Mass Transport Analysis of the Enhanced Buffer Capacity of the Bicarbonate-CO Buffer in a Phase-Heterogenous System: Physiological and Pharmaceutical Significance.

The bicarbonate buffer capacity is usually considered in a phase-homogeneous system, at equilibrium, with no CO transfer between the liquid buffer phase and another phase. However, typically, an in vitro bicarbonate buffer-based system is a phase-heterogeneous system, as it entails continuously sparging (bubbling) the dissolution medium with CO in a gas mixture, at constant ratio, to maintain a constant partial pressure of CO and CO molarity at a prescribed value, with CO diffusing freely between the gas and the aqueous phases. The human gastrointestinal tract is also a phase-heterogeneous system, with CO diffusing across the mucosal membrane into the mesenteric arterial blood, which serves as a sink for CO from the intestinal lumen.