Optimization study of BTEX extraction from soils spiked with two kinds of Brazilian diesel by HS SPME using Box–Behnken experimental design and multi-response analysis

Abstract

In this work the main sorption conditions were optimized in the solid-phase microextraction (SPME) mode head-space (HS) for extraction of BTEX (benzene, toluene, ethylbenzene, and xylene isomers) from soils spiked with Brazilian conventional diesel and desulphurized diesel. Using a 100 μm poly(dimethylsiloxane) coating, the optimal exposure time was 4 min at 45 °C in saturated solution of NaCl (36 g per 100 mL). The resulting limits of detection (LODs) were between 0.002 and 0.02 mg kg⁻¹. Statistics tools were used to assist in the selection of extraction variables in function to the best response (peak area) and the reproducibility (RSD%). Using Box–Behnken experimental design and desirability functions, an empirical model was developed through a response surface methodology to describe the effect of tested variables (temperature, time and ionic strength). Each experiment was carried out in triplicate. The most important result of this work is a fast and easy method (including solvent-free) that was optimized to determine BTEX in soils by the HS-SPME procedure combined with analysis of GC-FID that showed applicability in real samples (spiked soils with conventional Brazilian diesel and desulphurized diesel). It is postulated that this methodology that was intentionally developed to assess the natural biodegradation of BTEX in soils may also be used for environmental diagnostics in general.