GC/MS Monitoring of Selected PAHs in Soil Samples Using Ultrasound-assisted QuEChERS in Tandem with Dispersive Liquid-Liquid Microextraction

Abstract

Herein, a method consisting of ultrasound-assisted QuEChERS in tandem with dispersive liquid-liquid microextraction (DLLME) was developed for monitoring of selected polycyclic aromatic hydrocarbons (PAHs) in various soil samples using gas chromatography coupled to a single quadrupole mass spectrometry (GC/MS). Ultrasound-assisted QuEChERS was employed to extract the PAHs from 2.0 g of soil using 7 ml of initial extraction solvent (acetonitrile: water (5:2 v/v)) and the salt mixture. The resulting supernatant extract was cleaned through the addition of C18, PSA and the mix salt followed by centrifugation, decantation and filtration. Of the clean organic phase, 1.0 ml was withdrawn and added with12 µl of C2Cl4 (disperser solvent). The resulting mixture was then injected rapidly into an aqueous sample (5.0 ml) by a syringe for further preconcentration. As a result, the cloudy solution consisting of fine particles of the extraction solvent dispersed into the aqueous phase was formed. After centrifuging, the fine particles were sedimented at the bottom of the conical test tube (5.0 ± 0.5µl). Of which, 1.0 µl was injected to the GC/MS for monitoring of the PAHs. Several influential parameters including ultrasound extraction time, initial extraction and disperser solvent and their respective volumes were all evaluated to achieve the optimal conditions. Under the optimal conditions, limits of quantification (2.5-4.0 ng/g) and linear ranges (r2≥ 0.98) were obtained for the PAHs. The method was then successfully applied for the extraction and monitoring of the PAHs in the real soil samples. Accuracy of the method was evaluated by the relative recovery experiments on spiked samples with the results ranging from 81 to 92%. In the mean time, the relative standard deviations (RSDs) were found to be in the range of 4.8–15.9%.