An approximate analytical solution for the CO2 facilitated transport problem in sodium bicarbonate aqueous solutions is presented. The non-linear diffusion-reaction (NLDR) equations describing the CO2 facilitated transport process were solved after the reaction rate term was linearized through a Taylor series expansion around the limiting surfaces of the liquid membrane. The mathematical model for the CO2 facilitated transport includes four reactions occurring in the aqueous media. Predictions for the facilitation factor have been obtained from the physical diffusion regime to the chemical equilibrium reaction regime. The approximate predictions were compared with numerical calculations and experimental data from the open literature, and the results obtained were found to be in excellent agreement. (c) 2005 Elsevier B.V. All rights reserved.