Ultrasound-assisted extraction of nitropolycyclic aromatic hydrocarbons from soil prior to gas chromatography-mass detection

Continuous ultrasound-assisted extraction of nitropolycyclic aromatic hydrocarbons from soil prior to their individual separation and determination by gas chromatography (GC) with MS–MS detection is presented here. A multivariate optimisation of the variables affecting the continuous extraction step (namely, probe position, ultrasound radiation amplitude, percentage of duty cycle of ultrasonic exposure, sonication time, total extractant volume, extractant flow rate and temperature of the water-bath in which the extraction cell was placed) was performed. The method was compared with the reference EPA method 3540 using natural contaminated soils. Similar efficiencies were obtained but with a drastic reduction of both the extraction time (10 min versus 24 h) and the extractant volume (less than 10 ml versus 100 ml) by the proposed method. Detection limits of low picogram were obtained, with repeatability and reproducibility between 4.21–5.70 and 5.20–7.23%, respectively.