Ultra-preconcentration and determination of organophosphorus pesticides in soil samples by a combination of ultrasound assisted leaching-solid phase extraction and low-density solvent based dispersive liquid–liquid microextraction

An ultra-preconcentration technique composed of ultrasound assisted leaching-solid phase extraction (USAL-SPE) and low-density solvent based dispersive liquid–liquid microextraction (LDS-DLLME) coupled with gas chromatography-mass spectrometry (GC-MS) was developed for preconcentration and determination of organophosphorus pesticides (OPPs) in soil samples. Parameters that affect the efficiency of the procedure were investigated by a fractional factorial design (FFD). Afterwards, variables showing significant effects on the analytical responses were considered using response surface methodology (RSM) based on a central composite design (CCD). Under optimum conditions, the enrichment factors were 7215–9842, the linear range was 0.012–625 ng g−1 and limits of detection (LODs) were between 0.002 and 0.125 ng g−1. The relative standard deviations (RSDs) were in the range of 5.4–8.3% (n = 6), and the relative recoveries of OPPs from different soil samples were 84–98%. The proposed methodology constitutes a suitable approach for the analysis of OPPs in complex soil samples and requires minimum organic solvents consumption, sample manipulation and increased sample throughput.