The standardisation of mass transfer measurements for absorption systems is a key factor for the deduction of accurate mass transfer models for random and structured packing. Several papers ( Hoffmann et al. (2007) . Trans IChemE, A, 85 (A1), 40; Kunze et al. (2012) . Chem. Ingen. Techn., 84, 1931; Rejl et al. (2009) . Chem. Eng. Res. Des., 87, 695) already deal with this problem and recommendations are given for appropriate test systems, the execution of the experiments and particularly also for the experimental setup to be used. However, systematic investigations of the influences of the experimental setup configuration on the results of mass transfer measurements in absorption systems are published rarely.

Mass transfer measurements with the system ammonia–air/water have been performed at a pilot plant consisting of a DN 600 saturation column and a DN 450 measuring column, both made from polypropylene, and equipped with different random and structured packing. Although the used experimental setup of the pilot plant follows strictly the recommendations published in Hoffmann et al., experimental results may differ significantly depending on, for example, the locations of the gas and liquid sampling in the column, the raw gas concentrations of ammonia or the pre-treatment of packing.

The paper presents the results of the test series considering different effects on the derived mass transfer performance of the packing and addresses also problems as well as solutions concerning the sampling in a two-phase regime. The aim is to provide a valuable contribution to the efforts for the standardisation of mass transfer measurements in absorption systems.