Determination of the gas-to-liquid partitioning coefficients using a new dynamic absorption method (DynAb method)

Abstract

The determination of partitioning coefficients which describes the behaviour of a pollutant between phases (gas, liquid, solid) is of fundamental importance in different scientific areas (fate and behaviour of pollutants, design of abatement technologies, flavour release). A new and fast method, based on selected ion flow tube mass spectrometry, was developed to determine the gas-to-liquid partitioning coefficients (KAW) of volatile organic compounds (VOC). By using the dynamic absorption method (DynAb method), a gas stream with a known and constant compound concentration is bubbled through a liquid volume. The outlet gas concentration is continuously measured and results in a breakthrough curve. From the breakthrough curve of the measured gas concentration, KAW can be calculated. In contrast to the existing dynamic methods, KAW obtained by DynAb method does not assume equilibrium of the target compound between the liquid and the air bubble leaving the liquid and therefore avoids erroneous evaluation of KAW.The developed method was applied to determine KAW for five odorous VOCs (dimethyl sulphide, dimethyl disulphide, 2-methylpropanal, 3-methylbutanal and hexanal). KAW values can be determined in short time (less than 15 minutes) with a reproducibility of less than 5%. Measured KAW (mol m−3gas/mol m−3liquid) at 25°C are 8.61±0.20×10−2 for dimethyl sulphide, 5.90±0.23×10−2 for dimethyl disulphide, 1.27±0.06×10−2 for 2-methylpropanal, 1.43±0.05×10−2 for 3-methylbutanal and 1.41±0.03×10−2 for hexanal. The dependence of the partitioning coefficients on temperature (4 to 25°C) and ammonium sulphate concentration (0 to 300gL−1) were described by Van’t Hoff and Setchenow equations, respectively.