Fast method to quantify PAHs in contaminated soils by direct thermodesorption using analytical pyrolysis

A method for polycyclic aromatic hydrocarbon (PAH) quantification, based on pyrolysis at 450°C combined with gas chromatography coupled with mass spectrometry and flame ionization detection (Py-GC-MS/FID), was developed and compared to a conventional PAH quantification method using accelerated solvent extraction and GC-MS analyses. The PAH contents of three coking plant soils, one gas plant soil, two wood-treating facility soils and one certified reference material (CRM - BCR 524) were determined using both methods. The results obtained with both methods showed a good match, especially in the case of the CRM. The other soil samples presented higher variability which was greatly reduced by crushing the samples to lower particle size (from <500 to <100µm). Higher contents of low molecular weight (LMW) PAHs were quantified with the Py-GC-MS/FID than with the conventional method, probably because of a slight cracking phenomenon occurring during the pyrolysis and/or a loss of the LMW compounds during the sample concentration required for the conventional method. Because of the limited sample preparation and the fact that no solvent was used, the pyrolysis-based method was proven to be a faster, less expensive and more environmentally friendly than the classical methods for PAH quantification in contaminated soils.