Buffer Solutions in Drug Formulation and Processing: How pKa values Depend on Temperature, Pressure and Ionic Strength

Publication date: Available online 22 February 2019Source: International Journal of PharmaceuticsAuthor(s): Lisa Samuelsen, René Holm, Audrey Lathuile, Christian SchönbeckAbstractSolution pH is an important factor during drug formulation and processing. Changes in pH present challenges. Regulation of pH is typically managed by using a buffer system, which must have a suitable pKa. The pKa of buffers depends on temperature, pressure and ionic strength. In addition, the pKa can also be affected by the polarity of the solvent, e.g., by the addition of a co-solvent. Theoretical considerations and accessible experimental data were used to understand how the pKa values of pharmaceutically relevant buffers depend on these factors. Changes in temperature also affect the buffer pKa. Carboxylic acid moieties were least affected by changes in temperature. Buffers containing amino groups were most affected by changes in temperature, and the pKa decreased as temperature was increased. It was possible to predict accurately how buffer pKa varies with temperature, based on changes in enthalpy and heat capacity for the ionization reactions. Changes in pressure had a limited effect on buffer pKa for pressures
Source: International Journal of Pharmaceutics - Category: Drugs & Pharmacology Source Type: research

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