optimizing cryopreservation protocols.

Purpose of the Study:

• To quantitatively characterize phosphate species in frozen sodium phosphate (NaP) solutions using 31P solid-state NMR (ssNMR).
• To determine the pH and ionic strength of freeze concentrates.
• To investigate the effect of trehalose on the stability of frozen NaP buffer solutions.

Main Methods:

• Utilized 31P solid-state NMR (ssNMR) spectroscopy to analyze frozen sodium phosphate solutions.
• Quantified crystallized disodium phosphate dodecahydrate (Na2HPO4·12H2O) content.
• Determined concentrations of H2PO4- and HPO42- in freeze concentrates to calculate pH and ionic strength.

Main Results:

• Direct quantification of phosphate species in frozen NaP buffer was achieved for the first time.
• Identified crystallized disodium phosphate dodecahydrate and quantified H2PO4- and HPO42- in freeze concentrates.
• Observed that trehalose effectively mitigates pH shifts by preventing selective salt crystallization, a novel spectroscopic finding.

Conclusions:

• 31P ssNMR provides a powerful method for analyzing frozen phosphate buffer composition and physicochemical properties.
• Trehalose acts as a cryoprotectant by inhibiting salt crystallization, thereby stabilizing freeze concentrate pH.
• These findings offer crucial insights for developing more stable and effective cryopreservation formulations.