Study of desorption kinetics of polycyclic aromatic hydrocarbons (PAHs) from solid matrices using internally cooled coated fiber Original Research Article

The kinetics of desorption of hydrophobic organic compounds (HOCs) from soil and sediment particles is important both from environmental and analytical chemistry points of view. Reliable techniques are required for prediction of desorption behaviour of HOCs from contaminated soils and sediments. In this study internally cooled coated fiber device, in which a PDMS hollow fiber extraction phase is cooled with liquid CO2, was used as an exhaustive extraction sorbent phase for extraction of desorbed organic compounds (e.g. polycyclic aromatic hydrocarbons, PAHs) from both laboratory-spiked and naturally contaminated solid sample into the gaseous headspace in a batch system. The extraction time profiles were obtained at two different elevated temperatures (above 100 °C) for spiked sand and silica gel matrices. The slow desorption rate constants at each temperature were determined from desorption plots and the apparent activation energies of desorption were obtained from Arrhenius equations. The apparent activation energies of desorption of naphthalene, acenaphthylene and acenaphthene, from spiked silica gel, were approximately 60 kJ mol−1, and were higher, 70 and 100 kJ mol−1 for fluoranthene and anthracene, respectively. The fast and slow desorption rates and apparent activation energies of desorption for PAHs were obtained by spiking a naturally contaminated sediment sample with deuterated PAHs (PAHs-d10). The activation energies of native PAHs were higher than those of spiked deuterated PAHs, suggesting that the native compounds were more affected by retarded pore diffusion or slow mass transfer through glassy sorbent organic matter (SOM). The proposed technique in the present study is fully automated, and can extract the contaminants from the solid matrix fast and exhaustively, which makes it more time efficient and versatile compared to the commonly used technique for desorption studies, i.e. vial desorption.