Polycyclic aromatic hydrocarbons (PAHs) in forest soils: Critical evaluation of a new analytical procedure

A new method is presented allowing the determination of PAHs in the highly problematic organic humus layers of forest soils. Emphasis was put on the extraction process and on a reliable quantification procedure. Fundamental elements of the developed method are: saponification of samples in an ultrasonic bath, partitioning of PAHs into hexane, clean-up of extracts by means of solid-phase extraction, and quantification by GC-MS using deuterated internal standards. Saponification was successful, probably due to hydrolysis and expansion effects on the humus matrix, hence sorbed PAHs were more accessible to the solvent and could be extracted more efficiently. The presented extraction procedure is therefore an interesting alternative to conventional solvent extraction methods, especially for sorptive carbon-rich matrices. The developed method guarantees an accurate and reproducible determination of PAHs in extremely difficult matrices even at trace levels. This was shown by testing the efficiency of the individual steps of the method, and by sample exchange with an external laboratory.