The apparent pKa of a solution can depend upon many factors, including temperature, pressure, and ionic strength. To better understand the temperature effect on phosphate equilibria in the solutions, phosphate concentrations, and pKa values were fitted at 25°C and 0°C to estimate the effect of temperature lowering (Figure ). The following modified Van't Hoff equation was employed, which accounts for the temperature dependence of the equilibrium constant by incorporating enthalpy and heat capacity changes: