Features of Preconcentration and Determination of PAHs in Soils with High Organic Matter Content by Gas Chromatography–Mass Spectrometry

Specific features of the preconcentration and determination of polycyclic aromatic hydrocarbons (PAHs) in humus-rich soils by gas chromatography–mass spectrometry (GC–MS) are studied. The QuEChERS technique and dispersive liquid–liquid microextraction (DLLME) were employed to extract PAHs from soils using acetone and binary extractants of various compositions, including acetonitrile–dichloromethane, acetonitrile–acetone, acetone–hexane, acetone–chloroform, acetone–dichloromethane, and ethyl acetate–dichloromethane. Recoveries of low- and medium-molecular-weight PAHs using these solvent mixtures reached approximately 100%, while the acetone–dichloromethane mixture yielded over 90% recovery for high-molecular-weight PAHs. Under optimized GC–MS conditions with QuEChERS extraction, the limits of quantification (LOQ) for fluoranthene, pyrene, chrysene, and triphenylene reached 5 µg/kg, and for the remaining PAHs, 10 µg/kg in humus-rich soils. It was shown that the reliable GC–MS determination of lower concentrations of PAHs requires both the elimination of the matrix effect and the preconcentration of the analytes. The sequential application of QuEChERS and DLLME techniques enabled a decrease in the limits of quantification by GC–MS to 1.8 µg/kg for fluoranthene, pyrene, chrysene, and triphenylene, and to 3.5 µg/kg for the remaining PAHs. The optimized procedure for PAH determination in humus-rich soils was validated using real chernozem samples.