Buffer solutions in drug formulation and processing: How pK_a values depend on temperature, pressure and ionic...

Area of Science:

• Pharmaceutical Science
• Physical Chemistry

Background:

• Solution pH is critical in drug formulation and processing.
• Buffer systems are essential for pH regulation, requiring a suitable pKa.
• Buffer pKa is influenced by temperature, pressure, ionic strength, and solvent polarity.

Purpose of the Study:

• To investigate the impact of various factors on the pKa values of pharmaceutically relevant buffers.
• To provide theoretical and experimental insights into buffer pKa behavior under different conditions.

Main Methods:

• Utilized theoretical considerations and accessible experimental data.
• Analyzed the effect of temperature, pressure, ionic strength, and solvent polarity on buffer pKa.
• Correlated buffer pKa changes with enthalpy and heat capacity of ionization reactions.

Main Results:

• Temperature significantly affects buffer pKa, with carboxylic acid buffers showing less change than amino group buffers.
• Buffer pKa decreased with increasing temperature for amino group buffers.
• Pressure changes had a minimal effect below 100 MPa but could alter pKa by up to 0.5 units at higher pressures.
• Ionic strength and solvent polarity showed minor influences on buffer pKa.

Conclusions:

• Accurate prediction of buffer pKa variation with temperature is achievable using thermodynamic parameters.
• Controlling ionic strength and solvent polarity can maintain buffer stability during drug formulation.
• This research provides valuable data for optimizing buffer selection and pH control in pharmaceutical development.