An environmentally friendly sample pre-treatment method based on magnetic ionic liquids for trace determination of nitrotoluene compounds in soil and water samples by gas chromatography–mass spectrometry using response surface methodology

In this study, a new sample preparation strategy termed ultrasonic-assisted dispersive magnetic ionic liquid/magnetic solid wire microextraction (UA-DMIL/MSW-ME) has been developed for simultaneous determination of fifteen nitrotoluene compounds (NTCs) in the soil and water samples. The extraction was performed by dispersing a magnetic ionic liquid (MIL) into the sample solution using ultrasonic irradiation. After completing the extraction, by stopping the sonication, a neodymium wire (NW) was placed inside the sample solution allowing the MIL containing the pre-concentrated analytes to cover the surface of NW with a thin layer due to the magnetic forces. Afterward, the MIL-coated NW was subjected to a homemade syringe and directly injected into a gas chromatography–mass spectrometry (GC–MS) instrument for thermal desorption of analytes; then, quantitative measurements were taken. The central composite design was applied to explore some parameters influencing the extraction efficiency. Ultimately, under the optimized conditions, the proposed method was successfully implemented to analyze NTCs in the real samples (coastal and forestal soils, river water, and industrial wastewater) and acceptable results were obtained. The resultant calibration curves were linear over the concentration range of 0.07–80 μg/L (R2 > 0.993). The estimated limits of detection and quantification were lower than 0.07 μg/L, and the enrichment factors were between 3538 and 3817. The wire-to-wire and single-wire reproducibility values were found to be lower than 5.8% (n = 6). The intra- and inter-day repeatability varied below 5.5% (n = 6), and the relative recoveries were calculated between 91–110 and 89–108% for soil and water samples, respectively.