On-site sample preparation for benzo[a]pyrene in soils via pipette-tip based extraction with hydrophobic deep...

A novel field-deployable sample-preparation strategy for the determination of benzo[a]pyrene in soils was developed based on pipette-tip assisted extraction using a hydrophobic deep eutectic solvent (DES) followed by dispersive liquid-liquid microextraction (DLLME) and high-performance liquid chromatography with fluorescence detection (HPLC-FLD). This approach represents a field-assisted extraction method, combining on-site sampling with lab-based detection. In the proposed approach, 1000 mg of soil is placed into a disposable pipette tip equipped with a porous frit and sealed with a PTFE membrane, after which 6.0 mL of a methanol-diluted thymol:hexanol DES (1000 mg, 1:1, mol/mol) is aspirated and dispensed through the sample seven times, enabling rapid and efficient on-site extraction of benzo[a]pyrene directly at the sampling site. The obtained extract is transported to the laboratory, where the addition of water induces phase separation and concentrates the analyte into a small hydrophobic DES phase suitable for direct HPLC-FLD injection without evaporation or clean-up. The extraction process requires less than 10 min and does not involve heating, sonication, or mechanical agitation. The method provides a linear response in the range of 5 to 100 μg kg^-1 with a coefficient of determination R² = 0.999, a limit of detection of 2 μg kg^-1 and a limit of quantification of 5 μg kg^-1. Intra- and inter-day precision did not exceed 7 %, while recoveries from spiked and certified reference soils ranged from 88 % to 113 %. The results were statistically indistinguishable from those obtained by a GC-MS reference procedure at the 95 % confidence level. The proposed methodology represents the first implementation of hydrophobic deep eutectic solvents for on-site soil extraction of polycyclic aromatic hydrocarbons using a pipette-tip format. By decoupling sampling from laboratory analysis and enabling transport of extracts instead of bulk soil, the approach significantly reduces logistical constraints, contamination risks and solvent consumption, offering a powerful new platform for rapid environmental monitoring of carcinogenic PAHs.