The interfacial area in the Taylor (slug) gas-liquid flow in a microchannel was measured by the Danckwerts' (chemical) method, using CO2 absorption from the CO2/N-2 mixture into KHCO3/K2CO3 buffer solutions, containing NaOCI as a catalyst. The rate of absorption was determined and the Danckwerts' plots were constructed. Reasonable agreement with the geometrical area measured photographically was obtained. This fact allowed to determine for the first time the mass transfer coefficients separately for liquid film and liquid caps. A correlation for the calculation of mass transfer coefficients has been proposed. (C) 2011 Elsevier Ltd. All rights reserved.